The Synthesis and Evaluation of
Polyaromatic Profluorescent Nitroxide
Probes for the Detection of Photo-
oxidative Polymer Degradation
Vanessa Lussini
Bachelor of Applied Science (Chemistry)
Submitted in fulfilment of the requirement for the degree of Doctorate of Philosophy
School of Molecular Design & Synthesis
Faculty of Science and Engineering
Queensland University of Technology
2019
P a g e | i
I. ABSTRACT
This PhD project focused on the synthesis and evaluation of novel photo-stable
profluorescent nitroxide (PFN) probes. The stability and performance of the newly
synthesised probes were assessed under harsh photolytic environments and compared
with previously synthesised PFN probes.
The synthesis of novel profluorescent mono- and bis-isoindoline nitroxides utilising
napthalimide and perylene diimide structural cores are described. Analysis of their
physical characteristics revealed that the nitroxide-fluorophore probes displayed
strongly suppressed fluorescence in comparison to their corresponding non-radical,
diamagnetic methoxyamine derivatives. Extinction coefficients, excitation wavelength
and emission wavelengths for the new probes were also determined.
Evaluation of the photo-stability of non-radical derivatives in cyclohexane,
demonstrated their enhanced longevity over 9,10-bis(phenylethynyl)anthracene, the
fluorophore used in previously prepared profluorescent nitroxide probes. The
performance and stability of the novel PFNs in two commercially available polymers
(PTMSP and TOPAS®) was also examined. The PFN containing films were exposed
to thermo- and photo-oxidative degradation conditions. In both systems, the novel
PFNs were able to detect polymer degradation by fluorescence. The alkyne linked
perylene was the most stable probe in the film according to UV-Vis. However, all
nitroxide bearing PFNs prepared from napthalimide and perylene diimide cores were
found to be more photo-stable in comparison to their corresponding non-radical
diamagnetic methoxyamine derivatives.
P a g e | ii
Finally, the most photostable PFN, alkyne linked perylene diimide was tested against
true weathering effects in the Brisbane summer, doped within a TOPAS® film. With
the addition of additives, free tetramethylisoindoline nitroxide and commercial
additive, Tinuvin P, it was possible to extend the longevity of the film and the effective
lifetime of the PFN probe. The selective demethylation to liberate the one nitroxide
radical showed interesting properties of increased sensitivity but decreased stability
compared with the di-nitroxide containing PFN. Overall, in a true weather setting, it
was shown that with additives, the PFN could signal local degradation sites via simple
fluorescence. However, addition of highly fluorescent PFNs (spin removed) acts like
a prodegradent to the TOPAS® film according to IR-ATR.
In summary, this thesis has developed a new range of photo-stable PFN probes for
detection of photo-oxidative degradation. They were able to detect radical production
in both synthetic aging conditions and in a true weathering environment. The
synthesised PFN proved to be more sensitive than previous techniques and was more
reproducible. This shows the potential scope of this project.
P a g e | iii
II. KEYWORDS
Degradation, Fluorescence, Fluorophore, Free radical, Isoindoline, Naphthalimide,
Nitroxide, Perylene diimide, Photo-oxidation, Polymer, Profluorescent, PTMSP,
TOPAS®, Weathering
P a g e | iv
III. PUBLICATIONS ARISING FROM THIS
PROJECT
Journal Articles
Prasad, K.; Lekshmi, G. S.; Ostrikov, K.; Lussini, V.; Blinco, J.; Mohandas, M.;
Vasilev, K.; Bottle, S.; Bazaka, K.; Ostrikov, K., Synergic bactericidal effects of
reduced graphene oxide and silver nanoparticles against Gram-positive and Gram-
negative bacteria. Scientific Reports 2017, 7 (1), 1591.
Lussini, V. C.; Colwell, J. M.; Fairfull-Smith, K. E.; Bottle, S. E., Profluorescent
nitroxide sensors for monitoring photo-induced degradation in polymer films. Sensors
and Actuators B: Chemical. 2017, 241, 199-209.
Lussini, V. C.; Blinco, J. P.; Fairfull-Smith, K. E.; Bottle, S. E., Polyaromatic
profluorescent nitroxide probes with enhanced photostability. Chemistry. 2015, 21,
18258-18268.
Ahn, H.-Y.; Fairfull-Smith, K. E.; Morrow, B. J.; Lussini, V.; Kim, B.; Bondar, M. V.;
Bottle, S. E.; Belfield, K. D., Two-photon fluorescence microscopy imaging of cellular
oxidative stress using profluorescent nitroxides. Journal of the American Chemical
Society. 2012, 134, 4721-4730.
P a g e | v
Conference Lectures
Vanessa Lussini, John Colwell, James Blinco, Kathryn Fairfull-Smith, Steven Bottle.
“Nitroxide probes for monitoring photodegradation in polymers” RACI QLD
Polymers Group Student Symposium, Brisbane, Australia, February 2016.
Vanessa Lussini, John Colwell, James Blinco, Kathryn Fairfull-Smith, Steven Bottle.
“Nitroxide probes for monitoring photodegradation in polymers” Brisbane Biological
and Organic Chemistry Symposium, Gold Coast, Australia, November 2015.
Vanessa Lussini and Steven Bottle. “Monitoring degradation in aircrafts” Australian
International Aerospace Congress, Avalon, Australia, February 2015.
Vanessa Lussini and Steven Bottle. “Early detection of polymer degradation”
Nanotechnology and Molecular Science HDR Symposium, Brisbane, Australia,
February 2015. (Best Talk Prize)
Vanessa Lussini and Steven Bottle. “Nitroxide probes for monitoring photo-
degradation in polymers” DMTC Student Conference, Melbourne, Australia, October
2014.
Vanessa Lussini and Steven Bottle. “Nitroxide probes for monitoring photo-
degradation in polymers” Nanotechnology and Molecular Science HDR Symposium,
Brisbane, Australia, February 2014.
Vanessa Lussini and Steven Bottle. “Nitroxide probes for monitoring photo-
degradation in polymers” DMTC Student Conference, ANTSO, Australia, October
2013.
P a g e | vi
Vanessa Lussini, Liam A. Walsh, John M. Colwell, Kathryn Fairfull-Smith and Steven
Bottle. “The synthesis and evaluation of novel perylene-based profluorescent nitroxide
probes for monitoring photo-stability in polymers” RACI QLD Polymers Group
Student Symposium, Brisbane, Australia, September 2012.
Vanessa Lussini, Liam A. Walsh, John M. Colwell, Kathryn Fairfull-Smith and Steven
Bottle. “The synthesis and evaluation of novel perylene-based profluorescent nitroxide
probes for monitoring photo-stability in polymers” RACI QLD Polymers Group
Student Symposium, Brisbane, Australia, August 2011.
Conference Posters
Vanessa Lussini and Steven Bottle. “Monitoring degradation in aircraft coatings”
DMTC Annual Conference, Canberra, Australia, March 2016.
Vanessa Lussini and Steven Bottle. “Monitoring degradation in aircraft coatings”
DMTC Annual Conference, Canberra, Australia, March 2015.
Vanessa Lussini and Steven Bottle. “Profluorescent nitroxides in monitoring
degradation in aircraft coatings” Australian Aerospace Innovation Awards, Avalon,
Australia, February 2015.
Media
Lussini, V (2015) Interviewed by Kelly Higgins-Devine on ABC Brisbane Radio
Women in Science, 8 March 2016
Smith, B (2015, September 21) Metal paint that reveals the rusty patches. COSMSO.
Pp 31
P a g e | vii
Woolett, S (July 2015) Aerospace award for RACI student, Chemistry in Australia. pp
7
Amanda Weaver (May 2015) Aircraft ‘sunscreen’ wins top prize. QUT links, pp 16
Creedy, S (2015, March 6) The big ideas fly from airshow’s innovators and award
winners. The Australian. pp 33-34
Atfield, C (2015, February 24) QUT researcher takes out aviation award. The Sydney
Morning Herald. Retrieved from http://www.smh.com.au/
Atfield, C (2015, February 24) QUT researcher takes out aviation award. The Brisbane
Times. Retrieved from http://www.brisbanetimes.com.au/
Young Innovator award to DMTC PhD candidate (24 February 2015) Retrieved from
http://dmtc.com.au/young-innovator-award-to-dmtc-phd-candidate/
Lussini, V (2015) Interviewed by Natasha Mitchell on ABC Radio National Life
Matters, 24 February 2015
Young Innovator award to DMTC PhD candidate (24 February 2015) Retrieved from
http://dmtc.com.au/young-innovator-award-to-dmtc-phd-candidate/
QUT PhD student becomes first woman to win Aerospace Australia award (24
February 2015) Retrieved from https://www.qut.edu.au/news/news?news-id=85436
Oliver, L. (2015, February 19) Scientist’s aviation research takes flight. The
Westerner, pp 1-2,6.
P a g e | viii
Queensland PhD student nominated for national aviation award (6 February 2015)
Retrieved from http://www.defenceindustries.qld.gov.au/defence-industries/media-
and-resources/queensland-phd-student-nominated-for-national-aviation-award.html
Aerospace Australia Industry Innovation Award nominees announced (6 February
2015) Retrieved from http://australianaviation.com.au/2015/02/aerospace-australia-
industry-innovation-award-nominees-announced/
Aviation Innovation Awards shortlist announced (28 January 2015) Retrieved from
http://www.australiandefence.com.au/news/aviation-innovation-awards-shortlist-
announced
P a g e | ix
IV. TABLE OF CONTENTS
I. Abstract ............................................................................................................. i
II. Keywords ........................................................................................................ iii
III. Publications Arising From This Project .......................................................... iv
Journal Articles ........................................................................................................ iv
Conference Lectures ................................................................................................. v
Conference Posters .................................................................................................. vi
Media ...................................................................................................................... vi
IV. Table of Contents ............................................................................................ ix
V. List of Figures ................................................................................................ xii
VI. List of Schemes ............................................................................................ xxii
VII. List of Tables................................................................................................ xxv
VIII. Abbreviations .............................................................................................. xxvi
IX. Declaration ................................................................................................ xxviii
X. Note to the Reader ..................................................................................... xxviii
XI. Acknowledgments ....................................................................................... xxix
1. Introduction ...................................................................................................... 1
1.1. Synthetic Polymers ........................................................................................ 1
1.2. Nitroxide Free Radicals ............................................................................... 12
1.3. Perylene Diimide ......................................................................................... 29
1.4. Applications of this Project ......................................................................... 31
1.5. Project Outline ............................................................................................. 32
1.6. Relationship of the Research Papers ........................................................... 36
2. Synthesis and Characterisation ...................................................................... 38
P a g e | x
2.1. Synthesis of Nitroxide ................................................................................. 38
2.2. 1st Generation Perylene Diimide based PFNs.............................................. 54
2.3. Synthesis of Naphthalimide PFNs ............................................................... 63
2.4. Synthesis of the Bay Region of Perylene Diimide PFNs ............................ 73
2.5. Experimental ................................................................................................ 84
3. Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability
...................................................................................................................... 118
3.1. Abstract ...................................................................................................... 120
3.2. Introduction ............................................................................................... 121
3.3. Results and Discussion .............................................................................. 123
3.4. Conclusions ............................................................................................... 138
3.5. Experimental Section ................................................................................. 139
3.6. Acknowledgements ................................................................................... 155
4. Profluorescent nitroxide sensors for monitoring photo-induced degradation in
polymer films ........................................................................................................... 157
4.1. Abstract ...................................................................................................... 160
4.2. Key words .................................................................................................. 160
4.3. Introduction ............................................................................................... 160
4.4. Experimental .............................................................................................. 164
4.5. Results and Discussion .............................................................................. 167
4.6. Conclusions ............................................................................................... 184
4.7. Acknowledgements ................................................................................... 185
5. Profluorescent nitroxide sensors for monitoring the natural aging of polymer
materials ................................................................................................................... 186
5.1. Abstract ...................................................................................................... 189
5.2. Key words .................................................................................................. 189
5.3. Introduction ............................................................................................... 189
P a g e | xi
5.4. Materials .................................................................................................... 193
5.5. Sample preparation .................................................................................... 194
5.6. Analysis methods ...................................................................................... 195
5.7. Results and discussion ............................................................................... 196
5.8. Conclusion ................................................................................................. 216
5.9. Acknowledgements ................................................................................... 217
6. The Synthesis and Stability of Ferrari Red- Type Compounds .................. 218
6.1. Introduction ............................................................................................... 218
6.2. Experimental ............................................................................................. 220
6.3. Results and Discussion .............................................................................. 226
6.4. Conclusion ................................................................................................. 232
7. Conclusions and Future Work ...................................................................... 233
7.1. Conclusions ............................................................................................... 233
7.2. Future Work .............................................................................................. 235
8. References .................................................................................................... 242
9. Appendix ...................................................................................................... 261
9.1. Supplementary Information for Polyaromatic Profluorescent Nitroxide
Probes with Enhanced Photostability (Chapter 3) ................................................ 261
9.2. Supplementary Information for Profluorescent nitroxide sensors for
monitoring the natural aging of polymer materials (Chapter 5) ........................... 300
P a g e | xii
V. LIST OF FIGURES
Figure 1: World and European polymer production annually 1950-2016 (graph created
from data compiled from PlasticsEurope's Market Research and Statistics Group. 7-10
...................................................................................................................................... 1
Figure 2: The pathway to synthesis of the polyolefin, polyethylene, from the ethylene
monomer. ...................................................................................................................... 3
Figure 3: General schemes of oxidation of polymeric materials ................................. 6
Figure 4: Early examples of free radicals ................................................................... 13
Figure 5: Examples of Bis(t-alkyl) nitroxides ............................................................ 15
Figure 6: 1,1,3,3-tetraalkylisoindolin-2-yloxyls ........................................................ 16
Figure 7: Jablonski diagram64 .................................................................................... 19
Figure 8: Tethering of fluorophore to a nitroxide ...................................................... 21
Figure 9: Reduction of a rhodamine probe ................................................................. 22
Figure 10: PFN used by Ristovski’s group- BPEANO (23) and the PFN used by
Micallef and Colwell- TMDBIO (24) ........................................................................ 23
Figure 11: Degradation of PFN-doped polypropylene aged under O2 at 150ºC
monitored in parallel by chemiluminescence, FTIR-ATR and spectrofluorimetry. 35
.................................................................................................................................... 24
Figure 12: Comparison of non-degraded (top) and degraded (bottom) polypropylene
doped with TMDBIO104 ............................................................................................. 25
Figure 13: Polyaromatic hydrocarbons used in the PFN chromophore constructs .... 27
Figure 14: Water soluble PFNs .................................................................................. 28
Figure 15: Photo-stable PFN bases ............................................................................ 29
Figure 16: Chemical structures of PTCDA (42) , generic PDI (41) and the bay addition
locations positions in the ring system.125 ................................................................... 30
Figure 17: Target compounds for new robust PFN sensors ....................................... 33
Figure 18: Trimethylethylisoindoline by-product (53) .............................................. 41
Figure 19: Dimer (60) formed during diazonium reaction ......................................... 46
Figure 20: 1H NMR comparison of the 3 major products in deuterated chloroform.
Top: 90 (top), 89 (middle) and 44 (bottom). .............................................................. 59
Figure 21: 1H NMR comparison of the 3 major products (after the Fenton chemistry)
in deuterated chloroform. Top: 89 (top), 92 (middle) and 91 (bottom). .................... 60
P a g e | xiii
Figure 22: New and improved target compounds and their methoxyamine derivatives
.................................................................................................................................... 62
Figure 23: 1H NMR comparison of the aromatic region of 105 (top) and 104 (bottom)
in deuterated chloroform. ........................................................................................... 68
Figure 24: 1H NMR comparison of the aromatic region of 106 (bottom) and 104 (top)
in deuterated chloroform. ........................................................................................... 70
Figure 25: 1H NMR comparison of the aromatic region of 106 (bottom) and 107 (top)
in deuterated chloroform. ........................................................................................... 72
Figure 26: 1H NMR of 113/121 in deuterated chloroform. Expanded regions of protons
‘f’ and ‘e’ to show the ratio of the isomers 113 and 121. .......................................... 77
Figure 27: 1H NMR comparison of the aromatic region of 117 (bottom) and 118 (top)
in deuterated chloroform. ........................................................................................... 80
Figure 28: Expanded region of the 1H NMR of 114 showing the isomer ratio between
1,6 and 1,7 .................................................................................................................. 82
Figure 29: 1H NMR comparison of the aromatic region of 117 (bottom), 115 (middle)
and 118 (top) in deuterated chloroform. .................................................................... 84
Figure 30: Chemical structures of perylene diimide 42, perylene-based profluorescent
nitroxides 44 and 129 and 9,10-bis(phenylethynyl)anthracene-based profluorescent
nitroxide 23. ............................................................................................................. 122
Figure 31: Fluorescence spectra of 1,8-napthalimide-based probes 105 (—) and 104
(···), 9 μM in cyclohexane; 106 (—) and 107 (···), 3 μM in cyclohexane, following
excitation at 350 nm. ................................................................................................ 134
Figure 32: Fluorescence spectra of perylene-based probes 114 (—), 116 (---) and 115
(···), 1 μM in chloroform, following excitation at 525 nm. ..................................... 135
Figure 33: Fluorescence loss (calculated as a percentage from the fluorescence
intensity at λmax) for cyclohexane solutions of 9,10-bis(phenylethynyl)anthracene 29
(-♦-, λmax = 470 nm), 104 (-■-, λmax = 408 nm), 106 (-Δ-, λmax = 407 nm), 113 (-x-, λmax
= 534 nm), 117 (-●-, λmax = 522 nm) and 114 (-+-, λmax = 557 nm) following photo-
irradiation at 765 Wm-2 and 40ºC. ........................................................................... 138
Figure 34: Tethering of a fluorophore to a nitroxide to form a PFN probe ............. 162
Figure 35: The structures of the polymers used in this study, PTMSP and TOPAS®
.................................................................................................................................. 163
Figure 36: Nitroxides used in this study and their non-radical (fluorescent)
methoxyamine derivatives ....................................................................................... 164
Figure 37: UV-Vis absorbance (dotted lines) and fluorescence emission (solid lines)
spectra of perylene fluorophore 114 in TOPAS® at various concentrations ranging
from 0.025 to 0.0025 w%, showing no evidence of any bathochromic shifts in the
bands or any obvious fluorescence quenching that might arise from aggregation. . 168
P a g e | xiv
Figure 38: Change in fluorescence emission of PTMSP films doped either with 29, 1
(-■-/left axis) or the nitroxide analogue, 23 (-♦-/right axis) with respect to UV ageing
time (hours). ............................................................................................................. 169
Figure 39: Change in fluorescence emission of PTMSP films doped either with ether-
linked naphthalimide fluorophore 104 (-■-/left axis) or the nitroxides analogue 105 (-
♦-/right axis) with respect to UV ageing time (hours). ............................................ 170
Figure 40: Change in fluorescence emission of PTMSP films doped either with alkyne-
linked naphthalimide fluorophore 106 (-■-/left axis) or the nitroxides analogue 107 (-
♦-/right axis) with respect to ageing time (hours). ................................................... 171
Figure 41: Change in fluorescence emission of the PTMSP films doped with either
ether-linked perylenediimide fluorophore 117 (-■-/left axis) or the nitroxides analogue
118 (-♦-/right axis) with respect to ageing time (hours)........................................... 172
Figure 42: Change in fluorescence emission of the PTMSP films doped with either
alkyne-linked perylenediimide fluorophore 114 (-■-/left axis) or the nitroxides
analogue 116 (-♦-/right axis) with respect to ageing time (hours). .......................... 172
Figure 43: Changes in the fluorescence emission of PTMSP films doped with non-
radical analogues, 29 (-■-, λmax = 470 nm), 104 (-▲-, λmax = 410 nm), 106 (-●-, λmax =
430 nm), 117 (-▬-, λmax = 560 nm) and 114 (-♦-, λmax = 615 nm) following photo-
irradiation at 250 Wm-2 and 40ºC for up to 6 h. Note: data collection was stopped at 6
hours as discolouration gave higher intensities than I0. ........................................... 173
Figure 44: Changes the fluorescence emission of PTMSP films doped with the
nitroxides, 23 (-■-, λmax = 470 nm), 154 (-▲-, λmax = 408 nm), 107 (-●-, λmax = 428
nm), 118 (-▬-, λmax = 550 nm) and 116 (-♦-, λmax = 610 nm) following photo-
irradiation at 250 Wm-2 and 40ºC for up to 10 h. ..................................................... 174
Figure 45: Change of the fluorescence emission for the PFN 116 in PTMSP from 0-10
h ageing compared to its non-radical analogue, 114 at time zero in PTMSP, showing
that the 116 has not achieved complete switch-on after 10 h ageing. ...................... 176
Figure 46: Change in fluorescence emission from PTMSP films doped with PFN non-
radical analogues (29, 105, 106, 117 and 114) over time at 70°C in the dark. ........ 177
Figure 47: UV-Vis spectra from undoped (blank) PTMSP (-) and TOPAS® (-) films.
.................................................................................................................................. 178
Figure 48: Change in the fluorescence emission from TOPAS® films doped with
PFNs (■, Right axes), relative change in UV-Vis absorbance of PFNs (♦, Left axes)
and relative change in UV-Vis absorbance of the non-radical analogues (●, Left axes)
during photo-ageing. (a) 104/105 (b) 106/107 (c) 117/118 (d) 114/116 .................. 180
Figure 49: Change of the fluorescence emission for the PFN 116 in TOPAS® from 0-
504 h ageing compared to its non-radical analogue, 114 at time zero in TOPAS®,
showing that the PFN 116 has only achieved a small fraction of complete switch-on
after 504 h ageing. .................................................................................................... 182
P a g e | xv
Figure 50: UV-Vis absorbance at 250 nm (subtracted from UV-Vis absorbance at 400
nm) for the blank (undoped) TOPAS® film with respect to time in the suntest (left
axis, ■) and the oxidation index calculated from ATR-IR data from the blank
(undoped) TOPAS® film with respect to time in the suntest (right axis, ♦) ........... 183
Figure 51: Tethering of a fluorophore to a nitroxide to form a profluorescent nitroxide
(PFN), and trapping of carbon-centred free-radicals (formed during polymer
degradation), causing the PFN to switch from a non-fluorescent to a fluorescent state.
.................................................................................................................................. 191
Figure 52: Fluorescent and profluorescent probes used in this study. The fully
fluorescent non-radical analogue 114 is used as an indicator for the potential response
from the profluorescent probes 115 and 116............................................................ 192
Figure 53: Structure of TOPAS® (the cyclic olefin copolymer used in this study),
TMIO (55; a HALS analogue) and Tinuvin P (1; a common UV absorber). .......... 193
Figure 54: Oxidation indices as determined by FTIR-ATR for TOPAS® films aged in
the laboratory (Suntest) and outdoors (data of weather comparisons are summarised in
). ............................................................................................................................... 198
Figure 55: Fluorescence emission and oxidation indices of a laboratory-aged PFN
(115)-containing TOPAS® film. ............................................................................. 200
Figure 56: Fluorescence emission during natural weathering on the rooftop for
TOPAS® films doped with compounds 115 and 116 (0.025 wt%). ........................ 201
Figure 57: Relative change in UV-Vis absorbance for TOPAS® films doped with
compounds 114, 115 and 116 (0.025 wt%) during natural exposure on the rooftop.
.................................................................................................................................. 202
Figure 58: Relative change in fluorescence emission during natural weathering for
TOPAS® films doped with compounds 114 (fully fluorescent non-radical PFN
analogue), 115 (mononitroxide) and 116 (dinitroxide) at 0.025 wt%...................... 204
Figure 59: Oxidation indices as determined by FTIR-ATR for rooftop-exposed
TOPAS® films doped with compounds 114, 115 and 116 (0.025 wt%) and an additive-
free control sample. .................................................................................................. 206
Figure 60: Oxidation indices as determined by FTIR-ATR (left) and relative change
in UV-Vis absorbance (right) for TOPAS® films doped with compound 114,
115 and 116 (0.025 wt%) during aging in the laboratory (Suntest) and outdoors
weathering (other data for rooftop and suntest comparisons are summarised in )... 207
Figure 61: Relative change in UV-Vis absorbance of aged TOPAS® films doped
with PFN-analogue 114 (0.025 w%); compared to TOPAS® films containing PFN-
analogue 114 + TMIO (1, 2 and 4 eqv. of 114) with respect to radiant exposure (MJ/m2)
on the rooftop. .......................................................................................................... 209
Figure 62: Relative change in UV-Vis absorbance of aged TOPAS® films doped
with PFN-analogue 114 (0.025 w%); compared to TOPAS® films containing PFN-
P a g e | xvi
analogue 114 + Tinuvin P (0.1, 0.3 and 0.5 wt%) with respect to radiant exposure
(MJ/m2) on the rooftop. ............................................................................................ 210
Figure 63: Relative change in UV-Vis absorbance of aged TOPAS® films doped with
PFN-analogue 114 (0.025 w%); compared to TOPAS® film containing PFN analogue
114 + Tinuvin P (0.3 wt%), TOPAS® film containing PFN-analogue 114 + TMIO (2
eqv. of 114) and TOPAS® film containing PFN-analogue 114 + both Tinuvin P (0.3
wt%) and TMIO (2 eqv. of 114) with respect to radiant exposure (MJ/m2) on the
rooftop. ..................................................................................................................... 211
Figure 64: Relative change in UV-Vis absorbance of aged TOPAS® films doped with
PFN 115 (0.025 w%); compared to TOPAS® film containing PFN 115 + Tinuvin P
(0.3 wt%), TOPAS® film containing PFN 115 + TMIO (2 eqv. of 115) and TOPAS®
film containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 115) with
respect to radiant exposure (MJ/m2) on the rooftop. ................................................ 212
Figure 65: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films
doped with PFN 115 (0.025 w%); compared to TOPAS® film containing PFN 115 +
Tinuvin P (0.3 wt%), TOPAS® film containing PFN 115 + TMIO (2 eqv. of 115) and
TOPAS® film containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of
115) with respect to radiant exposure (MJ/m2) on the rooftop. ............................... 213
Figure 66: Fluorescence maximum trace of aged TOPAS® films doped with PFN 115
(0.025 w%); compared to TOPAS® film containing PFN 115 + Tinuvin P (0.3 wt%),
TOPAS® film containing PFN 115 + TMIO (2 eqv. of 115) and TOPAS® film
containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 115) with respect
to radiant exposure (MJ/m2) on the rooftop. ............................................................ 214
Figure 67: Fluorescence maximum trace of aged TOPAS® films doped with PFN 116
(0.025 w%); compared to TOPAS® film containing PFN 116 + Tinuvin P (0.3 wt%),
TOPAS® film containing PFN 116 + TMIO (2 eqv. of 116) and TOPAS® film
containing PFN 3 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 116) with respect
to radiant exposure (MJ/m2) on the rooftop. ............................................................ 216
Figure 68: Compounds used in this study ................................................................ 219
Figure 69: Polymer films used in photo-oxidative degradation experiment ............ 220
Figure 70: Fluorescence loss (calculated as a percentage from the fluorescence
intensity at λmax) for PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-
, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to UV ageing time (hours).
.................................................................................................................................. 227
Figure 71: Fluorescence loss (calculated as a percentage from the fluorescence
intensity at λmax) for PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-
, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to ageing time (hours) at 70°C.
.................................................................................................................................. 228
P a g e | xvii
Figure 72: Fluorescence loss (calculated as a percentage from the fluorescence
intensity at λmax) for PTMSP films doped with 116 with respect to UV (-■-) or thermal
(-♦-) ageing time (hours). ......................................................................................... 229
Figure 73: Fluorescence loss (calculated as a percentage from the fluorescence
intensity at λmax) for TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-
▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to UV ageing time (hours).
.................................................................................................................................. 230
Figure 74: Fluorescence loss (calculated as a percentage from the fluorescence
intensity at λmax) of 116 doped in PTMSP (-■-) or TOPAS (-♦-) films with respect to
UV ageing time (hours) ............................................................................................ 231
Figure 75: Fluorescence loss (calculated as a percentage from the fluorescence
intensity at λmax) for TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-
▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to ageing time (hours) at
70°C. ........................................................................................................................ 232
Figure 76: Synthetic targets for varying the perylene diimide PFN ........................ 236
Figure 77: Different potential nitroxides for perylene diimide PFNs ...................... 237
Figure 78: Potential synthetic goals for photo-stable PFNs ..................................... 238
Figure 79: Synthetic route for potential new perylene diimide PFNs ...................... 240
Figure 80: 1H NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-
tetramethylisoindoline (64) ...................................................................................... 262
Figure 81: 13C NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-
tetramethylisoindoline (64) ...................................................................................... 263
Figure 82: HPLC (70% MeOH/ Water) chromatogram of 5-Hydroxy-2-methoxy-
1,1,3,3-tetramethylisoindoline (64) .......................................................................... 263
Figure 83: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104) ........................................ 264
Figure 84: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104) ........................................ 265
Figure 85: HPLC (70% MeOH/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-
4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104) ..... 265
Figure 86: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide (105) ......................... 266
Figure 87: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-
(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide (105) ............ 267
Figure 88: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide (105) ......................... 267
Figure 89: Quantum Yield of fluorescence calculations for 104 and 105 ............... 268
P a g e | xviii
Figure 90: 1H NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline
(62) ........................................................................................................................... 269
Figure 91: 13C NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline
(62) ........................................................................................................................... 269
Figure 92: HPLC (70% MeOH/ Water) chromatogram of 5-Amino-2-methoxy-
1,1,3,3-tetramethylisoindoline (62) .......................................................................... 270
Figure 93: 1H NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-
tetramethylisoindoline tetrafluoroborate (63) .......................................................... 271
Figure 94: 13C NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-
tetramethylisoindoline tetrafluoroborate (63) .......................................................... 271
Figure 95: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106) .................................... 272
Figure 96: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106) .................................... 273
Figure 97: HPLC (75% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-
(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106) ... 273
Figure 98: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-naphthalimide (107) ....................... 274
Figure 99: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-
(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-naphthalimide (107) ......... 275
Figure 100: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-naphthalimide (107) ....................... 275
Figure 101: Quantum yield of fluorescence calculations for 106 and 107 .............. 276
Figure 102: 1H NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-
methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy
diimide (117) ............................................................................................................ 277
Figure 103: 13C NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-
methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy
diimide (117) ............................................................................................................ 277
Figure 104: HPLC (75% THF/ Water) chromatogram of N,N-Di-(2,5-di-tert-
butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-
3,4,9,10-tetracarboxy diimide (117) ......................................................................... 278
Figure 105: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide
(118) ......................................................................................................................... 279
Figure 106: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-
butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-
3,4,9,10-tetracarboxy diimide (118) ......................................................................... 279
P a g e | xix
Figure 107: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide
(118) ......................................................................................................................... 280
Figure 108: Quantum yield of fluorescence calculations for 117 and 118 .............. 280
Figure 109: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-
1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide
(114) ......................................................................................................................... 281
Figure 110: 13C NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-
1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide
(114) ......................................................................................................................... 282
Figure 111: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-
butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-
3,4,9,10-tetracarboxy diimide (114) ........................................................................ 282
Figure 112: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide
(116) ......................................................................................................................... 283
Figure 113: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-
butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-
3,4,9,10-tetracarboxy diimide (116) ........................................................................ 284
Figure 114: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide
(116) ......................................................................................................................... 284
Figure 115: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115) .... 285
Figure 116: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115) .... 286
Figure 117: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-
butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-
1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide
(115) ......................................................................................................................... 286
Figure 118: Quantum yield of fluorescence calculations for 114, 116 and 115 ...... 287
Figure 119: 1H NMR spectrum of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-
2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (98) .......................................... 288
Figure 120: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (98) ...... 288
P a g e | xx
Figure 121: EPR (DCM) spectrum of N-(Octylphenyl)-N’(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (98) ...... 289
Figure 122: Quantum yield of fluorescence calculations for 98 and 99 .................. 289
Figure 123: 1H NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (99) ............. 291
Figure 124: 13C NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (99) ............. 291
Figure 125: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(2-
methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide
(99) ........................................................................................................................... 292
Figure 126: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (90) ...... 293
Figure 127: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (90) ...... 293
Figure 128: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-
N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide
(90) ........................................................................................................................... 294
Figure 129: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (90) ...... 294
Figure 130: Quantum yield of fluorescence calculations for 90 and 92 .................. 295
Figure 131: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (92) ............. 296
Figure 132: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-
1,1,3,3-tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (92) . 296
Figure 133: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-
N’-(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-
diimide (92) .............................................................................................................. 297
Figure 134: 1H NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-
perylene-3,4,9,10-tetracarboxy diimide (130) .......................................................... 298
Figure 135: 13C NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-
perylene-3,4,9,10-tetracarboxy diimide (130) .......................................................... 298
Figure 136: HPLC (80% THF/ Water) chromatogram of N,N’-(2,5-Di-tert-
butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide (130) ....... 299
Figure 137: Quantum yield of fluorescence calculations for 113 and 130 .............. 299
Figure SI 138: Fluorescence maximum trace of aged TOPAS® films doped with PFN
116 (0.025 w%) during aging in the laboratory (Suntest) and outdoors weathering.
.................................................................................................................................. 301
P a g e | xxi
Figure SI 139: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films
doped with PFN-analogue 114 (0.025 wt%) with respect to radiant exposure (MJ/m2)
on the rooftop. .......................................................................................................... 302
Figure SI 140: Relative change in UV-Vis absorbance for aged TOPAS® films doped
with PFN 115 (0.025 wt%) with respect to radiant exposure (MJ/m2) on the rooftop.
.................................................................................................................................. 303
P a g e | xxii
VI. LIST OF SCHEMES
Scheme 1: An example of the coupled electron and proton-transfer mechanism using
2-(2-hydroxy-5-methylphenyl)benzotriazole (1). (a) Photoinduced formation of
charge-transfer activated complex. (b) Proton transfer from the activated complex.33
.................................................................................................................................... 10
Scheme 2: Phenolic antioxidant pathway. .................................................................. 11
Scheme 3: Amine antioxidant pathway, known as the Denisov cycle. 11, 34 .............. 12
Scheme 4: Resonance of nitroxides and reversible redox structures ......................... 14
Scheme 5: Disproportionation reaction ...................................................................... 14
Scheme 6: Disproportionation of tert-butyl phenyl nitroxides .................................. 15
Scheme 7: Unfavourable α-cleavage of TMIO .......................................................... 16
Scheme 8: Radical trapping of nitroxides .................................................................. 17
Scheme 9: The quantitative reaction to detect hydroxyl radicals with the use of a
profluorescent nitroxide via Fenton chemistry ........................................................... 23
Scheme 10: An example of photo chemical induced living radical polymerization .. 27
Scheme 11: Synthetic route to 2-benzyl-1,1,3,3-tetramethylisoindoline 49 .............. 39
Scheme 12: High yielding acid catalysed condensation of phthalic anhydride 48 .... 39
Scheme 13: Exhaustive methylation of 48 with methyl magnesium iodide .............. 40
Scheme 14: Synthetic route to 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57 .. 42
Scheme 15: Synthetic route to 5-hydroxy- 1,1,3,3-tetramethylisoindolin-2-yloxyl, (59)
.................................................................................................................................... 45
Scheme 16: Formation of hydroxyl radical via Fenton reaction to liberate methyl
radicals from DMSO .................................................................................................. 47
Scheme 17: The reaction pathway of the methoxyamine derivatives ........................ 48
Scheme 18: Synthetic scheme to the 5-ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl
69 ................................................................................................................................ 49
Scheme 19: Lithiated species ..................................................................................... 50
Scheme 20: Improved iodination of TMI ................................................................... 52
Scheme 21: The reaction pathway to afford the methoxyamine derivatives ............. 53
Scheme 22: The reaction pathway to afford the cyano nitroxide 83 and its
methoxyamine derivative 84 ...................................................................................... 54
Scheme 23: The unsuccessful first synthetic pathway to form a PDI PFN ................ 55
P a g e | xxiii
Scheme 24: The unsuccessful partial hydrolysis and reforming of the anhydride .... 56
Scheme 25: Single pot reaction and its side products ................................................ 58
Scheme 26: Unsuccessful single pot synthesis of PFN 94 ......................................... 61
Scheme 27: General reaction scheme for first generation perylene PFNs ................. 63
Scheme 28: The overall synthetic scheme of naphthalene-based PFNs .................... 64
Scheme 29: Nucleophilic substitution reaction employed for the synthesis of 105 .. 65
Scheme 30: Nucleophilic substitution reaction to link the protected nitroxide to
synthesis 104 and then oxidise to afford the nitroxide moiety 105............................ 66
Scheme 31: Proposed deprotection mechanism via N-oxidation and subsequent Cope-
type elimination147 ...................................................................................................... 67
Scheme 32: Sonogashira coupling to form 106 ......................................................... 69
Scheme 33: Oxidation to form nitroxide moiety of 107 ............................................ 71
Scheme 34: Overall synthetic scheme for bay region perylene PFNs ....................... 74
Scheme 35: Products of bromination reaction (112).................................................. 75
Scheme 36: Synthetic scheme for the condensation reaction to form 113 ................ 76
Scheme 37: The nucleophilic substitution reaction to form 117 from 113 ................ 78
Scheme 38: Oxidation of 117 to form PFN 118 ........................................................ 79
Scheme 39: Sonogashira reaction to form 114 .......................................................... 81
Scheme 40: Oxidation of 114 to form the nitroxide radical of 116 ........................... 82
Scheme 41: Oxidation of 114 to form the nitroxide radical of 115 ........................... 83
Scheme 42: Synthetic route to ether linked naphthalimide-based profluorescent
nitroxide 105. ........................................................................................................... 124
Scheme 43: Synthetic route to 5-hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline
64. ............................................................................................................................. 125
Scheme 44: Synthetic route to ethynyl linked naphthalimide-based profluorescent
nitroxide 107. ........................................................................................................... 126
Scheme 45: Synthetic route to ether linked perylene-based profluorescent nitroxide
118. ........................................................................................................................... 128
Scheme 46: Synthetic route to ethynyl linked perylene-based profluorescent nitroxides
116 and 115. ............................................................................................................. 129
Scheme 47: Synthetic route to imide linked perylene-based profluorescent nitroxide
98. ............................................................................................................................. 131
Scheme 48: Synthetic route to imide linked perylene-based profluorescent nitroxide
90. ............................................................................................................................. 132
P a g e | xxiv
Scheme 49: Synthesis of 2,5-bis(2-octyl-1-dodecyl)-3,6-diphenylpyrrolo[3,4-
c]pyrrole-1,4(2H,5H)-dion (131) ............................................................................. 222
Scheme 50: The synthetic route to 2,5-bis(2-octyl-1-dodecyl)-3,6-di(2-methoxy-
1,1,3,3- tetramethylisoindoline)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion, 133 ......... 224
P a g e | xxv
VII. LIST OF TABLES
Table 1: Photophysical properties of naphthalimide- and perylene diimide-based
nitroxide probes and their methoxyamine adducts................................................... 133
Table 2: Summary of PFN fluorescence changes in PTMSP films doped with PFNs or
their non-radical analogues during ageing. .............................................................. 175
Table 3: Summary of PFN sensor performance and stability in TOPAS® films
following photo-oxidative degradation. ................................................................... 181
Table 4: Solar exposure, temperature and rainfall conditions for rooftop weathering
and laboratory aging. ................................................................................................ 197
Table SI 5: Summary of aged TOPAS® films doped with PFNs (0.025 wt%) and
varying concentrations of 55 and 1 aged in the Suntest and aged on the rooftop. ... 304
P a g e | xxvi
VIII. ABBREVIATIONS
Abs Absorbance
AcOH Acetic Acid
Ar: Aryl
b: Broad signal
d: Doublet
DCM: Dichloromethane
dd Doublet of doublets
dec.: Decomposed
DMF: N,N-Dimethylformamide
DMSO: Dimethyl sulfoxide
EI: Electron impact
EPR: Electron paramagnetic resonance
Eqv: Equivalent
ESI: Electrospray ionization
Et: Ethyl
Et2O: Diethyl ether
EtOAc: Ethyl acetate
EtOH: Ethanol
FTIR-ATR: Fourier transform infrared spectroscopy- attenuated total reflectance
h: Hour
HPLC: High performance liquid chromatography
HRMS: High resolution mass spectrometry
IR: Infrared
P a g e | xxvii
ISC: Intersystem crossing
m: Multiplet
m-CPBA: 3-Chloroperoxybenzoic acid
me: Methyl
MeMgI: Methyl magnesium iodine
MeOH: Methanol
mol/L: Moles per litre
mol: Moles
M.p: Melting point
MS: Mass spectrometry
nm: Nanometres
NMR: Nuclear magnetic resonance
Pd/C: Palladium on charcoal
PFN: Profluorescent nitroxide
Ph: Phenyl
ppm: Parts per million
PTMSP: Poly(1-trimethylsilyl)-1-propyne
RT: Room temperature
s: Singlet
t: Triplet
THF: Tetrahydrofuran
TLC: Thin layer chromatography
TMIO: 1,1,3,3-Tetramethylisoindoline-2-yloxyl
UV: Ultraviolet
P a g e | xxviii
IX. DECLARATION
This work has not previously been submitted for a degree or diploma in any university.
To the best of my knowledge and belief, this dissertation contains no material
previously published or written by another person except where due reference is made
in the dissertation itself.
Vanessa Lussini
X. NOTE TO THE READER
Chapters 3, 4 and 5, are as stated, previously published via peer review to allow thesis
by published papers. However, these paper chapters have minor changes from the
published papers to fit the flow of the thesis, and to reduce confusion. There are
changes to the numbering of the sections, compounds, figures, tables and schemes to
remove double ups within the thesis.
QUT Verified Signature
P a g e | xxix
XI. ACKNOWLEDGMENTS
Firstly, I must thank my supervisory team, Prof. Steven Bottle, Assoc. Prof. Kathryn
Fairfull-Smith, Dr. James Blinco and Dr. John Colwell (my pseudo supervisor). I know
I probably was not the easiest student to supervise and I know there were many times
where you probably wanted to kill me but thank you for sticking with me. Your
guidance and support during the long draughts of positive results did not go unnoticed.
Thank you for your pointers during design of experiments and your endless feedback
on drafts. Your doors were always open and all your advice got me to this point.
To my M6 family, thank you for all the banter. This PhD wouldn’t have been so
enjoyable without the lunch time breaks, pub crawls and random debates. You helped
me come in on the weekends because I knew there would always be someone around
to keep me from going crazy. Particular mention to the organic group, thanks for the
support in group meetings and having my back if I had a bad week.
Defence Materials Technology Centre, you did not just give me financial support; you
gave me a professional family. I have looked forward to every meeting, every
workshop and every conference, not just for the material but for the friendships I had
made. Without your connections, I would not have won the aerospace Australia award,
which has changed my life. I truly hope that I continue to work with you.
My mates, wow you guys have dealt with a lot. Sorry for disappearing for weeks at a
time and for random rants at weird hours. I know you guys didn’t always care about
my project but thanks for listening. A PhD can be very lonely but knowing you guys
were only a text away meant a lot. You keep me grounded when my ego enlarged but
P a g e | xxx
you lifted me up at my lowest. Only you guys truly know the emotional drain of a PhD
and I’m sure I have successfully turned you off doing one.
Grace, you truly witnessed how hard the last 5% is. Thank you for your moral support
and not allowing me to give up. I knew I couldn’t let you go when you selflessly
offered to proof my paper drafts. It has been a long journey, thank you for
understanding. I love you and bring on our next journey.
Last but obviously not least, my family. You guys were my support all the way
through, from big hugs to home cooked meals. No matter how bad my research was
going, you were always proud. I knew I could never disappoint you and every small
achievement was a celebration. This PhD is dedicated to you.
C H A P T E R O N E
P a g e | 1
1. INTRODUCTION
1.1. Synthetic Polymers
The production of the current widespread, convenient and affordable synthetic
polymers and plastics has been an area of significant and ongoing research interest.1-2
Henri Braconnot was the first to discover a polymer, chitin, in 1811,3 although Jöns
Berzelius coined the term ‘polymer’ in 1827.4 The first exclusively synthetic polymer,
Bakelite, was synthesised by Leo Baekeland in 1907.5 Industrial research by Wallace
Carothers in the 1930s and a critical shortage of rubber during WWII saw a significant
increase in synthetic polymer production.6 Since 1950, there has been an exponential
growth of polymer production worldwide.7 In 1950, global polymer production was
1.3 million tonnes annually and in 2016 it reached approximately 335 million tonnes.8
Figure 1: World and European polymer production annually 1950-2016 (graph created from data
compiled from PlasticsEurope's Market Research and Statistics Group. 7-10
C H A P T E R O N E
P a g e | 2
As the use of polymeric materials became more popular, the number of polymer
classes increased. There are now a wide assortment of polymer structural types, with
differing strengths, flexibilities, appearances and densities for different applications.7,
9 However, only five of these classes constitute almost 75% of the total global polymer
demand. 9 In order of demand these are:
1. Polyethylene (Low Density (LDPE); Linear Low Density (LLDPE) and High
Density(HDPE))
2. Polypropylene (PP)
3. Polyvinylchloride (PVC)
4. Polystyrene (Solid (PS) and Expanded (EPS))
5. Polyethylene Terephthalate (PET)
Polyolefins account for over 50% of the total global production of polymers. This
group includes polymers such as polyethylene which are synthesised with a simple
alkene monomer (Figure 2). The popularity of polyolefins is due to their inexpensive
synthesis and inert characteristics. However, as 40% of the total global polymer
production of polyolefins is for short-life products such as packaging, the degradation
and recycling of these products has become a primary focus in recent decades and will
be discussed later within this thesis.7
C H A P T E R O N E
P a g e | 3
Figure 2: The pathway to synthesis of the polyolefin, polyethylene, from the ethylene monomer.
1.1.1. Polymer Degradation
The degradation of a polymer involves several physical and chemical reactions. As the
degradation process is accompanied by small structural changes, this can lead to the
quality of the polymeric material being significantly compromised. This results in the
properties changing and ultimately leads to a loss in functionality.11 In order to extend
the serviceable lifetime of polymeric materials, the chemical processes involved in
polymer degradation have been studied extensively.
The degradation pathway of polyolefins is typically a chain of complicated radical
reactions resulting in several products. It is said to be an auto-oxidative process and it
is proposed to follow these simplified general reactions1:
• Initiation: when radicals are generated in the presence of a source of energy.
• Propagation: when the radical is transferred from one chain to another.
Crosslinking occurs when the overall molecular weight increases and chain
scission occurs when the overall molecular weight decreases. This happens
C H A P T E R O N E
P a g e | 4
when the concentration of radicals increases in the polymer matrix. Often once
this process has begun, it will continue at an increasing rate until termination.
• Termination: when radicals react with each other to form inert products. This
stabilises the polymer by reducing the number of radicals.
Different polymeric materials have characteristic modes of degradation.6 Each
polymer can degrade through a variety of mechanisms; yet it is often difficult to
determine the process through which degradation has occurred. For example, varying
temperatures and radiation levels provide different sources of energy and therefore
different potential pathways to aid the degradation processes.11
The sources of degradation vary, depending upon the environmental conditions in
which the polymer is used, its manufacturing history and the structure of the polymer
itself. These all play an integral role in controlling the overall rate determining step of
initiation. Degradation processes which polymers may undergo in everyday use are:12
1. Thermal: occurs when the polymer is heated to a temperature where it
undergoes chemical changes without simultaneous involvement of another
compound. This may occur during processing, and it often involves
oxidation.13
2. Mechanical: occurs with the application of forces or physical breakage,
resulting in potential chain scission.12
3. Ultrasonic: occurs with the use of sound at certain frequencies that can
induce the polymer chains to vibrate and split.12
4. Chemical: occurs when corrosive chemicals or gases (i.e. ozone), attack
the structure of the polymer, causing chain scission and oxidation.12
C H A P T E R O N E
P a g e | 5
5. Biological: this is specific to polymers that contain functional groups that
can be attacked by microorganisms, such as esters.12, 14
6. Radiation: on exposure to sunlight or high energy radiation, either the
polymer itself or impurities which are left in the polymer from processing,
can absorb the radiation and initiate reactions. In the case of high energy
radiation, the polymer chains will split directly.12
Despite the popularity of polyolefins, they display extremely low resistance to
oxidative degradation. They need a combination of processing, heat and stabilisers to
guarantee their long-term performance.15 This is common for many polymeric
materials when exposed to an oxygen rich environment. Excess oxygen accelerates
oxidation reactions and the formation of oxygen derived radicals which further
accelerates the degradation process.16-17
1.1.2. Weathering
When polymeric materials are used in an outdoor environment, they are subjected to a
wide variety of environmental factors. This process is known as weathering and is
influenced by a number of factors which can have both individual and combined
effects on the resulting behaviour of a material.18 The outdoor environment can vary
in a number ways; sunlight, temperature, rainfall and wind. These factors also vary
widely in duration, intensity and sequence.19 However, the main influence on the
weathering of polymeric materials is the involvement of oxygen, shown below in
Figure 3.
C H A P T E R O N E
P a g e | 6
Figure 3: General schemes of oxidation of polymeric materials
1.1.2.1. Photo-Oxidative Degradation
For most polymeric materials, the main cause of weathering is photo-oxidative attack,
which is the combined action of oxygen and sunlight on the chemical structure.19
Photo-oxidation is classified into two main types depending on the mode of light
absorption. Energy can be absorbed through units or groups which form part of the
polymer, such as aromatic pendant groups, or it can be absorbed through an impurity
within the polymer matrix which contains a chromophore.20-21 Polyolefins normally
do not contain UV absorbing chromophores, but trace amounts of chromophore-
containing impurities often remain after processing such as polymerisation catalyst
residues which can lead to photo-oxidation of the polymer.22-23
C H A P T E R O N E
P a g e | 7
The initiation step of polymer degradation is caused by radical formation following
photon absorption. The degradation is normally concentrated on the surface of the
material. This is due to high rates of initiation which leads to oxygen depletion in the
solid state. This depletion is normally due to the low oxygen diffusion in the polymer.
1.1.3. Accelerated Weathering
The degradation of many polymer materials occurs at a slow rate outdoors, with no
apparent change in properties for extended periods. This has resulted in the need for
accelerated artificial exposure tests to reduce the significant amount of time required
to observe measurable degradation outdoors.
Accelerated ageing of polymers is often used to give insight into the serviceable
lifetime of polymers in particular environments. Relating laboratory ageing
experiments to real lifetimes is a difficult task, due to the many variables experienced
during actual in-use conditions.14 For example, one accelerated ageing protocol is
photo-oxidative testing, using xenon arc solar simulators. A range of solar simulators
are available, but these often do not emulate environmental elements such as morning
dew, pollution or changing temperatures throughout the day, all of which will affect
the degradation behaviour of polymer materials.24 Therefore, accelerated testing and
outdoor exposure should be used in combination to understand how the accelerated
ageing protocol used relates to the lifetime of a material outdoors.25
1.1.4. Degradable Materials
As mentioned, polymers are often used for short life products, therefore polymer
degradation is not always an undesirable process; with control, it can have beneficial
C H A P T E R O N E
P a g e | 8
outcomes to the environment. The disposal of plastics causes problems because of the
same properties which make them useful: durable, inert, and resistant. The National
Geographic Society26 believes there are 5.25 trillion pieces of plastic debris in the
ocean27, 269,000 tones float on the surface, while some four billion plastic microfibers
per square kilometre litter the deep sea.28 It is not surprising that there is currently
extensive research into environmentally degradable plastics, to alleviate plastic waste
disposal problems.
An optimal degradable material is one that is reduced to carbon dioxide, water and
minerals, leaving no environmentally harmful residues. There are three major methods
to degrade polymers:29
1. Biodegradation: The polymer is broken down by microbes metabolizing the
polymers into harmless products.
2. Chemodegradation: The polymer is degraded through chemical treatment.
3. Photo-degradation: The actions of ultraviolet light (usually sunlight) break
downs the polymer chains.
Degradable polymers benefit the environment by reducing waste, they can also present
great advantages for farmers by enabling control over moisture and weed growth.30
Biodegradable polymers have also found uses in medicine in areas such as drug
delivery, wound management and tissue engineering. 31-32 However, to gain control
over rates of degradation these polymers typically contain stabilisers and UV
absorbers.
C H A P T E R O N E
P a g e | 9
1.1.5. Stabilisers
Most polymers require some form of protection against the effects of solar radiation
to create control over their serviceable lifetime. Completely effective stabilisation is
never achieved in a commercial practice. In many cases, antioxidants and light
stabiliser degradation products can actually reduce the final stability of the polymer.12
As previously mentioned, polyolefins are unstable under weathering conditions but
with the addition of stabilisers, their useable life span can be increased dramatically.
To protect polyolefins from oxidative damage, antioxidant-based stabilisers are added
to trap the radical intermediates formed during degradation. This can lengthen the
initiation stage which is called the induction period. There are two main types of
antioxidants usually employed: phenolics and hindered amines.11, 21 Alternatively to
reduce the overall amount of radicals produced during degradation, a UV absorber can
be added to a polymer to absorb the UV irradiation associated with weathering.
1.1.5.1. UV Absorbers
In the case of UV absorbers, it is essential that they cause rapid dissipation of the
absorbed UV radiation via a suitable intramolecular rearrangement. Ortho-
hydroxyaromatics are designed to absorb the UV portion of the sunlight spectrum in
the range of 290-400 nm. The deactivation is thought to be due to an excited state
intramolecular proton transfer (ESIPT) mechanism.33 This results in a decrease of
energy being absorbed by the material thereby increasing its useful lifetime, Scheme
1.
C H A P T E R O N E
P a g e | 10
Scheme 1: An example of the coupled electron and proton-transfer mechanism using 2-(2-hydroxy-5-
methylphenyl)benzotriazole (1). (a) Photoinduced formation of charge-transfer activated complex. (b)
Proton transfer from the activated complex.33
1.1.5.2. Phenolic Antioxidants
Phenolic antioxidants are a diverse group of stabilizers. They can also absorb UV light
and chelate metals. As previously mentioned, free radicals mediate the degradation of
polymers. The two main types of radicals involved in polymer degradation are carbon-
and oxygen-centred radicals, R• and ROO•, that can be scavenged by the chain-
breaking antioxidants through an electron acceptor process, Scheme 2.
C H A P T E R O N E
P a g e | 11
Scheme 2: Phenolic antioxidant pathway.
1.1.5.3. Hindered Amine Stabilizers (HAS)
Hindered amine stabilizers were initially designed to act as light stabilizers (HALS)
although they have been shown to also increase thermal stability. At present, hindered
amine stabilizers are used as additives in most polymers, due to their ability to lengthen
their useable lifetime. Aromatic and heterocyclic amines are also popular stabilizers
for PO rubbers and coatings.
Aminoxyl radicals are formed during light exposure, or from chemical oxidisation.
They have antioxidant, antifatigue, antiozomant and photostabilizing properties due to
their able to scavenge R• and ROO•, which is a key stabilization pathway. The
regenerative property of the nitroxyl specie adds to the popularity as an additive. This
process known as the Denisov cycle, shown in Scheme 3.11, 34
C H A P T E R O N E
P a g e | 12
Scheme 3: Amine antioxidant pathway, known as the Denisov cycle. 11, 34
The stability of polypropylene during processing and its long term performance
depends on the heavy use of stabilisers which are designed to scavenge the free radicals
or their reactive precursors formed during degradation.35 The effectiveness of HAS
rely on the oxidation of the secondary or tertiary amine by the polymer-bound
hydroperoxide to form a nitroxide moiety. This then acts as a potent scavenger of
polymer alkyl radicals.11
1.2. Nitroxide Free Radicals
Free radicals are defined as an atom, compound or ion with an odd number of electrons
which are typically highly reactive and are generally short-lived transition species,
such as the radicals formed during polymer degradation. Nitroxides, however, are a
group of compounds that contain a stable, kinetically persistent free radical.
Nitroxides, also known as aminoxyl or nitroxyl radicals, contain a tertiary nitrogen
bonded to an oxygen radical which provides unique stability, allowing them to be
isolated and measured by EPR spectroscopy. The first nitroxide radical was an
inorganic nitroxide called Fremy’s salt (10) and was reported in 1845.36 Research in
this area was further progressed with the preparation of 4-oxo-2,2,6,6-
C H A P T E R O N E
P a g e | 13
tetramethylpiperidine-N-oxyl radical (4-oxo-TEMPO, 11) which displayed a
persistent nitroxide radical by Lebedev and Kazarnovsky in 1959.37
Figure 4: Early examples of free radicals
The popularity of nitroxides grew due to their distinctly unique physical and chemical
properties. Research into nitroxides has led to long list of applications in polymeric
materials,38 spin probes in biophysics,39 mechanistic probes in organic chemistry,40
and nitroxide-mediated polymerization control agents.41 One of the most important
features of nitroxides is their paramagnetic properties. The positive magnetic
susceptibility arising from the spin of the unpaired electron (S = ½) has in recent times
been used in the applications of spin labels which was pioneered by McConnell and
his collaborators in 1965.42-43
1.2.1. Nitroxide Stability
The stability of nitroxides is due to the stabilization energy (ca. ~120 kJmol-1 /32
kcal/mol)44 of the unpaired electron shared between the oxygen and nitrogen atoms,
shown in Scheme 4.45 In addition to this, the orbital overlap interaction between the
nitrogen non-bonding lone pair and the unpaired electron generates a three electron, 2
centre π bond, giving rise to the unique radical stability observed over other radical
species. Nitroxides can readily undergo reversible redox reactions; they can either be
oxidized to the oxoammonium ion or reduced to the hydroxylamine respectively,
Scheme 4.
C H A P T E R O N E
P a g e | 14
Scheme 4: Resonance of nitroxides and reversible redox structures
A radical commonly reacts with another radical species to form a stable product.
Although in the case of nitroxides, the formation of a O-O dimer is energetically
unfavourable due to the formation of a weak heteroatom nitrogen-oxygen-oxygen-
nitrogen bond being generated.46-47 The addition of steric bulk around the radical also
decreases the likelihood of bi-molecular reactions with itself.
It has been shown that nitroxides containing one or more hydrogens on the α-carbon
to the nitroxide group are typically unstable. These species preferentially undergo
disproportionation reactions to form nitrones and hydroxylamine species.48-49 The rate
of disproportionation depends on the surrounding substituents and solvent, Scheme 5.
Scheme 5: Disproportionation reaction
In addition to this, increased conjugation around the α-position may increase
thermodynamic stability to the system but it results in a less stable radical. This is due
to the formation of a stable carbon centred radical which results in a new pathway for
disproportionation.50 This is shown by tert-butyl phenyl nitroxide (12),51 in Scheme 6.
C H A P T E R O N E
P a g e | 15
Scheme 6: Disproportionation of tert-butyl phenyl nitroxides
Volodarsky45 summarised the factors which contribute to the stability of nitroxide free
radicals. The thermodynamic stability to the radical is due to the delocalization of the
unpaired electron over the N-O bond. The potential for dimerization is lowered due to
formation of the weak NO-ON bond. A reduction in bimolecular reactions can be
achieved by bulky substituents attached to the nitrogen atom. From these observations,
it has been widely concluded that bis(t-alkyl) nitroxides are now widely recognised as
the most stable of the nitroxide classes.52
Figure 5: Examples of Bis(t-alkyl) nitroxides
1.2.2. Isoindoline Nitroxides
Isoindoline nitroxides (17) are known for their superior chemical and thermal
stability.53 The earliest example of an isoindoline nitroxide was reported by Rozantsev
C H A P T E R O N E
P a g e | 16
in the 1960s with the synthesis of 1,1,3,3-tetraethylisoindolin-2-yloxyl (TEIO).54-55
Isoindoline nitroxides include all 1,1,3,3-tetraalkylisoindolin-2-yloxyls and their
aromatic-substituted derivatives, as shown in Figure 6.
Figure 6: 1,1,3,3-tetraalkylisoindolin-2-yloxyls
Isoindoline nitroxides are based on a rigid carbon framework which accounts for their
superior chemical and thermal stability.56 As previously mentioned, the absence of α-
hydrogens decreases disproportionation and α-cleavage reactions, Scheme 7. The
steric bulk around the radical group also increases the stability within the molecule as
it does not allow the radical to participate as easily in bi-molecular reactions with itself.
The aromatic ring adds rigidity to these compounds, making them less susceptible to
ring opening reactions.
Scheme 7: Unfavourable α-cleavage of TMIO
The aromatic ring also allows the incorporation of additional functionality and
therefore enables the synthesis of more complex structures with little impact to
nitroxide moiety.53 Due to the paramagnetic properties of nitroxides, they can be
difficult to characterise by NMR spectroscopy. The UV chromophore therefore is an
advantage for other analytical techniques such as HPLC and fluorescence
C H A P T E R O N E
P a g e | 17
spectroscopy. Nitroxides are also unreactive towards alkene radical addition and inert
to free radical attack with the exception of radical recombination at the nitroxide.57
1.2.3. Radical Trapping by Nitroxides
Nitroxide radicals are known for their stability against bimolecular reactions, however,
when in the presence of carbon, sulphur or phosphourus centred radicals, they react
readily at close to diffusion-controlled speeds (~107-109 M-1s-1).58 These rates can be
influenced by temperature59 solvent58 and the structure of the nitroxide (resonance
stabilization and steric protection).60 Nitroxides tend not to react with oxygen centred
radicals, due to the formation of a unstable product.57 The radical trapping reactions of
nitroxides with alkyl radicals results in a strong alkoxyamine product which is
diamagnetic so the process can easily be followed by loss of spin observed using EPR
spectroscopy or by the sharpening of the signals in the 1H NMR spectrum.
Scheme 8: Radical trapping of nitroxides
1.2.4. Excited State Quenching by Nitroxides
Nitroxides are known to be efficient quenchers of the excited singlet, doublet, triplet
and excimeric states. The mechanism is thought to be due to electron-exchange-
induced intersystem crossing and vibrational quenching/internal conversion from the
triplet state to the ground state.61-62
C H A P T E R O N E
P a g e | 18
As shown by the Jablonski diagram in Figure 7, in the normal fluorescence process, a
fluorophore can be excited from the singlet ground state (S0) to excited vibrational
energy levels through the absorption of a photon. This process is extremely rapid
taking about 10-15 s, although the return to ground state is considerably slower taking
from 10-14 s to several seconds.63 Immediately after arriving in the electronically
excited state, the molecule can dissipate some energy through vibrational relaxation
and internal conversion until it descends to the lowest vibrational level of the
electorally excited singlet state (S1). The excited molecule can then return to the
ground state via a number of pathways. This may happen through internal conversion
through excess energy being lost through molecular vibrations. This happens if the
energy difference between the ground and lowest excited state is small. Although when
there is significant difference, the excess energy can be released as the emission of a
photon (fluorescence) or by the classically spin forbidden process of intersystem
crossing (ISC).63 The molecule can also relax far from the first excited triple state (T1)
through emission of a photon, known as phosphorescence.
C H A P T E R O N E
P a g e | 19
Figure 7: Jablonski diagram64
Due to the lack of electronic repulsion in the triplet state compared to the singlet, the
triplet state lies below the excited singlet state in energy. Because the population of
the triplet state from the singlet state involves a change in spin angular momentum, the
process is classically forbidden. However, transitions from the lowest exited singlet
state to the triplet state are called singlet-triplet intersystem crossing. Most aromatic
molecules undergo some degree of intersystem crossing from the lowest excited
singlet state.
In paramagnetic species, such as nitroxides, fluorescence is reduced through the
enhanced prevalence of ISC. This process utilizes the unpaired nitroxide electron,
C H A P T E R O N E
P a g e | 20
which changes the multiplicity of the electronic states, such that doublet states (D0 and
Dn) are formed from the singlet ground state (S0) and the lowest singlet excited state
(S1) respectively, whilst the excited triplet state (T1) becomes the lowest excited
doublet state. Consequently, the previously spin forbidden transitions (S1 → T1 and T1
→ S0) become spin allowed processes.65
1.2.5. Profluorescent Nitroxides (PFNs)
The ability for a nitroxide to quench the excited singlet states of an aromatic
hydrocarbon occurs through intermolecular electron exchange interactions between
the nitroxide and the excited state compound within a collision complex.66 Stryer and
Griffith67 first proposed this could be used in applications in 1965. Fluorescence
quenching by nitroxides was utilised first by Bystryak68 but Blough66 demonstrated
the use of this property in profluorescent nitroxides with a number of seminal
publications. It has been shown that if a paramagnetic species, such as a nitroxide, is
tethered to a fluorophore, its fluorescence is quenched. However, if the nitroxide
radical is lost through a radical trapping or redox process, a diamagnetic product is
formed and this eliminates the intermolecular quenching pathway which results in the
return of the fluorophore’s fluorescence, Figure 8.66 A nitroxide tethered to a
fluorophore is therefore called a profluorescent nitroxide64 because the fluorescence is
suppressed until the radical moiety is trapped or undergoes redox chemistry to form a
diamagnetic species.
C H A P T E R O N E
P a g e | 21
Figure 8: Tethering of fluorophore to a nitroxide
1.2.6. Applications of Profluorescent Nitroxide Probes
Profluorescent nitroxides typically display suppressed fluorescence but the normal
fluorescence emission can be revealed by removal of the radical moiety through either
radical trapping or redox processes to yield the N-oxoammonium cation or
hydroxylamine. Profluorescent nitroxides therefore have the potential to be employed
as very sensitive probes for detecting alkyl radicals or redox changes.
Currently, PFNs have been employed to monitor overall cellular redox status and
detect oxidative stress.69-75 This is best shown by rhodamine (19) and sulforhodamine
B based PFNs which accumulated in the mitochondria due to their positive charge.
They have a unique reversible property of shuttling between the reduced and oxidized
form, allowing switch on and switch-off, functioning as cellular redox sensors, Figure
9. They also have a reasonably red-shifted wavelength for excitation and emission to
avoid simple absorbance in biological systems.74, 76-78
C H A P T E R O N E
P a g e | 22
Figure 9: Reduction of a rhodamine probe
Oxygen containing free radicals are involved in many pathological reactions.
Hydroxyl radical (•OH) is often reported as the most reactive and toxic oxygen radical,
and it is notoriously difficult to detect. The two most common techniques used for
hydroxyl radical detection are electron spin resonance (ESR) and aromatic
hydroxylation, however, these methods suffer from lack of selectivity, insensitivity,
limited stability and difficulties in quantification. This has resulted in the use of PFNs
to be used as a probe to detect •OH via Fenton chemistry. Fenton chemistry is the
reaction of •OH with DMSO to quantitatively to produce a methyl radical (•CH3). The
methyl radical then reacts with the PFN to produce a stable methoxyamine, Scheme 9.
This produces fluorescence increments which is proportional to the amount of •CH3
generated from the reaction of •OH with DMSO. Therefore being able to confirm the
concentration of •OH in a simple, sensitive and cost-effective manner.79-82
C H A P T E R O N E
P a g e | 23
Scheme 9: The quantitative reaction to detect hydroxyl radicals with the use of a profluorescent nitroxide
via Fenton chemistry
PFNs have been used extensively by the Ristovski group and others in the field of
environmental sciences.83-93 They have been shown to detect the formation of reactive
oxidative species (ROS), such as in cigarette smoke,85 burning logwood,86 diesel
exhaust89 and biodiesel exhaust.88 The ROS source is bubbled through impingers
containing a dilute PFN 23 (Figure 10) solution, which allows fluorescence detection
at the PFN’s emission wavelength.
Figure 10: PFN used by Ristovski’s group- BPEANO (23) and the PFN used by Micallef and Colwell-
TMDBIO (24)
In polymer chemistry, PFNs have been employed to monitor post polymerisation
transformations, 94-97 and to detect the aging of materials.35, 98-103 Micallef et al. used a
phenanthrene-based nitroxide, 24 (Figure 10) to detect free radical formation during
the degradation of unstabilised polypropylene.35
C H A P T E R O N E
P a g e | 24
The degradation was followed by infrared spectroscopy, chemiluminescence and
fluorescence, in parallel. This study showed that the profluorescent probe technique
was more sensitive than the established techniques, Figure 11. which showed little to
no information about the induction period.
Figure 11: Degradation of PFN-doped polypropylene aged under O2 at 150ºC monitored in parallel by
chemiluminescence, FTIR-ATR and spectrofluorimetry. 35
The fluorescence produced by the probe was strong enough to be imaged by
photography, Figure 12. This allowed simple and visible comparison of different
stages of degradation on the same film. This shows its true real world application in
detecting the useful lifetime of the polymer.
0
50
100
150
200
250
300
0 30 60 90 120 150 180 210 240 270 300 330 360 390
Time (min)
I Flu
ore
sce
nce (
a.u
)
0
1000
2000
3000
4000
5000
6000
I CL (
Counts
/mg/s
)
1
2
3
4
5
Oxid
ation Index
Fluorescence
■ Oxidation Index
Chemiluminescence
◊ Fluorescence
Oxidation Index
Chemiluminescence
C H A P T E R O N E
P a g e | 25
Figure 12: Comparison of non-degraded (top) and degraded (bottom) polypropylene doped with
TMDBIO104
This study was extended further with structural changes to the PFNs used and
degradation of the polymer systems under a photo-oxidative environment. The PFNs
did show some success, however there was evidence of photo-bleaching
fluorophore.101 Colwell et al. 99 also showed that the addition of stabilizers to these
systems had no adverse interactions.
1.2.7. PFN Design
PFNs have been used to provide mechanistic insight into the initiation period of
polymer degradation which is not possible using current techniques.101 However, these
results can be complicated due to PFN degradation.35 The linkage between the
nitroxide and the fluorophore can often be cleaved, resulting in the fluorescence being
returned without the nitroxide moiety undergoing any chemical transformation. For
example, a nitroxide linked to a fluorophore through an ester or amide linkage is
potentially susceptible to hydrolysis and consequential separation of the nitroxide
moiety from the fluorophore.53 One approach to overcome this potential limitation in
the use of PFNs is to build the fluorophore into the nitroxide formwork by carbon-
carbon linkages.35, 53, 105-106 This strategy may also increase fluorescence quenching by
C H A P T E R O N E
P a g e | 26
decreasing the distance of the nitroxide radical to the fluorophore and holding the
nitroxide moiety in a locked geometry within the fused π system.64
Another important strategy to improve a PFN for a particular task is altering the
fluorophore used. Fluorescence switch-on can be improved by choosing a fluorophore
with a high fluorescence quantum yield. Particular fluorophores can be used to change
the excitation and emission wavelength regimes to allow the PFN to be tuneable for
the desired application.
Shorter wavelengths can be required to minimize spectral overlap in orthogonal, multi-
dye systems. However, longer wavelengths are often desired to avoid absorbance
overlap in biological chromophores. Simple polyaromatics hydrocarbons are the
simplest system use, where longer wavelength can be simply achieved with increased
aromaticity. There is a large selection of polyaromatic hydrocarbons PFNs, based on
naphthalene 25,61, 66, 79-80, 87, 95-96, 105, 107 anthracene 26,81, 87, 108 pyrene 27,70, 109
diphenylanthracene 28,53, 69, 98, 105, 110 bis(phenylethynyl)anthracene 29,53, 69, 83, 85-86, 89-
90, 92, 98 phenanthrene 30,35, 98-101, 105, 110 and stilbene 31 98-99, 111-112 chromophores which
all have tailored excitation and emission wavelengths.
C H A P T E R O N E
P a g e | 27
Figure 13: Polyaromatic hydrocarbons used in the PFN chromophore constructs
There are many other unique fluorophores used in PFN design, such as, azaphenalene
97, 101, 106, cyanine,113 dansyl,67, 69, 71-72, 99 coumarin,94, 109, 114-115 nitrobenzofurazan,109
benzothioxanthene,116 dibenzocyclooctyne,75 and quinoline.73, 102-103, 115, 117
Goto et al. used quinoline based PFN 31 in photo-induced living radical
polymerization (LRP).117 Alkoxyamines adducts are well known to be useful
mediators for LRP, resulting in well-defined low-polydispersity polymers.
Alkoxyamine dissociates to form the carbon-centred radical and the nitroxide radical.
This dissociation can be controlled photo-chemical reaction with the use of certain
fluorophores, Scheme 10.
Scheme 10: An example of photo chemical induced living radical polymerization
C H A P T E R O N E
P a g e | 28
As previously illustrated, PFNs are often used in biological systems to monitor overall
cellular redox status and detect oxidative stress. This relies on the PFN being water-
soluble and its emission wavelength not overlapping with common biological systems.
Chromophores that have been utilized include fluorescein 34,69, 118 fluorescamine 35,82,
93 9-diethylamino-5-benzo[α]phenoxazinone (Nile red) 36,78 4,4-difluoro-4-bora-
3a,4a-diaza-s-indacene (BODIPY) 37, 78, 119-120 and rhodamine 38.74, 76-77 Even metal
complexes such as ruthenium complexed with a phenanthroline ligand, 39 which can
be applied not only as a redox sensor but also as an EPR and photophysical probe for
monitoring the interaction with B-DNA has been reported.78
Figure 14: Water soluble PFNs
However, when focusing on stability, the only PFNs that can be found in literature
with suitable photo-stability, employ naphthalene imide 40 121 and perylene diimide
C H A P T E R O N E
P a g e | 29
bases 41,122-123 Figure 15. This is now the focus of future PFN design in detection of
photo-oxidative polymer degradation.
Figure 15: Photo-stable PFN bases
1.3. Perylene Diimide
Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) is the first known example of
this polyaromatic class, described as early as 1912.124 Although PTCDA was never
used as a pigment, it led to a number of perylene diimide pigments (PDI). The first of
the pigments to emerge was dimethylimide in 1913 but it was not until the 1950s that
Harmon Colours developed a number of varying pigments and made them on an
industrial scale.
C H A P T E R O N E
P a g e | 30
Figure 16: Chemical structures of PTCDA (42) , generic PDI (41) and the bay addition locations positions
in the ring system.125
The popularity of PTCDA is due to its two synthetic handles that can undergo a
condensation reaction with an amine to give an imide derivative (PDI). Although
PTCDA shows reasonable potential for reactions, its insolubility limits number of
possible chemical transformations.126
Perylene diimides have been extensively studied in dye and pigment research due to
their excellent chemical, thermal, photo and weather stability.124, 127 Furthermore,
many perylene diimides display other interesting properties such as near-unity
fluorescence quantum yields and high photo-chemical stability which have enabled
their use in other applications involving light harvesting and charge transport.128-130
They also have a longer wavelength of fluorescence and UV absorption which avoid
the normal absorptions and emissions of common additives. Many PDIs have been
employed as photosensitizers in energy and electron-transfer reactions131 and have
very high resonance stabilization energy and π-π interactions due to their planar
molecular structure.132
Modification of PTCDA to increase solubility by the addition of substituents at the
N,N0 positions (PDIs) was first employed by the Langhals, Figure 16.133 It was noted
that addition of groups to form imide bonds increased the solubility of the resulting
PDI in organic solvents (parent compound is PTCDA). An alternative approach to
overcome solubility limitations is to incorporate substituents in the “bay”-region of the
perylene unit as substitution at these positions increases solubility through slightly
twisting the perylene unit to disrupt planar π-π stacking interactions, Figure 16.134-136
It has been stated that incorporated bulky groups into the bay positions can increase
C H A P T E R O N E
P a g e | 31
solubility by several orders of magnitude,136 which can be linked to easier purification,
high yields and assumed better polymer distribution.
As a class, perylene diimide pigments offer high tinctorial strength; as well as excellent
light and weather fastness. They have excellent solvent stability; good migration
stability in plastics; fastness to overcoating paints; high chemical inertness and
superior thermal stability.124 Due to these properties they are used in high grade paints
where their relative high cost is outweighed by their quality and durability.
1.3.1. Perylene-based PFNs
For the chromophore properties alluded to above, perylene diimides represent an
attractive base structure from which to build new generation PFNs with superior photo-
stability to enable potential monitoring of the photo-oxidative degradation of organic
materials. The structurally rigid, isoindoline-based nitroxides are attractive target
moieties for enhanced stability PFNs, as the aryl ring extends the conjugation without
delocalizing the spin. Isoindoline nitroxides are more photo-stable than the piperidine-
based nitroxides, being less prone to degradation by hydrogen atom abstraction and by
α-cleavage with UV irradiation.137
1.4. Applications of this Project
Weathering effects that result in corrosion of the structure can be prevented using
protective coatings, such as polymers. Although, as the polymer degrades, small
surface cracks can appear in the polymer’s physical structure that result in the failure
of the coating to adequately protect the surface. Therefore, careful monitoring of the
coating is essential to maintain the integrity of the structure, yet current techniques
C H A P T E R O N E
P a g e | 32
lack sensitivity in detecting materials failure. This has resulted in the necessity for
periodic maintenance of coatings to avoid the potential catastrophic failure of
materials.
In this work, it was hypothesised that by linking a robust isoindoline nitroxide to a
known photo-stable fluorophore, it will be possible to generate a more photo-stable
PFN, able to withstand the harsh photo-oxidative environment of a degrading polymer
coating during weathering. This will avoid unnecessary maintenance of coatings,
which will save time, money and weight to the structure.
1.5. Project Outline
The main objective of this project was to synthesise new robust profluorescent
nitroxides (PFNs) which can detect the photo-oxidative degradation of polymers. The
primary focus during the design of the PFNs was the use of photo-stable fluorophores,
such as naphthalene imides and perylene diimides. The nitroxide moiety could be
linked through an imide bond by a condensation reaction with the anhydride of the
fluorophore and a primary amine containing nitroxide. Another synthetic methodology
involving halogenation of the fluorophore ring would allow a nucleophilic substitution
reaction with a hydroxyl containing nitroxide to form an ether linkage, or Sonogashira
coupling with an alkyne bearing nitroxide to form an alkyne linkage, Figure 17.
C H A P T E R O N E
P a g e | 33
Figure 17: Target compounds for new robust PFN sensors
The second component of this project involves the examination of the physical
properties of the prepared profluorescent nitroxides. With the synthesis of their non-
radical analogue via Fenton chemistry, determination of the extinction coefficients and
quantum yields of the new PFNs will be undertaken. This will assess the nitroxide’s
ability to quench the excited state of fluorescence, and therefore its sensitivity as a
potential probe for monitoring the photo-degradation of materials. Perylene diimides
have a longer wavelength of absorbance and fluorescence emission, which is outside
the typical absorbance window for common polymers, stabilizers and absorbers.
Further extension of this fused aromatic ring system is possible through increased
conjugation through the linker to the aromatic ring of the isoindoline moiety.
The third component of this thesis examined the photo-oxidative stability of the
synthesised PFNs. This analysis was first undertaken in a liquid model to avoid
complications with solubility within the polymer matrix. The irradiation source, a
Heraeus Suntest CPS+, is a laboratory based artificial irradiation source. The analysis
C H A P T E R O N E
P a g e | 34
of the irradiated PFNs was followed by UV absorbance and fluorescence, in parallel.
The diamagnetic methoxyamine analogues were also examined to avoid complications
arising from the presence of the nitroxide unit. All photo-oxidative stability tests were
done in comparison with the known, thermal stable, 9,10-
bis(phenylethynyl)anthracene (BPEA) fluorophore. The nitroxide containing PFNs
were then tested to observe the potential antioxidant effect of the nitroxide moiety on
the degradation rate of the fluorophore.
In the forth component of this thesis, the novel PFNs were assessed as probes for
monitoring the photo-oxidative degradation of two different polymer matrixes,
PTMSP and TOPAS® using artificial weathering. This involved evaluation of their
solubility, photo-stability, thermal stability and finally their ability to detect
degradation by fluorescence compared with classical techniques.
Numerous additives can typically be found in traditional commercial polymer
coatings. The PFN therefore also needs to be examined in the presence of antioxidant
species (the parent isoindoline nitroxide is employed as a model antioxidant) and UV
absorbers (commercially available UV absorber, Tinuvin P). This demonstrates the
amenability of the PFN to be an effective probe in the presence of other additives. This
is important as different polymer applications will in turn lead to different weathering
conditions and additive levels.
Finally, laboratory accelerated artificial exposure results were compared against
photo-degradation achieved using true weathering conditions. This was done to ensure
that the PFNs were only affected by UV irradiation and no other weathering effects
such as moisture, wind, pollution, etc.
C H A P T E R O N E
P a g e | 35
C H A P T E R O N E
P a g e | 36
1.6. Relationship of the Research Papers
The flow diagram below shows the relationship between the aims of the PhD project
and the outcomes reported in published manuscripts. Note published paper chapters
have minor changes to fit the flow of the thesis, changes to the numbering of the
sections, compounds, figures, tables and schemes to remove double ups within the
thesis.
C H A P T E R O N E
P a g e | 37
Chapter 1- Introduction
An overview of the literature in polymers, polymer
degradation/stability, nitroxides, PFNs and the
perylene diimide fluorophore.
Chapter 2- Synthesis and Characterisation
A more detailed discussion around the synthesis and the characterisation of nitroxides, PFNs and
their non-radical derivatives. Including an experimental section of compounds that are not
included in the following chapters
Chapter 4: Profluorescent nitroxide sensors for monitoring photo-induced degradation in polymer films
Analysis of laboratory based photo-oxidative and thermal-oxidative stability studies of all PFNs and their non-radical analogues doped in PTMSP and
TOPAS® films. 10.1016/j.snb.2016.09.104
Chapter 5: Profluorescent nitroxide sensors for monitoring the natural aging of polymer materials
A detailed study into the differences between accelerated weathering conditions compared to a true Brisbane summer. With focus on photo-degradation rates of
films doped with PFNs compared to blank TOPAS films, with the addition of radical traps in different concentration and addition of UV absorbers in different
concentrations and their effect of photo-degradation rates.
Chapter 3: Polyaromatic Profluorescent Nitroxide Probes with Enhanced
Photostability
A brief discussion about the synthesis of PFNs with analysis of their physical
characteristics such as excitation and emission wavelengths, extinction
coefficients and quantum yields. Photo-oxidative stability of the non-radical
analogues was analysed in cyclohexane which gave promising results.
10.1002/chem.201503393
Chapter 6: The synthesis and stability of novel Ferrari-Red PFN
Analysis of laboratory based photo-oxidative and thermal-oxidative
stability studies of the novel Ferrari red based compounds doped in
PTMSP and TOPAS® films.
C H A P T E R T W O
P a g e | 38
2. SYNTHESIS AND CHARACTERISATION
A note to the reader: This chapter does discuss reactions which have been previously
published and/or are discussed in the later chapters. However, this chapter investigates
mechanisms, purification, characterisation and additional reactions that remain
unpublished in detail.
2.1. Synthesis of Nitroxide
To prepare the target photo-stable PFNs, amine, hydroxyl and alkyne bearing
isoindoline nitroxide were required. As discussed in the previous chapter (1.2),
Rozantsev synthesised the earliest example of an isoindoline nitroxide.54-55 Giroud and
Rossat pioneered the first development of the 1,1,3,3-tetramethylisoindolin-2-yloxyl
based nitroxides in 1979.138 However, Griffins139 and co-workers developed the
synthetic pathway to TMIO (55) in moderate yield which is followed below.
Developments by Bolton140 showed their synthetic potential for nitration at the 5
position of the aromatic ring which was followed by synthetic advancements 141 142
Research within the QUT Free Radical research group101, 105-106, 143-145 has optimised
the synthetic pathway to yield amino, phenolic and alkyne bearing isoindoline
nitroxides.
2.1.1. Synthesis of 2-benzyl-1,1,3,3-tetramethylisoindoline (49)
Scheme 11 was first published by Griffiths in 1973.139 A number of improvements143
have since been developed with remarkable scale-ups.
C H A P T E R T W O
P a g e | 39
Scheme 11: Synthetic route to 2-benzyl-1,1,3,3-tetramethylisoindoline 49
The first step of the synthetic pathway involved the synthesis of N-benzylphthalimide
48 through the acid catalysed condensation of commercially available phthalic
anhydride 47 and benzylamine (50), Scheme 12.
After reflux for one hour, the reaction is complete, and the product precipitates out
once poured into ice water. The desired N-benzylphthalimide 48 can then be
recrystallised from hot ethanol giving quantitative yields.
Scheme 12: High yielding acid catalysed condensation of phthalic anhydride 48
The first step of the reaction is a ring opening reaction by nucleophilic attack by the
amine of the benzylamine on the carboxyl group of the starting material. If the
temperature is not high enough, the intermediate (51) often precipitates out of solution.
During reflux, the acid promotes the ring closing reaction to generate the hemiaminal
(52) that then undergoes dehydration to produce the desired N-benylphthalimide 48.
Melting point was found to be 116-120 °C which agrees with the literature146 melting
point of 115- 117 °C. Proton NMR of the product agreed with published values, with
C H A P T E R T W O
P a g e | 40
particular notice of the benzyl CH2 hydrogens having a singlet signal, integrating for
2 at 4.871 ppm.
The second step in Scheme 11 is conversely more difficult. This step uses the Grignard
reaction to form the desired tetramethylisoindoline product from the N-
benzylphthalimide 48 starting material. The reaction was performed on a large 100 g
scale and gives the modest yield of 20% after recrystallisation.
The Grignard reagent is synthesised by drop-wise addition of methyl iodide to a
solution of magnesium in diethyl ether under an argon atmosphere. Once the Grignard
reagent is formed, it was concentrated by distillation. N-benzylphthalimide 48
dissolved in anhydrous toluene was then added drop-wise at a rate that allowed the
temperature to remain constant. This step can be extremely exothermic due to the
reactivity of the methyl magnesium iodine to the carbonyl groups of N-
benzylphthalimide, Scheme 13. However, elimination of the magnesium salt for
tetramethylation via the iminium ion is difficult due to the poor leaving group qualities
of the salt. High temperatures are needed for the modest 20% yield of the
tetramethylated product. Any ether needs to be removed by distillation before heating
to reduce the yield of the by-product, trimethylethyl product 53 (Figure 18) which was
first isolated by Griffiths139. The mixture was refluxed for 3 hours.
Scheme 13: Exhaustive methylation of 48 with methyl magnesium iodide
C H A P T E R T W O
P a g e | 41
Any remaining Grignard reagent was then quenched, the product is extracted, passed
through a basic alumina column, and recrystallised from hot methanol.
Recrystallisation is also necessary to remove the trimethylethylisoindoline by-product
(53) which is an oil at room temperature.
Figure 18: Trimethylethylisoindoline by-product (53)
Melting point was found to be 58-62 °C which agreed with the literature139 value of
63-64 °C. The addition of methyl protons was observed in 1H NMR by a singlet signal
integrating for 12 hydrogens at 1.3 ppm. Furthermore, the [MH+] parent peak was
observed at 266.1934 m/z (calc. 266.1903) in the ESI high resolution mass spectrum.
Quenching and purification of 49 has become personalised due to its difficulty, size
and solubility issues of the reaction work-up. Hexane should be poured into the
mixture when the reaction mixture is still warm. This aids the breakdown of
magnesium complexes that form during the quenching of the reaction, if complexes
persist, refluxing for an hour to help disturb the solids. This removes complications of
product being stuck in the insoluble purple salt complexes. It also eliminates the
tedious scraping and washing with hexane. Previously, the quenched hexane solution
is bubbled with air overnight. However, the hexane solution can be reduced under
vacuum with a small amount of alumina gel present. This technique removes the
excess toluene with more confidence and the dried alumina can be dry loaded for a
shorter and therefore quicker filtration. If toluene persists, the purple impurity passes
through the basic alumina filtration and elutes with the product. If the yield is
C H A P T E R T W O
P a g e | 42
considerably lower, the filtrate can be back extracted with chloroform, which dissolves
all solids. The complex mixture is then purified via column chromatography. This
process is longer and more expensive, but all solids are processed to increase the yield
of 49.
The synthesis is now split into many synthetic pathways to yield a number of nitroxides
which can be coupled to the fluorophore in different reactions to form novel PFNs.
2.1.2. Synthesis of 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl
(57)
Scheme 14: Synthetic route to 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57
Debenzylation of the Grignard product to form 54 was achieved in quantitative yield.
This reaction involves a hydrogenation at 50 psi for 3 hours when no starting material
can be observed, and the more polar product, 1,1,3,3 tetramethyllisoindoline 54 is
formed. 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO) 55 can then be synthesised
through oxygenation using meta-chloroperoxybenzoic acid (m-CPBA). It was found
that the hydrogenation reaction could be skipped, going straight from 49 to the
nitroxide product 55. However, avoiding this reaction resulted in a number of side
C H A P T E R T W O
P a g e | 43
products. This step was thus included, to avoid complicated purification with an
increased yield.
Characterization of the debenzylation was achieved through 1H NMR spectroscopy
and ESI+ HRMS. The 1H NMR spectrum was particularly valuable for confirming
successful debenzylation of the 2-benzyl-1,1,3,3-tetramethylisoindoline 49 precursor,
the loss of the characteristic CH2 (4.0 ppm), simplification of the aromatic region and
the broad singlet which corresponds to the secondary amine. Parent [MH+] peaks were
observed using ESI HRMS analysis with a peak at 176.1418 m/z, calculated at
175.1361.
The formation of the nitroxide moiety of the desired 1,1,3,3-tetramethylisoindine-2-
yloxyl 55 was formed by mild oxidation of 1,1,3,3-tetramethylisoindoline 54 using m-
CPBA. m-CPBA contains a weak peroxide bond which is displaced by the isoindoline
secondary amine. It then forms a hydroxylamine species, which is further oxidised by
oxygen in the atmosphere to form the desired nitroxide moiety. Previously Bottle et
al. have used the H2O2 -tungstate oxidation approach to generate the nitroxide moiety.
The disadvantage of this reaction is the 3 day reaction time in comparison to the near
instant reaction using m-CPBA. The reaction was left to stir overnight but peers have
quoted reactions at 30 minutes on smaller scales.147
Once the nitroxide radical has been formed, normal characterisation using NMR can
no longer be used due to their paramagnetic characteristic. The liberated methyl radical
via Fenton chemistry as able to trap the nitroxide in the presence of DMSO, this
reaction will be spoken about in more detail in the Section 2.1.4.
C H A P T E R T W O
P a g e | 44
This compound was characterised by melting point, HRMS (ESI) and EPR. The
melting point of 125-127 °C agreed with literature139 (128-129 °C). HRMS (ESI)
showed a peak which corresponded to [M+Na]+ at 213.1124 m/z (calcd. for
C12H16NNaO• [M+Na]+ 213.1130). The broadened NMR nicely complements the
sharp 3 peak EPR signal, confirming the nitroxide radical spin.140, 148
Nitration of the 1,1,3,3-tetramethylisoindolin-2-yloxyl 55 was first performed by
Bolton in 1993.140 However, it had previously been performed on the 1,1,3,3-
tetraethylisoindine-2-yloxyl.138 It resulted in a high yield of the desired product
1,1,3,3-tetramethyl-5-nitroisoindoline-2-yloxyl 56. This reaction demonstrates the
stability of the isoindoline nitroxide even when treated with concentrated acids. The
nitroxide product was obtained in high yield, with no evidence of decomposition after
work-up.
During addition of concentrated sulfuric acid, there is an immediate, strong colour
change to the reaction mixture. This is due to oxidation of the nitroxide to form the
oxoammonium salt. The nitroxide is easily recovered with oxidisation during work-up
to recover the desired product.
The desired compound 56 has a melting point of 155-158 °C was seen which agreed
with literature139 (160-162 °C). IR (ATR) showed the NO2 absorbance at 1526 cm-1.
HRMS (ESI) showed the parent [M+] 235.1207 m/z and the 258.1119 (1) [M+Na]
(calcd. for C12H15N2O3• [M] 235.11).
The simple reduction of the nitro group of the 1,1,3,3-tetramethyl-5-nitroisoindoline-
2-yloxyl 56 to the amine is the final reaction for one of the target nitroxides, 5-amino-
1,1,3,3-tetamethylisoindolin-2-yloxyl 57. Reduction at 50 psi in a hydrogen
C H A P T E R T W O
P a g e | 45
environment with use of Pd/C as the catalyst resulted in a quantitative yield of the
desired amine hydroxylamine product. The reaction resulted in the hydroxylamine
analogue due to the reducing environment being strong enough to convert the nitroxide
at the same time. This was easily overcome by re-oxidation to the nitroxide by addition
of the PdO2 in open atmosphere.
TLC showed that the compound had a reduced Rf value and no visible starting material
was present, indicating reaction completion. The product was further characterised by
HRMS (ESI) and IR (ATR). HRMS (ESI) gave the parent [M+H]+ 205.1698 m/z and
the 228.1237 m/z [M+Na] peak. IR (ATR) showed R-NH2 absorbances at 3356 and
3435 cm-1.
This product was then used in imide formation with the anhydride group of the PTCDA
(42) to form PDI PFNs. This reaction will be discussed further in Section 2.2.
2.1.3. Synthesis of 5-hydroxy-1,1,3,3-tetramethylisoindolin-2-
yloxyl (59)
Scheme 15: Synthetic route to 5-hydroxy- 1,1,3,3-tetramethylisoindolin-2-yloxyl, (59)
Previous synthesis of the phenol nitroxide by our research group was achieved through
a dilute acid catalysed reaction under reflux from the amino nitroxide which resulted
in a low overall yield of 41%.149 The diazonium salt of the nitroxide could be isolated
C H A P T E R T W O
P a g e | 46
in a high yield of 98%, and was moderately stable in a moisture free environment and
could be subsequently converted to the phenol in high yield.150
Nitrosyl tetrafluoroborate is extremely sensitive to moisture so the glove box was used
while weighing the reagent out. The reaction and addition were in a constant saturated
argon environment. The addition was drop-wise while stirred on an acetonitrile dry ice
bath. The acetonitrile solvent was freshly distilled, and the ether used to precipitate the
product was dried over sodium wire. It was found that if the ether was not dry it
catalysed the formation of the dimer 60, Figure 19 (isolated from the methoxyamine
starting material).151
Figure 19: Dimer (60) formed during diazonium reaction
Confirmation of the diazonium was achieved by FT-IR via the N≡N absorbance at
2200 cm-1. The melting point resulted in decomposition at 86-88°C with the assumed
evolution of nitrogen. HRMS (ESI) only showed the product without the boron counter
ion, plus lithium, 223.1062 m/z.
To prepare the phenol (59), the diazonium nitroxide 58 was simply refluxed at 100°C
for 24 hours in deionised water. The reaction was extracted periodically with ether to
remove the product and push the reaction completion. The isolation of the diazonium
salt resulted in a much higher yield of the hydoxyl nitroxide 59 than previous synthetic
routes.149
C H A P T E R T W O
P a g e | 47
2.1.4. Synthesis of 5-hydroxy-2-methoxy-1,1,3,3-
tetramethylisoindoline (64)
As previously mentioned, formation of the nitroxide moiety creates difficulty when
using the simple technique of NMR to characterise the compounds. The radical of the
nitroxide can also reduce stability of the compound in some reactions. To simplify the
compounds reactivity, the methyl protection group can be generated via Fenton
chemistry.
Hydroxyl radicals (OH·) can be produced from hydrogen peroxide in the presence of
a transition metal such as Fe2+. The hydroxyl radicals produced react with the solvent
(DMSO) to liberate methyl radicals that are consequently trapped by the nitroxide
moiety, to give the desired methoxyamine derivative, Scheme 16.
Scheme 16: Formation of hydroxyl radical via Fenton reaction to liberate methyl radicals from DMSO
C H A P T E R T W O
P a g e | 48
Scheme 17: The reaction pathway of the methoxyamine derivatives
Due to the limited stability of the 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57)
and 5-hydroxy-1,1,3,3-tetramethylisoindolin-2-yloxyl (59) radicals the formation of
the methoxyamine derivative was performed on 1,1,3,3-tetramethyl-5-
nitroisoindoline-2-yloxyl (56). The normal palladium catalysed hydrogenation route
was then taken to form the amine (62), which was obtained as a low melting crystalline
solid in quantitative yield.
The diazionum salt (63) was formed using the same procedure as for the nitroxide.
Although the procedure resulted in a higher yield of 97% and cleaner product
according to its sharp melting point and white crystalline solid formed upon
precipitation from dry ether. This product was not purified any further and was
subsequently refluxed in water to offend the phenol in an 80% yield with loss of yield
probably due lower solubility of 63 in water compared to the more polar nitroxide
product.
All products showed the desired methoxyamine hydrogens, integrating for 3 protons
at ~3.8 ppm. The products also lost the characteristic yellow colour of the nitroxide
C H A P T E R T W O
P a g e | 49
analogues. However, this was not evident until the prducts were purified and any trace
races of iron, which is present in the Fenton chemistry reaction, were removed.
This product was used in the nucleophilic substitution reaction with the brominated
naphthalene diimide and brominated perylene diimide material which is discussed
further in Sections 2.3.1 and 2.4.3
2.1.5. Synthesis of 5-ethynyl-1,1,3,3-tetramethylisoindolin-2-
yloxyl (69)
Scheme 18: Synthetic scheme to the 5-ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl 69
The first reaction in the, synthesis of 69, Scheme 18, was a one pot oxidative
debenzylation and bromination of the isoindoline aromatic ring to afford 5-bromo-
1,1,3,3-tetramethylisoindoline 65 which was first performed by Reid141 in a 40% yield.
Improvements were published by Micallef with an improved yield of 95%.142
However, a yield of 62% was achieved in this project, with the low yield possibly
being caused by over bromination or wet solvent during quenching.
C H A P T E R T W O
P a g e | 50
The Sonogashira coupling has been extensively studied within the research group. Due
to the low reactivity of the brominated isoindoline nitroxide towards palladium-
catalysed reactions, the iodo nitroxide was used to improve the viability of the reaction.
Aryl-iodides are known to undergo oxidative addition more readily in Pd-catalysed
couplings.53 This was overcome by iodination of the brominated analogue through
standard lithiation techniques. The reaction was performed at low temperature due to
the instability of the lithiated species. An excess (3 equiv.) of iodine was then added
to quench the lithiated species affording the N-iodoamine species in 2 steps, Scheme
19. Hydrogen peroxide was then used to reduce the resulting N-iodoamine species to
the desired secondary amine 5-iodo-1,1,3,3-tetramethylisoindoline 66.
Scheme 19: Lithiated species
There is no Rf change between the brominated species (65) and the newly formed iodo
product but there is a modest downfield shift of the aromatic proton peaks in the 1H
NMR spectrum. This can be rationalised by the reduced electron withdrawing
character of the iodo substituted analogue. This reaction is sensitive to water and can
result in the formation of 72 if hydrogen from the water is formed during the quenching
step.
The nitroxide moiety was achieved through oxidation with m-CPBA in quantitative
yield. At this point, the di-halogenated by-products can be separated through solubility
differences in hexane.
C H A P T E R T W O
P a g e | 51
Although literature procedures had shown105 that coupling of alkynes, such as
(trimethylsily)acetylene resulted in a high yield of 92%, it was found that the coupled
product had a similar Rf to the starting material and were therefore hard to separate by
column chromatography. To avoid these separation issues, 2-methyl-3-butyn-2-ol was
used despite the lower literature yield of 78%. This resulted in a much simpler
separation of trace un-reacted starting material, by- products (TMIO (55) and bromo-
TMIO (77)) and other non-polar impurities due to increased polarity of the hydoxyl
group. It was also found that addition of the protected alkyne to already refluxing KOH
resulted in a more soluble reaction mixture and a higher yield of 69.
The alkyne (69) was confirmed by HRMS (ESI), EPR and IR (ATR). The m/z, plus 2
hydrogens [M+2] was seen in HRMS (ESI) 216.1504 m/z, also 237.1254 [M+Na]+
(calcd. for C14H18NO• [M+2H]1+ 216.1388). EPR showed the desired 3 peak signal for
a nitroxide radical. Melting point agreed with literature105 value of 126-128°C. The
characteristic C≡C was seen by IR (ATR) at 2097 cm-1 and C≡C-H at 3276 cm-1.
2.1.6. Improved lodination
As described above, 5-iodo-1,1,3,3-tetramethylisoindoline (66) has characteristically
been synthesised via lithiation of the 5-bromo-1,1,3,3-tetramethylisoindoline (65).
However, a novel synthetic scheme has been developed using strongly electrophilic
iododium ions (I+).152 This method uses potassium iodide and periodic acid in
concentrated sulphuric acid to produce IOSO3H which allows direct iodination,
Scheme 20: Improved iodination of TMI.
C H A P T E R T W O
P a g e | 52
Scheme 20: Improved iodination of TMI
The published literature152 reported a ratio of 5-iodo-1,1,3,3-tetramethylisoindoline
(66) to 5,6-iodo-1,1,3,3-tetramethylisoindoline (73) of 7:3 respectively. However, the
literature stated addition of the starting material (54) as a solid to the previously formed
iodonium ion solution with thorough stirring. The di-iodo (73) by-product could be
reduced through slow addition of the iodonium solution to a chilled sulphuric acid
solution of 54. 1H NMR indicated an improved yield of 89 % for the mono (66), 6.8
% for the di (73) and 4.27 % unreacted 54. This had an improved yield of 89%
compared to the literature 34%. However, purification of the N-amino derivatives is
particularly difficult due to broadening of the elution bands of amines in column
chromatography coupled with the close Rf values of the di-iodo (73) and mono (66)
analogues. The product was therefore oxidised as a mixture and the nitroxide purified
by recrystallisation.
The oxidation of the secondary amine to form distinctive orange crystals of the
nitroxide moiety was achieved using m-CPBA. It was found that removal of all the m-
CPBA is difficult with only washing with base, so a short silica column was employed
using DCM as the elute.
C H A P T E R T W O
P a g e | 53
2.1.7. The synthesis of 5-ethynyl-2-methoxy-1,1,3,3-
tetramethylisoindoline (81)
Scheme 21: The reaction pathway to afford the methoxyamine derivatives
Since the Fenton reaction is performed in DMSO, solubility limitations can arise.
These limitations will be discussed in detail later in the chapter. Synthesis was
designed to remove the nitroxide moiety before tethering to the fluorophore to form
the target PFN. This methylamine can later be removed on the PFN via oxidation using
DCM as the solvent.
The synthesis of the alkyne was thus repeated for the methyloxyamine derivative, with
the only optimisation being the use of less polar solvent mixtures while performing
column chromatography. All products were white low melting point solids.
The product, 81, was used in the Sonogashira reactions with the brominated
naphthalene diimide and brominated perylene diimide material was discussed further
in Sections 2.3.2 and 2.4.5
C H A P T E R T W O
P a g e | 54
2.1.8. The synthesis of 5-cyano-2-methoxy-1,1,3,3-
tetramethylisoindoline (83)
Scheme 22: The reaction pathway to afford the cyano nitroxide 83 and its methoxyamine derivative 84
The procedure for palladium-catalyzed cyanation was adapted from Schareina,153
however it was applied to the 1,1,3,3,-tetramethylisoindoline by Thomas144 for the first
time. The reaction employs potassium hexacyanidoferrate(II) as the nitrile source. The
catalyst was removed from th reaction mixture via a plug filtrated using silica and
DCM/ethyl acetate mixture as the elute. The total elute was taken through to the next
step due to it polar properties. The secondary anime was then oxidised to afford the
nitroxide moiety. The nitroxide free radical was removed through Fenton reaction to
give the methoxyamine derivative 84.
2.2. 1st Generation Perylene Diimide based PFNs
2.2.1. Attempt 1
As mentioned in the previous chapter (1.3), PTCDA (42) can be easily solubilised
through the condensation reaction with a primary amine, ‘R-NH2’ to form an imide
C H A P T E R T W O
P a g e | 55
bond. It was first proposed that by the simple step-wise addition of one equivalent of
‘R-NH2’ a selective mono-addition to one anhydride of PTCDA could be achieved,
leaving the second anhydride free for secondary addition of the nitroxide (85). One
equivalent of the primary amine and one equivalent of PTCDA (42) were solubilised
by heating imidazole above its melting point of 130°C for 6 hours. However, TLC at
6 hours indicated a large amount of starting material and product with the same Rf as
the N,N′-‘R’ 3,4,9,10-perylenetetracarboxylic diimide (41) product. After purification
by column chromatography, the reaction was found to be unsuccessful with 41 as the
major product. This was due to the dramatic increase of solubility of 85 from 42, which
resulted in an increase of reactivity.125 This lead to rapid secondary addition and
consumption of the amine. This hypothesis was confirmed by the ~50% yield of the
N,N′-‘R’ 3,4,9,10-perylenetetracarboxylic diimide (41) and 50% unreacted PTCDA
(42), Scheme 23.
Scheme 23: The unsuccessful first synthetic pathway to form a PDI PFN
C H A P T E R T W O
P a g e | 56
2.2.2. Attempt 2
According to literature, 41 can undergo partial hydrolysis of the imide bond to form
the anhydride 85.126, 154-156 This would result in the consumption of the previous
reaction (a) by-products in Scheme 24.
Scheme 24: The unsuccessful partial hydrolysis and reforming of the anhydride
N,N′-‘R’ 3,4,9,10-perylenetetracarboxylic diimide (41) was heated at 85°C in a basic
solution of KOH for 1.5 hours. The product was then precipitated out of solution with
HCl and acetic acid. TLC showed the formation of a new product with increased
polarity. NMR indicated a reduced symmetry and a decreased number of signals in the
aromatic region. Using initial characterisation, reaction (b) appeared to have worked.
However, the subsequent condensation reaction (d) failed to result in the target
compound 85. It was assumed that the anhydride reformation was unsuccessful and
the di- acid 87 was present. The successful removal of the second ‘R’ group would
show reduced symmetry and in decrease of signals in the aromatic region using NMR.
ATR-IR showed a broad OH stretching but initially that was mistaken for water. After
C H A P T E R T W O
P a g e | 57
the acid was assumed to be present a further experiment was performed to recyclize
the diacid 87 to give the anhydride 85 (c). This was done by refluxing in acetic
anhydride. However, TLC showed the generation of many unidentifiable products
which were unable to be purified.
2.2.3. Attempt 3
The third proposed synthesis was a one pot mixed addition. One equivalent of 2,5-di-
tert-butylaniline (88) was first reacted as the ‘R-group’. The amine was heated in
imidazole with one equivalent of 57 and one equivalent of 42 with a Lewis acid catalyst
(zinc acetate) for 6 hours at 130°C. The reaction gave 3 major products by TLC. It was
determined that the least polar product was 89 and the most polar was 44 by Rf
comparison with authentic compounds, shown in Scheme 25. The unknown middle
fraction was isolated by column chromatography in 22% yield. The product was
characterised first by 1H NMR spectroscopy which showed broadened signals which
is characteristic for the presence of a nitroxide radical. The nitroxide was also
confirmed by EPR, which showed a typical 3-line signal.
C H A P T E R T W O
P a g e | 58
Scheme 25: Single pot reaction and its side products
As a result of the large molecular size of the compound 90, only part of the NMR
spectra of the compound was affected by the radical, Figure 20. This resulted in the
‘aniline’ signals being visible in the NMR spectrum, Figure 20. It was noticed that the
integration was halved in the corresponding signals for 2,5- di-tert- butylphenyl
compared to aromatic hydrogens on the perylene diimide structure. Analysis by HPLC
confirmed the purity of the compound, which proved that it wasn’t a mixture of the
two symmetrical PDI compounds 89 and 44.
C H A P T E R T W O
P a g e | 59
Figure 20: 1H NMR comparison of the 3 major products in deuterated chloroform. Top: 90 (top), 89
(middle) and 44 (bottom).
To gain further information, a methylamine derivative of the target compound was
synthesised to sharpen the NMR signals by removal of the nitroxide moiety. The
nitroxide radical was trapped with methyl radicals generated by using Fenton
chemistry. The 1H from this product 90 revealed signals at 7.09, 7.21 and 7.30 ppm
for the aromatic isoindoline portion of the molecule, which indicates the success of the
nitroxide incorporation in the previous reaction, Figure 20.
C H A P T E R T W O
P a g e | 60
Figure 21: 1H NMR comparison of the 3 major products (after the Fenton chemistry) in deuterated
chloroform. Top: 89 (top), 92 (middle) and 91 (bottom).
Synthesis of the second target compounds, 94 was attempted using the first one pot
mixed addition method, using ethylene glycol solubilising chain as the ‘R-group’. It
was found to be unsuccessful due to the differing reactivities of the aromatic and
aliphatic amines, Scheme 26. The reaction gave N,N′-
Bis(methoxytetreethyleneglycol)perylene-3,4,9,10-tetracarboxyl-bisimide (95) as the
major product as identified by TLC comparison with authentic compound. It was
hypothesised that the reactivity of the primary amine on the glycol was greater than
the aniline of the TMIO.
C H A P T E R T W O
P a g e | 61
Scheme 26: Unsuccessful single pot synthesis of PFN 94
C H A P T E R T W O
P a g e | 62
2.2.4. Improved Target Compound Synthesis
Figure 22: New and improved target compounds and their methoxyamine derivatives
A series of new target compounds were proposed, all solubilising ‘R-groups’ were
aniline based amines, Figure 22. All three target compounds and methyl derivatives
were synthesised. The reaction gives a yield of ~25% for the target compound and
~50% in the Bis-R. This reaction could be improved by differing the equivalent of the
R-groups to increase yield of the target compound. The reaction is a one pot reaction
but it results in an extensive purification process by column chromatography. Due to
the low solubility of the perylene diimide derived products, this process is very time
consuming and expensive.
C H A P T E R T W O
P a g e | 63
Scheme 27: General reaction scheme for first generation perylene PFNs
Due to poor solubility of the perylene diimide PFNs in DMSO, the yield of the
methoxyamine via Fenton chemistry was poor in comparison to other small molecule
derivatives. It was noted that sonication in DMSO resulted in side reactions which was
further comfirmed by other group members.88 Development of a method for facile
removal of the methyl group to liberate the nitroxide radical has now been developed
and will be detailed further in the future work section, 7.2.
2.3. Synthesis of Naphthalimide PFNs
Due to the synthetic complications with the perylene diimides PFNs, the naphthalene
fluorophore (naphthalimide) was used as a model reaction. Naphthalimide’s structure
and reactivity is similar to perylene diimide’s, however due to its high solubility, it
results in higher yields. These properties will later be compared to see if these
advantages outweigh perylene’s physical stability and high quantum yields.
C H A P T E R T W O
P a g e | 64
Scheme 28: The overall synthetic scheme of naphthalene-based PFNs
Rotstein et al.157 electrophilic halogenation literature procedure for the bromination of
the naphthalene ring was followed due to its simplicity and near quantitative yield. A
simple condensation reaction to form the imide using the literature conditions
described by Hamel.158 It gave a cream solid with a melting form of 205-207°C in high
yield. HPLC and proton NMR was used to demonstrate its purity. Through ESI+
HRMS analysis the [M+ Na] peaks were observed for 103 at 486.0910 m/z and
488.0894 m/z in the ESI mass spectrum which corresponded to 79Br and 81Br isotopes
of 103 respectively (calc. 486.1045 and 488.1024). It was observed that there was a
notable fluorescence decrease due to heavy atom quenching.159-162
C H A P T E R T W O
P a g e | 65
2.3.1. Synthesis of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide
(105)
Scheme 29: Nucleophilic substitution reaction employed for the synthesis of 105
The first approach for further functionalisation of the brominated naphthalene (103)
was to react phenol nitroxide (59) in a base assisted nucleophilic phenoxide
substitution reaction. This was achieved by heating with KOH in DMF to give
substituted naphthalimide 105 in quantitative yield (99%) following the procedure
published by Hamel.158 Due to the nitroxide moiety being present, EPR was performed
to show the radical species. The product showed the desired [M+Na]+ peak at
612.28855 m/z. (cal. 589.3066) using HRMS ESI and ATR-IR showed the
characteristic absorption band due to the nitroxide moiety.
C H A P T E R T W O
P a g e | 66
Scheme 30: Nucleophilic substitution reaction to link the protected nitroxide to synthesis 104 and then
oxidise to afford the nitroxide moiety 105
As discussed, perylene diimides have limited solubility in DMSO, this resulted in the
nitroxide moiety being removed at an early stage in the synthesis. Therefore 5-
hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64) was used and undergoing the
same nucleophilic substitution with bromo naphthalimide (103) in a basic DMF
solution with mild heat to give substituted naphthalimide 104 in high yield (84%)
following the procedure published by Hamel.158 Characterisation was confirmed by
NMR and MS. Through ESI+ HRMS analysis the [M+ Na] peak were observed for
104 at 627.3095 m/z (calc. 627.3199 [M+Na]). Proton NMR showed all 11 aromatic
signals and the methoxyamine group at 3.81ppm. Removal of the methoxyamine of
104 was readily achieved to yield nitroxide 105 in good yield (78%) by oxidation with
m-CPBA in a Cope-type elimination, as illustrated in Scheme 31.147
C H A P T E R T W O
P a g e | 67
Scheme 31: Proposed deprotection mechanism via N-oxidation and subsequent Cope-type elimination147
Both methods proved to be successful, however Fenton chemistry is known to have
limitations. It proves to have varying yields, the large compounds have low solubility
in DMSO and is hard to scale up. Oxidation in this case seemed successful and easier
to follow because all the products could be characterised by proton NMR apart from
the final nitroxide product.
C H A P T E R T W O
P a g e | 68
Figure 23: 1H NMR comparison of the aromatic region of 105 (top) and 104 (bottom) in deuterated
chloroform.
Proton NMR analysis shows that with the nitroxide radical present, the signals on the
aromatic ring of TMIO (a, b and c) disappear due to the paramagnetic effect of the
radical. However, this effect is distance dependent, with only the signals within the
circle surrounding above being affected. However, the 2,5-di-tert-butylaniline signals
(d, e and f) are still strong and sharp. Due to the bent structure of the ether linkage,
signal k is not visible, however proton G which is furthest away out of the naphthalene
signals still shows its doublet characteristic properties.
C H A P T E R T W O
P a g e | 69
2.3.2. Synthesis of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-
1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-naphthalimide
(106)
Scheme 32: Sonogashira coupling to form 106
The alkyne link naphthalimide nitroxide, 106 was prepared via palladium-catalysed
Sonogashira coupling using similar conditions to a previously successful nitroxide
moiety coupling to a fluorophore.53 The coupling of the bromo naphthalimide 103 with
the alkyne bearing methoxyamine 81 in the presence of CuI and freshly prepared
tetrakis(triphenylphosphine)palladium(0)163 gave the desired substituted
naphthalimide 106 in high yield (90%).
As mentioned, the nitroxide moiety can be present during Sonogashira reaction,
however removal of the nitroxide radical via Fenton chemistry will cause
complications. This is due to the vulnerability of alkyne linkages to radical attack
experienced during a Fenton reaction, therefore methylamine was used due to the
previous success of oxidative removal of the methyl group. When comparing the
C H A P T E R T W O
P a g e | 70
methoxyamine of the ether and the alkyne linked naphthalimide, there are many
similarities, as shown in Figure 24.
Figure 24: 1H NMR comparison of the aromatic region of 106 (bottom) and 104 (top) in deuterated
chloroform.
When comparing the methoxyamine of the ether and the alkyne linked naphthalimide
there is the same multiplicity for each signal as expected and the ppm for the 2,5-di-
tert-butylaniline signals are identical. The isoindoline aromatic signals move up-field
on the ether linker PFN however, the large change is on the naphthalene ring. Where
signal ‘k’ moves almost 1 ppm downfield on the ether linked PFN. Showing the effect
of shielding due to the bent structure of the ether linkage compared to the straight
alkyne linkage.
C H A P T E R T W O
P a g e | 71
2.3.3. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-
naphthalimide (107)
Scheme 33: Oxidation to form nitroxide moiety of 107
Deprotection of the methoxyamine on the nitroxide of 106 was accomplished under
similar oxidative conditions as the ether linked naphthalimide to afford nitroxide 107
in excellent yield (97%). This reaction was done carefully to ensure the alkyne was
not also oxidised. Reaction was complete within 5 minutes and was quenched using
2M NaOH. EPR showed the characteristic nitroxide 3 peak signal. The product had a
slightly higher melting range of 165-170°C compared with other literature examples
but purity was confirmed by HPLC.
Due to the size of the molecules, both the ether linked and alkyne linked naphthalimide
PFN had regions within the NMR which were unaffected by the paramagnetic nature
of the nitroxide. They are affected by broadening as highlighted in Figure 25.
C H A P T E R T W O
P a g e | 72
Figure 25: 1H NMR comparison of the aromatic region of 106 (bottom) and 107 (top) in deuterated
chloroform.
The protons assigned to the isoindoline ring (a, b and c) do not appear when the
nitroxide moiety is present (circled above). However, as the distance increases, the
paramagnetic broadening effects decrease, and the fluorophore’s hydrogen signals
appear unaffected. This allowed comparison to the methoxyamine derivative due to
the little change in the ppm between the methoxyamine and the nitroxide.
C H A P T E R T W O
P a g e | 73
2.4. Synthesis of the Bay Region of Perylene Diimide PFNs
Perylene diimides have shown their photo-stability as fluorophores which has been
reviewed in the previous section (1.3). Due to the success of the naphthalene imide
reactions, the same reactions were planned for the perylene diimide fluorophore due
to their similar physical properties. However, perylene has a larger aromatic ring
system which results in multiple addition points.
Conditions for the bromination of the perylene bay region was first reported by Boehm
et al. in 1997.134 It resulted in a mixture of 1,7 and 1,6 regioisomers and a small
amount of tribromo, illustrated in Scheme 35. However, it is well known that the
separation of the regioisomers are difficult due to their limited solubility.164
C H A P T E R T W O
P a g e | 74
Scheme 34: Overall synthetic scheme for bay region perylene PFNs
C H A P T E R T W O
P a g e | 75
2.4.1. Synthesis of dibromoperylene-3,4,9,10-tetracarboxylic
dianhydride (112)
Scheme 35: Products of bromination reaction (112)
The bromination of PTCDA (42) is well reported in the literature. It requires harsh
reaction conditions with the use of Br2 in refluxing concentrated sulphuric acid and a
catalytic amount of iodine.165 Based on previous reported observations, it was
presumed that the crude mixture contains both the 1,7- dibromo-perylene dianhydride
(112) and 1,6-dibromo-perylene dianhydride (119) regioisomers and potentially a
small amount of the 1,6,7-tribromo-perylene dianhydride (120). However, limited
solubility meant that these regioisomers could not be detected by 1H NMR
spectroscopy at 400 MHz.127 The reaction mixture was neutralised which resulted in
precipitation of the products. The products were thoroughly washed with water and
dried in an oven. The products are not soluble in organic solvents and as result of this,
they are reacted as a crude mixture and purified after the following reaction step.165
C H A P T E R T W O
P a g e | 76
2.4.2. Synthesis of N,N′-Bis(2,5-di-tert-butylphenyl)-1,7-dibromo-
3,4,9,10-perylene dicarboximide (113)
Scheme 36: Synthetic scheme for the condensation reaction to form 113
Imidization of the crude brominated perylene dianhydride product was performed by
refluxing in propionic acid with 2,5-di-tert-butylaniline. It resulted in a dramatic
increase in solubility compared to other perylene diimide compounds by twisting the
planar structure to disfavour the formation of π-π aggregates. 1H NMR spectroscopy
of the mixture showed predominantly the 1,7-dibromo-perylene diimide 113, however
the 1,6-dibromo perylene diimide regioisomer was found in 34% of the mixture and
1% of the 1,6,7-tribromo compound, Figure 26. Separation of the desired compound
113 from the other isomers by column chromatography could not be achieved. In the
literature, purification of similar isomers could be achieved by recrystallisation,
although this was also found to be unsuccessful.166 The mixture therefore was carried
forward without further purification.
C H A P T E R T W O
P a g e | 77
Figure 26: 1H NMR of 113/121 in deuterated chloroform. Expanded regions of protons ‘f’ and ‘e’ to show
the ratio of the isomers 113 and 121.
C H A P T E R T W O
P a g e | 78
2.4.3. Synthesis of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-
methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-
3,4,9,10-tetracarboxy diimide (117)
Scheme 37: The nucleophilic substitution reaction to form 117 from 113
The dibromo-perylene diimide 113 isomer mixture underwent nucleophilic
substitution with phenol containing methoxyamine 64. The reaction was successful in
a high yield of 87% of the perylene dimethoxyamine 117 under basic conditions. Some
literature references use strong bases such as NaH to deprotonate the phenol but K2CO3
proved to be strong enough.
The isolated product showed both the 1,7-dimethoxyamine-perylene diimide 117 and
its 1,6-dimethoxyamine-perylene diimide regioisomer in a ratio of 3:2 respectively by
1H NMR spectroscopy. This could be seen by the slight chemical shift between the 1,6
isomer to the 1,7 isomer, Figure 26. For the application of these compounds separation
of these two isomers was not required. Unfortunately, mass spectroscopy was not
possible due to poor solubility.
C H A P T E R T W O
P a g e | 79
2.4.4. The synthesis of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-
(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-
3,4,9,10-tetracarboxy diimide (118)
Scheme 38: Oxidation of 117 to form PFN 118
Oxidation of dimethoxyamine 117 with m-CPBA under mild conditions gave the
desired nitroxide 118 in excellent yield (99%). Although, 118 was not isomerically
pure (because of the previous bromination step), it was not purified further as
pronounced solubility differences between the isomers were not observed. The
presence of the 1,6-regioisomer showed no evidence of absorbance or fluorescence
shifting in the spectra.
Due to the size of the molecules, the paramagnetic broadening effect exhibited by the
nitroxide moiety only affected part of the molecule (circled). This allowed detection
of the fluorophore’s hydrogens and the 2,5-di-tert-butylaniline signals for comparison
to the methoxyamine derivative. It is noted that there is little change in the chemical
shift between the methoxyamine and the nitroxides, Figure 27.
C H A P T E R T W O
P a g e | 80
Figure 27: 1H NMR comparison of the aromatic region of 117 (bottom) and 118 (top) in deuterated
chloroform.
C H A P T E R T W O
P a g e | 81
2.4.5. Synthesis of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-
methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-
3,4,9,10-tetracarboxy diimide (114)
Scheme 39: Sonogashira reaction to form 114
Sonogashira coupling of 1,7-dibromo perylene diimide 113 with the alkyne bearing
methoxyamine 81 in the presence of CuI and Pd(PPh3)4 resulted in a moderate (52%)
yield of the perylene dimethoxyamine 114. Analysis of the isolated product by 1H
NMR spectroscopy revealed the presence of 1,7-dimethoxyamine-perylene diimide
114 (54%) and the 1,6-dimethoxyamine-perylene diimide regioisomer (46%), Figure
28. The mixture was not further purified. It was found that if too much catalyst was
added a highly fluorescent spot was isolated. The structure was not able to be
ascertained, but it appeared to still have the perylene fluorophore with covalently
bonded triphenylphosphines by the presence of a signal in the phosphorous NMR.
However, the location of the covalent bond was unknown because crystals were unable
to be obtained.
C H A P T E R T W O
P a g e | 82
Figure 28: Expanded region of the 1H NMR of 114 showing the isomer ratio between 1,6 and 1,7
2.4.6. The synthesis of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-
(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-
3,4,9,10-tetracarboxy diimide (116)
Scheme 40: Oxidation of 114 to form the nitroxide radical of 116
Oxidation to yield the nitroxides moiety was facile using slow addition of 2.5
equivalents of m-CPBA to a chilled stirring solution of 114. The reaction only took 15
minutes but resulted in a quantitative yield when quenched with water and washed
C H A P T E R T W O
P a g e | 83
with dilute NaOH. As the alkyne linkage is also sensitive to oxidation, the reaction
was carefully monitored to ensure overoxidation did not occur. While only moderate
yields of the desired product could be isolated, it was also found to be selective to
oxidation of the nitroxide.
Scheme 41: Oxidation of 114 to form the nitroxide radical of 115
With addition of 1 equivalent of m-CPBA to a chilled solution was stirred 114 resulted
in both the production of 116 and the desired 115 with unreacted starting material. 114
could be easily isolated and further reacted to form more of the desired PFNs, both the
di and mono nitroxide. 115 would be characterised by the broadened NMR but the
methoxy group could be seen but with the EPR signal confirming the nitroxide radical.
The HPLC confirmed the pure product.
C H A P T E R T W O
P a g e | 84
Figure 29: 1H NMR comparison of the aromatic region of 117 (bottom), 115 (middle) and 118 (top) in
deuterated chloroform.
Proton NMR showed the distance dependent effect of paramagnetic broadening. This
is shown by the visible 2,5-di-tert-butylaniline signals but the disappearance of the
aromatic signals on the TMIO aromatic ring. The perylene diimide signals were still
seen but with a broadened effect. The stacked NMR spectrums, Figure 29 shows the
lack of shielding change between the 3 alkyne perylene diimide products and the
paramagnetic effect dependence on distance.
2.5. Experimental
Note to the reader: This section only includes the experiments which are not included
in following Sections: 3.5 and 6.2.
2.5.1. General Procedure
All other materials and reagents were of analytical reagent grade purity, or higher and
were purchased from Sigma Aldrich, Australia. All reactions were monitored using
C H A P T E R T W O
P a g e | 85
Merck Silica Gel 60 F254 TLC plates and visualized with UV light. Column
chromatography was performed using silica gel 60 Å (230 - 400 mesh). 1H NMR
spectra were run at 400 MHz and 13C NMR spectra at 100 MHz. Chemical shifts (δ)
for 1H and 13C NMR spectra run in CDCl3 are reported in ppm relative to the solvent
residual peak: proton (δ = 7.26 ppm) and carbon (δ= 77.2 ppm). Multiplicity is
indicated as follows: s (singlet); d (doublet); t (triplet); m (multiplet); dd (doublet of
doublet); br s (broad singlet). Coupling constants are reported in Hertz (Hz). Mass
spectra were recorded using either electrospray or electron impact (where specified)
as the ionization technique in positive ion mode. All MS analysis samples were
prepared as solutions in methanol. Infrared spectra were recorded as neat samples
using a Nicolet 5700 Nexus Fourier Transform infrared spectrometer equipped with a
DTGS TEC detector and an Attenuated Total Reflectance (ATR) accessory. Analytical
HPLC was performed on a Hewlett Packard 1100 series HPLC, using an Agilent prep-
C18 scalar column (10 μm, 4.6 × 150 mm) at a flow rate of 1 mL/min. All UV/Vis
spectra were recorded on a single beam Varian Cary 50 UV-Vis spectrophotometer.
Fluorescence measurements were performed on a Varian Cary 54 Eclipse fluorescence
spectrophotometer equipped with a standard multicell Peltier thermostatted sample
holder. Melting points were measured on a Gallenkamp Variable Temperature
Apparatus by the capillary method and are uncorrected. EPR spectroscopy was carried
out on a Magnettech MiniScope EPR spectrometer using a suitable nonpolar solvent
at room temperature. All air-sensitive reactions were carried out under ultra-high
purity argon. Diethyl ether and toluene were dried by storing over sodium wire. THF
was freshly distilled from sodium benzophenone ketal, acetonitrile from calcium
hydride and DMF from 4Å molecular sieves. TOPAS® 8007x10 was a gift from Ciba
Speciality Chemicals. PTMSP was purchased from ABCR GmbH. Cyclohexane was
C H A P T E R T W O
P a g e | 86
purified by washing with concentrated sulphuric acid until the wash was colourless,
followed by water, aq Na2CO3 and again water until neutral, and freshly distilled over
calcium hydride. All other materials and reagents were of analytical reagent grade
purity, or higher and were purchased from Sigma Aldrich, Australia.
2.5.2. N-Benzylphthalimide (48)
N-benzylphthalimide (48) was synthesised according to a procedure adapted from
those published by Manley-King.146
Phthalic anhydride (47) (106.64 g, 0.72 mol) was added to glacial acetic acid (500
cm3) in a round bottom flask (1 L). As the mixture stirred, benzylamine (~120cm3)
was added drop-wise. The mixture was refluxed for 1 hr, on completion the hot mixture
was poured onto a beaker of ice water (1.5 L). The mixture was then stirred until the
ice had melted. The white precipitate, N-benzylphthalimide was recovered by vacuum
filtration into a 2 L flask and washed with cold water. N-benzylphthalimide was
recrystallised with a minimum amount of boiling ethanol. The crystals were dried by
vacuum filtration to yield 48 as long white crystals. (138.9 g, 80.7 %). M.p. 116-120
°C (lit146 M.p. 115- 117 °C). 1H NMR (CDCl3): δ = 4.871 (s, 2H, N-CH2-Ar), 7.332
(m, 2H, Ar), 4.56 (d, 2H, J = 7.43 Hz, Ar), 7.725 (qu, 3H, J = 2.74 Hz, Ar) and 7.866
(qu, 2H J =2.74 Hz, Ar).
C H A P T E R T W O
P a g e | 87
2.5.3. 2-Benzyl-1,1,3,3-tetramethylisoindoline (49)
2-Benzyl-1,1,3,3-tetramethylisoindoline (49) was synthesised according to a
procedure adapted from those published by Griffiths et al.139
Pre-dried magnesium (120 g, 4.93 mol, 11.7 equiv.) and three small crystals of I2 were
placed in a round bottom flask (3 L) fitted with a still head, two dropping funnels,
thermometer, mechanical stirrer and two twin helix condensers connected in series
above the still head to which ice cold water was delivered with a peristaltic pump. A
positive pressure of argon was applied, with subsequent evacuation of the system
under vacuum and a positive pressure of argon reapplied.
Addition of anhydrous diethyl ether (400 mL) to the vessel was followed by the drop-
wise addition of methyl iodide (155 mL, 2.49 mol, 5.9 equiv.) via one of the dropping
funnels. The other dropping funnel was maintained with a constant supply of
anhydrous diethyl ether which was added periodically in order to keep a constant rate
of reaction. Once addition of the methyl iodide was complete, the mixture was stirred
until all activity had subsided, with subsequent concentration of the Grignard solution
by distillation until the interior temperature reached 80 °C.
Upon cooling the reaction mixture to 64 °C, a solution of N-benzylphthalimide (48)
(100 g, 0.421 mol, 1.0 equiv.) in dry toluene (800 mL) was added via both dropping
funnels at such a rate as to maintain a constant temperature. Following this addition,
diethyl ether was further reduced through distillation until a reaction temperature of
C H A P T E R T W O
P a g e | 88
110 °C was reached. The reaction mixture was then refluxed for 3 hours and then
further concentrated by distillation.
Once cooled, the mixture was diluted with n-hexanes (1.5 L), mixed thoroughly and
exposed to the atmosphere. The resulting purple slurry was filtered through celite
under vacuum, and the filtrate bubbled with air over night. This filtrate was
subsequently passed through a column of basic alumina, and the solvent was removed
under reduced pressure to give a golden oil which crystallized under vacuum and was
re-crystalised using methanol. (20 g, 19%) M.p. 56-58 °C (lit.139 M.p. 63-64 °C). 1H
NMR (CHCl3, 400MHz): δ= 1.3 (s, 12H, CH3-C), 3.99 (s, 2H, N-CH2-Ar), 7.13 (dd, J
= 3.08 Hz, 2H, Ar), 7.21-7.30 (m, 5H, Ar), 7.46 (d, J = 7.09 Hz, 2H, Ar). HRMS (ESI):
m/z (%) = 266.1934 (100) [MH+], calcd. for C19H24N [M+H]+ 266.1909.
2.5.4. 1,1,3,3-Tetramethylisoindoline (54)
1,1,3,3-Tetramethyllisoindoline (54) was synthesised according to a procedure
adapted from those published by Griffiths et al.139
2-Benzyl-1,1,3,3-tetramethyllisodoline (49) (1.8607 g, 7.011 mmol) was dissolved in
acetic acid and added to the reaction vessel with 10% Pd/C (0.2 g) catalyst. The vessel
was flushed with nitrogen 3 times, followed by hydrogen 3 times. The vessel was then
shaken at 40 PSI for ~6 hrs. The solution was then filtered through celite to remove
the catalyst and the bulk of the solvent was removed by reduced pressure. The mixture
was then neutialised using 5M NaOH and extracted with ether (3 x 50 mL). The
C H A P T E R T W O
P a g e | 89
combined organic layers were washed with water (3x 15 mL), followed by brine (30
mL) and dried over anhydrous sodium sulphate. The ether was removed by reduced
pressure to give 1,1,3,3-tetramethylisoindoline 54. The product was a low melting light
yellow solid. (1.305 g, 99 %). 1H NMR (CHCl3, 400MHz): δ= 1.46 (s, 12H, CH3-C),
7.12 (dd, J = 3.23 Hz, 2H, Ar), 7.25 (dd, J = 3.23 Hz, 2H, Ar). HRMS (ESI): m/z (%)
= 176.1418 (100) [M+H]+ calcd. for C12H18N [M+H]+ 176.1439.
2.5.5. 1,1,3,3-Tetramethylisoindolin-2-yloxyl (55)
1,1,3,3-Tetramethylisoindolin-2-yloxyl (55) was synthesised according to a procedure
adapted from those published by Chan et al.167
1,1,3,3-Tetramethylisoindoline (54) (1.029 g, 5.87 mmol) was dissolved in DCM in a
round bottom flask. 3-Chloroperoxybenzoic acid (1.4892 g, 8.63 mmol, 1.5 equiv.)
was added while stirring in an ice bath. The solution was left to stir for an hour, as it
returned to room temperature. Once completion, aqueous 2.5M sodium hydroxide was
added to deprotonate m-CPBA and the product was extracted with DCM (3 x 50 mL).
The combined organic layers were washed with water (3 x 20 mL), followed by brine
(50 mL) and dried over anhydrous sodium sulphate. The yellow liquid was
concentrated by vacuum to result in a dry yellow powder. (1.0824 g, 97 %). M.p. 115-
117 °C (lit.139 M.p. 128-129 °C). HRMS (ESI): m/z (%) = 213.1124 (15) [M+Na], calcd.
for C12H16NNaO• [M+Na] 213.1130.
C H A P T E R T W O
P a g e | 90
2.5.6. 1,1,3,3- Tetramethyl-5-nitroisoindolin-2-yloxyl (56)
1,1,3,3-Tetramethyl-5-nitroisoindolin-2-yloxyl (56) was synthesised according to a
procedure 138 adapted from those published by Bolton et al. 140
1,1,3,3-Tetramethylisoindolin-2-yloxyl (55) (0.5047 g, 4.625 mmol) was dissolved in
glacial acetic acid and placed in an ice bath without freezing. Sulfuric acid (2 mL, 7.2
mmol, 13.7 equiv.) was added slowly followed by conc. nitric acid (1 mL, 3.1 equiv.)
drop-wise with avoidance of overheating. The solution turned a red colour and it was
left to stir at R.T. until the solution lightened to yellow (~3 hrs). The mixture was then
quenched with 2.5M sodium hydroxide to a pH of 7. The product was extracted with
diethyl ether (3 x 25 mL). The combined organic layers were washed with water (3 x
10 mL), followed by brine (30 mL). The solvent was removed under reduced pressure
to give 1,1,3,3-tetramethyl-5-nitroisoindolin-2-yloxyl (56), as a strongly coloured
brown/orange solid. It was then recrystallised from hot ethanol to give well-formed
large orange crystals. (0.784 g, 72.13 %). M.p. 155 °C (lit.139 M.p. 160-162 °C). IR
(ATR) νmax 782 (=C-H), 839 (N-O), 1347 (R3N), 1526 (NO2), 2978 cm-1 (alkyl CH3).
HRMS (ESI): m/z (%) = 235.1207 (60) [M]+, 258.1119 (1) [M+Na], calcd. for
C12H15N2O3• [M] 235.1083
C H A P T E R T W O
P a g e | 91
2.5.7. 2-Methoxy-5-nitro-1,1,3,3-tetramethylisoindoline (61)
To characterise the target compound 56 the methoxyamine analogue (61) was
synthesised according to Fairfull-Smith.53, 147
1,1,3,3-Tetramethyl-5-nitroisoindolin-2-yloxyl (56) (74 mg, 0.315 mmol) was
dissolved in DMSO to which iron (II) sulphate heptahydrate (2.17 g, 7.8 mmol) was
added, where the solution changed from yellow to a dark brown. The flask was cooled
without freezing and 30 % hydrogen peroxide (1.33 mL) was added dropwise. The
reaction was then left to stir to 30 minutes at RT. The solution was poured into a beaker
of stirring ice water. The product was extracted with diethyl ether (3 x 10 mL) and
washed repeatedly with water (10 x 5 mL) to ensure DMSO had been removed. The
organic layer was concentrated by vacuum to give the desired product 61 (99 %, 78
mg). 1H NMR (CHCl3, 400MHz): δ= 1.57 (s, 12H, CH3-C), 3.78 (s, 3H, CH3-O), 7.23
(d, J = 8.36 Hz, 1H, Ar), 7.96 (d, J = 2.20 Hz, 1H, Ar), 8.12 (dd, J = 8.36, 2.20 Hz, 1H,
Ar). M.p. 60-63 °C.
2.5.8. 5-Amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57)
C H A P T E R T W O
P a g e | 92
5-Amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57) was synthesised according to a
procedure138 adapted from those published by Bolton et al.140
1,1,3,3-Tetramethyl-5-nitroisoindolin-2-yloxyl (56) (0.402 g, 1.71 mmol) was
dissolved in methanol (10 mL) and palladium on carbon (10% wt. loading, 41 mg)
added. The solution was placed in a Parr hydrogenator under an atmosphere of
hydrogen (40 psi) with shaking for 3 hours. The resulting suspension was filtered
through celite and the celite washed thoroughly with methanol. The combined filtrates
were concentrated at reduced pressure to give tetramethylisoindolin-2-yloxyl (57). The
product was a light yellow solid. (0.305 g, 99 %). HRMS (ESI): m/z (%) = 205.1698
(10) [MH+], 228.1237 (100) [M+Na], calcd. for C12H17N2NaO• [M+Na] 228.1239.
M.p. 172-175 °C. IR (ATR) νmax 762 (=C-H), 820 (N-O), 1336 (R3N), 2971 (alkyl
CH3), 3356 and 3435 cm-1 (RNH2).
2.5.9. 5-Diazonium-1,1,3,3- tetramethylisoindolin-2-yloxyl
tetrafluoroborate (58)
5-Diazonium-1,1,3,3-tetramethylisoindolin-2-yloxyl tetrafluoroborate (58) was
synthesised according to a procedure adapted from those published by Doyle and
Bryker.168
A solution of 5-amino-1,1,3,3-tetramethylisoindoline (57) (50 mg, 2.436x10-4 mol) in
dry acetonitrile (0.3 mL) was added dropwise to a stirring solution of nitrosyl
tetrafluoroborate (56.9 mg, 4.487 x10-4 mol) in dry acetonitrile (1.2 mL) at -30 °C (dry
C H A P T E R T W O
P a g e | 93
ice/acetonitrile bath). Once the addition was complete, the reaction was left to warm
to room temperature for 30 min. Dry diethyl ether (3 mL) with added dropwise to the
reaction and the mixture was left to stir to ensure precipitation. The white precipitate
of 11 was collected by filtration, washed with dry diethyl ether and stored under argon
in the freezer (47.8 mg, 97.6 %). IR (ATR) νmax 2200 cm-1 (N≡N). M.p. 86-88°C
(Dec.). HRMS (ESI): m/z (%) = 223.1062 (20) [M-(BF4-)+Li]+, calcd. for
C12H15LiN3O•+ [M-(BF4
-)+Li]+ 224.1370.
2.5.10. 5-Hydroxy-1,1,3,3-tetramethylioindolin-2-yloxyl (59)
58 (25 mg, 8.22x10-5 mol) was dissolved in deionised water (50 mL). The mixture was
refluxed at 100 °C for 48 hours, once cooled the solution was extracted with DCM (3
x 15 mL), washed with water (15 mL) and dried over sodium sulphate. The combined
organic layers were concentrated by vacuum to yield a pale yellow solid. The aqueous
layer was refluxed again at 110 °C over night worked up again to yield more product.
(15.9 mg, 93.7 %). M.p. 155 °C (lit.139 M.p. 160-162 °C). IR (ATR) νmax 782 (=C-H),
839 (N-O), 1347 (R3N), 2978 cm-1 (alkyl CH3).
2.5.11. 5-Bromo-1,1,3,3-tetramethylisoindoline (65)
C H A P T E R T W O
P a g e | 94
5-Bromo-1,1,3,3- tetramethylisoindoline (65) was synthesised according to a
procedure adapted from those published by Keddie.105, 145
A solution of 2-benzyl-1,1,3,3-tetramethylisoindoline 49 (2.5 g, 9.5 mmol, 1.0 equiv.)
in DCM (30 mL) was cooled in an ice bath to 0 °C and placed under an atmosphere of
argon. A solution of liquid Br2 (1.1 mL, 21.5 mmol, 2.3 equiv.) in DCM (40 mL) was
then added, followed by anhydrous AlCl3 (4.5 g, 34 mmol, 3.6 equiv.). The reaction
was maintained with stirring for one hour then poured onto ice (~ 75 mL) and stirred
for 15 mins. The resulting solution was basified (pH 14) with 10M NaOH and
extracted with DCM (3 × 100 mL). The combined organic phases were washed with
H2O (50 mL) and dried over anhydrous sodium sulphate. The solvent was removed by
vacuum to yield a yellow residue. The residue was then dissolved in methanol (~ 15
mL) and NaHCO3 (~ 100 mg) added. To this solution was added aqueous H2O2 (30%)
until no further effervescence could be detected. 2M H2SO4 (40 mL) was then added
(caution: effervescent) and the solution then washed with DCM (3 × 100 mL). The
combined organic phases were then back extracted with 2 M H2SO4 (3 × 100 mL). The
combined acidic aqueous phases were then cooled in an ice bath, basified (pH 14) with
10 M NaOH and extracted with DCM (5 × 100 mL). The combined organic phases
were then washed with H2O (100 mL) and dried over anhydrous sodium sulphate. The
solvent was removed in vacuo to afford 65 as a low melting white solid. (1.48 g, 62
%). 1H NMR (400 MHz, CDCl3): δ (ppm) = 1.45 (d, J = 3.6 Hz, 12H, 4×CH3), 1.87 (s,
1H, NH), 7.00 (d, J = 8.0 Hz, 1H, Ar), 7.25 (d, J = 1.6 Hz, 1H, Ar), 7.37 (dd, J = 8.0,
1.6 Hz, 1H, Ar).
C H A P T E R T W O
P a g e | 95
2.5.12. 5-Iodo-1,1,3,3-tetramethylisoindolin (66)
5-Iodo-1,1,3,3- tetramethylisoindoline (66) was synthesised according to a procedure
adapted from those published by Keddie.105
A solution of 5-bromo-1,1,3,3-tetramethylisoindoline 65 (1.6 g, 6.3 mmol, 1.0 equiv.)
in anhydrous THF (17.8 mL) was cooled to - 78 °C (dry ice / acetone). n-BuLi (1.6 M
in n-hexanes, 10.7 mL, 17.12 mmol, 2.7 equiv.) was then added (drop-wise) and the
resulting mixture stirred for 15 minutes. A solution of I2 (4.8 g, 18.9 mmol, 3.0 equiv.)
in anhydrous THF (40 mL) was then added (drop-wise) and the reaction allowed to
return to room temperature. The reaction mixture was then poured into ice / H2O (~
100 mL) and basified (pH 14) with 5M NaOH. The resulting solution was then
extracted with DCM (5 × 100 mL) and the combined organic phases washed with water
and dried over anhydrous sodium sulphate. The solvent was removed by vacuum to
yield a clear residue which was then dissolved in methanol (~ 30 mL) and NaHCO3 (~
90 mg) added. To this solution was added aqueous H2O2 (30 %) (~ 18 mL) followed
by 2M H2SO4 (500 mL) (caution: effervescent). The resulting solution was washed
with DCM (3 × 500 mL) and the combined organic phases back extracted with 2M
H2SO4 (3 × 500 mL). The combined acidic aqueous phases were then basified (pH 14)
with 10M NaOH and extracted with DCM (5 × 500 mL). The combined organic phases
were then washed with H2O (200 mL) and dried over anhydrous sodium sulphate. The
solvent was removed by vacuum to afford 66 as a low melting white solid. (0.951 g,
50.3 %). 1H NMR (400 MHz, CDCl3): δ (ppm) = 1.45 (s, 12H, 4×CH3), 1.76 (s, 1H,
C H A P T E R T W O
P a g e | 96
NH), 7.46 (d, J = 1.2 Hz, 1H, Ar), 7.58 (dd, J = 8.0, 1.6 Hz, 1H, Ar). HRMS (ESI):
m/z (%) = 302.0575 (30) [M+H], calcd. for C12H17IN [M+H]+ 302.0406.
2.5.13. Improved synthesis of 5-Iodo-1,1,3,3-tetramethylisoindolin
(66)
5-Iodo-1,1,3,3- tetramethylisoindoline (66) was synthesised according to a procedure
adapted from those published by Fairfull-Smith.152
Periodic acid (0.27 eqv., 3.16 g, 1.8 x10-2 mol) was dissolved in ~50 mL of conc.
sulphuric acid and stirred at 0°C, while potassium iodide (0.85 eqv., 2.55 g, 1.53x10-2
mol) was added in small portions. It was then stirred at RT for 15min, it was then
transferred into a dropping funnel. 49 was then dissolved in ~50 mL of conc. sulphuric
acid and stirred at 0°C, the potassium iodide solution was added dropwise over 30
mins, after which the reaction was further stirred at RT for 3 hours. The reaction was
then poured slowly onto ice and basified using NaOH pellets slowly until the mixture
was basic and extracted with DCM (3 x 100 mL), washed with water (5 x 50 mL) and
dried over NaSO4. The reaction was purified by filtration of a hot reaction mixture in
hexane. Yield: 4.77 g of mono iodo (89 %), 512 mg of di iodo (6.8 %) and 133 mg of
unreacted (4.27 %) by 1H NMR. No characterisation was performed due to difficult
purification.
C H A P T E R T W O
P a g e | 97
2.5.14. 5-Iodo-1,1,3,3-tetramethylisoindolin-2-yloxyl (67)
5-Iodo-1,1,3,3- tetramethylisoindolin2-yloxyl (67) was synthesised according to a
procedure adapted from those published by Keddie.105
5-Iodo-1,1,3,3-tetramethylisoindoline (66) (0.951 g, 3.58 x10-3 mmol, 1.0 equiv.) was
dissolved in DCM (25 mL) and cooled to 0 °C in an ice bath. m-CPBA (77%, 0.859 g,
4.98 x10-3 mmol, 1.3 equiv.) was added slowly to the stirring solution and stirred for
30 minutes at 0 °C. The reaction mixture was then allowed to return to room
temperature and H2O (200 mL) added. The organic phase was then washed with 2M
NaOH (3 × 100 mL) then brine (100 mL) and dried over anhydrous sodium sulphate.
The solvent was then removed in vacuo followed by recrystallization from ethanol to
afford 67 as an orange crystalline solid (1.0656 g, 99 %). HRMS (ESI): m/z (%) =
302.0575 (25) [M(-O•)+2] calcd for C12H17IN• [M(-O•)+2] 302.0406, EPR: g =
2.0062, aN = 1.429 mT.
2.5.15. 5-(3-Hydroxy-3-methyl)butynyl-1,1,3,3-
tetramethylisoindolin-2-yloxyl (68)
C H A P T E R T W O
P a g e | 98
5-(3-Hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (68) was
synthesised according to a procedure adapted from those published by Keddie.105
A solution of 5-iodo-1,1,3,3-tetramethylisoindoline (67) (1 g, 3.163 mmol, 1.0 equiv.),
4-diazabicyclo[2.2.2]octane (DABCO) (1.1 g, 9.49 mmol, 3.0 equiv.) and palladium
(II) acetate (1.8 mg, 0.095 mmol, 0.03 equiv.) in acetonitrile (25 mL) was heated to 75
°C . 2-Methyl-3-butyn-2-ol (1.5 mL, 15.815 mmol, 5.0 equiv.) was then added and the
reaction maintained with stirring for 16 hours. The solvent was removed in vacuo and
the crude reaction mixture purified via silica gel chromatography to afford 68 as a low
melting brown solid (679 mg, 79 %). No characterisation was performed due to
difficulty in purification.
2.5.16. 5-Ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (69)
5-Ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (69) was synthesised according to a
procedure adapted from those published by Keddie et al.105
To a solution of 5-(3-hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-
yloxyl 68 (679 mg, 2.49 mmol, 1.0 equiv.) in anhydrous toluene (100 mL) was added
solid KOH (1.1 g, 19.6 mmol, 7.8 equiv.). The reaction was brought to reflux and
maintained with stirring for 1 hour. The reaction was then allowed to return to room
temperature, washed with H2O (3 × 200 mL), brine (200 mL) and dried over anhydrous
sodium sulphate. The solvent was removed in vacuo and the crude reaction mixture
purified by silica gel column chromatography (30% ethyl acetate in hexane) then
C H A P T E R T W O
P a g e | 99
recrystallized from ethanol to afford 69 as an orange crystalline solid. (223.8 mg, 41.9
%). HRMS (ESI): m/z (%) = 216.1504 (7.5 %) [M+2] 237.1254 (2%) [M+Na]+, calcd.
for C14H18NO• [M+2H]1+ 216.1388. EPR: g = 2.0058, aN = 1.429 mT. M.p. (Lit. 126-
128°C105). IR (ATR) νmax 661 (=C-H), 835 (N-O), 1362 (R3N), 2097 (C≡C), 2978
(ArC-H), 3196 (alkyl CH3), 3276 cm-1 (C≡C-H).
2.5.17. 5-Bromo-1,1,3,3-tetramethylisoindolin-2-yloxyl (77)
5-Bromo-1,1,3,3-tetramethylisoindolin-2-yloxyl (77) was synthesised according to a
procedure adapted from those published by Chan et al.167
1,1,3,3-Tetramethylisoindoline (65) (25.92 mg, 0.102 mmol) was dissolved in DCM
(20 mL) in a round bottom flask. m-CPBA (34.32 mg, 0.153 mmol, 1.5 equiv.) was
added while stirring at room temperature. At completion of the reaction, 2.5M sodium
hydroxide was added to deprotonate m-CPBA and the product was extracted with
DCM. The organic layer was washed with water (30 mL), fellow by brine (30 mL) and
dried over anhydrous sodium sulphate. The yellow liquid was concentrated by vacuum
to result in a dry yellow powder. (24.7 mg, 90 %). EPR: g = 2.0059, aN = 1.429 mT.
2.5.18. 5-Bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (78)
C H A P T E R T W O
P a g e | 100
5-Bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (78) was synthesised according to
a procedure adapted from those published by Fairfull-Smith.53
5-Bromo-1,1,3,3-tetramethylisoindolin-2-yloxyl (77) (278.3 mg, 1.034 mmol) was
dissolved in DMSO to which iron sulphate (718.6 mg, 2.585 mmol) was added, where
the solution changed from yellow to a dark brown. The flask was cooled without
freezing and peroxide (175 uL) was added dropwise. The reaction was then left to stir
for 30 minutes at RT. The solution was poured into water and extracted with diethyl
ether and washed with water several times to ensure DMSO has been removed. The
organic layer was concentrated by vacuum to give the desired product 78, a pale yellow
low melting solid. (89.9%, 264.4 mg). 1H NMR (400 MHz, CDCl3) δ 1.423 (s, 12H,
CH3); 3.764 (s, 3H, O-CH3); 7.03 (d, 1H, Ar-H), 7.173 (s, 1H, Ar-H); 7.29 (dd, 1H,
Ar-H).
2.5.19. 5-Iodo- 2-methoxy-1,1,3,3-tetramethylisoindoline (79)
5-Iodo-2-methoxy-1,1,3,3-tetramethylisoindoline (79) was synthesised according to a
procedure adapted from those published by Keddie.105
A solution of 5-bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (78) (264.4 mg, 0.93
mmol, 1.0 equiv.) in anhydrous THF (3 mL) was cooled to - 78 °C (dry ice / acetone). n-
BuLi (1.6 M in n-hexanes, 1.767 mL, 2.82 mmol, 2.7 equiv.) was then added (dropwise)
and the resulting mixture stirred for 15 minutes. A solution of I2 (793 mg, 3.1 mmol, 3.3
equiv.) in anhydrous THF (6.5 mL) was then added (dropwise) and the reaction allowed
C H A P T E R T W O
P a g e | 101
to return to room temperature. The solution was poured onto ice and extracted with DCM
(3x 50 mL) and washed with a satuated solution of sodium thiosulphate (3 x 50 mL) until
the solution turned colourless and washed with water. The organic layer was dried on
sodium sulphate and concentrated by vacuum. The mixture was purified by column
chromatography (n-hexanes: DCM, 1: 5) to yield a colourless oil 79. (0.109 mg, 0.329
mmol, 35.4%). 1H NMR (400 MHz, CDCl3) δ 1.41 (s, 12H, CH3); 3.76 (s, 3H, O-CH3);
6.85 (d, J = 8.01 Hz, 1H, Ar-H), 7.41 (s, 1H, Ar-H); 7.54 (dd, J = 7.41, 1.85 Hz, 1H,
Ar-H).
2.5.20. 5-(3-Hydroxy-3-methyl)butynyl-2-methoxy-1,1,3,3-
tetramethylisoindoline (80)
5-(3-Hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (80) was
synthesised according to a procedure adapted from those published by Keddie.105
A solution of 5-bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (79) (781 mg, 2.358
mmol, 1.0 equiv.), 4-diazabicyclo[2.2.2]octane (DABCO) (0.8 g, 9.49 mmol, 4.0
equiv.) and palladium (II) acetate (12 mg, 0.095 mmol, 0.03 equiv.) in acetonitrile (2.6
mL) was heated to 75 °C . 2-Methyl-3-butyn-2-ol (1.15 mL, 1.18 mmol, 5.0 equiv.)
was then added and the reaction maintained with stirring for 16 hours. The solvent was
removed in vacuo and the crude reaction mixture purified via silica gel
chromatography (Ether: Hexane 1:3) to afford 80 as a brown oil (408.3 mg, 60.3 %).
C H A P T E R T W O
P a g e | 102
1H NMR (400 MHz, CDCl3) δ 1.06 (s, 12H, CH3); 3.11 (s, 1H, OH); 3.764 (s, 3H, O-
CH3); 7.01 (d, 1H, Ar-H), 7.154 (s, 1H, Ar-H); 7.27 (dd, 1H, Ar-H).
2.5.21. 5-Ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline (81)
5-Ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline (81) was synthesised according
to a procedure adapted from those published by Keddie.105
To a solution of 5-(3-hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-
yloxyl (80) (0.5 g, 1.74 mmol, 1.0 equiv.) in anhydrous toluene (50 mL) was added
solid KOH (0.8 g, 14.32 mmol, 7.8 equiv.). The reaction was brought to reflux and
maintained with stirring for 1 hour. The reaction was then allowed to return to room
temperature, washed with H2O (3 × 200 mL), brine (200 mL) and dried over anhydrous
sodium sulphate. The solvent was removed in vacuo and the crude reaction mixture
purified by silica gel column chromatography (Ether : n-hexanes, 1 : 3) to afford 81 as
an pale cream solid (0.362 g, 1.58 mmol, 90.7 % yield). 1H NMR (400 MHz, CDCl3)
δ 1.43 (s, 12H, CH3); 3.05 (s, 1H, H-C≡C), 3.78 (s, 3H, O-CH3); 7.06 (d, 1H, J = 7.63
Hz, Ar-H), 7.25 (d, J = 0.7 Hz, 1H, Ar-H); 7.38 (dd, 1H, J = 7.83 & 1.13 Hz, Ar-H).
13C NMR (62.9 MHz) δ: 28.12, 65.47, 66.98, 76.48, 83.95, 120.81, 121.57, 125.37,
131.29, 145.46, 146.17. IR (ATR) νmax 710 (=C-H), 828 (N-O), 1048 (C-O), 1373
(R3N), 2109 (C≡C), 2974 (ArC-H), 2974 (alkyl CH3), 3292 cm-1 (C≡C-H).
C H A P T E R T W O
P a g e | 103
2.5.22. N,N’-Bis (2,5- di-tert- butylbenyl) Perylene 3,4,9,10-
tetracarboxyl-bisimide (89)
N,N’-Bis (2,5- di-tert- butylphenyl) Perylene 3,4,9,10-tetracarboxyl-bisimide (89) was
synthesised according to the procedure published by Langnals.133
Perylen-3,4,9,10-tetracarboxylic dianhydride (42) (0.5 g, 1.275 mmol), 2,5-di-tert-
butylaniline (88) (1.025 g, 4.99 mmol, 4 equiv.) and zinc acetate (0.175 g, 0.954 mmol,
0.75 equiv.) were added to a round bottom flask, using imidazole (~2.5 g) as the
solvent. The mixture was heated at 130 °C for 6 hr under argon. The mixture was
allowed to cool, 2M HCl (100 mL) was added to dissolve imidazole, and the product
was extracted with chloroform (50 mL). The organic layer was washed with water (20
mL), brine (20 mL) and dried with anhydrous magnesium sulphate. Solvent was
removed by reduced pressure to give a red solid. Purification was performed through
column chromography in (methanol: chloroform, 1: 50). The product was then
recrystallized from hot toluene to give the clean product 89 (0.077g, 0.99%). 1H NMR
(CHCl3, 400MHz): δ = 1.33 (s, 18H, CH3-C-Ar), 1.36 (s, 18H, CH3-C-Ar), 7.05 (d,
2H, J = 2.11 Hz, Ar), 7.50 (dd, 2H, J = 8.92, 2.11 Hz, Ar), 7.63 (d, 2H, J = 8.92 Hz,
Ar), 8.83 (dd, 8H, J = 24.17, 7.75 Hz, Ar)
C H A P T E R T W O
P a g e | 104
2.5.23. 2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-
methylbenzenesulfonate (123)
2-[2-[2-(2-Methoxyethoxy)ethoxy]ethoxy]ethyl 4-methylbenzenesulfonate (123) was
synthesised following the procedure published by Snow.169
Tetraethyl-eneglycol monomethyl ether (9.57 g, 45.95 mmol) was added to a round
bottom flask containing THF (20 mL). Sodium hydroxide (5 g) was dissolved in water
(20 mL) and added slowly to the stirring mixture which was at 0 oC. Tosyl chloride
(15 g, 78.68 mmol, 1.7equiv.) in of THF (20 mL) was added dropwise over 15 mins.
The reaction was left to warm to room temperature then stirred O/N. The product was
basified with 1M NaOH and extracted with diethyl ether (3x 50 mL). The product was
washed with water (3x 50 mL) and dried over anhydrous sodium sulphate. The solvent
was removed by vacuum to yield a pale pink oil. (15.724 g, 98.77 %). 1H NMR
(CHCl3, 400MHz): δ= 2.44 (s, 3H, CH3-Ar) 3.36 (s, 3H, CH3-O), 3.6 (m, 14H, CH2-
CH2-O), 4.15 (t, 2H, J = 4.68 Hz, CH2-S), 7.31 (d, 2H, J = 7.79 Hz, Ar), 7.79 (d, 2H,
J = 8.26 Hz, Ar).
2.5.24. 2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-
nitrobenzene (124)
C H A P T E R T W O
P a g e | 105
2-[2-[2-(2-Methoxyethoxy)ethoxy]ethoxy] ethyl-4-nitrobenzene (124) was
synthesised following the procedure published by Ikeda.170
2-[2-[2-(2-Methoxyethoxy)ethoxy]ethoxy]ethyl 4-methylbenzenesulfonate (123)
(6.24 g, 17.21 mmol) was added to a flask containing 4-nitrophenol (3 g, 21.57 mmol,
1.25 equiv.) and potassium carbonate (2.98 g, 21.56 mol, 1.5 equiv.). The solids were
dissolved in acetonitrile (100 mL) and refluxed at 90 °C for 5 hours. The solid was
collected and the filtrate was concentrated by reduced pressure to yield an oil. This oil
was dissolved in DCM and washed with 1M NaOH to remove the 4-nitrophenol, and
then by water. (0.343 g, 4.5 %). 1H NMR (CHCl3, 400MHz): δ= 3.36 (s, 3H, CH3-O),
3.52- 3.73 (m, 12H, CH2CH2-O), 3.88 (t, 2H, J = 5.62 Hz, CH2CH2-O), 4.21 (t, 2H, J
= 4.71 Hz, CH2CH2-O), 6.97 (d, 2H, J = 9.19 Hz, Ar), 8.18 (d, 2H, J = 9.18 Hz, Ar).
2.5.25. 2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline
(125)
2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-nitrobenzene (124) (0.343 g, 1.04
mmol) was dissolved in ethyl acetate and added to the reaction vessel with palladium
on carbon (10% wt. loading, 40 mg) catalyst. The solution was placed in a Parr
hydrogenator under an atmosphere of hydrogen (40 psi) with shaking for 5 hours. The
reaction was checked by TLC (ethyl acetate) to ensure the reaction was complete. The
resulting suspension was filtered through celite and the celite washed thoroughly with
methanol. The combined filtrates were concentrated at reduced pressure to give 125.
The product was a light brown oil. (0.3359 g, 100 %). 1H NMR (CHCl3, 400MHz): δ=
C H A P T E R T W O
P a g e | 106
3.37 (s, 3H, CH3-O), 3.53-3.72 (m, 12H, CH2-CH2-O), 3.81 (t, 2H, J = 4.7 Hz, CH2-
CH2-O), 4.04 (t, 2H, J = 5.09 Hz, CH2-CH2-O), 6.62 (d, 2H, J = 8.41 Hz, Ar), 6.75 (d,
2H, J = 8.81 Hz, Ar).
2.5.26. N,N’- bis (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-
4-aniline)- perylene 3,4,9,10-tetracarboxyl-bisimide (126)
N,N’- bis (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- perylene
3,4,9,10-tetracarboxyl-bisimide (126) was synthesised adapting the procedure
according to Langnals.133
Perylen- 3,4,9,10- tetracarboxylic dianhydride (42) (28.2 mg, 0.07189 mmol), 125
(37.7 mg, 0.126 mmol, 1.75 equiv) and zinc acetate (30 mg, 0.164 mmol, 2.25 equiv)
were added to a round bottom flask, using imidazole (~2 g) as the solvent. The mixture
was heated at 130°C for 6 hours under an argon atmosphere. The mixture was allowed
to cool after which aqueous 2M hydrogen chloride was added to dissolve imidazole,
and the product was extracted with chloroform (5 x 50 mL). The combined organic
layers were washed with water (2 x 20 mL), brine (20 mL) and dried with anhydrous
magnesium sulphate. Solvent was removed by reduced pressure to give a red solid.
Column chromography was performed (methanol: chloroform 1: 25) and 126 was
C H A P T E R T W O
P a g e | 107
isolated as a red solid. (87 mg, 99%). 1H NMR (CHCl3, 400MHz): δ = 3.39 (s, 6H,
CH3-O), 3.55-3.76 (m, 24H, CH2-CH2-O), 3.91 (t, 2H, J = 4.9 Hz, CH2-CH2), 4.22 (t,
2H, J = 4.9 Hz, CH2-Ar), 7.09 (d, 4H, J = 8.83 Hz, Ar), 7.29 (d, 4H, J = 8.59 Hz, Ar),
8.45 (d,4H, J = 7.86 Hz, Ar), 8.63 (d, H, J = 7.85 Hz, Ar).
2.5.27. N- (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-
aniline)- N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-
perylene 3,4,9,10-tetracarboxyl-bisimide (96)
N- (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- N’(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene 3,4,9,10-tetracarboxyl-bisimide (96) was
synthesised adapting the procedure according to Langnals.133
Perylen- 3,4,9,10- tetracarboxylic dianhydride (42) (102.419mg, 0.218 mmol, 1
equiv.), aniline TEG 125 (78.1 mg, 0.261 mmol, 1.2 equiv), amino-1,1,3,3-
tetramethylisoimdolin-2-yloxyl 57 (53.57 mg, 0.261 mmol, 1.2 equiv) and zinc acetate
(100 mg, 0.55 mmol, 2.2 equiv) were added to a round bottom flask, using imidazole
(~2 g) as the solvent. The mixture was heated at 130°C for 6 hr under argon. The
mixture was allowed to cool, aqueous 2M HCl was added to dissolve imidazole, and
the product was extracted with chloroform (5 x 50 mL). The combined organic layer
was washed with water (2 x 20 mL), brine (20 mL) and dried with anhydrous
C H A P T E R T W O
P a g e | 108
magnesium sulphate. Solvent was removed by reduced pressure to give a red solid.
Column chromography was performed (methanol: chloroform, 1: 100) showing 3
major fractions. The second fraction was found to be the target compound 96. (49.9
mg, 22.2 %). 1H NMR (CHCl3, 400MHz): δ= 1.63 (s, 6H, CH3), 3.40 (s, 3H, O-CH3),
3.56-3.93(m, 16H, CH2-O-CH2), 4.22 (b, 2H, CH2-Ar), 7.11 (b, 2H, Ar), 7.29 (b, 2H,
Ar), 8.42 (b, 2H, Ar), 8.49 (b, 2H, Ar), 8.65 (b, 4H, Ar).
2.5.28. N- (methoxy-1,1,3,3-tetramethylisoindoline N’- (2-[2-[2-(2-
methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- perylene
3,4,9,10-tetracarboxyl-bisimide (97)
To characterise the target compound 96 the methoxyamine analogue was synthesised
according to Fairfull-Smith.53
Hydrogen peroxide solution (30%, 5 equiv.) was added dropwise to a solution of N-
(2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- N’(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene 3,4,9,10-tetracarboxyl-bisimide (96) and
iron(II) sulphate heptahydrate (2.5 equiv.) in a solution of minimal DMSO. The
resulting solution was stirred at room temperature for 30 minutes and then poured into
icy sodium hydroxide (1M). The mixture was extracted with chloroform (20 mL) and
washed (5 x 50 mL) with water several times to remove DMSO. It was dried over
C H A P T E R T W O
P a g e | 109
anhydrous sodium sulphate and concentrated for reduced pressure. The product was
purified by column chromography (methanol: chloroform, 3: 100) to yield a red solid.
1H NMR (CHCl3, 400MHz): δ= 1.48 (s, 6H, CH3), 1.51 (s, 6H, CH3), 3.39 (s, 3H, O-
CH3), 3.56-3.93 (m, 16H, CH2-O-CH2), 4.22 (t, 2H, J = 4.91 Hz, CH2-Ar), 7.09 (d, 1H,
J = 8.41 Hz, Ar), 7.10 (d, 2H, J = 8.41 Hz, Ar), 7.20 (dd, 1H, J = 8.08, 1.77 Hz, Ar),
7.28 (d, 3H, J = 8.52 Hz, 2xAr), 8.54- 8.77 (m, 8H, Ar). 13C NMR (62.9 MHz) δ: 13.11,
13.16, 21.68, 25.69, 28.35, 29.15, 30.19, 31.79, 32.69, 36.08, 36.37, 58.04, 64.51,
66.14, 66.7, 68.65, 69.53, 69.63, 69.66, 69.88, 70.95, 114.41, 120.92, 121.53, 122.2,
122,45, 122.51, 125.42, 126.31, 126.57, 128.54, 130.63, 133.64, 133.69, 144.72,
145.54, 157.94, 162.48, 162.58.
2.5.29. N,N’-Bis (octylphenyl)-perylene 3,4,9,10-tetracarboxyl-
bisimide (127)
N,N’-Bis (octylphenyl) Perylene 3,4,9,10-tetracarboxyl-bisimide (127) was
synthesised adapting the procedure according to Langnals.133
Perylen- 3,4,9,10- tetracarboxylic dianhdride (42) (50mg, 0.136 mmol), 4-octylaniline
(61.2 mg, 0.30 mmol, 2.2 equiv.) and zinc acetate (50mg, 0.30 mmol, 2.2 equiv.) were
added to a round bottom flask, using imidazole (~2 g) as the solvent. The mixture was
heated at 130°C for 6 hours under argon. The mixture was allowed to cool 2M aqueous
HCl was added to dissolve imidazole, and the product was extracted with chloroform
(5 x 50 mL). The combined organic layers were washed with water (2 x 20 mL), brine
C H A P T E R T W O
P a g e | 110
(20 mL) and dried with anhydrous magnesium sulphate. Solvent was removed by
reduced pressure to give a red solid. Column chromatography was performed
(methanol: chloroform 1: 25). 127 was isolated as a red solid. (97 mg, 98 %).1H NMR
(CHCl3, 400MHz): δ= 2.71 (t, 4H, J = 4.95 Hz, CH2-Ar), 7.25 (d, 2H, J = 7.95 Hz,
Ar), 7.39 (d, 2H, J = 7.95 Hz, Ar), 8.70 (d, 4H, J = 7.92 Hz, Ar), 8.76 (d, 4H, J = 8.42
Hz, Ar).
2.5.30. N- N’ -Bis (1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene
3,4,9,10-tetracarboxyl-bisimide (44)
N- N’ Bis (1,1,3,3-tetramethylisoindolin-2-yloxyl)- perylene 3,4,9,10-tetracarboxyl-
bisimide (44) was synthesised adapting the procedure according to Langnals.133
A mixture of 3,4,9,10-perylenetetracarboxylic dianhydride (42) (50 mg, 0.127 mmol,
1 equiv.), 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57) (0.12 g, 0.51 mmol, 4
equiv.), zinc acetate (46 mg, 0.245 mmol 2 equiv.) and imidazole (0.864 g, 12.7 mmol
10 equiv.) was heated at 130oC under an atmosphere of argon for 6 hours. Aqueous
hydrochloric acid (2 M, 10 mL) was added and the mixture was diluted with
chloroform (50 mL). The organic phase was separated, washed with aqueous
hydrochloric acid (2 M, 2 × 50 mL) and water (2 × 50 mL), dried (anhydrous Na2SO4)
and concentrated in vacuo. Purification by column chromatography (eluent 2%
methanol/chloroform, sample dry loaded using chloroform) gave the desired
compound as a red powder (94 mg, 97%). Recrystallisation from DCM/MeOH/toluene
C H A P T E R T W O
P a g e | 111
(50: 50: 1) gave red needles. M. p. >300 °C (dec.). MS (ESI): m/z (%) = 789 (6)
[M+Na]+. HRMS: calcd. for C48H38N4O6Na [M+Na]+. Elemental analysis found
789.2689; found 789.2655. (Found: C 68.74, H 5.04 N 6.57 Calc. C48H38N4O6.4H2O:
C 68.72, H 5.53, N 6.68%), EPR: g = 2.006, aN = 1.429 mT.
2.5.31. N- N’ Bis (methoxy-1,1,3,3-tetramethylisoindoline)-
Perylene 3,4,9,10-tetracarboxyl-bisimide (91)
To characterise the target compound the methoxyamine analogue (91) was synthesised
according to Fairfull-Smith.53
To a solution of nitroxide (44) (25 mg, 0.033 mmol) in DMSO (5 mL) was added
FeSO4.7H2O (18 mg, 0.066 mmol) and H2O2 (30% aqueous solution, 100 μL). The
reaction was maintained with stirring for 30 min. at room temperature under an
atmosphere of argon. Water (10 mL) was added and the resulting mixture was
extracted with chloroform (3 × 10 mL). The combined organic layers were dried
(anhydrous Na2SO4) and concentrated in vacuo. The obtained residue was purified
using silica gel chromatography (eluent 2% methanol/chloroform, sample dry loaded
using chloroform) to give the desired compound as a red powder (21 mg, 80 %). M. p.
>300 °C (dec.) 1H NMR (400 MHz, CDCl3) δ 1.50 (br s, 24H, 4 × CH3), 3.82 (s, 6H,
OCH3), 7.09 (d, J = 1.8 Hz, 2H, Ar-H), 7.21 (dd, J = 7.9, 1.9 Hz, 2H, Ar-H), 7.30 (d,
J = 7.8 Hz, 2H, Ar-H), 8.71 (d, J = 8.1 Hz, 4H, Ar-H), 8.77 (d, J = 8.1 Hz, 4H, Ar-H).
The compound was insufficiently soluble in CDCl3 to obtain a satisfactory 13C NMR
C H A P T E R T W O
P a g e | 112
spectrum. MS (ESI): m/z (%) = 797 (100) [M+H]+. HRMS: calcd. for C50H45N4O6
[M+H]+ 797.3339; found 797.3298.
2.5.32. 4-Bromo-1,8-naphthalic anhydride (102)
4-Bromo-1,8-naphthalic anhydride (102) was synthesised according to a procedure
adapted from those published by Rotstein et al.157
To a two necked round-bottomed flask equipped with a magnetic stirring bar was 1,8-
naphthalic anhydride 101 2 g, (10.09 mmol) and 12 mL of 4 M aqueous potassium
hydroxide (2.7 g) and was heated slightly to dissolve. The flask was cooled to 0 °C
and the contents treated with bromine (0.77 mL) over the course of 2 hr. The flask was
fitted with a reflux condenser and heated to 60 °C for 16 h. After cooling to room
temperature, the contents of the flask were acidified with 10 mL H2SO4, and refluxed
for 1 h. When cooled to room temperature, the product was collected by suction
filtration and washed with cold water, methanol and diethyl ether to give the desired
product (3.0431 g, 99 %) as a grey solid. 1H NMR (400 MHz, CDCl3) δ 7.93 (t, J =
7.88 Hz, 1H, Ar-H), 7.13 (d, J = 7.88 Hz, 1H, Ar-H), 7.46 (d, J = 7.88 Hz, 1H, Ar-H),
8.70 (m, 2H, Ar-H), 8.77. M.p. 210-220 °C. (Lit.171 M.p. 218-220). MS (ESI): m/z (%)
= 298.9142 and 300.0122 (18) [M+Na]+, calcd for C12H5BrNaO3 [M+Na]+ 298.9320.
C H A P T E R T W O
P a g e | 113
2.5.33. 1,7-Dibromoperylene-3,4:9,10-tetracarboxydianhydride
(112)
1,7-Dibromoperylene-3,4,9,10-tetracarboxydianhydride (112) was synthesised
according to a procedure adapted from those published by Ahrens et al.165
3,4,9,10-Perylenetetracarboxylic dianhydride (2 g, 6.819 mmol) was added to 30 mL
concentrated sulfuric acid and stirred at 55 °C for 24 hr in a 2 necked flask. Iodine
(0.048 g,) was added to the reaction mixture and stirred for an additional 5 hr. at 55
°C. Bromine (0.582 mL) was added dropwise to the reaction flask over 1 hr. and stirred
for 24 hr. at 85 °C. Excess bromine was then displaced with N2. Water (66 ml) was
added dropwise to the cooled mixture and the precipitate filtered off through 4 filter
papers. The crude product was washed with 220 ml 86 % H2SO4 followed by water
(two times) and dried in the oven to afford crude red powder (32.32 g, 81%). This
product was used without further purification and characterisation due to
insolubility.165
C H A P T E R T W O
P a g e | 114
2.5.34. N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide
(103)
N-(2,5-di-tert-butylphenyl)-4-bromo-1,8-naphthalimide (103) was synthesised
according to a procedure adapted from those published by Hamel et al.158
In a round-bottom flask equipped with a condenser, 4- bromo-1,8-naphthalic
anhydride (1 g, 3.61 mmol) and 2,5-di-tert-butylaniline (1.48 g, 7.22 mmol) were
dissolved in quinoline. Zinc acetate dihydrate (350 mg, 1.59 mmol) was added and the
mixture was heated at 200 °C for 5 hr. After cooling to room temperature, the mixture
was poured in to acidic water (2 M, 50 mL). The aqueous layer was fully extracted
with DCM (3x 30 mL). After drying with sodium sulphate, the extract was
concentrated and the crude product was purified on silica gel chromatography to yield
a beige solid (4.58g, 93%). M.p. 205- 210 °C. (Lit.158 M.p. 214 °C). 1H NMR (400
MHz, CDCl3) δ 1.29 (s, 9H, CH3); 1.34 (s, 9H, CH3); 7.03 (d, 1H, J = 1.86 Hz, Ar-H);
7.48 (dd, 1H, J = 8.08 Hz, J = 3.11 Hz, Ar-H); 7.61 (d, 1H, J =8.70 Hz, Ar-H); 7.89 (t,
1H, J = 6.84 Hz, Ar-H); 8.08 (d, 1H, J = 8.7 Hz, Ar-H); 8.49 (d, 1H, J = 9.23 Hz, Ar-
H); 8.63 (d, 1H, J = 8.70 Hz, Ar-H); 8.73 (d, 1H, J = 7.46 Hz, Ar-H). 13C NMR (62.9
MHz) d 31.36, 31.84, 34.37, 35.62, 122.72, 123.58, 126.47, 127.82, 128.33, 128.92,
129.53, 130.70, 130.95, 131.31, 131.77, 132.61, 132.73, 133.66, 143.86, 150.23,
C H A P T E R T W O
P a g e | 115
164.70, 164.75 Hz. HRMS (ESI): m/z (%) = 486.0910 and 488.0894 (95) [M+Na]+,
calcd for C26H26BrNNaO2 [M+Na]+ 486.1045.
2.5.35. N,N’-(2,5-di-tert-butylphenyl)-dibromoperylene-3,4,9,10-
tetracarboxy diimide (113)
N,N-(2,5-Di-tert-butylphenyl)-dibromoperylene-3,4,9,10-tetracarboxy diimide (113)
was synthesised according to a procedure adapted from those published by Dubey et
al. 166
Crude dibromoperylene-3,4,9,10-tetracarboxylic dianhydride (112) (1.12 g, 2.0178
mmol), was suspended in propionic acid (100 mL) and subsequently di- tert-
butylaniline ( 1.12 g, 5.454 mmol) was added. The reaction mixture was refluxed at
140 °C under stirring for 48 h, cooled to room temperature and poured into water
(200mL). The precipitate was filtered off, thoroughly washed with several portions of
water, and dried in the oven to give the crude product. The crude product was
chromatographed on silica with (n-hexanes: DCM, 1:3) to yield regioisomeric mixture
of 1,7- and 1,6-dibromoperylene diimides (2.7 g, 77%) as major product and 1,6,7-
tribromoperylene diimide as the minor. 166 Trans: 1H NMR (400 MHz, CDCl3) δ 1.29
(s, 9H, CH3); 1.30 (s, 9H, CH3); 1.31 (s, 9H, CH3), 1.32 (s, 9H, CH3); 6.99 (dd, 2H, J
= 2.2 & 1.1 Hz, Ar); 7.475 (dd, 2H, J = 8.55 & 2.33 Hz, Ar); 7.60 (d, 2H, J = 8.5 Hz,
Ar); 8.78 (d, 2H, J = 8.21 Hz, Ar); 8.99 (s, 2H, Ar); 9.54 (dd, 2H, J = 8 & 1.78 Hz,
C H A P T E R T W O
P a g e | 116
Ar). Cis: 1H NMR (400 MHz, CDCl3) δ 1.29 (s, 9H, CH3); 1.30 (s, 9H, CH3); 1.31 (s,
9H, CH3), 1.32 (s, 9H, CH3); 6.99 (dd, 2H, J = 13.1 & 1.89 Hz, Ar); 7.475 (dd, 2H, J
= 8.55 & 2.33 Hz, Ar); 7.60 (d, 2H, J = 8.5 Hz, Ar); 8.79 (d, 2H, J = 8.21 Hz, Ar); 8.99
(s, 2H, Ar); 9.55 (dd, 2H, J = 8 & 1.78 Hz, Ar).
2.5.36. N-(2,5-di-tert-butylphenyl)-4-(phenoxy)-1,8-naphthalimide
(128)
N-(2,5-di-tert-butylphenyl)-4-(phenoxy)-1,8-naphthalimide (128) was synthesised
according to a procedure adapted from those published by Hamel et al. 158
Regent 103 (40 mg, 8.61 x10-5 mol) and phenol (9.73 mg, 1.03 x10-4 mol) were
dissolved in a small amount of freshly distilled DMF. While stirring potassium
hydroxide (4.8 mg, 1.03 x10-4 mol) was added and the mixture was refluxed at 100°C
for 24 hrs. The mixture was allowed to cool to room temperature and then diluted
slowly with 2M NaOH solution (20 mL) while stirring. The precipitate was collected
and washed with water. It was then dissolved in DCM (50 mL) and washed further
with water, dried over sodium sulphate and concentrated by vacuum. Column
chromography was performed in chloroform to yield a yellow oil. 1H NMR (400 MHz,
CDCl3) δ 1.28 (s, 9H, CH3); 1.32 (s, 9H, CH3); 6.95 (d, J = 8.22 Hz, 1H, Ar-H); 7.00
C H A P T E R T W O
P a g e | 117
(d, 1H, J = 2.35 Hz, Ar-H); 7.23 (d, 1H, J =7.83 Hz, Ar-H); 7.33 (t, 1H, J =7.43 Hz,
Ar-H); 7.44 (dd, 1H, J = 8.61 Hz, J = 2.35 Hz, Ar-H); 7.51 (t, 1H, J = 8.22 Hz, Ar-H);
8.57 (d, 1H, J = 8.61 Hz, Ar-H); 8.83 (t, 1H, J = 7.43 Hz, Ar-H); 8.51 (d, 1H, J = 8.61
Hz, Ar-H); 8.72 (d, 1H, J = 7.43 Hz, Ar-H); 8.78 (d, 1H, J = 8.61 Hz, Ar-H). IR (ATR)
νmax 784 (=C-H), 1105 (C-O), 1352 (R3N), 1485 (aryl C-C), 1666 (C=O), 2871 cm-1
(alkyl CH3).
C H A P T E R T H R E E
P a g e | 118
3. POLYAROMATIC PROFLUORESCENT
NITROXIDE PROBES WITH ENHANCED
PHOTOSTABILITY
The Authors listed below have certified* that:
1. They meet the criteria for authorship in that they have participated in the
conception, execution, or interpretation, of at least that part of the publication
in their field or expertise;
2. They take public responsibility for their part of the publication, except for the
responsible author who accepts overall responsibility for the publication;
3. There are no other authors of the publication according to these criteria;
4. Potential conflicts of interest have been disclosed to (a) granting bodies, (b) the
editor or publisher of journals or other publications, and (c) the head of the
responsible academic unit and
5. They agree to the use of the publication in the student’s thesis and its
publication on the Australasian Research Online database consistent with any
limitations set by the publisher requirements
In the case of this chapter:
C H A P T E R T H R E E
P a g e | 119
Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability
Chemistry: A European Journal
Published 3 November 2015
Contributor Statement of contribution*
Vanessa Lussini Wrote the first manuscript and edited all co-author’s draft
changes. Synthesised, characterised and analysed all the
compounds used. Designed/conducted experiments and
performed the data analysis.
James P. Blinco Overall supervision of the project, guided during
experimental design and edited final manuscript
Kathryn E. Fairfull-
Smith
Overall supervision of the project, guided during synthesis
and experimental design and assisted during manuscript
design and editing.
Steve E. Bottle Original design of the project, overall supervision of the
project and edited final manuscript
Principal Supervisor Confirmation
I have sighted email or other correspondence from all Co-authors confirming their
certifying authorship.
Name Signature Date
QUT Verified Signature
C H A P T E R T H R E E
P a g e | 120
Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability
V. C. Lussini,[a,b] J. P. Blinco,[a] K. E. Fairfull-Smith*[a] and S. E. Bottle*[a,b]
Received: 27 August 2015
Published Online: 3 November 2015
DOI: 10.1002/chem.201503393
[a] ARC Cenre of Excellence for Free Radical Chemistry and Biotechnology
School of Chemistry, Physics and Mechanical Engineering
Faculty of Science and Engineering
Queensland University of Technology (QUT)
GPS Box 2434, Brisbane, QLD 4001, Australia
E-Email: [email protected]; [email protected]
[b] Defence Materials Technology Centre
Level 2 Wakefield Street, Hawthorne, VIC 3122, Australia
3.1. Abstract
Novel profluorescent mono- and bis-isoindoline nitroxides linked to napthalimide and
perylene diimide structural cores are described. These nitroxide-fluorophore probes
display strongly suppressed fluorescence in comparison to their corresponding non-
radical diamagnetic methoxyamine derivatives. The perylene based probe possessing
two isoindoline systems tethered through ethynyl linkages was shown to be the most
photostable in solution, demonstrating significantly enhanced longevity over the 9,10-
C H A P T E R T H R E E
P a g e | 121
bis(phenylethynyl)anthracene fluorophore used in previous profluorescent nitroxide
probes.
3.2. Introduction
Profluorescent nitroxides (PFNs)64, 172 are compounds bearing a stable nitroxide free
radical covalently linked to a fluorophore moiety. These species typically display low
levels of fluorescence as a result of excited state quenching by the nitroxide radical.
However, when PFNs scavenge alkyl radicals to form diamagnetic alkoxyamines, or
undergo reduction to yield a hydroxylamine118, their fluorescence is once again
restored. PFNs have been employed as extremely responsive fluorescent probes for the
detection of free-radicals formed during the degradation and aging of polymeric
materials.101 The doping of polymers with PFNs facilitates a convenient, non-
destructive and rapid method for the real-time monitoring, imaging and mapping of
radicals formed during the degradation process.56 To this effect, we have previously
demonstrated that profluorescent nitroxide probes offer a highly sensitive method to
assess the earliest stages of radical-mediated thermo-oxidative degradation of polymer
films, where conventional methods can lack sensitivity.35 However, a limitation of this
technique is evident under photo-oxidative conditions where photobleaching of the
fluorophore can occur once non-radical adducts are generated. A potential solution to
overcome complications arising from insufficient fluorophore photostability is to
incorporate more photostable fluorophores into the structural framework of the PFN.
Perylene diimides (of general structure 42, Figure 30) have been extensively studied
in dye and pigment research due to their excellent chemical, thermal, photo and
weather stability.124 Furthermore, many perylene diimides display other interesting
properties such as near-unity fluorescence quantum yields and high photochemical
C H A P T E R T H R E E
P a g e | 122
stability which have enabled their use in other applications.128-130 For these reasons,
perylene diimides represent attractive base structures from which to build new
generation PFNs with superior photostability to potentially enable the monitoring of
the photodegradation of organic materials. In addition, structurally rigid, isoindoline-
based nitroxides are attractive moieties for novel enhanced stability PFNs, as the aryl
ring extends the conjugation without delocalizing the spin. Isoindoline nitroxides are
more photo-stable than the piperidine-based nitroxides, being less prone to degradation
by hydrogen atom abstraction and by α-cleavage with UV irradiation.137 The first
example of an isoindoline-based probe was the perylene-linked nitroxide 44 that was
developed as a non-photobleaching probe for imaging cellular oxidative stress using
two-photon fluorescence microscopy.69
Figure 30: Chemical structures of perylene diimide 42, perylene-based profluorescent nitroxides 44 and
129 and 9,10-bis(phenylethynyl)anthracene-based profluorescent nitroxide 23.
Perylene-based nitroxide containing compounds have previously been synthesised for
spintronic applications and time-resolved EPR.173-175 Recently an isoindoline and
perylene-based profluorescent nitroxide was used to monitor the degradation of
C H A P T E R T H R E E
P a g e | 123
melamine-formaldehyde crosslinked polyesters under accelerated weathering
conditions.123 This PFN probe (129), which was employed to assess the impact of both
temperature and UV-irradiance on polymer degradation for a range of polyesters,
possessed a branched alkyl substituent to enhance solubility. Perylene-based
compounds have well-known solubility limitations and this is a complication with both
PFNs 44 and 129. An alternative approach to overcome solubility limitations is to
incorporate nitroxides in the “bay”-region of the perylene unit (positions 1 and 7,
structure 42, Figure 30), as substitution at these positions increases solubility through
slightly twisting the perylene unit to disrupt planar π-π stacking interactions.134-135
Herein we describe several novel profluorescent nitroxides including perylene based
systems substituted in the bay region with mono- and bis-nitroxides. Ether and alkynyl
linkers were used to connect the nitroxide to the fluorophore and this approach was
extended to also include naphthalene PFNs. A range of perylene diimides bearing
imide linked isoindoline nitroxides and solubility enhancing ditertbuylarylamines was
also generated to compare properties with the bay region substitution approach. In
addition to the synthetic details and description of the physical properties of the new
perylene- and naphthalene-based profluorescent nitroxides, we also report a
comparison of the photostability of the new probes with 9,10-
bis(phenylethynyl)anthracene (Figure 30 Compound 23), the fluorescent core which
features in the current state-of-art applications of profluorescent probes.53, 85, 91
3.3. Results and Discussion
Before the synthesis of the perylene-based bay-region substituted profluorescent
nitroxides was attempted, the required chemistry was explored using a model system
based on the structure of N-substituted naphthalimides. It was envisioned that the
C H A P T E R T H R E E
P a g e | 124
nitroxide could be more easily tethered to the fluorophore unit through ether or ethynyl
linkages by reaction with a halogenated naphthalimide. Exploiting the recently
reported methodology for the facile transformation of a methoxyamine into a nitroxide
using m-CPBA,147 a protected nitroxide was employed in the synthesis (to allow NMR
characterization) with the protecting group removed in the final synthetic step to reveal
the paramagnetic nitroxide. Thus, bromo naphthalimide 103 was reacted with 5-
hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 59 in a base assisted nucleophilic
phenoxide substitution reaction by heating with KOH in DMF to give substituted
naphthalimide 105 in high yield (84%) (Scheme 42). Removal of the methoxyamine
of 105 was readily achieved to yield nitroxide 104 in good yield (78%) by oxidation
with m-CPBA in a Cope-type elimination process.
Scheme 42: Synthetic route to ether linked naphthalimide-based profluorescent nitroxide 105.
The protected nitroxide 64 was accessed from the corresponding nitro methoxyamine
61 by reduction to the amino methoxyamine 62, followed by generation of the
diazonium tetrafluoroborate salt 58 and its subsequent hydrolysis to give phenol 59
(Scheme 43).
C H A P T E R T H R E E
P a g e | 125
Scheme 43: Synthetic route to 5-hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 64.
It was envisioned that the desired ethynyl tethered naphthalimide nitroxide 107 could
be prepared via a palladium-catalysed Sonogashira coupling using similar conditions
to those that have been successfully employed previously in the presence of the
nitroxide moiety.53 The coupling of the bromo naphthalimide 103 with the alkyne
bearing methoxyamine 81 in the presence of CuI and freshly prepared
tetrakis(triphenylphosphine)palladium(0)163 gave the desired substituted
naphthalimide 106 in high yield (90%) (Scheme 44). Deprotection of 106 was
accomplished under similar facile conditions to afford nitroxide 107 in excellent yield
(97%).
C H A P T E R T H R E E
P a g e | 126
Scheme 44: Synthetic route to ethynyl linked naphthalimide-based profluorescent nitroxide 107.
Following the success of the naphthalimide nitroxide substitution reactions, we turned
our attention towards the use of this chemistry to prepare perylene-based
profluorescent nitroxides which incorporated nitroxides at the bay-region of the
perylene unit. Substitution at these positions is well known via bromine atoms which
can easily be exchanged by phenol166 or alkyne176 groups as a method to functionalise
the perylene core and thereby improve its solubility by twisting the planar structure to
disfavour the formation of π-π aggregates.
The required 1,7-dibromo-perylene dianhydride was prepared by the I2-catalysed
bromination of the corresponding perylene dianhydride in sulfuric acid following
literature procedures.165 Based on previous reported observations, it was presumed that
the crude mixture contains both the 1,7- and 1,6-dibromo-perylene dianhydride
regioisomers and potentially a small amount of the 1,6,7-tribromo compound.
However, limited solubility meant that these regioisomers could not be detected by 1H
NMR spectroscopy at 400 MHz.164 Imidization of the crude brominated perylene
dianhydride product mixture with 2,5-di-tert-butylaniline in refluxing propionic acid
afforded a more soluble product mixture which was shown by 1H NMR spectroscopy
C H A P T E R T H R E E
P a g e | 127
to predominantly contain the 1,7-dibromo-perylene diimide 121, along with the 1,6-
dibromo perylene diimide regioisomer and a small amount of the 1,6,7-tribromo
compound in a ratio of 65:34:1 respectively. Separation of the desired compound 113
by column chromatography could not be achieved and the mixture was therefore
carried forward without further purification. Nucleophilic substitution of 1,7-dibromo-
perylene diimide 113 with methoxyamine 64 under basic conditions yielded perylene
dimethoxyamine 117 in high yield (87%) (Scheme 45). The isolated product was
shown by 1H NMR spectroscopy to contain both the 1,7-dimethoxyamine-perylene
diimide 117 and its 1,6-dimethoxyamine-perylene diimide regioisomer in a ratio of 3:2
respectively. Subsequent oxidation of dimethoxyamine 117 with m-CPBA under mild
conditions gave the desired nitroxide 118 in excellent yield (99%). Although 118 was
not isomerically pure (as a result of the previous bromination step), it was not purified
further as pronounced solubility differences between the isomers were not observed
(solubility differences have previously enabled the separation of other bay-
functionalised perylene diimide regioisomers166) and it was assumed that the presence
of the 1,6-regioisomer would have little impact on the resulting absorbance and
fluorescence spectra.
C H A P T E R T H R E E
P a g e | 128
Scheme 45: Synthetic route to ether linked perylene-based profluorescent nitroxide 118.
Sonogashira coupling of 1,7-dibromo perylene diimide 113 with the alkyne bearing
methoxyamine 81 in the prescence of CuI and Pd(PPh3)4 resulted in a moderate (52%)
yield of the perylene dimethoxyamine 114 (Scheme 46). Analysis of the isolated
product by 1H NMR spectroscopy revealed the presence of 1,7-dimethoxyamine-
perylene diimide 114 (54%) and the 1,6-dimethoxyamine-perylene diimide
regioisomer (46%). The mixture was not further purified. Oxidation to yield the
nitroxide moiety was facile using 2.5 equivalents of m-CPBA and resulted in an
excellent yield (99%) of nitroxide 116 after 15 minutes. It was also established that
when only 1.0 equivalent of m-CPBA was employed, a mono-nitroxide 115 could be
formed in moderate yield (55%) by the selective removal of a single methoxyamine
protecting group.
C H A P T E R T H R E E
P a g e | 129
Scheme 46: Synthetic route to ethynyl linked perylene-based profluorescent nitroxides 116 and 115.
As a comparison to the bay-expanded perylene-based profluorescent nitroxides, we
also sought to synthesise perylene diimides bearing imide linked isoindoline
nitroxides. We have previously reported the synthesis of perylene-based dinitroxide
44 by the condensation of 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57 with
3,4,9,10-perylenetetracarboxylic dianhydride 42 in the presence of zinc acetate in
molten imidazole in high (97%) yield.127 As the solubility of nitroxide 44 was
extremely poor in the majority of organic solvents, it was decided to focus on the
preparation of unsymmetrical perylene diimides which would incorporate both a
nitroxide unit and a solubilising group tethered through the covalent imide bonds onto
the perylene unit similar to the approach employed by Nagao.177
Initial attempts to generate a mono-nitroxide containing perylene diimide involved the
stepwise addition of 2,5-di-tert-butylaniline to 3,4,9,10-perylenetetracarboxylic
dianhydride 42 in the presence of zinc acetate in molten imidazole at 130ºC as a means
C H A P T E R T H R E E
P a g e | 130
to generate the monoanhydride which could subsequently be reacted with nitroxide 57.
Under these conditions, the reaction afforded a 1:1 mixture of the symmetrical N,N′-
bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide 89 and unreacted
3,4,9,10-perylenetetracarboxylic dianhydride 42 according to 1H NMR spectroscopy.
Attempts to selectively hydrolyse one imide bond of N,N′-bis(2,5-di-tert-butylphenyl)-
3,4,9,10-perylenedicarboximide using potassium hydroxide154 and subsequently react
the resulting monoimide monoanhydride with 5-amino-1,1,3,3-tetramethylisoindolin-
2-yloxyl 57 also did not give the desired perylene-based nitroxide (this route has been
noted to often proceed with difficulty155).
We expected that the increased solubility of the initially formed monoimide over the
dianhydride staring material (42) would lead to the rapid formation of the symmetrical
diimide, as described previously. Therefore it was reasoned that the desired nitroxide
/ N-octylaryl containing perylene diimides (98) could be accessed (after separation) in
one pot starting with a mixture of both aryl amines (Scheme 47). This simpler approach
proved to be effective, with the treatment of 3,4,9,10-perylenetetracarboxylic
dianhydride 42 with N-octylaniline and amino nitroxide 57 in the presence zinc acetate
in molten imidazole yielding the perylene nitroxide 98 in 26% yield following isolation
by chromatography (the corresponding symmetrical diimides were also isolated).
C H A P T E R T H R E E
P a g e | 131
Scheme 47: Synthetic route to imide linked perylene-based profluorescent nitroxide 98.
Similarly, perylene nitroxide 90 was synthesised from a stoichiometric mixture of 2,5-
di-tert-butylaniline and nitroxide 57 in a 22% yield following purification (Scheme
48). The corresponding methoxyamine derivatives 99 and 92 were prepared using
Fenton chemistry. The obtained isolated yields for these reactions were low, however
this can be rationalised by the poor solubility of nitroxides 99 and 92 in DMSO.
C H A P T E R T H R E E
P a g e | 132
Scheme 48: Synthetic route to imide linked perylene-based profluorescent nitroxide 90.
The naphthalimide- and perylene diimide-based profluorescent nitroxide probes (105,
107, 118, 116, 98, 90) and their corresponding methoxyamines adducts (104, 106, 117,
114, 99, 92) were then examined for their photophysical properties (Table 1). The
napthalimide-based compounds (105 and 104) displayed absorbance spectra
characteristic of their parent fluorophore, N-(2,5-di-tert-butylphenyl)-1,8-
naphthalimide (λmax = 350 nm, ε = 10 647 M-1cm-1).178 The ethynyl-linked compounds
107 and 106 both displayed a 13 nm red-shift which is consistent with extension of the
π-conjugation system. A comparison of the fluorescence quantum yields of nitroxides
105 and 107 (ΦF = 5.6 × 10-4 and 4.5 × 10-4 respectively) with their corresponding
methoxyamines 104 and 106 (ΦF = 9.04 × 10-2 and 0.169 respectively) revealed a
substantial suppression of fluorescence (Table 1, Figure 31). The values obtained for
the quantum yields of fluorescence for napthalimide methoxyamine adducts 104 and
106 were consistent with previously reported values for 1,8-naphthalimide derivatives
possessing electron rich substituents which give lowered fluorescence quantum yields
C H A P T E R T H R E E
P a g e | 133
as a result of their suggested ability to undergo photo-induced electron transfer
processes.179-180
Table 1: Photophysical properties of naphthalimide- and perylene diimide-based nitroxide probes and
their methoxyamine adducts.
Compound λabs
(nm)
Extinction
coefficient
λem (nm) Quantum
yield (ΦF)
ΦF
(NOMe/NO•)
104[a] 357 13089[c] 408 0.0904[e] -
105[a] 355 9277.7[c] 412 0.0006[e] 150.7
106[a] 370 21924[c] 428 0.169[e] -
107[a] 368 24704[c] 434 0.0005[e] 338
117[b] 542 35106[d] 576 0.295[f] -
118[b] 536 26699[d] 566 0.0174[f] 17.0
114[b] 565 28811[d] 587 0.0996[f] -
116[b] 560 13224[d] 582 0.0044[f] 22.6
115[b] 562 22052[d] 576 0.0094[f] 10.6
98[b] 525 20733 [d] 535 0.0535[f] 9.5
99[b] 525 7667[d] 535 0.508[f] -
90[b] 525 21000[d] 535 0.0267[f] 15.7
92[b] 525 19350[d] 535 0.4198[f] -
113 526 54740[d] 546 0.811[f] -
103 336 16410[c] 436 0.0069[e] -
130 536 29520[d] 572 0.7619[f] -
[a] Absorbance and fluorescence spectra recorded in cyclohexane. [b] Absorbance and
fluorescence spectra recorded in chloroform. [c] Measured at 350 nm in M-1cm-1. [d]
Measured at 525 nm in M-1cm-1. [e] Measured in cyclohexane using anthracene as
C H A P T E R T H R E E
P a g e | 134
standard (350 nm excitation, ΦF =0.36).181 [f] Measured in chloroform using N,N′-
bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide as standard (525 nm
excitation, ΦF =0.99).131
Figure 31: Fluorescence spectra of 1,8-napthalimide-based probes 105 (—) and 104 (···), 9 μM in
cyclohexane; 106 (—) and 107 (···), 3 μM in cyclohexane, following excitation at 350 nm.
The perylene-based compounds (98, 99, 90, 92) all displayed absorbance maxima at
525 nm (Table 1), which is consistent with their parent compound N,N′-bis(2,5-di-tert-
butylphenyl)-3,4,9,10-perylenedicarboximide 89 (DBPI, λmax = 525 nm). Substitution
at the perylene bay region, through ether and ethynyl linkages, extended the maximum
absorbance wavelength from 525 nm for nitroxides 98 and 90 to 536 nm and 560 nm
for nitroxides 118 and 116 respectively. Accordingly the wavelength of maximum
fluorescence emission was extended from 535 nm for nitroxides 98 and 90 to 566 nm
and 582 nm for nitroxides 118 and 116 respectively (Table 1). This fluorescence shift
can be justified by the extended conjugation system contained within perylene
compounds substituted at the bay region. A comparison of the fluorescence emission
C H A P T E R T H R E E
P a g e | 135
from the nitroxides (118, 116, 98 and 90) and their corresponding methoxyamine
adducts (117, 114, 99 and 92) showed a significant fluorescence suppression arising
from the presence of the nitroxide moiety.
Figure 32: Fluorescence spectra of perylene-based probes 114 (—), 116 (---) and 115 (···), 1 μM in
chloroform, following excitation at 525 nm.
This fluorescence suppression effect was most pronounced (~23 fold) in di-nitroxide
116 where fluorescence quantum yields of 0.0044 and 0.1 where obtained for 116 and
methoxyamine 114 respectively (Table 1). The mono-nitroxide analogue 115 still
demonstrated strongly suppressed fluorescence (ΦF = 0.009) even by a single nitroxide
group (Figure 32).
Perylene diimides typically exhibit high fluorescence quantum yields (close to
unity)125 and Wille et al. have previously reported a comparable fluorescence quantum
yield for perylene nitroxide 131 trapped with a 2-cyanoprop-2-yl radical to be 0.95 in
DCM.123 However, in this study, a significant decrease in the fluorescence quantum
C H A P T E R T H R E E
P a g e | 136
efficiencies of the perylene methoxyamines 117, 114, 99 and 92 was observed, as
demonstrated by the obtained fluorescence quantum yield values of 0.295, 9.96 × 10-
2, 0.508 and 0.42 respectively (Table 1). To investigate whether the alkyl R-group of
the alkoxyamine may influence the quantum yield, a different alkoxyamine adduct was
prepared through reaction of nitroxide 118 with radicals derived from the reaction of
ethyl 2-bromoisobutyrate with copper catalyst. However, the fluorescence quantum
efficiency of the resulting alkoxyamine adduct was similar to that of methoxyamine
117 (data not shown). The isoindoline heterocyclic ring component of the
methoxyamines may lead to the observed decrease in fluorescence quantum yield, as
1,7-dipyrrolidino based perylene diimides exhibit lowered quantum yields due to
significant amino-to-perylene diimide quadrupolar charge-transfer character.164, 182-183
To test this, an analogue (130) of methoxyamine 117 was prepared where the
isoindoline rings at positions 1 and 7 on the perylene unit were replaced with phenoxy
groups. For160 this compound, a higher value of 0.7619 for the fluorescence quantum
yield was obtained. This supports the hypothesis that the low fluorescence quantum
yields arise from charge-transfer processes between the N lone pair of the isoindoline
ring and the π-system of the perylene unit.
Preliminary assessment of the photostability of the newly synthesised profluorescent
nitroxides was achieved by comparing the relative photostability of the methoxyamine
adducts (104, 106, 117 and 114) against 9,10-bis(phenylethynyl)anthracene (the
fluorescent core which features in the current state-of-art profluorescent probe 29) and
N,N′-bis(2,5-di-tert-butylphenyl)-1,7-dibromo-3,4,9,10-perylene dicarboximide 113.
Profluorescent nitroxide 23 displays significant fluorescence suppression (>20 fold)
and has been shown to have considerable thermal stability98, 100 yet its performance
under photo-oxidative conditions has not been reported. To obtain a clear picture of
C H A P T E R T H R E E
P a g e | 137
the relative stability of the fluorphores involved, the non-radical methoxyamine
analogues were analyzed. This removes any complications arising from the stabilizing
effect of the nitroxide antioxidant. Thus the photostabilities of compounds 104, 106,
113, 117, 114 and 9,10-bis(phenylethynyl)anthracene 29 study were assessed by
irradiating samples in cyclohexane in a Heraeus Suntest CPS+ device operating at an
irradiation level of approximately 765 Wm-2 and held at 40ºC. Methoxyamines 99 and
92 could not examined due to their limited solubility in cyclohexane. The fluorescence
intensity at the λmax value for each compound was recorded periodically and the
percentage loss of fluorescence for each compound is shown in Figure 33. The least
stable fluorophore in this environment was 9,10-bis(phenylethynyl)anthracene (29)
which displayed a 50% decrease in fluorescence after only ~2 hours of photo-
irradiation. The fluorescence performance of the naphthalimide fluorophores 104 and
106 was much more robust, giving a 50% emission reduction after ~8 and ~20 hours
photo-irradiation respectively. The bay-region brominated perylene 113 showed a
photo-stability similar to the napthalimide fluorophore 106. The fluorescence from the
perylene fluorophores 117 and 114, however demonstrated substantial stability with a
reduction to 50% emission not being reached until 50 and 80 hours respectively. There
was also a trend showing that substitution at the bay-region of perylene with an alkyne
linker produced a more photostable compound than substitution with an ether linkage.
These results demonstrate the increased photostability of the bay-region substituted
perylene compounds 117 and 114 over the napthalimide or 9,10-
bis(phenylethynyl)anthracene based fluorophores. The rapid loss of fluorescence from
9,10-bis(phenylethynyl)anthracene is not surprising as photodegradation of this
fluorophore is known to proceed by the addition of photogenerated singlet oxygen to
the anthracene core to form a 9,10-endoperoxide.184 This highlights the limited value
C H A P T E R T H R E E
P a g e | 138
of this fluorophore as a profluorescent probe to monitor photo-oxidative damage in
materials. Based on these results, bay-substituted perylene systems on the other hand
show considerably more potential in this regard.
Figure 33: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) for
cyclohexane solutions of 9,10-bis(phenylethynyl)anthracene 29 (-♦-, λmax = 470 nm), 104 (-■-, λmax = 408
nm), 106 (-Δ-, λmax = 407 nm), 113 (-x-, λmax = 534 nm), 117 (-●-, λmax = 522 nm) and 114 (-+-, λmax = 557 nm)
following photo-irradiation at 765 Wm-2 and 40ºC.
3.4. Conclusions
Novel profluorescent mono- and bis-isoindoline nitroxides containing napthalimide
and perylene diimide structural cores and their respective methoxyamine adducts were
synthesised. The methoxyamine derivatives of the napthalimide-based probes (104
and 106) were prepared by nucleophilic substitution and palladium-catalysed
Sonogashira coupling reactions from the corresponding aryl bromides in high yield
(84 and 90%). Subsequent deprotection gave the desired nitroxides (105 and 107) in
C H A P T E R T H R E E
P a g e | 139
good yield. The bay region substituted bis-methoxyamine adducts of the perylene-
based probes (117 and 114) were prepared in a similar fashion in moderate-high yield
(52 and 87%) with deprotection again yielding the bis-nitroxides (118 and 116) in
excellent yield. Selective removal of a single methoxyamine group from the bis-
methoxymine 114 was also achieved with stoichiometric control of m-CPBA to give
mono-nitroxide 115 in moderate yield (55%). Unsymmetrical perylene-based probes
(98 and 90) bearing an imide linked nitroxide and an imide linked solubilizing group
were prepared in one pot from 3,4,9,10-perylenetetracarboxylic dianhydride and a
mixture of the corresponding aryl amines in modest yield (26% and 22%). The
corresponding methoxyamines (99 and 92) were accessed by subsequent reaction of
the nitroxides (98 and 90) with methyl radicals. The prepared profluorescent
compounds demonstrated strongly suppressed fluorescence emission even though the
measured fluorescence quantum yields for the corresponding methoxyamine
derivatives were lower than typical perylenes. Assessment of the photostability of the
newly prepared compounds revealed that the bay-region substituted perylene
compounds 117 and 114 displayed enhanced photostability over the napthalimide
compounds (104 and 106), bay-region brominated perylene 15 and 9,10-
bis(phenylethynyl)anthracene 29. These results suggest that perylene-based
profluorescent nitroxides (118, 116 and 115) may provide a sensitive technique for
assessing the early stages of photo-oxidative polymer degradation.
3.5. Experimental Section
3.5.1. General procedures
All starting materials and reagents were purchased from Sigma Aldrich. All reactions
were monitored using Merck Silica Gel 60 F254 TLC plates and visualized with UV
C H A P T E R T H R E E
P a g e | 140
light. Column chromatography was performed using silica gel 60 Å (230 - 400 mesh).
1H NMR spectra were run at 400 MHz and 13C NMR spectra at 100 MHz. Chemical
shifts (δ) for 1H and 13C NMR spectra run in CDCl3 are reported in ppm relative to the
solvent residual peak: proton (δ = 7.26 ppm) and carbon (δ= 77.2 ppm). Multiplicity
is indicated as follows: s (singlet); d (doublet); t (triplet); m (multiplet); dd (doublet of
doublet); br s (broad singlet). Coupling constants are reported in Hertz (Hz). Mass
spectra were recorded using either electrospray or electron impact (where specified)
as the ionization technique in positive ion mode. All MS analysis samples were
prepared as solutions in methanol. Infrared spectra were recorded as neat samples
using a Nicolet 870 Nexus Fourier Transform infrared spectrometer equipped with a
DTGS TEC detector and an Attenuated Total Reflectance (ATR) accessory. Analytical
HPLC was performed on a Hewlett Packard 1100 series HPLC, using an Agilent prep-
C18 scalar column (10 μm, 4.6 × 150 mm) at a flow rate of 1 mL/min. All UV/Vis
spectra were recorded on a single beam Varian Cary 50 UV-Vis spectrophotometer.
Fluorescence measurements were performed on a Varian Cary 54 Eclipse fluorescence
spectrophotometer equipped with a standard multicell Peltier thermostatted sample
holder. Melting points were measured on a Gallenkamp Variable Temperature
Apparatus by the capillary method and are uncorrected. EPR spectroscopy was carried
out on a Magnettech MiniScope EPR spectrometer using a suitable nonpolar solvent
at room temperature. All air-sensitive reactions were carried out under ultra-high
purity argon. Diethyl ether and toluene were dried by storing over sodium wire. THF
was freshly distilled from sodium benzophenone ketal, acetonitrile from calcium
hydride and DMF from 4Å molecular sieves.
Tetrakis(triphenylphosphine)palladium(0) was freshly prepared according to literature
procedures.163 N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide 103 was
C H A P T E R T H R E E
P a g e | 141
prepared in 2 steps using literature procedures from commercially available 1,8-
naphthalic anhydride.157, 185 N,N′-Bis(2,5-di-tert-butylphenyl)-1,7-dibromo-3,4,9,10-
perylene dicarboximide 113 was prepared in 2 steps from perylene-3,4,9,10-
tetracarboxylic dianhydride using established methods.[16] 2-Methoxy-5-nitro-1,1,3,3-
tetramethylisoindoline 61[14] and 5-ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline
81105 were prepared using established literature protocols.145
3.5.2. 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 64
A solution of 5-diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline
tetrafluoroborate 63 (84.1 mg, 2.64 × 10-4 mol) in deionised water (25 mL) was heated
at reflux for 5 hr. The solution was cooled and extracted with DCM (5 × 10 mL). The
combined DCM layers were washed with water (1 × 10 mL) and dried over sodium
sulphate. The organic layer was concentrated in vacuo to yield 64 as a pale yellow
crystalline solid. The aqueous layer was heated at reflux overnight and worked up
using the above procedure to yield a second portion of product (43 mg, 81%). M.p.
134-136°C. 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.40 (s, 12H, CH3-C), 2.84
(s, 3H, NH2), 3.77 (s, 3H, CH3-O), 6.56 (d, J = 1.91 Hz, 1H, Ar-H), 6.69 (dd, J = 8.07,
1.91 Hz, 1H, Ar-H), 6.97 (d, J = 8.07 Hz, 1H, Ar-H). 13C NMR (100 MHz, CDCl3,
25°C, TMS): δ= 65.4, 66.7, 67.0, 108.4, 114.5, 122.5, 137.5, 146.9, 155.0. HRMS
(ESI): m/z (%) = 222.1649 (10) [M+H]+; calcd. for C13H20NO2 [M+H]+ 222.1494.
3.5.3. N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-1,8-naphthalimide 104
N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide 103 (31.478 mg, 6.778 × 10-
5 mol) and 5-hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 64 (15 mg, 6.778 ×
C H A P T E R T H R E E
P a g e | 142
10-5 mol) were dissolved in freshly distilled DMF (10 mL). Potassium hydroxide (4
mg, 6.778 × 10-5 mol) was added and the stirring solution was heated at 100°C for 24
hrs. The mixture was allowed to cool to room temperature and then diluted slowly with
2 M NaOH (10 mL) with stirring. The precipitate was collected and washed with water
(3 × 5 mL) until the filtrate ran clear. It was then dissolved in DCM (50 mL) and
washed further with water (10 mL), dried over sodium sulphate and concentrated in
vacuo. Purification by silica gel column chromatography in chloroform yielded 104 as
a yellow solid (34.4 mg, 84%). M.p. 122-125°C. 1H NMR (400 MHz, CDCl3, 25°C,
TMS): δ=1.29 (s, 9H, CH3); 1.32 (s, 9H, CH3); 1.46 (s, 6H, CH3); 1.49 (s, 6H, CH3);
3.81 (s, 3H, O-CH3); 6.95-7 (m, 3H, Ar-H); 7.07 (dd, 1H, J = 8.22, 1.96 Hz, Ar-H);
7.20 (d, 1H, J = 8.22 Hz, Ar-H); 7.44 (dd, 1H, J = 8.61, 2.35 Hz, Ar-H); 7.57 (d, 1H,
J = 8.7 Hz, Ar-H); 7.82 (dd, 1H, J = 7.78, 7.30 Hz, Ar-H); 8.52 (d, 1H, J = 8.22 Hz,
Ar-H); 8.71 (dd, 1H, J = 7.23, 1.49 Hz, Ar-H); 8.77 (dd, 1H, J = 8.50, 1.38 Hz, Ar-H).
13C NMR (100 MHz, CDCl3, 25°C, TMS): δ=15.3, 31.2, 31.7, 34.2, 34.8, 50.8, 65.5,
67.2, 110.3, 114.1, 116.7, 119.8, 122.9, 123.4, 124.0, 126.1, 126.5, 127.8, 128.7, 128.8,
130.1, 132.3, 133.0, 133.3, 142.6, 143.8, 147.9, 150.0, 154.0, 160.4, 164.8, 165.4. IR
(ATR) νmax 781 (=C-H), 1050 (C-O), 1352 (R3N), 1484 (aryl C-C), 1664 (C=O), 2961
cm-1 (alkyl CH3). HRMS (ESI): m/z (%) = 627.3095 (34) [M+Na]+; calcd. for
C39H44N2O4Na [M+Na]+ 627.3199.
3.5.4. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide
105
mCBPA (6.12 mg, 2.84 x 10-5 mol) was added to an ice-cold solution of N-(2,5-di-tert-
butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-
C H A P T E R T H R E E
P a g e | 143
naphthalimide 104 (8.6 mg, 1.42 x 10-5 mol) in DCM (20 mL). The solution was stirred
for an hour at room temperature and then chilled in an ice-bath and treated with 2 M
aqueous NaOH until the solution was basic. The resulting solution was extracted with
DCM (3 × 10 mL) and the combined organic layers were washed with base (5 × 10
mL) and water (1 × 30 mL). The organic phase was dried over sodium sulphate and
concentrated in vacuo. Purification by silica gel column chromography (chloroform)
gave 105 as a yellow solid (7.3 mg, 78%). M.p 150-152°C. 1H NMR (400 MHz,
CDCl3, 25°C, TMS): δ=1.30 (s, 9H, 3 × CH3); 1.33 (s, 9H, 3 × CH3); 7.1 (s, 1H, Ar-
H); 7.46 (d, 1H, J = 8.73 Hz, Ar-H); 7.60 (d, 1H, J = 8.73 Hz, Ar-H); 7.87 (br s, 1H,
Ar-H); 8.59 (br s, 1H, Ar-H); 8.75 (d, 1H, J = 5.97 Hz, Ar-H); 8.80 (br s, 1H , Ar-H).
IR (ATR) νmax 782 (=C-H), 1138 (C-O), 1375 (R3N), 1487 (aryl C-C), 1667 (C=O),
2968 cm-1 (alkyl CH3). HRMS (ESI): m/z (%) = 612.2855 (35) [M+Na]+, calcd. for
C38H41N2O4Na [M+Na]+ 612.2964. EPR: g = 2.0058, aN = 1.429 mT.
3.5.5. 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline 62
2-Methoxy-5-nitro-1,1,3,3-tetramethylisoindoline 61 (78 mg, 3.12 x 10-4 mol) was
dissolved in methanol (10 mL) and palladium on carbon (10% wt. loading, 24 mg)
added. The solution was placed in a Parr hydrogenator under an atmosphere of
hydrogen (40 psi) with shaking for 3 hours. The resulting suspension was filtered
through celite and the celite washed thoroughly with methanol. The combined filtrates
were concentrated at reduced pressure to give 62 as a cream solid in quantitative yield.
M.p. 52-54°C. 1H NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.41 (s, 12H, 4 x CH3),
2.84 (s, 2H, NH2), 3.77 (s, 3H, O-CH3), 6.35 (d, J = 2.35 Hz, 1H, Ar-H), 6.52 (dd, J =
8.22, 2.35 Hz, 1H, Ar-H), 6.92 (d, J = 8.22 Hz, 1H, Ar-H). 13C NMR (100 MHz,
CDCl3, 25°C, TMS): δ= 65.4, 66.7, 67.0, 108.2, 114.5, 122.2, 135.5, 145.7, 146.4.
C H A P T E R T H R E E
P a g e | 144
HRMS (ESI): m/z (%) = 221.1792 (10) [M+H]+, calcd. for C13H21N2O [M+H]+
221.1654.
3.5.6. 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline
tetrafluoroborate 63
A solution of 5-amino-2-methoxy-1,1,3,3-tetramethylisoindoline 62 (117 mg, 5.3135
× 10-4 mol) in dry acetonitrile (0.5 mL) was added dropwise to a stirring solution of
nitrosyl tetrafluoroborate (124.1 mg, 10.628 × 10-4 mol) in dry acetonitrile (1 mL) at
-30 °C (dry ice/acetonitrile bath). Once the addition was complete, the reaction was
left to warm to room temperature for 30 min. Dry diethyl ether (3 mL) with added
dropwise to the reaction and the mixture was left to stir to ensure precipitation. The
white precipitate of 63 was collected by filtration, washed with dry diethyl ether and
stored under argon in the freezer (165.4 mg, 98 %). M.p. 138-140°C. 1H NMR (400
MHz, CDCl3, 25°C, TMS): δ= 1.45 (s, 12H, 4 × CH3), 3.73 (s, 3H, CH3-O), 7.93 (d, J
= 9 Hz, 1H, Ar-H), 8.60 (d, J = 4.3 Hz, 1H, Ar-H), 8.62 (s, 1H, Ar-H). 13C NMR (100
MHz, CDCl3, 25°C, TMS): δ= 65.4, 65.8, 68.3, 108.4, 115.0, 122.8, 125.6, 127.0,
133.5, 148.1, 159.0. IR (ATR) νmax 2200 cm-1 (N≡N). HRMS (ESI): m/z (%) =
322.1624 (45) [M+3H]3+, calcd. for C13H18BF4N3O [M+3H]3+ 322.1714.
3.5.7. N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide 106
N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide 103 (16 mg, 0.0349 mmol),
triethylamine (1.4 mL), copper (I) iodide (3.32 mg, 3.49 × 10-6 mol) and Pd(PPh3)4 (4
mg, 3.46 × 10-6 mol) were dissolved in dry THF (1.4 mL). The mixture was submitted
to 4 freeze-pump-thaw cycles. A solution of 5-ethynyl-2-methoxy-1,1,3,3-
C H A P T E R T H R E E
P a g e | 145
tetramethylisoindoline 81 (20 mg, 0.0872 mmol) in dry THF (0.5 mL) was added to
the mixture and the tube was sealed under argon and heated at 80°C for 24 hours. The
reaction mixture diluted with DCM (5 mL) and washed with 2 M aqueous HCl (3 × 5
mL). The organic phase was run through basic alumina and then purified by silica gel
column chromatography in diethyl ether/DCM 1:3 to give 106 as a yellow solid (19.4
mg, 90 %). M.p. 150°C (dec). 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ= 1.29 (s,
9H, 3 × CH3); 1.32 (s, 9H, 3 × CH3); 1.49 (s, 12H, 4 × CH3); 3.81 (s, 3H, O-CH3); 6.99
(d, 1H, J = 1.8 Hz, Ar-H); 7.18 (d, 1H, J = 8.11 Hz, Ar-H); 7.43 (s, 1H, Ar-H); 7.45
(dd, 1H, J = 8.26, 1.8 Hz, Ar-H); 7.58 (s, 1H, Ar-H); 7.59 (dd, 1H, J = 7.67, 2.41 Hz,
Ar-H); 7.89 (t, 1H, J = 7.97 Hz, Ar-H); 7.99 (d, 1H, J = 7.66 Hz, Ar-H); 8.61 (d, 1H,
J = 7.67 Hz, Ar-H); 8.70 (d, 1H, J = 7.36 Hz, Ar-H); 8.82 (d, 1H, J = 8.41 Hz, Ar-
H).13C NMR (100 MHz, CDCl3, 25°C, TMS): δ= 14.2, 21.5, 22.7, 29.4, 29.7, 31.2,
31.7, 32.0, 35.0, 34.3, 35.5, 65.6, 67.1, 67.3, 85.78, 99.7, 121.0, 122.0, 122.4, 123.4,
125.2, 126.3, 127.5, 127.8, 128.1, 128.8, 130.8, 130.9, 131.3, 132.1, 132.8, 132.8,
143.8, 146.0, 147.1, 150.1, 164.8, 165.0. IR (ATR) νmax 782 (=C-H), 1050 (C-O), 1237
(Ar-O-C), 1356 (R3N), 1709 (C=O), 2206 (C≡C), 2958 cm-1 (alkyl CH3).
3.5.8. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-
naphthalimide 107
N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl-
1,8-naphthalimide 106 (11.6 mg, 0.0189 mmol) was dissolved in DCM (25 mL) and
m-CPBA (7 mg, 2.84 x10-5 mol) was added slowly to the stirring solution. After 10
minutes, the reaction was complete following analysis by TLC (DCM) and 2 M NaOH
was added (25 mL) and the resulting mixture was washed with water (5 x 10 mL).
C H A P T E R T H R E E
P a g e | 146
Purification by silica gel column chromatography (DCM) gave 107 as a yellow oil
(11.2 mg, 99%). M.p 165-170°C. IR (ATR) νmax 782 (=C-H), 1064 (C-O), 1236 (Ar-
O-C), 1356 (R3N), 1709 (C=O), 2205 (C≡C), 2968 cm-1 (alkyl CH3). EPR: g = 2.0064,
aN = 1.402 mT.
3.5.9. N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-
tetracarboxy diimide 117
Anhydrous K2CO3 (1.5 mg, 1.13 × 10-4 mol) and 5-hydroxy-2-methoxy-1,1,3,3-
tetramethylisoindoline 64 (10 mg, 4.52 × 10-5 mol) were added to an NMP (20 mL)
solution of 1,7-dibromoperylene dianhydride 113 (20.89 mg, 2.26 × 10-5 mol). The
mixture was stirred at 120°C for 8 hr under an atmosphere of argon, cooled to room
temperature and then treated with aqueous 1 M HCl (~20 mL) to precipitate the
product. The precipitate was collected by filtration and washed with water until
neutrality. The resulting solid was dissolved in DCM, dried over sodium sulphate and
concentrated in vacuo. The product was purified by silica gel chromatography (DCM)
to yield a yellow solid (23.8 mg, 87.4%). M.p: 196-199°C. Analysis by 1H NMR
spectroscopy revealed a 1:4 mixture of 1,7 and 1,6 regioisomers. N,N-Di-(2,5-di-tert-
butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy) perylene-
3,4,9,10-tetracarboxy diimide 117: 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.25
(s, 18H, CH3); 1.26 (s, 18H, CH3); 1.43 (s, 24H, CH3); 3.77 (s, 6H, O-CH3); 6.95 (m,
6H, Ar-H); 7.13 (dd, 2H, J = 1.95, 8.25 Hz, Ar-H); 7.42 (dd, 2H, J = 1.96, 8.68, Hz,
Ar-H); 7.55 (d, 2H, J = 8.68 Hz, Ar-H); 8.40 (d, 2H, J = 1.74 Hz, Ar-H); 8.68 (dd, 2H,
J = 1.3, 8.46 Hz, Ar-H); 9.65 (dd, 2H, J = 5.64, 8.68 Hz, Ar-H). N,N-Di-(2,5-di-tert-
butylphenyl)-1,6-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy) perylene-
C H A P T E R T H R E E
P a g e | 147
3,4,9,10-tetracarboxy diimide: 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.25 (s,
18H, CH3); 1.26 (s, 18H, CH3); 1.43 (s, 24H, CH3); 3.77 (s, 6H, O-CH3); 6.95 (m, 6H,
Ar); 7.13 (dd, 2H, J = 1.95, 8.25 Hz, Ar); 7.42 (dd, 2H, J = 1.96, 8.68 Hz, Ar); 7.55 (d,
2H, J = 8.68 Hz, Ar); 8.32 (d, 2H, J = 1.74 Hz, Ar); 8.75 (dd, 2H, J = 1.3, 8.46 Hz,
Ar); 9.60 (dd, 2H, J = 5.64, 8.68 Hz, Ar). 13C NMR (100 MHz, CDCl3, 25°C, TMS):
δ=30.4, 31.4, 31.7, 34.2, 35.5, 65.5, 67.0, 67.2, 113.1, 118.5, 118.5, 122.6, 123.6,
124.2, 125.5, 126.4, 127.5, 127.7, 128.8, 129.0, 129.7, 130.6, 131.7, 132.4, 133.8,
133.79, 142.2, 143.7, 148.0, 150.1, 154.3, 154.4, 155.6, 156.6, 163.7, 163.9, 164.4,
264.6. IR (ATR) νmax 753 (=C-H), 1050 (C-O), 1258 (Ar-O-C), 1336 (R3N), 1707
(C=O), 2958 cm-1 (alkyl CH3).
3.5.10. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-
tetracarboxy diimide 118
mCBPA (7.46 mg, 4.33 x 10-5 mol) was added to an ice-cooled solution of N,N-di-(2,5-
di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)
perylene-3,4,9,10-tetracarboxy diimide 117 (26 mg, 2.16x10-5 mol) in DCM (25 mL).
The solution was stirred for an hour at room temperature and then cooled in an ice bath
and quenched with 2 M aqueous NaOH until the solution was basic. The aqueous phase
was extracted with DCM until the organic layer was colourless and the combined
organic layers washed with 2 M NaOH (5 × 10 mL) and water (2 × 10 mL) and then
dried over sodium sulphate and concentrated in vacuo. The product was purified by
silica gel column chromatography (5% diethyl ether in DCM) to yield a 118 as a purple
solid (22 mg, 87%). The isomers were not separated. M.p 196-200°C. IR (ATR) νmax
C H A P T E R T H R E E
P a g e | 148
752 (=C-H), 1113 (C-O), 1261 (Ar-O-C), 1337 (R3N), 1706 (C=O), 2962 cm-1 (alkyl
CH3). EPR: g = 2.0064, aN = 1.406 mT.
3.5.11. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-
tetracarboxy diimide 114
1,7-Dibromoperylene diimide 113 (16.1 mg, 0.0174 mmol), triethylamine (1 mL),
copper (I) iodide (1.66 mg, 0.0872 mmol) and Pd(PPh3)4 (2 mg, 0.00174 mmol) were
dissolved in dry THF (1 mL). The mixture was submitted to 4 freeze-pump-thaw
cycles. A solution of 5-ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline 81 (20 mg,
0.0872 mmol) in a small amount of dry THF (0.5 mL) was added to the mixture and
the tube was sealed under argon and heated at 80°C for 48 hours The reaction mixture
was dissolved in DMC (50 mL) and washed with 2 M HCl (3 × 10 mL), run through
basic alumina and then purified by silica gel column chromatography (20% hexane in
DCM) to give 114 as a red solid (7.59 mg, 36%). M.p. 163-170°C. 1H NMR (400
MHz, CDCl3, 25°C, TMS): δ=1.32 (s, 18H, CH3); 1.34 (s, 18H, CH3); 1.48 (s, 12H,
CH3); 1.50 (s, 12H, CH3); 3.80 (s, 3H, O-CH3); 7.04 (s, 2H, Ar-H); 7.22 (d, 2H, J =
8.59 Hz, Ar-H); 7.44 (s, 2H, Ar-H); 7.49 (m, 2H, Ar-H); 7.59 (dd, 2H, J = 1.2, 7.68
Hz, Ar-H); 7.62 (d, 2H, J = 1.2, 7.68 Hz, Ar-H); 8.81 (m, 2H, Ar-H); 8.98 (s, 2H, Ar-
H); 10.40 (d, 2H, J = 8.59 Hz, Ar-H). IR (ATR) νmax 752 (=C-H), 1050 (C-O), 1262
(Ar-O-C), 1346 (R3N), 1707 (C=O), 2188 (C≡C), 2958 cm-1 (alkyl CH3).
C H A P T E R T H R E E
P a g e | 149
3.5.12. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-
3,4,9,10-tetracarboxy diimide 116
m-CPBA (5.4 mg, 3.77 x10-5 mol) was added slowly to an ice-cooled solution of N,N-
(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)
perylene-3,4,9,10-tetracarboxy diimide 114 (23 mg, 1.88 x10-5 mol) was dissolved in
ice-cooled DCM (50 mL). The solution was stirred for an hour at room temperature
and then cooled in an ice bath and quenched with 2 M aqueous NaOH. The aqueous
phase was extracted with DCM until the organic level was colourless and the combined
organic layers washed with water (5 × 10 mL), dried over sodium sulphate and
concentrated in vacuo. The compound was purified by column chromatography (10%
diethyl ether in DCM) to yield a 114 as a red solid (22 mg, 99%). M.p. 162-167°C. 1H
NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.32 (s, 18H, CH3); 1.34 (s, 18H, CH3); 7.00
(s, 2H, Ar-H); 7.50 (d, 2H, J = 5.38 Hz, Ar-H); 7.61 (d, 2H, J = 5.38 Hz, Ar-H); 8.56
(br s, 2H, Ar-H); 8.84 (br s, 2H, Ar-H); 8.98 (br s, 2H, Ar-H); 10.44 (br s, 2H, Ar-H).
IR (ATR) νmax 752 (=C-H), 1068 (C-O), 1223 (Ar-O-C), 1325 (R3N), 1708 (C=O),
2192 (C≡C), 2961 cm-1 (alkyl CH3). EPR: g = 2.0064, aN = 1.443 mT.
3.5.13. N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-
1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-
tetracarboxy diimide 115
N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-
ethynyl) perylene-3,4,9,10-tetracarboxy diimide 114 (18.9 mg, 1.55 x10-5 mol) was
C H A P T E R T H R E E
P a g e | 150
dissolved in ice-cooled DCM (40 mL) and m-CPBA (2.7 mg, 1.55 x10-5 mol) was
added slowly to the stirring solution. The reaction was allowed to warm to room
temperature and after 1 hr, 2 M aqueous NaOH (10 mL) was added. The resulting
solution was washed with water (2 × 20 mL), dried (anhydrous Na2SO4) and
concentrated in vacuo. Purification of the obtained residue by column chromatography
(DCM) gave 115 as a red solid (8.8 mg, 47%). M.p. 202-206°C. 1H NMR (400 MHz,
CDCl3, 25°C, TMS): δ=1.32 (s, 18H, CH3); 1.33 (s, 18H, CH3); 3.84 (s, 1.5H, O-CH3)
6.99 (s, 2H, Ar-H TB); 7.47 (d, 2H, J = 11.86 Hz, Ar-H); 7.61 (d, 2H, J = 8.21 Hz, Ar-
H); 8.55 (b, 2H, Ar-H TB); 8.80 (b, 2H, Ar-H P); 8.97 (b, 2H, Ar-H P); 10.42 (b, 2H,
Ar-H). EPR: g = 2.0066, aN = 1.414 mT.
3.5.14. General procedure for the synthesis of compounds 98 and
90
Perylene-3,4,9,10-tetracarboxylic dianhydride 42 (1 equiv.), aniline derivative (1.2
equiv.), amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57 (1.2 equiv.), zinc acetate
(0.75 equiv.) and imidazole (2 g) were combined and heated at 130°C for 6 hrs under
an argon atmosphere. The mixture was allowed to cool and 2 M aqueous HCl was
added to dissolve the imidazole. The resulting solution was extracted with chloroform
and the combined organic layers washed with water, brine and dried with anhydrous
magnesium sulphate. The solvent was removed under reduced pressure and
purification by silica gel column chromatography (in mixtures of methanol and
chloroform) gave the target compounds.
C H A P T E R T H R E E
P a g e | 151
3.5.15. N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-
perylene-3,4,9,10-tetracarboxyl-diimide 98
The general procedure detailed above was employed using N-octylaniline (29.7 mg,
0.144 mmol). Purification using column chromatography (3% methanol/chloroform)
gave 98 as a red solid (24 mg, 26%). M.p. >300°C (dec.) 1H NMR (400 MHz, CDCl3,
25ºC, TMS): δ=0.6- 0.8 (m, 3H, CH3), 1.2-1.4 (m, 12H, CH2), 1.7 (s, 6H, 2 × CH3),2.71
(br s, 2H, CH2-Ar), 7.34 (br s, 1H, J = 8.06 Hz, Ar-H), 8.55 (br s, 4H, Ar-H), 8.71 (br
s, 4H, Ar-H). Not all 1H NMR signals were observed due to paramagnetic broadening
by the nitroxide radical. IR (ATR) νmax 750 (=C-H), 1259 (Ar-O-C), 1362 (R3N), 1725
(C=O), 2923 cm-1 (alkyl CH3). EPR: g = 2.0058, aN = 1.408 mT.
3.5.16. N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-
tetracarboxyl-diimide 90
The general procedure detailed above was employed using 2,5-di-tert-butylaniline (16
mg, 0.078 mmol). Purification using column chromatography (1%
methanol/chloroform) gave 90 as a red solid (11 mg, 22%). M.p. >300°C (dec.) 1H
NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.55 (s, 18H, 6 × CH3), 7.08 (br s, 1H, Ar-
H), 7.49 (d, 1H, J = 8.23 Hz, Ar), 7.61 (d, 1H, J = 7.88 Hz, Ar-H), 8.70 (d, 4H, J =
5.78 Hz, Ar-H), 8.79 (d, 4H, J = 7.02 Hz, Ar-H). Not all 1H NMR signals were
observed due to paramagnetic broadening by the nitroxide radical. IR (ATR) νmax 745
(=C-H), 1072 (C-O), 1257 (Ar-O-C), 1358 (R3N), 1703 (C=O), 2961 cm-1 (alkyl CH3).
EPR: g = 2.0055, aN = 1.44 mT.
C H A P T E R T H R E E
P a g e | 152
3.5.17. General procedure for the synthesis of compounds 99 and
92
Hydrogen peroxide solution (30%, 5 equiv.) was added dropwise to an ice-cooled
solution of perylene-based nitroxide (1 equiv.) and iron(II) sulphate heptahydrate (2.5
equiv.) in a solution of minimal DMSO. The resulting solution was stirred at room
temperature for 30 minutes and then poured onto ice-cold sodium hydroxide (1 M
aqueous solution). The mixture was extracted with chloroform and washed with water
several times to remove the DMSO. The organic phase was dried over anhydrous
sodium sulphate and concentrated in vacuo. Purification by silica gel column
chromatography (3% methanol/chloroform) gave the target compounds.
3.5.18. N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-
tetracarboxyl-diimide 99
The general procedure detailed above was employed using N-(octylphenyl)-
N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide
98 to give the desired compound 99 as a red solid (12 mg, 12%). M. p. >300°C (dec.)
1H NMR (400 MHz, CDCl3, 25°C, TMS): δ= 0.6- 0.8 (m, 3H, CH3), 1.2-1.6 (m, 12H,
CH2), 1.48 (s, 6H, 2 × CH3), 1.51 (s, 6H, 2 × CH3), 2.71 (t, 2H, J = 7.74 Hz, CH2-Ar),
3.81 (s, 3H, CH3-O), 7.09 (d, 1H, J = 1.61 Hz, Ar-H), 7.20 (dd, 1H, J = 7.74, 1.94 Hz,
Ar-H), 7.26 (d, 1H, J = 8.06 Hz, Ar-H), 7.28 (d, 1H, J = 8.71, Ar-H), 7.38 (d, 1H, J =
8.06 Hz, Ar-H), 8.67 (d, 4H, J = 8.06, Ar-H), 8.75 (dd, 4H, J = 7.74, 2.28 Hz, Ar-H).
13C NMR (100 MHz, CDCl3, 25°C, TMS): δ=13.1, 21.7, 28.5, 28.7, 30.9, 64.5, 66.2,
C H A P T E R T H R E E
P a g e | 153
120.9, 122.3, 122.5, 127.2, 128.5, 130.8, 133.8, 133.9, 162.6. IR (ATR) νmax 750 (=C-
H), 1073 (C-O), 1276 (Ar-O-C), 1379 (R3N), 1723 (C=O), 2924 cm-1 (alkyl CH3).
3.5.19. N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-
tetracarboxyl-diimide 92
The general procedure detailed above was employed using N-(2,5-di-tert-
butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-
tetracarboxyl-diimide 90 to give the desired compound 92 as a red solid (10 mg, 7 %).
M. p. >300°C (dec.) 1H NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.25 (s, 9H, 3 ×
CH3), 1.34 (s, 9H, 3 × CH3), 1.51 (s, 12H, 4 × CH3), 3.81 (s, 3H, CH3-O), 7.04 (d, 1H,
J = 1.44 Hz, Ar-H), 7.08 (d, 1H, J = 1.44 Hz, Ar-H), 7.2 (dd, 1H, J = 8.2, 1.93, Ar-H),
7.29 (d, 1H, J = 8.68 Hz, Ar-H), 7.48 (d, 1H, J = 8.68 Hz, Ar-H), 7.61 (dd, 1H, J = 8.2,
1.93 Hz, Ar-H), 8.72 (m, 8H, Ar-H). 13C NMR (100 MHz, CDCl3, 25°C, TMS): δ=
14.3, 22.9, 29.1, 29.6, 29.9, 29.9, 32.1, 38.9, 65.7, 67.35, 122.1, 122.8, 123.5, 123.7,
124.4, 126.7, 127.5, 129.8, 131.9, 134.1, 134.9, 146.0, 146.8, 163.7, 182.1. IR (ATR)
νmax 800 (=C-H), 1019 (C-O), 1257 (Ar-O-C), 1346 (R3N), 1704 (C=O), 2974 cm-1
(alkyl CH3).
3.5.20. N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-
3,4,9,10-tetracarboxy diimide 130
Anhydrous K2CO3 (1.5 mg, 1.13 x10-4 mol) and phenol (10 mg, 4.52 x10-5 mol) were
added to a solution of 1,7-dibromoperylene dianhydride 113 (20.89 mg, 2.26 x10-5
mol) in NMP (20 mL). The mixture was stirred at 120°C overnight under an
atmosphere of argon, then cooled to room temperature and the product was
C H A P T E R T H R E E
P a g e | 154
precipitated by the addition of aqueous 1 M HCl (20 mL). The precipitate collected by
filtration and washed with water until neutrality. The solid was then dissolved in DCM
(50 mL), dried over sodium sulphate and concentrated in vacuo. Purification by silica
gel chromatography (DCM) gave 130 as a red solid (19.3 mg, 91%). Analysis by 1H
NMR spectroscopy revealed a 2:1 mixture of 1,7 and 1,6 regioisomers. N,N’-(2,5-Di-
tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide 27: 1H
NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.26 (s, 18H, CH3); 1.28 (s, 18H, CH3); 1.43
(s, 24H, CH3); 6.96 (m, 2H, Ar-H); 7.19 (d, 4H, J = 7.89 Hz, Ar-H); 7.45 (m, 6H, Ar-
H); 7.57 (dd, 2H, J = 8.15, 1.45 Hz, Ar-H); 8.41 (d, 2H, J = 1.4 Hz, Ar-H); 8.69 (dd,
2H, J = 8.14, 1.08 Hz, Ar-H); 9.66 (dd, 2H, J = 8.66, 6.16 Hz, Ar-H). N,N’-(2,5-Di-
tert-butylphenyl)-1,6-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide: 1H NMR
(400 MHz, CDCl3, 25ºC, TMS): δ=1.26 (s, 18H, CH3); 1.28 (s, 18H, CH3); 1.43 (s,
24H, CH3); 6.96 (m, 2H, Ar); 7.19 (d, 4H, J = 7.89 Hz, Ar-H); 7.45 (m, 6H, Ar-H);
7.57 (dd, 2H, J = 8.15, 1.45 Hz, Ar-H); 8.33 (d, 2H, J = 1.55 Hz, Ar-H); 8.75 (dd, 2H,
J = 8.2, 1.08 Hz, Ar-H); 9.60 (dd, 2H, J = 8.67, 5.88 Hz, Ar-H).
3.5.21. Photostability study
Separate solutions of 9,10-bis(phenylethynyl)anthracene and compounds 104, 106,
113, 117 and 114 were prepared in freshly distilled cyclohexane such that each gave a
UV absorbance reading of 0.2 (~10 μM). The 6 solutions were each stored in a screw
cap sealed quartz cell and were irradiated in a Heraeus Suntest CPS+ device operating
at an irradiation level of approximately 765 W/m2. The temperature of the chamber
was monitored by thermocouple and held at 40°C. The cells were held in location at
180°, perpendicular to the lamps. The solutions were analysed periodically (hours) by
both UV/vis spectroscopy (200-700 nm) and fluorimetry. Fluorescence loss was
C H A P T E R T H R E E
P a g e | 155
monitored at the following wavelengths: 9,10-bis(phenylethynyl)anthracene (λmax =
470 nm), 104 (λmax = 408 nm), 106 (λmax = 407 nm), 113 (λmax = 534 nm), 117
(λmax = 522 nm) and 114 (λmax = 557 nm).
3.5.22. Quantum yield and extinction coefficient calculations
Quantum yield efficiencies of fluorescence for compounds 103, 104, 105, 106, 107,
113, 117, 118, 114, 116, 115, 90, 92, 98 and 99 were obtained from measurements at
five different concentrations in cyclohexane or chloroform using the following
equation:
ФF sample = ФF standard × (Absstandard/Abssample) × (Σ[Fsample]/ Σ[Fstandard])
where Abs and F denote the absorbance and fluorescence intensity, respectively, and
Σ[F] denotes the peak area of the fluorescence spectra, calculated by summation of the
fluorescence intensity. Anthracene (ФF = 0.36) and N,N′-bis(2,5-di-tert-butylphenyl)-
3,4,9,10-perylenedicarboximide (ФF = 0.99) were used as standards. Extinction
coefficients were calculated from the obtained absorbance spectra.
3.6. Acknowledgements
We gratefully acknowledge financial support for this work from the Australian
Research Council Centre of Excellence for Free Radical Chemistry and Biotechnology
(CEO 0561607), the Defence Materials Technology Centre, which was established and
is supported by the Australian Government’s Defence Future Capability Technology
Centre (DFCTC) initiative and Queensland University of Technology.
Keywords: nitroxides • fluorescence • radicals • photooxidation
C H A P T E R T H R E E
P a g e | 156
C H A P T E R F O U R
P a g e | 157
4. PROFLUORESCENT NITROXIDE SENSORS FOR
MONITORING PHOTO-INDUCED DEGRADATION
IN POLYMER FILMS
The authors listed below have certified* that:
1. They meet the criteria for authorship in that they have participated in the
conception, execution, or interpretation, of at least that part of the publication
in their field or expertise;
2. They take public responsibility for their part of the publication, except for the
responsible author who accepts overall responsibility for the publication;
3. There are no other authors of the publication according to these criteria;
4. Potential conflicts of interest have been disclosed to (a) granting bodies, (b) the
editor or publisher of journals or other publications, and (c) the head of the
responsible academic unit and
5. They agree to the use of the publication in the student’s thesis and its
publication on the Australasian Research Online database consistent with any
limitations set by the publisher requirements
In the case of this chapter:
C H A P T E R F O U R
P a g e | 158
Profluorescent nitroxide sensors for monitoring photo-induced degradation in
polymer films
Sensors and Actuators B: Chemical.
Published: 19 September 2016
Contributor Statement of contribution*
Vanessa Lussini Wrote the first manuscript and edited all co-author’s draft
changes. Synthesised, characterised and analysed all the
compounds used. Designed/conducted experiments and
performed the data analysis.
John M. Colwell Overall supervision of the project, guided during
experimental design and assisted with manuscript design
and final data analysis
Kathryn E. Fairfull-
Smith
Overall supervision of the project, guided during
experimental design and edited final manuscript
Steve E. Bottle Original design of the project, overall supervision of the
project and edited final manuscript
Principal Supervisor Confirmation
I have sighted email or other correspondence from all Co-authors confirming their
certifying authorship.
Name Signature Date
QUT Verified Signature
C H A P T E R F O U R
P a g e | 159
Profluorescent nitroxide sensors for monitoring photo-induced degradation in
polymer films
Vanessa C. Lussini,a,b John M. Colwell,a,b Kathryn E. Fairfull-Smitha and Steven E.
Bottle*[a,b]
Received: 9 June 2916
Published Online: 19 September 2016
DOI: j.snb.2016.09.104
aARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School of
Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty,
Queensland University of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001,
Australia
bDefence Materials Technology Centre, School of Chemistry, Physics and Mechanical
Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT),
GPO Box 2434, Brisbane, QLD 4001, Australia
E-mail: [email protected]
C H A P T E R F O U R
P a g e | 160
4.1. Abstract
A range of profluorescent nitroxides (PFNs) were tested as probes to monitor photo-
induced radical-mediated damage in polymer materials. The most stable and sensitive
probe of the PFNs tested was an alkyne-linked perylenediimide PFN, 116, with
napthalimide and 9,10-bis(phenylethnyl)anthranene-based versions giving lower
stability and sensitivity. Results from photo-ageing of poly(1-trimethylsilyl)-1-
propyne (PTMSP) and the ethylene norbornene copolymer (TOPAS®) films doped
with PFN probes demonstrated that sensors employing these support materials deliver
significantly enhanced sensitivity compared to traditional techniques used to monitor
photo-oxidative degradation of polymers, such as infrared spectroscopy. This
enhanced sensitivity for detecting polymer damage improved methods for the
determination of the serviceable application lifetime of polymers.
4.2. Key words
Profluorescent nitroxide, TOPAS, PTMSP, Fluorescence, Degradation
4.3. Introduction
The application lifetimes of polymer materials are strongly influenced by the
environmental factors to which they are exposed. For many materials, oxidation is a
key influence on service lifetimes, with this degradation process being controlled by
temperature, oxygen concentration and other local factors such as reactive
contaminants that may affect oxidation rates. Laboratory-based studies can be used to
assess environmental effects on polymer degradation. However, it is often difficult to
translate the data generated in the laboratory to methods for actual service lifetime
C H A P T E R F O U R
P a g e | 161
prediction. This is, in part, due to the broad range of differing environments to which
polymer materials may be exposed. By combining laboratory-generated ageing data
and a number of field sensors (e.g., temperature, oxygen, chemical), in-service lifetime
predictions may be possible. However, to implement effective systems with sufficient
sensors would be costly and require significant analytical effort. As an alternative to a
suite of sensors, we have developed a simple, sensitive, profluorescent additive that
can be used as an oxidative environment sensor. The validity of this approach has been
successfully demonstrated 98, 186, however photo-stability and the phase distribution of
the probe are factors that control sensor performance. To address some of these issues
we have synthesised components with higher photo-stability.187
The sensor approach described herein is based on the use of profluorescent nitroxides
(PFNs) as free-radical probes. PFNs combine a paramagnetic nitroxide covalently
linked to a fluorophore where the nitroxide acts to quench the fluorescence of the
fluorophore. When the nitroxide radical is removed via radical-radical coupling, the
fluorescence is restored (Figure 34).66, 68 Radical-radical coupling of nitroxides with
transient carbon-centred radicals that are key intermediates in autooxidation reactions
allows PFNs to act as integrating sensors for the degradation process through the
formation of stable alkoxyamine adducts that build up over time.56, 118 PFNs can also
show high fluorescence suppression (over 300-fold 53), which can deliver higher
sensitivity for detecting free-radical polymer degradation than many other common
degradation monitoring techniques.188
By combining the sensitivity of PFNs with an oxidisable substrate, oxidative
environment sensors may be produced. Such sensors can be used to assess
environmental conditions that affect polymer degradation, and therefore give early
C H A P T E R F O U R
P a g e | 162
warning of the failure of the material. Previously described PFN-based sensors for
oxidative environment monitoring 98, 186 used an ethylene norbornene copolymer
(TOPAS®) as a relatively inert carrier and polyisoprene (PIP) as the oxidisable
substrate. It was found that the phase structure of this ternary system limited the sensor
response at temperatures below the glass transition of the inert carrier and, therefore,
further development of these materials as sensors was required.
Figure 34: Tethering of a fluorophore to a nitroxide to form a PFN probe
Although the PFN-based sensors described above performed well under thermal
ageing conditions, they were found to be less useful for monitoring photo-oxidative
degradation due to the limited photo-stability of the 9,10-
bis(phenylethynyl)anthracene-based PFN.101 More robust PFNs, based on
naphthalimide and perylenediimide fluorophores (Figure 36), were therefore
developed with these fluorophores providing considerably enhanced photo-oxidative
stability.189
Recently, a perylenediimide-based isoindoline profluorescent nitroxide was used to
monitor the degradation of melamine-formaldehyde crosslinked polyesters under
accelerated weathering conditions.123 This PFN probe was used to assess the impact of
both temperature and UV radiation on the degradation of two commercial polyesters.
The focus of this study, however, was limited to a single PFN. In the work described
herein, we have assessed the resistance of a new range of perylenediimide and
C H A P T E R F O U R
P a g e | 163
naphthalimide PFNs in two commercially-available polymers: poly(1-trimethylsilyl)-
1-propyne (PTMSP), and the ethylene norbornene copolymer, TOPAS® (8007x10
grade). These polymers can be used to produce easily handled films via solvent
casting, which readily allows incorporation of the PFNs under mild conditions. The
structures of the polymers studied (Figure 35), allows them to act as model substrates
for a range of other polymer materials such as polyethylene (TOPAS® as a model)
and unsaturated polymers such as polyisoprene (PTMSP as a model).
Figure 35: The structures of the polymers used in this study, PTMSP and TOPAS®
Both PTMSP 190-192 and TOPAS® 193 degrade when exposed to heat or UV light in air
through radical-mediated mechanisms and therefore, in combination with PFNs, they
can be used as sensitive oxidative environment sensors. Here, we describe the use of
perylenediimide and naphthalimide PFNs in PTMSP and TOPAS® matrices as photo-
oxidative environment sensors and highlight the most effective PFN based on the
photo-oxidative stability of these novel systems in the polymer studied.
C H A P T E R F O U R
P a g e | 164
Figure 36: Nitroxides used in this study and their non-radical (fluorescent) methoxyamine derivatives
4.4. Experimental
4.4.1. Materials
TOPAS® 8007x10 was a gift from Ciba Speciality Chemicals. PTMSP was purchased
from ABCR GmbH. Cyclohexane was purified using a literature procedure194 where
it was washed with concentrated sulphuric acid until the wash was colourless. The
organic layer was then washed with water, aq. Na2CO3 and again with water until the
C H A P T E R F O U R
P a g e | 165
wash solution was at a neutral pH. The washed cyclohexane was then distilled over
calcium hydride. PFNs 23, 105, 107, 118, and 116 along with the methoxyamine, non-
radical analogues, 104, 106, 117 and 114 were synthesised as described previously.53,
187 All other materials and reagents were of analytical reagent grade purity, or higher
and were purchased from Sigma Aldrich, Australia.
4.4.2. PTMSP sample preparation
Each of the compounds shown in Figure 36 (1.94 x10-7 mol) was dissolved in freshly
distilled cyclohexane (7.45 mL) in a 25x75 mm soda glass vial. PTMSP (293 mg) was
then added to each solution and the vials sealed and stirred for 48 hours in the dark.
Each solution was then poured into a Petri dish and the solvent allowed to evaporate
slowly over two days in the dark. Once the films were dry to the touch, they were
placed under vacuum until they reached a constant weight (24 h).
4.4.3. TOPAS® sample preparation
Each of the compounds shown in Figure 36 (4.3610-7 mol) was dissolved in freshly
distilled cyclohexane (16.94 mL) in a 2575 mm soda glass vial. TOPAS® pellets
(660 mg) were then added to each solution and the vials sealed and stirred for 4 hours
in the dark. Each solution was then poured into a Petri dish and the solvent allowed to
evaporate slowly over two days in the dark. Once the films were dry to the touch, they
were placed under vacuum until they reached a constant weight (24 h).
4.4.4. Photo-oxidation of films
Film samples were irradiated in an Heraeus Suntest CPS+ device delivering 250 W/m2.
The temperature in the chamber was set to 40°C. The films were oriented in parallel
C H A P T E R F O U R
P a g e | 166
to the lamp. Samples were removed periodically and analysed using UV-Vis,
Fluorescence and FTIR-ATR spectroscopy.
4.4.5. Thermo-oxidation of films
Films were placed in an oven at 70°C on metal racks, and separated by a 5 mm gap.
4.4.6. Characterisation
4.4.6.1. FTIR-ATR Spectroscopy
Infrared spectra were recorded as neat samples using a Nicolet 5700 Nexus Fourier
Transform infrared spectrometer equipped with a DTGS TEC detector and a Smart
Endurance single reflection ATR accessory equipped with a composite diamond IRE
with a 0.75 mm2 sampling surface and a ZnSe focussing element (Nicolet Instrument
Corp., Madison, WI). An Optical Path Difference (OPD) velocity of 0.6329 cm s-1 and
a gain of 8 were used. Spectra were collected over the range 4000-525 cm-1 using 32
scans at 4 cm-1 resolution. Oxidation indices were calculated by taking the ratio of the
maximum peak height in the carbonyl stretching region (1700-1715 cm-1) to the area
under the C-H deformation band (1400-1500 cm-1).
4.4.6.2. UV-Vis Spectroscopy
UV-Vis spectra were recorded on a Varian Cary 50 UV-Vis spectrophotometer.
Spectra were collected from 200-700 nm at a scan rate of 600 nm min-1. All spectra
were corrected to give an absorbance of zero at 700 nm.
C H A P T E R F O U R
P a g e | 167
4.4.6.3. Fluorescence Spectroscopy
Fluorescence spectroscopy was undertaken using a Varian Cary Eclipse fluorescence
spectrophotometer. Samples were loaded into a custom-made holding device and
excited at an angle of 45° to the surface, with the emission recorded from the back face
of the sample in order to minimise scattering effects. The excitation wavelength used
changed according to the compound present in the sample: 29; 383 nm, 23; 383 nm,
104; 362 nm, 105; 360 nm, 106; 378 nm, 107; 374 nm, 117; 540 nm, 118; 536 nm,
114; 568 nm, 116; 564 nm. Spectra were collected from 5 nm past the excitation
wavelength up to 700 nm at a scan rate of 600 nm min-1.
4.5. Results and Discussion
4.5.1. Film Preparation
PTMSP and TOPAS® films were prepared by solvent casting, which allowed the
PFNs to be evenly dispersed into the films at well-defined concentrations, without the
need for heating. Previous studies using PFNs and polymer systems have typically
relied on solution swelling of PFNs or melt processing, each of which lead to
limitations in precisely controlling the concentration of dopant. For melt processing,
thermal reactions at high temperature can consume some of the nitroxide before
degradation monitoring can be undertaken.99, 101 The mass of the PFN added to the
films (0.025 wt%) was kept low to reduce aggregation of the PFNs within the film.
There was no evidence of any bathochromic shifts in the bands or any obvious
fluorescence quenching that might arise from aggregation, shown in Figure 37.123, 195-
197
C H A P T E R F O U R
P a g e | 168
Figure 37: UV-Vis absorbance (dotted lines) and fluorescence emission (solid lines) spectra of perylene
fluorophore 114 in TOPAS® at various concentrations ranging from 0.025 to 0.0025 w%, showing no
evidence of any bathochromic shifts in the bands or any obvious fluorescence quenching that might arise
from aggregation.
4.5.2. PTSMP films
4.5.2.1. Photo-oxidative degradation
PTMSP has the highest gas permeability of all known synthetic polymers 192, 198-199
due to it being a loosely packed polymer with 20-34% free volume.198 As a result,
oxygen permeability is not limited through this glassy material and PTMSP is therefore
a good model for situations where diffusion-limited oxidation is not dominant.
PTMSP films were aged in an Heraeus Suntest xenon-arc solar simulator delivering
an irradiance of 250 W/m2 (21.6 MJ/m2/d), which corresponds to the approximate
average daily terrestrial irradiance received during the 2014-2015 summer in Brisbane,
Australia (21.4 MJ/m2/d).200 Films were periodically monitored by fluorescence, UV-
Vis and FTIR-ATR spectroscopy. The films doped with PFNs were compared to films
C H A P T E R F O U R
P a g e | 169
doped with the structurally-related non-radical methoxyamine analogues. Analysis in
this way provides insight into the rate of fluorescence switch-on from the PFN as
compared to the degradation rate of the parent fluorophore, as shown by the decrease
in fluorescence emission intensity for the non-radical adducts (29, 104, 106, 117 and
114) during ageing of the PTMSP-doped films.
Figure 38: Change in fluorescence emission of PTMSP films doped either with 29, 1 (-■-/left axis) or the
nitroxide analogue, 23 (-♦-/right axis) with respect to UV ageing time (hours).
The non-radical fluorophore 9,10-bis(phenylethynyl)anthracene, BPEA (29), shown
in Figure 38, started to degrade within two hours of UV exposure and its fluorescence
emission had decreased to 50% after 4 hours. BPEA 29 is known for its thermal
stability and its PFN analogue 29 has been used successfully for detecting alkyl
radicals with a high trapping ability.98 However, it is also known to have limited photo-
stability due to the reactivity of its anthracene core.201-202 Despite the rapid
photobleaching of the fluorophore, the BPEA-based nitroxide (23) still showed a
fluorescence emission increase of ~2.5 fold after ~1 hour of irradiation. It is likely that
C H A P T E R F O U R
P a g e | 170
degradation of the fluorophore and photobleaching occurs predominantly after the
conversion of most of the nitroxide free radicals, which act as stabilising antioxidants.
However the degradation of the fluorophore, (as shown in Figure 38 by the loss of
fluorescence emission from the BPEA parent compound, 29 after 3 hours) is at least
as large as the fluorescence increase generated by the PFN 23. Therefore, this PFN has
limited value as a sensor for photo-oxidative damage.
Figure 39: Change in fluorescence emission of PTMSP films doped either with ether-linked naphthalimide
fluorophore 104 (-■-/left axis) or the nitroxides analogue 105 (-♦-/right axis) with respect to UV ageing time
(hours).
C H A P T E R F O U R
P a g e | 171
Figure 40: Change in fluorescence emission of PTMSP films doped either with alkyne-linked
naphthalimide fluorophore 106 (-■-/left axis) or the nitroxides analogue 107 (-♦-/right axis) with respect to
ageing time (hours).
Both naphthalimide-based compounds (ether-linked, 104/105 (Figure 39) and alkyne-
linked, 106/107 (Figure 40)) showed comparable changes in fluorescence emission
during ageing. The non-radical analogues began to show photobleaching after 3 hours
and their fluorescence emission had decreased by a factor of two after 7-8 hours of
irradiation. This indicated that these structures were more photo-stable than the
anthracene-based fluorophores; 29 and 23. Both naphthalimide nitroxides showed
significant fluorescence switch-on under irradiation, with the ether-linked compound
105 reaching ~3-4-fold levels of increased fluorescence emission and the alkyne-
linked compound 107 peaking at a 3-fold increase in fluorescence emission. However,
degradation of the fluorophore (the rate of which is demonstrated by the
photobleaching of the methoxy amine) resulted in a 50% decrease in fluorescence
emission intensity after 7 hours of irradiation, indicating that photo-degradation
remains a significant factor in determining the probe response.
C H A P T E R F O U R
P a g e | 172
Figure 41: Change in fluorescence emission of the PTMSP films doped with either ether-linked
perylenediimide fluorophore 117 (-■-/left axis) or the nitroxides analogue 118 (-♦-/right axis) with respect
to ageing time (hours).
Figure 42: Change in fluorescence emission of the PTMSP films doped with either alkyne-linked
perylenediimide fluorophore 114 (-■-/left axis) or the nitroxides analogue 116 (-♦-/right axis) with respect
to ageing time (hours).
C H A P T E R F O U R
P a g e | 173
The perylenediimide-based compounds on the other hand, both the ether-linked,
117/118 (Figure 41) and the alkyne-linked, 114/116 (Figure 42) showed superior
photo-oxidative stability. Both of the non-radical analogues showed a lower rate of
photobleaching than the other chromophores studied and both of the nitroxides
continued to display increasing florescence emission during the ageing studies.
Figure 43: Changes in the fluorescence emission of PTMSP films doped with non-radical analogues, 29 (-■-
, λmax = 470 nm), 104 (-▲-, λmax = 410 nm), 106 (-●-, λmax = 430 nm), 117 (-▬-, λmax = 560 nm) and 114 (-♦-,
λmax = 615 nm) following photo-irradiation at 250 Wm-2 and 40ºC for up to 6 h. Note: data collection was
stopped at 6 hours as discolouration gave higher intensities than I0.
C H A P T E R F O U R
P a g e | 174
Figure 44: Changes the fluorescence emission of PTMSP films doped with the nitroxides, 23 (-■-, λmax = 470
nm), 154 (-▲-, λmax = 408 nm), 107 (-●-, λmax = 428 nm), 118 (-▬-, λmax = 550 nm) and 116 (-♦-, λmax = 610
nm) following photo-irradiation at 250 Wm-2 and 40ºC for up to 10 h.
When comparing the non-radical analogues (29, 104, 106, 117 and 114), Figure 43,
there is a clear distinction between the photo-oxidative stability of the fluorophores.
Perylenediimides were the most stable compounds, showing no decrease in
fluorescence emission over 10 hours of ageing. Their PFN analogues showed
continuing increases in fluorescence emission intensity with increasing irradiation
time. However, the alkyne-linked PFN 116 displayed the highest fluorescence
emission increase (40-fold) compared to the ether-linked 118 (10-fold), as shown in
Figure 44.
It has previously been demonstrated that both nitroxide radical need to be removed
before complete fluorescence switch-on is apparent for PFNs comprising 2 nitroxide
moieties 187. This results in a different rate of fluorescence switch-on between
difunctional perylenediimide-based PFNs and the monofunctional napthalimide-based
C H A P T E R F O U R
P a g e | 175
PFNs. However, this is not always apparent with the competing nature of
photobleaching of the fluorophore. Fluorescence data for the aged PTMSP-doped
films are summarised in Table 2.
Table 2: Summary of PFN fluorescence changes in PTMSP films doped with PFNs or their non-radical
analogues during ageing.
Time to reach maximum
fluorescence emission (h)
Relative fluorescence
increase from time zero
Non-radical
analogue
stability (h)[a]
Relative
fluorescence
achieved (%)[b]
23 3 2.7 3.5 49
105 5 3.5 7 73
107 4 3.0 7 23
118 >10 11 (10 h) >10 32
116 >10 42 (10 h) >10 49
[a] time at which the non-radical analogue was reduced to 50% fluorescence intensity compared to an
unaged sample.
[b] Fluorescence increase achieved relative to the maximum fluorescence emission from the
corresponding non-radical analogue.
C H A P T E R F O U R
P a g e | 176
Figure 45: Change of the fluorescence emission for the PFN 116 in PTMSP from 0-10 h ageing compared
to its non-radical analogue, 114 at time zero in PTMSP, showing that the 116 has not achieved complete
switch-on after 10 h ageing.
The pure PTMSP films degraded rapidly under the photo-oxidation conditions
delivered by the Heraeus Suntest CPS+ to the point of becoming too brittle to handle
after 10 hours of irradiation. PTMSP is known to degrade through a chain scission
mechanism to form low molecular weight products that contain carbonyl and hydroxy
groups.192, 203 Infrared spectroscopy can be used to follow the degradation process.
Here, FTIR-ATR was used and it was found that variations in the contact of the
degrading films with the ATR internal reflection element surface showed a large
variation across each of the samples (even after normalisation of the data referenced
to the total peak area from 1600-650 cm-1). Although FTIR-ATR analysis was unable
to provide a reproducible measure of the levels of oxidation of the samples, it did
confirm oxidative degradation was occurring. Along with FTIR-ATR data, evidence
of oxidation was provided through noticeable yellowing and enhanced film brittleness
after 6 hours irradiation. The films became too brittle to handle after 10 hours of
C H A P T E R F O U R
P a g e | 177
irradiation, independent of the additive present in the samples, with all films breaking
apart under the pressure from the anvil used in measuring the FTIR-ATR spectra.
4.5.2.2. Thermal Degradation
PTMSP films that did not contain a stabilising nitroxide radical, but retained the
fluorescent unit (29, 104, 106, 117 and 114) were thermally aged in the dark in an oven
at 70°C. This was done to ensure that the fluorophores were not affected by the
temperatures experienced during testing in the solar simulator. Thermally-aged films
showed no visible degradation, such as brittleness or loss in fluorescence emission
(Figure 46), which indicates that the fluorophores and the polymer used in this study
are thermally stable under the conditions used.
Figure 46: Change in fluorescence emission from PTMSP films doped with PFN non-radical analogues (29,
105, 106, 117 and 114) over time at 70°C in the dark.
C H A P T E R F O U R
P a g e | 178
Figure 47: UV-Vis spectra from undoped (blank) PTMSP (-) and TOPAS® (-) films.
4.5.3. TOPAS® Films
4.5.3.1. TOPAS® Photo-oxidative degradation
TOPAS® is within the family of cyclic olefin copolymers.193 It has high transparency,
high chemical resistance, low density, high thermal stability, low shrinkage, low
moisture absorption, and low birefringence.204-205 TOPAS®, like PTMSP, undergoes
radical induced degradation when exposed to photo-oxidative environments 193,
however at a more controlled rate.
PTMSP absorbs UV (Figure 47) which limits the amount of information that can be
collected regarding the fluorophore and its stability. In contrast, TOPAS® has the
advantage of being an optically transparent material (see Figure 47), which allows UV-
Vis spectra from doped samples to be monitored in parallel with fluorescence emission
during photo-oxidation of the films. UV-Vis spectroscopy can be used to give insight
C H A P T E R F O U R
P a g e | 179
into the stability of the fluorophore of the PFN and has been included in the analysis
below.
C H A P T E R F O U R
P a g e | 180
Figure 48: Change in the fluorescence emission from TOPAS® films doped with PFNs (■, Right axes),
relative change in UV-Vis absorbance of PFNs (♦, Left axes) and relative change in UV-Vis absorbance of
the non-radical analogues (●, Left axes) during photo-ageing. (a) 104/105 (b) 106/107 (c) 117/118 (d)
114/116
The PFNs survived longer in TOPAS® than they did in PTMSP due to the higher
overall stability of the film after photo-oxidative conditions. The alkyne-linked
naphthalimide probe 107 appeared to be the least stable of the tested PFNs, with its
C H A P T E R F O U R
P a g e | 181
UV-Vis absorbance decreasing by a factor of 2 after 50 hours of ageing. The ether-
linked naphthalimide, 105 was more stable with the fluorophore withstanding 96 hours
of irradiation before a loss of 50% of the fluorophore UV-Vis absorbance. The 105
PFN also gave a 20-fold fluorescence emission response up to 96 hours of irradiation.
Both of the perylenediimide PFNs on the other hand demonstrated significant stability,
requiring 504 and 168 hours for the ether-linked, 118 and alkyne-linked, 116
compounds respectively (Figure 48), at which time the fluorophores had lost half of
their absorbance compared to time zero. The free-radical containing PFNs tested
displayed enhanced stability compared to their non-radical analogues, showing that
the presence of the nitroxide induced a degree of protection, most likely through the
recognised antioxidant capabilities of this functional group.
Even though the ether-linked perylenediimide PFN 118 had a higher stability than the
alkyne-linked PFN 116, the alkyne-linked PFN showed a higher level of fluorescence
emission switch-on (40-fold), Figure 49. PFN 116 also showed significant
fluorescence change during ageing in the PTMSP films, allowing easier detection of
radical formation within the films. All of the absorbance and fluorescence data for the
aged TOPAS®-doped films are summarised in Table 3.
All TOPAS®-doped films were further tested to ensure films did not experience
thermal degradation in the photo-oxidative environment. The TOPAS®-doped films
were subjected to a dark oven at 70°C for an extended period of time. Like PTMSP,
the TOPAS® films demonstrated thermal stability with no evidence of spectrographic
change or changes in physical properties.
Table 3: Summary of PFN sensor performance and stability in TOPAS® films following photo-oxidative
degradation.
C H A P T E R F O U R
P a g e | 182
Time to reach
maximum
fluorescence
emission (h)
Fluorescence
increase from
time zero ()
PFN
stability[a]
Non-
radical
analogue
stability
(h)[a]
Relative
fluorescence
achieved
(%)[b]
105 144 20 96 70 33
107 72 6 50 20 7.2
118 264 3.2 504 90 11
116 504 40 168 100 3.7
[a] Time at which the fluorophore had lost half of its maximum absorbance compared to time zero.
[b] Fluorescence increase achieved relative to the maximum fluorescence emission from the
corresponding non-radical analogue.
Figure 49: Change of the fluorescence emission for the PFN 116 in TOPAS® from 0-504 h ageing
compared to its non-radical analogue, 114 at time zero in TOPAS®, showing that the PFN 116 has only
achieved a small fraction of complete switch-on after 504 h ageing.
C H A P T E R F O U R
P a g e | 183
As in PTMSP, TOPAS® also degrades through a mechanism that involves the
formation of reactive free radicals. The alkyl groups are oxidized to alkene and other
conjugated systems, which results in the normally transparent films becoming
yellow.205-206 This yellowing is observed in the UV-Vis, Figure 50. However, this
yellowing can be difficult to detect in PFN-doped samples due to the absorbance of
the PFN chromophores. Therefore, only the undoped TOPAS® film could be directly
monitored for yellowing during ageing.
Figure 50: UV-Vis absorbance at 250 nm (subtracted from UV-Vis absorbance at 400 nm) for the blank
(undoped) TOPAS® film with respect to time in the suntest (left axis, ■) and the oxidation index calculated
from ATR-IR data from the blank (undoped) TOPAS® film with respect to time in the suntest (right axis,
♦)
Analysis of IR spectra from the undoped, irradiated TOPAS® film showed the
formation of carbonyl bands due to oxidation at a similar rate to the yellowing at 250
nm detected in the UV-Vis. The correlation between the oxidation of alkyl groups and
the formation of carbonyl products during the degradation of film allowed IR to be
used as a monitor for photo-oxidative degradation in the presence of the PFN
C H A P T E R F O U R
P a g e | 184
chromophore. However, as the irradiation time increased, the uncertainty in the
oxidation index measurements became larger which is a recognised limitation of IR
monitoring.
There is no convincing evidence of yellowing and/or carbonyl formation in the aged
TOPAS® film until ~240 h, Figure 50 which is consistent with an oxidation induction
period. Studies have demonstrated that the useful lifetime of a polyolefin does not
extend much past this period.98, 188 These results indicate that PFNs detect radical
formation from time zero through increases in fluorescence intensity. This
demonstrates the usefulness of PFNs as sensitive probes to detect degradation caused
from radical formation within the oxidation induction period, where previous
techniques have limited success.
4.6. Conclusions
The aim of this study was to test the photo-oxidative stability of a unique group of
additives that probe the nature of degradation of two types of polymer materials,
PTMSP and TOPAS®. The nitroxide probe’s ability to switch on and report damage
occurring in PTMSP was demonstrated. However, degradation in the Heraeus Suntest
instrument was too severe, which caused rapid embrittlement of the polymer.
TOPAS® was more stable than PTMSP under the testing conditions and its
transparency allowed analysis by UV-Vis spectroscopy in parallel with fluorescence
spectroscopy, which gave insight into the stability of the fluorophores tested. It was
determined that perylenediimide-incorporated PFNs are more photo-stable than
naphthalimide PFNs in both the PTMSP and TOPAS® films. It was also determined
that the nitroxide-containing compounds have higher stability in the photo-oxidative
environment over their non-radical analogues. The alkyne-linked perylenediimide
C H A P T E R F O U R
P a g e | 185
PFN, 116 has an impressive switch on ability when exposed to photo-induced radicals,
and it is the most effective PFN probe of the group tested. UV-Vis and IR gave little
information about the early stages of the film’s degree of degradation, confirming the
value of the PFN technique as a tool to give insight into the oxidation induction period
and to predict the overall serviceable lifetime of the polymer. With improved photo-
stability, PFNs can now provide a sensitive and simple technique to monitor changes
during the induction period of the photo-oxidative degradation of polymers.
4.7. Acknowledgements
We gratefully acknowledge financial support for this work from the Australian
Research Council Centre of Excellence for Free Radical Chemistry and Biotechnology
(CEO 0561607), the Defence Materials Technology Centre, which was established and
is supported by the Australian Government’s Defence Future Capability Technology
Centre (DFCTC) initiative and Queensland University of Technology.
C H A P T E R F I V E
P a g e | 186
5. PROFLUORESCENT NITROXIDE SENSORS FOR
MONITORING THE NATURAL AGING OF
POLYMER MATERIALS
The Authors listed below have certified* that:
1. They meet the criteria for authorship in that they have participated in the
conception, execution , or interpretation, of at least that part of the publication
in their field or expertise;
2. They take public responsibility for their part of the publication, except for the
responsible author who accepts overall responsibility for the publication;
3. There are no other authors of the publication according to these criteria;
4. Potential conflicts of interest have been disclosed to (a) granting bodies, (b) the
editor or publisher of journals or other publications, and (c) the head of the
responsible academic unit and
5. They agree to the use of the publication in the student’s thesis and its
publication on the Australasian Research Online database consistent with any
limitations set by the publisher requirements
In the case of this chapter:
C H A P T E R F I V E
P a g e | 187
Profluorescent nitroxide sensors for monitoring the natural aging of polymer
materials
Drafted for Polymer Degradation and Stability
Contributor Statement of contribution*
Vanessa Lussini Wrote the first manuscript and edited all co-author’s draft
changes. Synthesised, characterised and analysed all the
compounds used. Designed/conducted experiments and
performed the data analysis.
John M. Colwell Overall supervision of the project, guided during
experimental design and assisted with manuscript design
and final data analysis
James Blinco Overall supervision of the project, guided during
experimental design and edited final manuscript
Kathryn E. Fairfull-
Smith
Overall supervision of the project, guided during
experimental design and edited final manuscript
Steve E. Bottle Original design of the project, overall supervision of the
project and edited final manuscript
Principal Supervisor Confirmation
I have sighted email or other correspondence from all Co-authors confirming their
certifying authorship.
Name Signature Date
QUT Verified Signature
C H A P T E R F I V E
P a g e | 188
Profluorescent nitroxide sensors for monitoring the natural aging of polymer
materials
Vanessa C. Lussini,a,b John M. Colwell,b James P. Blinco,a Kathryn E. Fairfull-Smitha
and Steven E. Bottle*a,b
[a] ARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School
of Chemistry, Physics and Mechanical Engineering, Faculty of Science and
Engineering, Queensland University of Technology (QUT), GPO Box 2434, Brisbane,
QLD 4001, Australia
[b] Defence Materials Technology Centre, School of Chemistry, Physics and
Mechanical Engineering, Faculty of Science and Engineering, Queensland University
of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001, Australia
E-mail: [email protected] ; Fax: +61 7 3138 1804; Tel: +61 7 3138 1356
C H A P T E R F I V E
P a g e | 189
5.1. Abstract
The utility of profluorescent nitroxides (PFNs) as sensitive probes to detect early stage
photo-oxidative degradation in a cyclic olefin copolymer, TOPAS®, during both
natural aging and accelerated aging under laboratory conditions is reported. PFN
additives in TOPAS® capture radicals to form fluorescent adducts as the material
degrades. The levels of fluorescence detectable from the polymer reflect the degree of
free-radical degradation in the material. PFN probes deliver enhanced sensitivity over
traditional analytical methods for the detection of photo-oxidative degradation of
TOPAS®. The probes are able to highlight polymer degradation occurring within the
oxidation “induction” period, where little change can be observed using infrared
spectroscopy; however, their efficacy does not extend far beyond this period. The
effective probe lifetime however can be significantly extended through the use of
common additives such as the UV absorber (Tinuvin P) and a hindered amine stabiliser
analogue (1,1,3,3-tetramethylisoindol-2-yloxyl, TMIO).
5.2. Key words
Perylenediimide, Photo-oxidative degradation, Profluorescent nitroxide, Sensor,
TOPAS, Weathering.
5.3. Introduction
Natural aging of polymer materials is complicated by many interconnected variables
207-208, with measurements over an extended period (>2 years) typically required to
ensure good reproducibility 209. The long timeframes required for testing are
influenced by typically slow rates of degradation and commonly observed degradation
C H A P T E R F I V E
P a g e | 190
“induction” periods, where there are no apparent changes in properties for extended
periods of time 186, 207, 210-214. Accelerated aging is often used to provide a rapid
assessment of degradation behaviour and serviceable lifetimes. However, relating
laboratory-based aging experiments to lifetimes arising from natural exposure is
difficult due to the many variables experienced during in-use conditions 209, 215-219.
Accelerated weathering devices often do not accurately emulate elements of the
environment that may influence the rate of degradation, such as morning dew,
pollution (acid rain) and temperature fluctuations throughout the day 24, 215. To
overcome both the time limitations on testing outdoors and the limitations of
accelerated weathering devices for emulating complex outdoor conditions, the
development of more sensitive methods that can detect changes in the degradation
induction period during outdoor exposure are required.
It has been shown 188, 220-222 that the length of the apparent degradation induction period
is dependent on the sensitivity of the analysis technique used for the measurement of
property changes. For many materials, early-stage degradation may be linked to the
formation of transient, carbon-centred free-radicals 1, 188, 223. Disruption of polymer
degradation by trapping carbon-centred free-radicals forms the basis of a range of
polymer stabilisation processes, including the use of Hindered Amine Stabilisers
(HAS) 21, 35, 224-225. In the mechanism of stabilisation by HAS, nitroxide free-radicals
are formed and these can scavenge carbon-centred free-radicals to give stable adducts
188. Based on this chemistry, sensitive profluorescent nitroxide probes have been
developed that can detect the extent, and even location of polymer damage during the
degradation induction period, with greater sensitivity than other reported methods 35,
64, 101.
C H A P T E R F I V E
P a g e | 191
Figure 51: Tethering of a fluorophore to a nitroxide to form a profluorescent nitroxide (PFN), and
trapping of carbon-centred free-radicals (formed during polymer degradation), causing the PFN to switch
from a non-fluorescent to a fluorescent state.
Profluorescent nitroxides (PFNs) are a group of compounds that contain a stable
nitroxide free radical linked to a fluorophore (Figure 51). They display low
fluorescence, but when they react with the alkyl radicals generated during polymer
degradation they form adducts that are fully fluorescent. This allows visualisation of
both the location and the degree of degradation that has occurred within a polymer 64.
The very low fluorescence quantum yield of PFNs compared to their alkoxyamine
adducts 53, 105-106, 118, 123, 145, 187, 226 makes them very sensitive probes for carbon-centred
free radical production during the very early stages of polymer degradation and good
candidates for monitoring degradation during the degradation induction period 35.
However, to act as probes during this period, the PFNs must be stable to the radical
environments within the polymer matrix and other external environmental factors,
such as direct UV exposure. Early studies using PFNs as probes for the photo-oxidative
degradation of polymers revealed limitations with the stability of some of the
fluorophores employed 186. To improve photo-stability, other more photo-stable PFNs
have been developed 187, 227. Initial testing of these PFNs using accelerated weathering
in laboratory tests showed that PFNs based on perylenediimide fluorophores (shown
in Figure 52) were the most photo-stable probes produced to-date. These
C H A P T E R F I V E
P a g e | 192
perylenediimide-based probes with improved photo-stability are the focus of the work
described herein.
Figure 52: Fluorescent and profluorescent probes used in this study. The fully fluorescent non-radical
analogue 114 is used as an indicator for the potential response from the profluorescent probes 115 and 116.
To assess the efficacy of PFNs to report polymer degradation, polymers that are known
to degrade via a free-radical process are required, as the PFN fluorescent response
arises from scavenging these species. The well-studied, free-radical-based degradation
behaviour of polyolefins therefore makes this ubiquitous class of polymers excellent
candidates to highlight the capability of PFN probes as reporters of this degradation.
TOPAS®, a simple cyclic olefin copolymer 193 (Figure 53) was used as a model
material due to its structural similarities to other polyolefins and the ability to prepare
solution-cast, optically transparent thin films, with controlled levels of additives, on a
small scale.
Typically, formulated plastics contain a range of stabilisers to increase service lifetime.
To determine if the PFN-technique still allows a record of early lifetime degradation
when such stabilisers are present, 1,1,3,3-tetramethylisoindol-2-yloxyl (TMIO, 55; a
HAS analogue) and Tinuvin P (1; a common UV absorber) (Figure 53) were added to
C H A P T E R F I V E
P a g e | 193
the TOPAS® films as representative photostabilisers in addition to the PFN-based
compounds shown in Figure 52. The stability and degradation-monitoring ability of
the PFN probes were assessed using both environmental and laboratory aging
conditions to determine their effectiveness as probes for free-radical damage in the
presence of common stabilisers.
Figure 53: Structure of TOPAS® (the cyclic olefin copolymer used in this study), TMIO (55; a HALS
analogue) and Tinuvin P (1; a common UV absorber).
1. Experimental
5.4. Materials
TOPAS® 8007X10 and Tinuvin P (1) were received as gifts from Ciba Speciality
Chemicals and were used without further purification. Cyclohexane was purified using
a literature procedure 194, where it was washed with concentrated sulphuric acid until
the wash was colourless. The organic layer was then washed with water, followed by
aq. Na2CO3 and washed again with water until the wash solution reached neutral pH.
The washed cyclohexane was then distilled over calcium hydride. Compounds 114 187,
115 187, 116 187 and 55 58 were synthesised as described previously. All other materials
and reagents were of analytical reagent grade purity, or higher and were purchased
from Sigma Aldrich, Australia.
C H A P T E R F I V E
P a g e | 194
5.5. Sample preparation
5.5.1. Doped TOPAS® sample preparation
Each of the compounds shown in Figure 52 (6.078 10-8 mol) were dissolved in
freshly distilled cyclohexane (4.57 mL) in glass vials. TOPAS® pellets (293 mg) were
then added to each solution to give a PFN concentration of ~0.025 wt%, and the vials
were sealed and stirred for 4 hours in the dark. The additives, TMIO (55) and Tinuvin
P (1), were then added in a range of concentrations (), and the mixtures allowed to stir
for a further 1 hour to ensure even dispersion. Each solution was then poured into an
individual Petri dish and the solvent was allowed to evaporate slowly over 2 days, in
the dark. Once the films were touch-dry, they were put under vacuum until their mass
was constant (~24 h). Final film thicknesses were approximately 100 µm. Samples for
outdoor weathering and laboratory ageing were then cut from the same film batches to
avoid differences in concentrations or physical characteristics.
5.5.2. Outdoor weathering
Outdoor weathering experiments were carried out in Brisbane, Australia at a latitude
and longitude of 27°28'38.7"S and 153°01'37.8"E, respectively, on the un-shaded,
fully exposed rooftop of a 14-storey building. Samples were placed in aluminium-
backed holders over a wooden support, at an angle of 180° to the sun for the period
from 18 December, 2014 to 28 January, 2015 (summer). Samples were removed
periodically and analysed using UV-Vis, Fluorescence and FTIR-ATR spectroscopy.
Values for precipitation, solar exposure and temperature were obtained from the
Australian Government Bureau of Meteorology, with the data summarised in Table 4.
C H A P T E R F I V E
P a g e | 195
The data were obtained from a weather station that was in close proximity to the aging
site: latitude 27°48'S, longitude 153°04'E, altitude 8 m 200.
5.5.3. Laboratory aging
Film samples were aged in an Heraeus Suntest CPS+ device (Atlas) at temperature of
35°C and an irradiance of 250 W/m2. The samples were oriented parallel to the lamp
and were removed periodically for analysis using UV-Vis, Fluorescence and FTIR-
ATR spectroscopy.
5.6. Analysis methods
5.6.1. FTIR-ATR spectroscopy
Infrared spectra were recorded as neat samples using a Nicolet 5700 Nexus Fourier
Transform infrared spectrometer equipped with a DTGS TEC detector and a Smart
Endurance single reflection ATR accessory. The ATR accessory contained a
composite diamond IRE with a 0.75 mm2 sampling surface and a ZnSe focussing
element (Nicolet Instrument Corp., Madison, WI). An Optical Path Difference (OPD)
velocity of 0.6329 cm s-1 and a gain of 8 were used. Spectra were collected in the range
4000-650 cm-1 using 32 scans at 4 cm-1 resolution. All films were examined in
triplicate. The data was processed using Grams/32 AI software and Microsoft Excel.
Oxidation indices were calculated by taking the ratio of the maximum peak height in
the carbonyl stretching region (1700-1715 cm-1) to the area under the C-H deformation
band (1400-1500 cm-1), using a baseline over the range, 1700-1400 cm-1.
C H A P T E R F I V E
P a g e | 196
5.6.2. UV-Vis spectroscopy
All UV-Vis spectra were recorded on a Varian Cary 50 UV-Vis spectrophotometer.
Spectra were collected in the range from 200-700 nm at a scan rate of 600 nm min-1.
All films were examined in triplicate. The spectra were baseline-corrected using a
linear offset to give an absorbance of zero at 600 nm and were further processed using
Microsoft Excel. The data are presented as the fractional change in maximum
absorbance between 500-600 nm compared to un-aged samples.
5.6.3. Fluorescence Spectroscopy
Fluorescence spectroscopy was undertaken using a Varian Cary Eclipse fluorescence
spectrophotometer. Samples were loaded into a custom-made holding device and
excited at an angle of 45° to the surface, with the emission recorded from the back face
of the sample in order to minimise scattering effects. The excitation wavelength used
changed according to the compound present in the sample: 114: 568 nm, 115: 564 nm,
116: 564 nm. Spectra were collected from 5 nm past the excitation wavelength to 700
nm. All films were examined in triplicate. The data were processed using Microsoft
Excel and are presented either as peak emission values or as the fractional change in
the maximum intensity between 600-650 nm compared to an un-aged sample.
5.7. Results and discussion
5.7.1. Film preparation
The solubility characteristics of perylenediimide-based compounds and the formation
of aggregates can be affected by solvent/matrix combinations and concentrations used.
We have previously shown via UV-Vis and fluorescence spectroscopy that the
C H A P T E R F I V E
P a g e | 197
perylenediimide-based compounds 114, 115 and 116 used here, do not aggregate when
solvent-cast from cyclohexane into TOPAS® at a concentration of 0.025 wt% 227. The
processing of TOPAS® films by solvent-casting allowed for uniform distribution of
additives and avoided the use of high temperatures that can cause some switch-on of
the PFN probe prior to testing 220.
5.7.2. Aging conditions of the TOPAS® films
To evaluate differences between natural weathering and laboratory exposure, film
samples were exposed to natural weathering conditions on the rooftop of a 14-storey
building during the 2014-2015 Brisbane, sub-tropical summer in Australia, and were
also aged in an Heraeus Suntest CPS+ xenon-arc solar simulator operating at an
irradiance of 250 W/m2 and 35°C. The radiant exposure conditions in the laboratory
aging experiments were selected to mirror the outdoor exposure conditions (Table 4).
The rates of oxidation for un-doped TOPAS® films aged in the laboratory were
comparable to the natural weathering conditions (Figure 54).
Table 4: Solar exposure, temperature and rainfall conditions for rooftop weathering and laboratory aging.
Aging conditions
Average daily
solar exposure
(MJ/m2)
Average
maximum daily
temperature
Total
rainfall
(mm)
Suntest laboratory
aging
21.6 35 0
Rooftop natural
exposure
21.34 30.8 338.4
C H A P T E R F I V E
P a g e | 198
FTIR-ATR analysis of the aged TOPAS® films showed strong bands corresponding
to oxidation products that have been reported previously for UV-exposed TOPAS®
228. There were four main bands in the carbonyl stretching region of the FTIR spectra:
a lactone band at 1780 cm-1; a vinyl band at 1650 cm-1; an unresolved ester band at
1740 cm-1; and a band at 1720 cm-1, representative of carboxylic acids and ketones.
For both aging environments, there was very little increase in the oxidation index
below 250 MJ/m2 of radiant exposure, Figure 54. This apparent induction period to
oxidation provides scope for using PFN sensors to monitor degradation of the
TOPAS® films, since PFNs have been previously shown to signal degradation before
oxidation can be observed using FTIR 35, 56, 64, 98-101, 106, 123, 186.
Figure 54: Oxidation indices as determined by FTIR-ATR for TOPAS® films aged in the laboratory
(Suntest) and outdoors (data of weather comparisons are summarised in ).
C H A P T E R F I V E
P a g e | 199
5.7.3. Using PFNs as sensors of photo-oxidation degradation
Many of the PFNs used in previously reported photo-degradation studies were not
stable under photo-oxidative ageing conditions 186, 227. The photo-stabilities of a
number of novel PFNs were recently compared and their ability to detect polymer
degradation in the early stages of the degradation induction period during laboratory
aging was assessed 227, 229. It was found that, within the group of compounds tested,
the alkyne-linked perylenediimide PFN (116) was the most stable PFN developed.
Therefore PFN 116, the mono-nitroxide analogue (115), and the non-radical, fully
fluorescent methoxyamine analogue (114) were used to monitor degradation during
weathering of films with, and without other additives commonly used in formulated
plastics.
The data shown in Figure 55 demonstrates the sensitivity achievable for perylene-
based PFN probes for the detection of the oxidative degradation of TOPAS®. The
mono-nitroxide PFN, 115 is able to detect the formation of carbon-centred free-
radicals in TOPAS® exposed to laboratory aging conditions well before oxidation can
be observed using FTIR-ATR. Indeed, the large uncertainty in the oxidation index
values shown in Figure 55 results from the very weak signals provided by FTIR-ATR,
reflecting the small number of carbonyl-containing oxidation products produced at
early degradation times. The sampling volume is also small, making heterogeneity
within the sample more prominent.
C H A P T E R F I V E
P a g e | 200
Figure 55: Fluorescence emission and oxidation indices of a laboratory-aged PFN (115)-containing
TOPAS® film.
5.7.4. Suitability of mono vs difunctional PFNs as probes for
polymer degradation
The sensitivity of PFNs for the detection of polymer degradation by fluorescence is
dependent on the number of nitroxide free radicals present in the PFN probe. In
solution studies, we have shown 229 that there is only a modest fluorescence increase
when one nitroxide radical reacts in a probe that has two nitroxides within its structure.
In the case of the perylenediimide based PFNs 115 and 116, one nitroxide compared
to two gives an increase in fluorescence quantum yield of 0.00944 and 0.00436
respectively. However, when one nitroxide in PFN 115 or both nitroxides in PFN 116
are converted to non-radical moieties, the fluorescence quantum yield for each rises
significantly. In this context, the non-radical PFN-analogue (114) has a 10-fold higher
fluorescence quantum yield (0.0996) over PFN 115 and more than 20-fold increase
over PFN 116 suggesting the latter would provide the greatest detectable response.
C H A P T E R F I V E
P a g e | 201
Figure 56: Fluorescence emission during natural weathering on the rooftop for TOPAS® films doped with
compounds 115 and 116 (0.025 wt%).
For TOPAS® films doped with either PFN 115 or PFN 116, carbon-centred radical
production can be detected as the films were aged as indicated by an increase in
fluorescence emission (Figure 56). However, PFN 115 produces a significantly
stronger signal than 116. The difunctional PFN 116 must react with two carbon-
centred radicals to deliver similar fluorescence emission as the monofunctional PFN
115 reacting with only one radical. This leads to different degrees of fluorescence
emission increase for each of these probes. Notably, the difunctional PFN 3, would be
expected to show limited mobility within the degrading polymer. After scavenging one
polymer radical, this PFN would become bound to the polymer backbone. This would
therefore limit this probe’s ability to undertake further trapping reactions, restricting it
to radicals formed in close proximity to the site of the first reaction. However, linking
polymer chains would off-set decreases in molecular weight arising from degradation
and this could potentially deliver enhanced application lifetimes for materials
containing this probe.
C H A P T E R F I V E
P a g e | 202
5.7.5. PFN Stability
Although the perylenediimide PFNs studied were found to be the most stable of those
tested to date 227, they still undergo some degree of transformation as demonstrated by
decreases in their UV-Vis absorbance over time. While less sensitive than
fluorescence, monitoring using UV-Vis spectroscopy is useful as it provides a total
signal arising from both the probe and probe adducts, independent of the presence of
nitroxide spin. The UV-Vis data shown in Figure 57 indicate that there is a slow loss
of, or at least chemical change in, the chromophore driven by irradiation, such that no
significant absorbance from the original chromophore can be detected after 400 MJ/m2
of irradiation. Notably, the fully fluorescent dimethoxy amine adduct (114), with no
nitroxide, shows the fastest rate of photo-bleaching. The mono-nitroxide PFN 115,
displays similar chromophore stability however the PFN 116 with two free nitroxides
shows a lower rate of bleaching.
Figure 57: Relative change in UV-Vis absorbance for TOPAS® films doped with compounds 114, 115 and
116 (0.025 wt%) during natural exposure on the rooftop.
C H A P T E R F I V E
P a g e | 203
The loss of fluorescence emission for the probes under irradiation (Figure 56) is most
evident when the rate of adduct formation becomes slower than the rate of photo-
bleaching. This is likely to happen as the concentration of PFN decreases (through
scavenging). Photo-bleaching is expected to correlate with the generation of singlet
oxygen which arises from reaction of the chromophore excited state with molecular
oxygen. Many molecules that absorb light can generate singlet oxygen 230-234 and such
photosensitizers generally possess high absorption coefficients, high quantum yields
and have excited triplet states at appropriate energy levels and lifetimes 234.
Perylenediimides are known to produce singlet oxygen during UV irradiation 235-238,
and this can lead to fluorophore bleaching. However, when the quantum yield of
fluorescence is low, such as with the PFN probes, there is less energy absorbed to
produce singlet oxygen. However, when the PFNs trap carbon-centred radicals and the
nitroxide spin is removed, their quantum yield of fluorescence increases substantially.
This makes these PFN adducts detectable by fluorescence spectroscopy, but also
increases pathways involving the production of reactive oxygen species such as singlet
oxygen. The higher stability of PFN 116 might be expected to arise from a combination
of the ability of this compound to remove a larger number of radicals from the
degrading polymer system, and its relatively low fluorescence quantum yield after
being singly-bound to a polymer chain by the trapping of a carbon-centred radical.
There is also the potential for excited state quenching for mono-adducts, which could
lead to an increase in the photo-stability for this molecule. The combination of these
factors would decrease the likelihood of singlet oxygen production and oxidative
attack on the fluorophore for PFN 116 which off-sets the decreased emission levels
over PFN 115.
C H A P T E R F I V E
P a g e | 204
Figure 58: Relative change in fluorescence emission during natural weathering for TOPAS® films doped
with compounds 114 (fully fluorescent non-radical PFN analogue), 115 (mononitroxide) and 116
(dinitroxide) at 0.025 wt%.
Whatever the cause and control of the bleaching process, its effects are manifested in
lower than expected peak fluorescence emission from the aged films, as shown by the
data in Figure 58. When doped into TOPAS® and aged under natural conditions, films
containing PFN 115 reached a maximum of ~50% of the theoretical “maximum”
fluorescence generated from un-aged films containing the fully fluorescent PFN-
analogue 114 at the same concentration. Films containing PFN 116 on the other hand,
reached only ~10% of the maximum potential fluorescence emission intensity and this
peak arises following considerably more irradiation (345 MJ/m2 versus 95 MJ/m2).
The lower peak fluorescence for PFN 116 is more likely to be due to degradation of
the fluorophore rather than the formation of still pro-fluorescent, single polymer chain
PFN 116 adducts. Despite the low fluorescence maxima detected in films employing
116, this PFN has more sensor potential because the fluorescent response takes longer
to be engendered and is more persistent.
C H A P T E R F I V E
P a g e | 205
5.7.6. PFN antioxidant effects
Oxidation indices from FTIR-ATR analyses were used to compare the degree of
degradation of blank TOPAS® films (without PFN) to the films containing PFN and
related additives (Figure 59). The data shows that PFN 116 acts as an antioxidant,
which is evident by the formation of IR-detectable oxidation products at a slower rate
than for un-doped films, although the levels are low and are at the limit of detection
by this technique. Notably, there are no obvious signs of degradation at this stage and
the IR indices do not exceed ~0.08. In our hands, IR detection is most reliable for IR
indices above 0.100 and blank TOPAS® films do not physically embrittle, or
significantly discolour, until IR indices reach ~0.300. In contrast, in films containing
114 and 115, there is evidence of low levels of IR-detectable oxidation products in
these TOPAS® films compared to an un-doped film. Although the loss of fluorescence
signal may be related to photo-bleaching and chromophore oxidation that does not
necessarily impact on the bulk polymer matrix, the detection of even small levels of
extra oxidation suggests some link to the degradation of the PFN-adducts formed in
the polymer. As discussed previously, conversion of the probe to the fluorescent (non-
radical, alkoxyamine) adducts may be expected, under further irradiation, to allow
some production of reactive oxygen species from the excited state fluorophore. In this
context, polymer degradation via singlet oxygen is well established 239-240. Small levels
of oxygenated species produced by irradiation of the fluorophore present in the
nitroxide-adducts generated by radical trapping would therefore be expected to
contribute to some extent to increased levels of degradation of the TOPAS® substrate
and these would be expected to rise as the nitroxide is consumed.
C H A P T E R F I V E
P a g e | 206
Figure 59: Oxidation indices as determined by FTIR-ATR for rooftop-exposed TOPAS® films doped with
compounds 114, 115 and 116 (0.025 wt%) and an additive-free control sample.
Although the fully fluorescent PFN-analogue 114 is an alkoxyamine, which would
reflect the fluorescence expected of PFN-polymer adducts, it is unlikely to perform
well as a HAS, as the methoxy group oxidatively unstable 147. Therefore, a degree of
degradation somewhat higher than that of the blank is expected for TOPAS® films
containing PFN 114. The PFN probe 115, as it is an antioxidant nitroxide, would be
expected to act as a stabiliser by trapping of carbon-centred radicals. However, as
shown in Figure 59, the oxidation of PFN 115-containing TOPAS® films was similar
to TOPAS® films containing the non-radical, PFN derivative 114. This enhanced
degradation, although small, is important as it indicates a potential impact on the long-
term stability of films containing this PFN. Notably, as seen in Figure 57 the rate of
chromophore loss for PFN 115 TOPAS® films matches that of PFN 114 films after
~95 MJ/m2 of radiant exposure.
C H A P T E R F I V E
P a g e | 207
Figure 60: Oxidation indices as determined by FTIR-ATR (left) and relative change in UV-Vis
absorbance (right) for TOPAS® films doped with compound 114, 115 and 116 (0.025 wt%) during
aging in the laboratory (Suntest) and outdoors weathering (other data for rooftop and suntest
comparisons are summarised in ).
There were slight differences when comparing the oxidation indices of films doped
with compounds 114, 115 and 116 when aged by true weathering conditions, compared
to laboratory aging conditions in the Suntest, Figure 60 (left column). Films doped
with PFN derivative 114 and PFN 115 were found to oxidise faster on the rooftop
compared to exposure in the Suntest apparatus. This may also be related to singlet
oxygen production, as the rooftop samples were exposed to weathering elements that
C H A P T E R F I V E
P a g e | 208
are not present in the Suntest, such as environmental contaminants that have been
shown to lead to singlet oxygen production 88, 241. Importantly, there is no evidence for
increased radical formation in the films aged on the rooftop compared to the Suntest,
which would be shown by an increase in fluorescence emission from the PFNs, Figure
SI 138. However, as discussed above, very weak signals and small sampling volume
leads to large uncertainty in the oxidation index values. Therefore, rooftop and suntest
data could be improved by higher sampling volume to lower error bars.
Fluorophore stability using laboratory aging conditions was similar to true weathering
conditions, Figure 60 (right column). PFN 116 was also found to be the most stable
PFN when exposed to laboratory aging conditions in the Suntest. Notably, there was
an induction period, perhaps attributable to temperature variations, before UV-Vis
absorbance could be used to detect degradation of the fluorophore for films that were
naturally aged in the environment (rooftop exposure) compared to the laboratory-aged
samples. After ~100 MJ/m2 irradiation, the rates of fluorophore degradation were
comparable. A summary of all the data comparisons, including PFN-analogue 114,
PFN 115 and PFN 116 are provided in the .
5.7.7. The effect of additives on the stability of PFNs in TOPAS®
films
Common additives such as the UV absorber Tinuvin P (1) and hindered amine
stabilisers of which TMIO (1,1,3,3-tetramethylisoindol-2-yloxyl, 55) is an analogue
are often added to formulated plastics to increase service lifetime. When these
compounds were added to TOPAS® films that contained the alkoxyamine PFN-
derivative 114 an increase in stability of the fluorophore was observed.
C H A P T E R F I V E
P a g e | 209
Figure 61: Relative change in UV-Vis absorbance of aged TOPAS® films doped with PFN-analogue 114
(0.025 w%); compared to TOPAS® films containing PFN-analogue 114 + TMIO (1, 2 and 4 eqv. of 114)
with respect to radiant exposure (MJ/m2) on the rooftop.
With increasing concentration of 55, the fluorophore’s UV-Vis signal retained longer
during photoirradiation (Figure 61). This is due to 55 acting as a radical trap in the
degrading polymer system, which reduces the likelihood of radical attack on the
fluorophore. An increase in stability in the film with the addition of 55 was also
observed as an overall decrease in the rate of oxidation detected by ATR-IR, Figure SI
139a.
C H A P T E R F I V E
P a g e | 210
Figure 62: Relative change in UV-Vis absorbance of aged TOPAS® films doped with PFN-analogue 114
(0.025 w%); compared to TOPAS® films containing PFN-analogue 114 + Tinuvin P (0.1, 0.3 and 0.5 wt%)
with respect to radiant exposure (MJ/m2) on the rooftop.
The UV absorber, Tinuvin P (1) provides ultraviolet protection through absorption of
radiation between the wavelength range from 300-400 nm, and it is relatively photo-
stable over long periods of exposure 242. When the concentration of 1 was increased
from 0.1, to 0.3 and then 0.5 wt% in TOPAS® films containing PFN-derivative 114,
the lifetime of the PFN-alkoxyamine derivative increased (Figure 62). As expected,
there was also an increase in the stability of the TOPAS® films with the addition of 5,
as shown by a decrease in the oxidation rate with increasing amounts of 1, Figure SI
139b.
There appeared to be a limiting effective concentration of 5 as there was only a small
difference in stability between films that contained 0.3 wt% of 1 and 0.5 wt% of 1, so
0.3 wt% of 1 was used in further studies. Similarly, there was only a small difference
in stability for films containing 2 equivalents of 55, compared to films with 4
equivalents of 55, so 2 equivalents of 55 were subsequently used.
C H A P T E R F I V E
P a g e | 211
Figure 63: Relative change in UV-Vis absorbance of aged TOPAS® films doped with PFN-analogue 114
(0.025 w%); compared to TOPAS® film containing PFN analogue 114 + Tinuvin P (0.3 wt%), TOPAS®
film containing PFN-analogue 114 + TMIO (2 eqv. of 114) and TOPAS® film containing PFN-analogue
114 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 114) with respect to radiant exposure (MJ/m2) on the
rooftop.
The combination of both the radical trap, TMIO (55) and UV absorber, Tinuvin P (1),
showed a combined antioxidant effect on the PFN’s fluorophore, Figure 63. This effect
has been shown for combinations of UV absorbers and free radical scavengers in
polymer systems, where lifetimes can be significantly increased 243-246. This synergy
is due each additive working through different mechanisms of stabilisation. This
increase of stability was further investigated with films containing PFNs 115 and 116.
It needs to be established that addition of stabilisers has no affect the detection of
photo-oxidative degradation of the TOPAS® films.
5.7.8. The effect of additives on PFNs in TOPAS® films
As previously discussed, the stability of the PFNs is related to the ability to remove
radicals and its lowered quantum yield, which reduces singlet oxygen production.
C H A P T E R F I V E
P a g e | 212
Therefore, addition of stabilisers shows the same positive effect of PFN 115 as shown
in PFN-analogue 114, Figure 64.
Figure 64: Relative change in UV-Vis absorbance of aged TOPAS® films doped with PFN 115 (0.025 w%);
compared to TOPAS® film containing PFN 115 + Tinuvin P (0.3 wt%), TOPAS® film containing PFN 115
+ TMIO (2 eqv. of 115) and TOPAS® film containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2
eqv. of 115) with respect to radiant exposure (MJ/m2) on the rooftop.
Like with PFN-analogue 114, enhanced stability is shown as the equivalents of TMIO
(55) is increased, see Figure SI 140a. Addition of 55 removes excess radicals from the
degrading polymer system, therefore reducing radical attack on the fluorophore.
Addition of 1 also reduces radical attack on the fluorophore via ultraviolet protection
of the film. This effect was previously discussed and is shown in Figure 62 with films
doped with PFN- analogue 114. As the weight percentage of 1 increased, there is an
improved stability of PFN 115, see Figure SI 140b. This results in a combined
protective antioxidant effect to the fluorophore of PFN 115 with addition of both 55
and 1, Figure 64.
C H A P T E R F I V E
P a g e | 213
Figure 65: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films doped with PFN 115
(0.025 w%); compared to TOPAS® film containing PFN 115 + Tinuvin P (0.3 wt%), TOPAS® film
containing PFN 115 + TMIO (2 eqv. of 115) and TOPAS® film containing PFN 115 + both Tinuvin P (0.3
wt%) and TMIO (2 eqv. of 115) with respect to radiant exposure (MJ/m2) on the rooftop.
The added stability of additives is also shown by an increase of stability in the film.
Addition of 55 serves to remove carbon-centred free-radicals from the degrading
TOPAS® films, retarding the auto-catalytic degradation reactions, which reduces the
number of oxidation products in the film. Addition of 1 decreases the production of
radicals by protecting film through absorption of radiation between the wavelength
range from 300-400 nm. The combined protection of the film is shown in Figure 65.
C H A P T E R F I V E
P a g e | 214
Figure 66: Fluorescence maximum trace of aged TOPAS® films doped with PFN 115 (0.025 w%);
compared to TOPAS® film containing PFN 115 + Tinuvin P (0.3 wt%), TOPAS® film containing PFN 115
+ TMIO (2 eqv. of 115) and TOPAS® film containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2
eqv. of 115) with respect to radiant exposure (MJ/m2) on the rooftop.
The decrease of film degradation can be detected by a rate change in fluorescence
production by the addition of a PFN. However, the non-fluorescent nitroxide TMIO
(55) possesses the same nitroxide structural moiety as is present in PFNs 115 and 116,
so it is able to compete with the PFNs to trap carbon-centred free-radicals. The
outcome of this competition is shown in Figure 66. Addition of 2 equivalents of
compound 55 delayed the fluorescence switch-on from PFN 115. This suggests that
fewer radicals were trapped by the PFN at early aging times and reflects the carbon-
centred free-radical trapping efficiency of 55. Addition of the UV absorber 1 at 0.3
wt% resulted in a delay in the generation of fluorescent adducts as well as decreasing
the value and the time when peak fluorescence emission was detected. This is likely
due to an overall reduction in the rate of film degradation due to the presence of the
UV absorber. Combining the 2 additives (55 and 1) further reduced the degree of
fluorescence switch on. The overall delayed fluorescence switch-on, therefore reduced
C H A P T E R F I V E
P a g e | 215
the quantum yield of the film. This thereby decreases the production of singlet oxygen
and subsequent degradation of the PFN chromophore, which is reflected in the more
persistent UV-Vis spectra. However, the addition of additives reduces the fluorescence
response of the PFN. This is due to the degradation of the fluorophore. PFN 115
reached a maximum fluorescence after 95 MJ/m2 of radiant exposure, and at that point
only 20% of the total UV-Vis absorbance has been lost. However, when 2 equivalents
of TMIO (55) is added to the film containing PFN 115, the maximum fluorescence is
reached after 240 MJ/m2 of radiant exposure. At 240 MJ/m2 only 40% of the UV-Vis
absorbance is present. This gives explanation of the poor maximum fluorescence.
There is less of an effect when dditives are added to films containing PFN 116,
compared to when PFN 115 was used. This is due to PFN 116 having an extra nitroxide
moiety per molecule compared to PFN 115, which results in the need to remove two
nitroxide groups per molecule to observe a significant increase in fluorescence, rather
than one (for PFN 2). If the nitroxide moiety is still present, addition of TMIO (55)
does not increase the stability of the fluorophore or the film substrate. Similarly,
addition of UV absorber (Tinuvin P, 1) had only a minor effect on the rate of
fluorescence increase for PFN 116. This is due to the already lowered fluorescence
quantum yield, Figure 67.
C H A P T E R F I V E
P a g e | 216
Figure 67: Fluorescence maximum trace of aged TOPAS® films doped with PFN 116 (0.025 w%);
compared to TOPAS® film containing PFN 116 + Tinuvin P (0.3 wt%), TOPAS® film containing PFN 116
+ TMIO (2 eqv. of 116) and TOPAS® film containing PFN 3 + both Tinuvin P (0.3 wt%) and TMIO (2
eqv. of 116) with respect to radiant exposure (MJ/m2) on the rooftop.
However, when focusing on Figure 67, addition of additives, 55 and 1 still allowed
fluorescent detection of radicals formed in the photo-oxidative degradation of
TOPAS®. The stabilisers not only reduce degradation of the TOPAS® film while
working in synergy, they reduced degradation of the PFN fluorophore. Although
maximum fluorescence was not seen in the film containing both additives, PFN was
still present, indicating fluorescence would continue to grow, allowing substantial
detection of photo-oxidative radical degradation.
5.8. Conclusion
This study has shown that PFNs are sensitive probes for the early stages of photo-
oxidative degradation of polymer materials. The PFN’s reporting lifetimes can be
extended with the addition of a radical trap (55). Their lifetime can also be improved
by addition of nitroxide moieties to the PFN structure, but this affects the PFN’s
C H A P T E R F I V E
P a g e | 217
sensitivity. The addition of a UV absorber (1) was also shown to affect the reporting
lifetime of the PFNs via a decrease in the rate of degradation of TOPAS® film
substrates, which also reduced consumption of the PFNs and led to a lower overall
fluorescence signal.
The sensitivity of PFNs to the detection of free-radicals allowed photodegradation to
be observed during the apparent induction period seen using infrared spectroscopy. By
signalling degradation within this induction period, these PFN probes may be able to
provide a sensitive, rapid method for determining relative lifetimes of materials during
natural exposure, thus reducing the time required for outdoor exposure studies.
5.9. Acknowledgements
We gratefully acknowledge financial support for this work from Queensland
University of Technology (QUT), the Australian Research Council Centre of
Excellence for Free Radical Chemistry and Biotechnology (CEO 0561607), and the
Defence Materials Technology Centre, which was established and is supported by the
Australian Government’s Defence Future Capability Technology Centre (DFCTC)
initiative.
C H A P T E R S I X
P a g e | 218
6. THE SYNTHESIS AND STABILITY OF FERRARI
RED- TYPE COMPOUNDS
6.1. Introduction
Corrosion is recognised as a major global financial issue, estimated to cost US$2.5
trillion, which is equivalent to 3.4% of global Gross Domestic Product (GDP).247-248
In the same NACE study, it was estimated that 15-35% of this cost could be prevented
using current control practises. One control method is the use of protective coats, such
as polymers. However, during exposure to sunlight and other weather effects,
polymers undergo degradation and can result in a loss of its structural integrity. This
may result in the development of surface cracks which allows oxygen and moisture to
react with the metal surface.249 Many techniques have been developed to minimise the
chance of this happening by monitoring and re painting systematically. This process
can be time consuming and expensive.
As mentioned in previous chapters, monitoring polymer degradation can lack
sensitivity using current techniques. However, profluorescent nitroxides have shown
the ability to locate and detect polymer damage by trapping the radicals formed during
the initiation stage. 35, 56, 64, 98-101, 106, 123, 186 The challenge has proven to be creating a
PFN stable enough to withstand the harsh environment of radical mediated polymer
degradation.64,35
It has been previously shown that using a photo-stable fluorophore, that PFN’s stability
can be lengthened. Ferrari Red based PFNs have been developed herein, based off the
photo-stable 3,6-diaryl-2,5-dihydro-1,4-dioxopyrrolo[3,4-c]pyrroles (DPP) pigment.
C H A P T E R S I X
P a g e | 219
The DPP pigment is known for its outstanding performance to withstand, heat, light
and weathering effects250-252. It was solubilised using a swallow tail (131) to test it as
a dye compared to its known pigment. However, there is no measurable technique for
testing the photo-stability of a certain compound due to the large number of variables.
In this experiment the Ferrari Red compounds will be compared against the previously
studied 9,10-bis(phenylethynyl)anthracene (29) which is known for its thermal
stability. It will also be tested against the most successful photo-stable PFN to date,
alkyne perylene diimide (116)
Figure 68: Compounds used in this study
The novel PFNs were exposed to photo-oxidative environment in two films, to test
their photo-oxidative stability in a solid model using PTMSP and TOPAS®, as they
were used in previous chapters. Like the previous study, the films were also exposed
to a thermo-oxidative environment to confirm the degradation pathway.
C H A P T E R S I X
P a g e | 220
Figure 69: Polymer films used in photo-oxidative degradation experiment
The methoxy amine derivatives were synthesised to avoid complication with the
antioxidant effect of the nitroxide. This process would simplify the degradation
analysis so only comments on the stability of the fluorophore can be made.
6.2. Experimental
6.2.1. Materials
TOPAS® 8007x10 was a gift from Ciba Speciality Chemicals. PTMSP was purchased
from ABCR GmbH. Cyclohexane was purified using a literature procedure194 where
it was washed with concentrated sulphuric acid until the wash was colourless. The
organic layer was then washed with water, aq. Na2CO3 and again with water until the
wash solution was at a neutral pH. The washed cyclohexane was then distilled over
calcium hydride. PFN 116 along with the methoxyamine, non-radical analogues, 114
were synthesised as described previously.53, 187. All other materials and reagents were
of analytical reagent grade purity, or higher and were purchased from Sigma Aldrich,
Australia.
6.2.1. PTMSP sample preparation
Each of the compounds shown in Figure 68 (1.94 x10-7 mol) was dissolved in freshly
distilled cyclohexane (7.45 mL) in a 25x75 mm soda glass vial. PTMSP (293 mg) was
then added to each solution and the vials sealed and stirred for 48 hours in the dark.
C H A P T E R S I X
P a g e | 221
Each solution was then poured into a Petri dish and the solvent allowed to evaporate
slowly over two days in the dark. Once the films were dry to the touch, they were
placed under vacuum until they reached a constant weight (24 h).
6.2.2. TOPAS® sample preparation
Each of the compounds shown in Figure 68 (4.3610-7 mol) was dissolved in freshly
distilled cyclohexane (16.94 mL) in a 2575 mm soda glass vial. TOPAS® pellets
(660 mg) were then added to each solution and the vials sealed and stirred for 4 hours
in the dark. Each solution was then poured into a Petri dish and the solvent allowed to
evaporate slowly over two days in the dark. Once the films were dry to the touch, they
were placed under vacuum until they reached a constant weight (24 h).
6.2.3. Photo-oxidation of films
Film samples were irradiated in an Heraeus Suntest CPS+ device delivering 250 W/m2.
The temperature in the chamber was set to 40°C. The films were oriented in parallel
to the lamp. Samples were removed periodically and analysed using UV-Vis,
Fluorescence and FTIR-ATR spectroscopy.
6.2.4. Thermo-oxidation of films
Films were placed in an oven at 70°C on metal racks, and separated by a 5 mm gap.
6.2.5. Characterisation
6.2.5.1. Fluorescence Spectroscopy
Fluorescence spectroscopy was undertaken using a Varian Cary Eclipse fluorescence
spectrophotometer. Samples were loaded into a custom-made holding device and
C H A P T E R S I X
P a g e | 222
excited at an angle of 45° to the surface, with the emission recorded from the back face
of the sample in order to minimise scattering effects. The excitation wavelength used
changed according to the compound present in the sample: 29; 383 nm, 131, 465 nm,
114, 568 nm, 116; 564 nm. Spectra were collected from 5 nm past the excitation
wavelength up to 700 nm at a scan rate of 600 nm min-1. All films were examined in
triplicate. The data were processed using Microsoft Excel and are presented as the
fractional change in the maximum intensity between 600-650 nm compared to an un-
aged sample.
6.2.6. Synthesis of Ferrari Red based products
Scheme 49: Synthesis of 2,5-bis(2-octyl-1-dodecyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion (131)
6.2.6.1. 2,5-dihydro-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (135)
A mixture of t-BuOK (252 mg, 2.25x10-3 mol, 2.3 equiv.) and benzonitrile 134 (100
mg, 9.697x10-4 mol, 1 equiv.) in 2-methyl-2-butanol (620 µL) was heated at 110 °C.
At this temperature and under vigorous stirring, dimethyl succinate (64 µL, 4.85x10-4
mol, 0.5 equiv.) was added and stirred for a 2 h at 110 °C, the mixture was cooled at
50 °C and treated with methanol (1.34 mL) and AcOH (0.17 mL). After cooling at
C H A P T E R S I X
P a g e | 223
room temperature, the precipitate was collected by filtration and washed repeatedly
with methanol to give 135 (7.7%).1H NMR (400 MHz, DMSO) δ 5.74 (s, 2H, NH);
7.56 (m, 6H, Ar); 8.47 (m, 4H, Ar).
6.2.6.2. 2,5-bis(2-octyl-1-dodecyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dion (131)
135 (15 mg, 5.2 x 10-5 mol) and anhydrous K2CO3 (21.6 g, 1.56 -4 mol, 3 equiv.) were
added to a dry round bottom flask and kept it under vaccum at 50 °C for one hour then
anhydrous N, N-dimethylformamide (DMF) (1 mL) was added under argon to the
above mixture. This mixture was then heated to 120°C under argon for 1h. 2-Octyl-1-
dodecylbromide (65.14 mg, 1.56 -4 mol, 3 equiv.) was added drop-wise, and the
reaction mixture was further stirred overnight at 130°C. The reaction mixture was
allowed to cool down to room temperature and poured into water (600 mL) and stirred
for 30 min. The product was extracted with chloroform, washed with DI water, and
dried over anhydrous MgSO4. Removal of the solvent afforded the crude product
which was further purified using column chromatography on silica gel (1:1
Chloroform/Hexane) to gave the product as an orange oil (5%).
1H NMR (400 MHz, CDCl3) δ 0.88 (t, 12H, J = 3.66 Hz, CH3); 1.05- 1.31 (m, 58H,
CH2); 3.73 (d, 4H, J = 7.76 Hz, CH2); 7.49 (m, 6H, Ar); 7.75 (m, 4H, Ar). IR (ATR)
νmax 7.92 (=C-H), 1093 (C-O), 1238 (R3N), 1465 (aryl C-C), 1673 (C=O), 2852 and
2921 cm-1 (alkyl CH3). 253
C H A P T E R S I X
P a g e | 224
Scheme 50: The synthetic route to 2,5-bis(2-octyl-1-dodecyl)-3,6-di(2-methoxy-1,1,3,3-
tetramethylisoindoline)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion, 133
6.2.6.3. 5-Cyano-1,1,3,3-tetramethylisoindoline (82)
5-Bromo-1,1,3,3- tetramethylisoindoline (65) (250 mg, 9.84 x 10-4 mol),
K4[Fe9CN)6].3H2O (103.25 mg, 0.25 eqv., 2.4 x 10-4 mol), CuI (22.5 mg, 0.1 eqv., 11.8
x10-4 mol), 1-butylimidazole (412 uL, 2eqv.,1.89 x 10-3 mol) and o-xylene (5 mL) as
the solvent were all added to a schlenk and heated to 180 °C for 4 days. Ethyl acetate
was poured into the tube once cooled and it was washed with 2M NaOH. Solids were
removed by filtration and solvent removed by vacuum. A short ethyl acetate column
was performed and everything to collected with the solvent, yielded a yellow oil with
assumed impurities. 1H-NMR (CHCl3, 400MHz): δ= 1.45 (s, 12H, CH3-C), 7.20 (d,
1H, Ar-H), 7.40 (s, 1H, Ar-H), 7.54 (dd, 1H, Ar-H).144
6.2.6.4. 5-Cyano-1,1,3,3-tetramethylisoindolin-2-yloxyl (83)
5-Cyano-1,1,3,3-tetramethylisoindoline (82) was dissolved in DCM and cooled in an
ice bath before m-CPBA was added slowly. Once addition was complete, the ice bath
was removed and allowed to return to RT and stirred for a further 6 hours. The solution
C H A P T E R S I X
P a g e | 225
turned a bright yellow colour and the reaction was basified with 2M NaOH, washed
with water (3x 20 mL) and purified by column chromatography (DCM). To yield a
crystalline yellow solid. (76 % over the 2 steps). IR (ATR) νmax 760 (=C-H), 833 (N-
O), 1372 (R3N), 2227 (C≡N), 2978 cm-1 (alkyl CH3). HRMS (ESI): m/z (%) =
217.2710 (30) [M+1]+, calcd for C13H16N2O• [M+1]+ 216.1263.144
6.2.6.5. 5-Cyano-2-methoxy-1,1,3,3-tetramethylisoindoline (84)
5-Cyano-1,1,3,3-tetramethylisoindolin-2-yloxyl (83) (150 mg, 6.968 x10-4 mol) and
FeSO4.7H2O (484 mg, 2.5eqv., 1.74 x 10-3 mol) were dissolved in DMSO and cooled
in an ice bath while H2O2 was added dropwise. Once the addition was complete, the
reaction was stirred at RT for 30 minutes. Once complete the mixture was poured into
2M NaOH, and extracted with ether (3 x 20 mL) then washed with water (3 x 10 mL).
Solvent was removed by vacuum and purified by column chromatography (10% ether
in hexane) to yield a colourless low melting solid.1H-NMR (CHCl3, 400MHz): δ= 1.43
(s, 12H, CH3-C), 3.77 (s, 3H, CH3-O), 7.19 (d, 1H, J = 7.88 Hz, Ar-H), 7.37 (s, 1H,
Ar-H), 7.52 (dd, 1H, J = 8.1 & 1.07 Hz, Ar-H). HRMS (ESI): m/z (%) = 231.1638 (15)
[M]+ 253.1453 (25) [M+Na] calcd. for C14H19N2O (M) 231.15.
6.2.6.6. 2,5-dihydro-1,4-dioxo-3,6-di(2-methoxy-1,1,3,3-
tetramethylisoindoline)pyrrolo[3,4-c]pyrrole (132)
A mixture of t-BuOK (252 mg, 2.25x10-3 mol) and 84 (223.3 mg, 9.697x10-4 mol) in
2-methyl-2-butanol (620 µL) was heated at 110 °C. At this temperature and under
vigorous stirring, dimethyl succinate (64 µL, 4.85x10-4 mol) was added and stirred for
2 h at 110 °C, the mixture was cooled at 50 °C and treated with methanol (1.34 mL)
and AcOH (0.17 mL). After cooling at room temperature, the precipitate was collected
C H A P T E R S I X
P a g e | 226
by filtration and washed repeatedly with methanol to give 132 (11.2%).250 1H NMR
(400 MHz, DMSO) δ 5.74 (s, 2H, NH); 7.56 (m, 6H, Ar); 8.47 (m, 4H, Ar).250
6.2.6.7. 2,5-bis(2-octyl-1-dodecyl)-3,6-di(2-methoxy-1,1,3,3-
tetramethylisoindoline)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion (133)
132 (19 mg, 6.625x10-5 mol) and anhydrous K2CO3 (28 mg, 1.988x10-4 mol) were
added to a dry round bottom flask and kept under vacuum at 50 °C for one hour then
anhydrous N, N-dimethylformamide (DMF) (1.34 mL) was added under argon to the
above mixture. This mixture was then heated to 120°C under argon for 1 h. 2-Octyl-
1-dodecylbromide (1.988x10-4 mol, 90 µL) was added drop-wise, and the reaction
mixture was further stirred overnight at 130°C. The reaction mixture was allowed to
cool down to room temperature next day and poured into water (600 mL) and stirred
for 30 min. The product was extracted with chloroform (3 x 10 mL), washed with DI
water (20 mL), and dried over anhydrous MgSO4. Removal of the solvent afforded the
crude product which was further purified using column chromatography on silica gel
(1:1 Chloroform/Hexane) to give the product as an orange oil. 1H NMR (400 MHz,
CDCl3) δ 0.88 (t, 12H, J = 3.66 Hz, CH3); 1.05- 1.31 (m, 58H, CH2); 3.73 (d, 4H, J =
7.76 Hz, CH2); 7.49 (m, 6H, Ar); 7.75 (m, 4H, Ar). IR (ATR) νmax 7.92 (=C-H), 1093
(C-O), 1238 (R3N), 1465 (aryl C-C), 1673 (C=O), 2852 and 2921 cm-1 (alkyl CH3).
6.3. Results and Discussion
6.3.1. Film Preparation
Ferrari red is initially a pigment, however to allow solution testing it was solubilised
using a long swallow tail. Swallow tail Ferrari red was dissolved in cyclohexane, and
the same solvent casting procedure from the previous chapters was used. Solvent
C H A P T E R S I X
P a g e | 227
casting is used to reduce the use of elevated temperatures to remove solvent, and it
also allows easy distribution of the compounds in low concentration.
6.3.2. PTMSP
PTMSP film was used in this study; its popularity is due to the increasing need for
high-performance separation membranes. Due to PTMSPs bulky substituents on its
polymer chain, it produced the most permeable non-porous polymer membrane among
the existing polymers. 254 PTMSP exhibits long-term stability when stored at room
temperature in the dark under vacuum but the material noticeably degrades when
exposed to heat, light or air.190 It is known to degrade through a radical mediated
mechanism which has been previously shown to be perfect for PFN detection.191
6.3.2.1. Photo-oxidative Degradation of PTMSP films
Figure 70: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) for
PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm)
with respect to UV ageing time (hours).
The films were exposed to the synthetic photo-oxidative environment by the Heraeus
Suntest. PTMSP has shown previously to produce radicals at a high rate over other
C H A P T E R S I X
P a g e | 228
films tested. Compounds with high fluorescence quantum yields are known to form
singlet oxygen which aids degradation of their own fluorophore, although it is not as
competitive as the radical attack from the degrading polymer system. This is shown in
Figure 70 by the loss of fluorescence during irradiation. Comparing the loss of
fluorescence can be used as a comparison tool to look at relative photo-oxidative
stability. Using this method, compound 114 has higher photo-oxidative stability over
29, due to 114 fluorescence loss being slower which shown in preceding chapters.
However, Ferrari red dye (131) performed poorly compared to both 29 and 114. This
was a surprising outcome due to the positive published literature.
6.3.2.2. Thermo-Oxidative Degradation of PTMSP Films
Figure 71: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) for
PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm)
with respect to ageing time (hours) at 70°C.
PTMSP films were thermally aged in the dark in an oven at 70°C. This was done to
ensure that the fluorophores were not affected by the temperatures experienced during
testing in the solar simulator. Thermally-aged films showed no visible degradation,
such as brittleness or loss in fluorescence emission Figure 71, which indicates that the
C H A P T E R S I X
P a g e | 229
fluorophores and the polymer used in this study are thermally stable under the
conditions used.
Figure 72: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) for
PTMSP films doped with 116 with respect to UV (-■-) or thermal (-♦-) ageing time (hours).
The number of radicals produced by the degrading system can be detected by
fluorescence given off by a PFN. PFN 116 was used to compare the radical production
in both environments, UV exposure and thermal due to its proven stability. It shows
there are fewer radicals produced when the films were exposed to thermal-oxidative
degradation environments compared to photo-oxidative. As irradiation continues in
the photo-oxidative environment, fluorescence reaches a maximum before tapering
off. As discussed this is due to degradation of the fluorophore. This degradation can
be caused by the high concentration of radicals within the polymer system.
6.3.3. TOPAS®
TOPAS® was the second film to be used in this photo-degradation study. It is within
the family of cyclic olefin copolymers.193 Cyclic copolymers have attractive properties
such as high transparency, low density, high thermal stability, low shrinkage, low
C H A P T E R S I X
P a g e | 230
moisture absorption, and low birefringence which allow them to be extremely
attractive for a range of applications.204
6.3.3.1. Photo-Oxidative Degradation of TOPAS® Films
Figure 73: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) for
TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568
nm) with respect to UV ageing time (hours).
As shown in previous chapters, TOPAS® degrades at a slower rate in a photo-
oxidative environment compared to PTMSP. This results in fewer radials attacking the
compound’s fluorophore that therefore results in a longer survival rate for the PFNs in
C H A P T E R S I X
P a g e | 231
TOPAS®. However, as shown by the loss of fluorescence in Figure 73, 131 still has a
poor performance in the photo-oxidative environment compared to 114.
Figure 74: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) of 116
doped in PTMSP (-■-) or TOPAS (-♦-) films with respect to UV ageing time (hours)
The radical production of PTMSP in a photo-oxidative environment is compared
against TOPAS® by the films being doped with PFN 116. PFN 116 is used to detect
the number of radicals produced by each degrading system by an increase of
fluorescence. This increase of fluorescence is shown in Figure 74. There is a rapid
increase of fluorescence by PFN 116 doped in PTMSP films compared TOPAS® film.
This confirms that the larger radical production within the polymer films results in
poorer preforming PFNs as shown by the fast fluorescence switch on followed by the
fluorescence drop off.
C H A P T E R S I X
P a g e | 232
6.3.3.2. Thermo-Oxidative Degradation of TOPAS® Films
Figure 75: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) for
TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568
nm) with respect to ageing time (hours) at 70°C.
When the films were exposed to a dark 70°C oven, they showed no signs of
degradation. Like PTMSP, it is because the TOPAS® films are more stable in this
environment and therefore there is less radical attack on the fluorophore.
6.4. Conclusion
The focus of this study was to synthesise a new group of photo-stable PFNs using a
Ferrari red pigment base. Although all literature appeared promising, the perylene
diimide based PFN was found to still be the more photo-stable in comparison. While
not proven, it was suspected that solubilising this pigment may have decreased its
stability due to the introduction of the weaker amide bond. Unfortunately, due to
previous testing methods, solubility of PFNs is needed for consistency throughout the
testing and this group of compounds were not investigated further.
C H A P T E R S E V E N
P a g e | 233
7. CONCLUSIONS AND FUTURE WORK
7.1. Conclusions
This PhD project has advanced knowledge in the area of photo-stable profluorescent
nitroxides. With particular focus on the detection of photo-oxidative induced
degradation via radical mediation using photo-stable profluorescent nitroxides.
Although the thesis did not focus only on the synthesis of the novel PFNs, it was the
most challenging aspect of the project. The difficultly came from the limited solubility
of the perylene diimide (PDI) core, therefore purification was tedious and generally
unsuccessful. Unsymmetrical perylene diimide were achieved via one pot mixed
synthesis, the maximum yield could only be statistical. Synthesis of the corresponding
methoxyamines was also challenging, with the perylene diimide PFN only being
selectively soluble in DMSO. Therefore, the deprotection of the methyl group to
liberate the nitroxide moiety was groundbreaking. Synthesis was moved away from
PDI PFNs with developments in bay region substitution. This resulted in dramatic
solubility in most organic solvents and these perylene diimide and naphthalimide
based PFN were then the focus for the rest of this thesis.
The attention then moved to the stability of these newly synthesised PFNs. The liquid
model photo-degradation experiment by the Hereus Suntest in cyclohexane was the
first evidence that all these novel PFNs were more photo-stable than the successful
BPEA PFN. PFNs doped in the polymer material, PTMSP showed the nitroxide
probe’s ability to switch on and report damage occurring in the degrading film.
However, degradation in the Heraeus Suntest instrument was too severe. This resulted
in TOPAS® being used due to its higher stability under the testing conditions and its
C H A P T E R S E V E N
P a g e | 234
transparency. The stability of the TOPAS® films resulted in higher stability of the
PFNs due to there being less radical attack on the fluorophores of the PFNs. It was
determined that perylenediimide-incorporated PFNs are more photo-stable than
naphthalimide PFNs in both the PTMSP and TOPAS® films. It was also determined
that the nitroxide-containing compounds have higher stability in the photo-oxidative
environment over their non-radical analogues. The alkyne-linked perylenediimide
PFN has an impressive switch on ability when exposed to photo-induced radicals, and
it is the most effective PFN probe of the group tested.
Accelerated weathering in the laboratory experiments proved to yield similar trends to
true weathering effects in a Brisbane summer. As previously shown, the radical
production of the degrading polymer system is the major effect on the serviceable
lifetime of the PFN. As the most successful PFN, the alkyne-linked perylenediimide
PFN indicated that TOPAS® degradation via radical production is only affected by
UV exposure. However, other effects were shown by ATR on the rooftop samples
which weren’t seen on the films by Suntest exposure. Which indicate that PFN probes
cannot be used as an absolute probe for polymer degradation. However, the PFN
appears to degrade at a similar rate if the UV exposure is kept the same.
It was concluded that the mechanism of the PFN is not affected by the addition of
radical trappers or UV absorbers which are often present in paint samples. Addition of
additives made the serviceable lifetime of the PFN tuneable depending on
concentration. Higher stability on the degrading film resulted in higher stability of the
PFN. The nitroxide moiety on the PFN was not only an antioxidant to its own
fluorophore but it was an antioxidant to the TOPAS® film too. However, once the
C H A P T E R S E V E N
P a g e | 235
nitroxide moiety was removed, the trapped PFN became a prodegradant via the
production of singlet oxygen.
FTIR-ATR is a well-known technique to detect polymer degradation. However, when
used in this thesis, it lacked sensitivity at the early stages of degradation and it was not
reproducible. It highlighted the benefit of PFN technology due to their sensitivity and
reproducibly as a probe for early detection of polymer degradation. With synthesis of
these novel photo-stable profluorescent nitroxide probes, we now can detect
degradation in harsh environments, such as photo-oxidative environments without the
probe failure.
7.2. Future Work
This project fragments into two distinct areas, synthesis and analysis. When focusing
on the synthesis, there are three distinct focuses; changing of the nitroxide; changing
the location of the nitroxide; and changing of the linker, which joins the nitroxide to
the fluorophore. This would allow several other elements of the PFN to be tested.
C H A P T E R S E V E N
P a g e | 236
Figure 76: Synthetic targets for varying the perylene diimide PFN
At the start of the project, the focus was addition of the nitroxide through the imide
bond but there were complications with low and variable yields, difficult purification,
and low solubility. Structure 136 continues the focus of the imide formation but with
addition of solubilising groups to the bay region. Due to the perylene diimide structure,
there are multiple points for addition around the bay region. With four solubilising
groups, compound 137, would have increased solubility, with potential for appealing
physical properties such as an increased quantum yield.
C H A P T E R S E V E N
P a g e | 237
Figure 77: Different potential nitroxides for perylene diimide PFNs
All PFNs synthesised throughout the project used TMIO as its nitroxide. There are
several known stable nitroxides which could be feasible. Using the ethyl nitroxide,
TEIO could make the more sensitive probe, compound 138. This would allow only
small radicals to be trapped over longer reactive polymer chains. TEMPO derivatives
139 also have many benefits such as Denisov mechanism, which would add to the
antioxidant effect of the nitroxide on the PFN during polymer degradation.
C H A P T E R S E V E N
P a g e | 238
Figure 78: Potential synthetic goals for photo-stable PFNs
The final aspect would be changing the linker. It was found that the alkyne linked
nitroxide was the most successful PFN, however this still has aspects which could be
improved. For example, the alkyne linker could be improved by coupling through a
Suzuki reaction, compound 140. Decreasing the distance between the nitroxide moiety
and the fluorophore is known to increase quenching character of the PFN. This linker
would also remove the reactivity of the alkyne to a more rigid carbon framework, 141.
This could be done by building the nitroxide moiety into the perylene frame. A similar
compound was synthesised by Blinco et al. using a naphthalene fluorophore, resulting
a successful azaphenalene PFN.106 Jiang et al. published a one pot Suzuki cross-
C H A P T E R S E V E N
P a g e | 239
coupling reaction and subsequent light-promoted cyclization to yield two regiospecific
pyridyl annelated bismides, 142.255 The product has a quantum yield of near one,
which would be beneficial for PFN quenching. The challenge would be in the synthesis
of the boronic acid nitroxide. Coronene, 143 are also shown to have high quantum
yields, Choi et al. showed the simple one pot reaction with similar conditions used in
a Suzuki-coupling which spontaneously cyclized to afford a coronene chromophore.256
The coronene reaction could be easily done, with all reagents being successfully made
and/or published. A graphene like perylene diimide compounds,144 was successfully
synthesised by Quin et al.257 With focus leaning towards nitroxide grafted carbon
fibre258 this will complement the current research nicely.258
C H A P T E R S E V E N
P a g e | 240
Figure 79: Synthetic route for potential new perylene diimide PFNs
The first generation of perylene diimide PFNs were abandoned due to poor solubility
and poor yields. The literature development of mild removal of the methoxy protecting
C H A P T E R S E V E N
P a g e | 241
group could improve the synthetic pathway. The pathway would include two extra
steps, however the low yielding methylation step in DMSO could be performed on the
smaller precursor molecule. Since PDI have high solubility in DCM, there is an
expected yield improvement and possible increase in selectivity which was seen during
formation of 115.
Only two factors were focussed on when determining the success of the PFNs
produced, high UV exposure and high temperature. When focusing on aircraft coatings
other factors must be considered, altitude, ranging pressures and, of course cooling
temperature. All of which can change the degradation pathway of the polymer and the
overall functionality of the material. However, this technology is not only limited to
aircraft coating, there should be a focus on all coatings which as exposed to the natural
elements, such as bridges and submarines. This would be interesting to detect all of
the effects of salt water and bacteria growth.
C H A P T E R E I G H T
P a g e | 242
8. REFERENCES
1. Peacock, A.,. C., A., Polymer Chemistry, Properties and Applications. Carl Hanser Verlag: Munich, 2006.
2. Stahl, G. A., A short history of polymer science. ACS Symp. Ser. 1981, 175 (Polym. Sci. Overview), 25-44.
3. Muzzarelli, R. A. A.; Boudrant, J.; Meyer, D.; Manno, N.; DeMarchis, M.; Paoletti, M. G., Current views on fungal chitin/chitosan, human chitinases, food preservation, glucans, pectins and inulin: A tribute to Henri Braconnot, precursor of the carbohydrate polymers science, on the chitin bicentennial. Carbohydr. Polym. 2012, 87 (2), 995-1012.
4. Seymour, R. B., Polymers are everywhere. J. Chem. Educ. 1988, 65 (4), 327.
5. Kaufmann, C. B., Leo H. Baekeland. ACS Symp. Ser. 2011, 1080 (100+ Years of Plastics: Leo Baekeland and Beyond).; 1-10.
6. Roylance, M.; Roylance, D. In Forms of polymer degradation: overview, CRC Press: 2014; pp 337-347.
7. PlasticsEurope, The compelling fact about plastics, An analysis of plastics production, demand and recovery for 2005 in Europe. Belgium, 2007.
8. PlasticsEurope Plastics- the Facts 2017; 2017.
9. PlasticsEurope The Complelling Facts about Plastics, the ananalysis of plastics production, demand and recovery for 2006 in Europe. ; Belgium, January, 2008.
10. PlasticsEurope An Analysis of European plastics production, demand and waste data; Belgium, 22/01/2015, 2014.
11. Vasile, C., Handbook of Polyolefins. 2000.CRC Press.
12. Edge, N. S. A. A. M., Fundamentals of Polymer Degradation and Stabilisation. Elsevier Science: Essex, England, 1992.
13. Pielchowski, K.; Njuguna, J.; Editors, Thermal Degradation of Polymeric Materials. Rapra: 2005; p 316.
14. Nicholson, J. W., The Chemistry of Polymers. RSC Publishing: Cambridge, 2012.
15. Gensler, R.; Plummer, C. J. G.; Kausch, H. H.; Kramer, E.; Pauquet, J. R.; Zweifel, H., Thermo-oxidative degradation of isotactic polypropylene at high temperatures: phenolic antioxidants versus HAS. Polym. Degrad. Stab. 2000, 67 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 195-208.
C H A P T E R E I G H T
P a g e | 243
16. Gijsman, P.; Sampers, J., Oxygen uptake measurements to identify the cause of unexpected differences between accelerated and outdoor weathering. Angew. Makromol. Chem. 1998, 261-262 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 77-82.
17. Sampers, J., Importance of weathering factors other than UV radiation and temperature in outdoor exposure. Polym. Degrad. Stab. 2002, 76 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 455-465.
18. Halliwell, S. M., Weathering of Polymers. iSmithers Rapra Publishing: 1992.
19. Sims, A. D. A. D., Weathering of Polymers. Applied Science: Essex, UK, 1983.
20. Allen, N. S.; Edge, M.; Bellobono, I. R.; Selli, E.; Editors, Current Trends in Polymer Photochemistry. Horwood: 1995; p 382.
21. Gijsman, P., The long-term stability of polyolefins. Technische Universiteit Eindhoven: Eindhoven, 1994.
22. Calhoun, A. P. A., Polymer Chemstry, Properties and Applications. Hanser 2006.
23. Gijsman, P.; Meijers, G.; Vitarelli, G., Comparison of the UV-degradation chemistry of polypropylene, polyethylene, polyamide 6 and polybutylene terephthalate. Polym. Degrad. Stab. 1999, 65 (3), 433-441.
24. Pospisil, J.; Nespurek, S., Photostabilization of coatings. Mechanisms and performance. Prog. Polym. Sci. 2000, 25 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 1261-1335.
25. Fraisse, F.; Kumar, A.; Commereuc, S.; Verney, V., Photo-oxidation of polymers: validation of oxygen uptake and relationship with extent of hydroperoxidation. J. Appl. Polym. Sci. 2006, 99 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 2238-2244.
26. Parker, L. Ocean Trash: 5.25 Trillion Pieces and Counting, but Big Questions Remain. http://news.nationalgeographic.com/news/2015/01/150109-oceans-plastic-sea-trash-science-marine-debris.
27. Marcus Eriksen , L. C. M. L., Henry S. Carson, Martin Thiel, Charles J. Moore, Jose C. Borerro, Francois Galgani, Peter G. Ryan, Julia Reisser, Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLoS One December 10, 2014.
28. Cózar, A.; Echevarría, F.; González-Gordillo, J. I.; Irigoien, X.; Úbeda, B.; Hernández-León, S.; Palma, Á. T.; Navarro, S.; García-de-Lomas, J.; Ruiz, A.; Fernández-de-Puelles, M. L.; Duarte, C. M., Plastic debris in the open ocean. Proceedings of the National Academy of Sciences 2014, 111 (28), 10239-10244.
29. Singh, G. O.; Malshe, V. C., Photodegradation of polymers, relevance for a coating chemist (part 2). Pop. Plast. Packag. 2010, 55 (7), 39-44, 49-54.
30. Salt, D., Making packaging greener: biodegradable plastics. Chem. Aust. 2002, 69 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 15-17.
C H A P T E R E I G H T
P a g e | 244
31. Hamad, K.; Kaseem, M.; Ko, Y. G.; Deri, F., Biodegradable polymer blends and composites: An overview. Polym. Sci., Ser. A 2014, 56 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 812-829.
32. Doppalapudi, S.; Jain, A.; Khan, W.; Domb, A. J., Biodegradable polymers-an overview. Polym. Adv. Technol. 2014, 25 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 427-435.
33. Paterson, M. J.; Robb, M. A.; Blancafort, L.; DeBellis, A. D., Theoretical Study of Benzotriazole UV Photostability: Ultrafast Deactivation through Coupled Proton and Electron Transfer Triggered by a Charge-Transfer State. Journal of the American Chemical Society 2004, 126 (9), 2912-2922.
34. Denisov, E. T., Mechanism of regeneration of hindered nitroxyl and aromatic amines. Polym. Degrad. Stab. 1989, 25 (2-4), 209-215.
35. Micallef, A. S.; Blinco, J. P.; George, G. A.; Reid, D. A.; Rizzardo, E.; Thang, S. H.; Bottle, S. E., The application of a novel profluorescent nitroxide to monitor thermo-oxidative degradation of polypropylene. Polym. Degrad. Stab. 2005, 89 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 427-435.
36. Tebben, L.; Studer, A., Nitroxides: Applications in Synthesis and in Polymer Chemistry. Angew. Chem., Int. Ed. 2011, 50 (22), 5034-5068.
37. Lebedev, O. L.; Kazarnovskii, S. N., Intermediate products of oxidation of amines by pertungstate. Tr. Khim. Khim. Tekhnol. 1959, 2, 649-65.
38. Gijsman, P. In Photostabilisation of polymer materials, John Wiley & Sons, Inc.: 2010; pp 627-679.
39. Goldstein, S.; Samuni, A. In Biologically relevant chemistry of nitroxides, John Wiley & Sons Ltd.: 2010; pp 567-578.
40. Berliner, L. J. In History of the use of nitroxides (aminoxyl radicals) in biochemistry: past, present and future of spin label and probe method, InTech: 2012; pp 3-24.
41. Nicolas, J.; Guillaneuf, Y.; Lefay, C.; Bertin, D.; Gigmes, D.; Charleux, B., Nitroxide-mediated polymerization. Prog. Polym. Sci. 2013, 38 (1), 63-235.
42. Stone, T. J.; Buckman, T.; Nordio, P. L.; McConnell, H. M., Spin-labeled biomolecules. Proc. Natl. Acad. Sci. U. S. A. 1965, 54 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1010-17.
43. Likhtenshtein, G. I., Nitroxides: 170 years of history in biology and biomedicine. Int. Res. J. Pure Appl. Chem. 2015, 8 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1-18.
44. Novak, I.; Harrison, L. J.; Kovac, B.; Pratt, L. M., Electronic Structure of Persistent Radicals: Nitroxides. Journal of Organic Chemistry 2004, 69 (22), 7628-7634.
45. Volodarsky, L. B.; Reznikov, V. A.; Ovcharenko, V. I., Synthetic Chemistry of Stable Nitroxides. CRC: 1994; p 240.
C H A P T E R E I G H T
P a g e | 245
46. Brik, M.-E., Chemistry of persistent free bi- and polyradicals. Heterocycles 1995, 41 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 2827-73.
47. Ingold, K. U.; Adamic, K.; Bowman, D. F.; Gillan, T., Kinetic applications of electron paramagnetic resonance spectroscopy. I. Self-reactions of diethyl nitroxide radicals. J. Amer. Chem. Soc. 1971, 93 (4), 902-8.
48. Bowman, D. F.; Gillan, T.; Ingold, K. U., Kinetic applications of electron paramagnetic resonance spectroscopy. III. Self-reactions of dialkyl nitroxide radicals. J. Amer. Chem. Soc. 1971, 93 (24), 6555-61.
49. Keana, J. F. W., Newer aspects of the synthesis and chemistry of nitroxide spin labels. Chem. Rev. 1978, 78 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 37-64.
50. Forrester, A. R.; Thomson, R. H.; Luckhurst, G. R., Nitroxide radicals. III. Formation of mononitroxides from binitrones. J. Chem. Soc. B 1968, (11), 1311-15.
51. Briere, R.; Rassat, A., Nitroxides. LXVIII. Synthesis and kinetic study of the decomposition of tert-butyl isopropyl nitroxide. Isotopic effect. Tetrahedron 1976, 32 (23), 2891-8.
52. Naik, N.; Braslau, R., Synthesis and applications of optically active nitroxides. Tetrahedron 1998, 54 (5/6), 667-696.
53. Fairfull-Smith, K. E.; Bottle, S. E., The synthesis and physical properties of novel polyaromatic profluorescent isoindoline nitroxide probes. Eur. J. Org. Chem. 2008, (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 5391-5400.
54. Sholle, V. D.; Krinitskaya, L. A.; Rozantsev, E. G., Unusual products from oxidation of tertiary amine. Izv. Akad. Nauk SSSR, Ser. Khim. 1969, (1), 149-51.
55. Rozantsev, E. G.; Sholle, V. D., Synthesis and reactions of stable nitroxyl radicals. I. Synthesis. Synthesis 1971, (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 190-202.
56. Fairfull-Smith, K. E.; Blinco, J. P.; Keddie, D. J.; George, G. A.; Bottle, S. E., A Novel profluorescent dinitroxide for imaging polypropylene degradation. Macromolecules 2008, 41 (Copyright (C) 2010 American Chemical Society (ACS). All Rights Reserved.), 1577-1580.
57. Griffiths, P. G.; Rizzardo, E.; Solomon, D. H., Quantitative studies on free radical reactions with the scavenger 1,1,3,3-tetramethylisoindolinyl-2-oxy. Tetrahedron Lett. 1982, 23 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 1309-12.
58. Beckwith, A. L. J.; Bowry, V. W.; Ingold, K. U., Kinetics of nitroxide radical trapping. 1. Solvent effects. Journal of the American Chemical Society 1992, 114 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 4983-92.
59. Chateauneuf, J.; Lusztyk, J.; Ingold, K. U., Absolute rate constants for the reactions of some carbon-centered radicals with 2,2,6,6-tetramethyl-1-piperidinoxyl. Journal of Organic Chemistry 1988, 53 (8), 1629-32.
60. Bowry, V. W.; Ingold, K. U., Kinetics of nitroxide radical trapping. 2. Structural effects. Journal of the American Chemical Society 1992, 114 (13), 4992-6.
C H A P T E R E I G H T
P a g e | 246
61. Green, S. A.; Simpson, D. J.; Zhou, G.; Ho, P. S.; Blough, N. V., Intramolecular quenching of excited singlet states by stable nitroxyl radicals. Journal of the American Chemical Society 1990, 112 (20), 7337-46.
62. Herbelin, S. E.; Blough, N. V., Intramolecular Quenching of Excited Singlet States in a Series of Fluorescamine- Derivatized Nitroxides. J. Phys. Chem. B 1998, 102 (42), 8170-8176.
63. Schulman, A. S. A. S. G., Introduction to Fluorescence Spectoscopy. John Wiley and Sons, Inc: New York, 1999.
64. Blinco, J. P.; Fairfull-Smith, K. E.; Morrow, B. J.; Bottle, S. E., Profluorescent nitroxides as sensitive probes of oxidative change and free radical reactions. Aust. J. Chem. 2011, 64 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 373-389.
65. Likhtenstein, G. I.; Ishii, K.; Nakatsuji, S. i., Dual chromophore-nitroxides: novel molecular probes, photochemical and photophysical models and magnetic materials. Photochem. Photobiol. 2007, 83 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 871-881.
66. Blough, N. V.; Simpson, D. J., Chemically mediated fluorescence yield switching in nitroxide-fluorophore adducts: optical sensors of radical/redox reactions. Journal of the American Chemical Society 1988, 110 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 1915-17.
67. Stryer, L.; Griffith, O. H., A spin-labeled hapten. Proc. Natl. Acad. Sci. U. S. A. 1965, 54 (6), 1785-91.
68. Bystryak, I. M.; Likhtenshtein, G. I.; Kotel'nikov, A. I.; Hankovskii, H. O.; Hideg, K., Effect of solvent molecular dynamics on the photochemical reduction of nitroxyl radicals. Zh. Fiz. Khim. 1986, 60 (11), 2796-802.
69. Ahn, H.-Y.; Fairfull-Smith, K. E.; Morrow, B. J.; Lussini, V.; Kim, B.; Bondar, M. V.; Bottle, S. E.; Belfield, K. D., Two-photon fluorescence microscopy imaging of cellular oxidative stress using profluorescent nitroxides. Journal of the American Chemical Society 2012, 134 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 4721-4730.
70. Lozinsky, E.; Martin, V. V.; Berezina, T. A.; Shames, A. I.; Weis, A. L.; Likhtenshtein, G. I., Dual fluorophore-nitroxide probes for analysis of vitamin C in biological liquids. J. Biochem. Biophys. Methods 1999, 38 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 29-42.
71. Vogel, V. R.; Rubtsova, E. T.; Likhtenshtein, G. I.; Hideg, K., Factors affecting photoinduced electron transfer in a donor-acceptor pair (D-A) incorporated into bovine serum albumin. J. Photochem. Photobiol., A 1994, 83 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 229-36.
72. Braslau, R.; Rivera, F.; Lilie, E.; Cottman, M., Urushiol Detection using a Profluorescent Nitroxide. Journal of Organic Chemistry 2013, 78 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 238-245.
73. Ivan, M. G.; Scaiano, J. C., A new approach for the detection of carbon-centered radicals in enzymatic processes using prefluorescent probes. Photochem. Photobiol. 2003, 78 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 416-419.
C H A P T E R E I G H T
P a g e | 247
74. Cao, L.; Wu, Q.; Li, Q.; Shao, S.; Guo, Y., Visualizing the changes in the cellular redox environment using a novel profluorescent rhodamine nitroxide probe. New J. Chem. 2013, 37 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 2991-2994.
75. Barzegar Amiri Olia, M.; Zavras, A.; Schiesser, C. H.; Alexander, S.-A., Blue 'turn-on' fluorescent probes for the direct detection of free radicals and nitric oxide in Pseudomonas aeruginosa biofilms. Org. Biomol. Chem. 2016, 14 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 2272-2281.
76. Rayner, C. L.; Bottle, S. E.; Gole, G. A.; Ward, M. S.; Barnett, N. L., Real-time quantification of oxidative stress and the protective effect of nitroxide antioxidants. Neurochem. Int. 2016, 92 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1-12.
77. Rayner, C. L.; Gole, G. A.; Bottle, S. E.; Barnett, N. L., Dynamic, in vivo, real-time detection of retinal oxidative status in a model of elevated intraocular pressure using a novel, reversibly responsive, profluorescent nitroxide probe. Exp. Eye Res. 2014, 129 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 48-56.
78. Bognar, B.; Jeko, J.; Kalai, T.; Hideg, K., Synthesis of redox sensitive dyes based on a combination of long wavelength emitting fluorophores and nitroxides. Dyes Pigm. 2010, 87 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 218-224.
79. Bian, Z.-Y.; Guo, X.-Q.; Zhao, Y.-B.; Du, J.-O., Probing the hydroxyl radical-mediated reactivity of peroxynitrite by a spin-labeling fluorophore. Anal. Sci. 2005, 21 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 553-559.
80. Yang, X. F.; Guo, X. Q., Study of nitroxide-linked naphthalene as a fluorescence probe for hydroxyl radicals. Analytica Chimica Acta 2001, 434 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 169-177.
81. Yang, X.-F.; Guo, X.-Q., Investigation of the anthracene-nitroxide hybrid molecule as a probe for hydroxyl radicals. Analyst (Cambridge, U. K.) 2001, 126 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1800-1804.
82. Jia, M.; Tang, Y.; Lam, Y.-F.; Green, S. A.; Blough, N. V., Prefluorescent nitroxide probe for the highly sensitive determination of peroxyl and other radical oxidants. Anal. Chem. (Washington, DC, U. S.) 2009, 81 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 8033-8040.
83. Crilley, L. R.; Knibbs, L. D.; Miljevic, B.; Cong, X.; Fairfull-Smith, K. E.; Bottle, S. E.; Ristovski, Z. D.; Ayoko, G. A.; Morawska, L., Concentration and oxidative potential of on-road particle emissions and their relationship with traffic composition: Relevance to exposure assessment. Atmos. Environ. 2012, 59, 533-539.
84. Hedayat, F.; Stevanovic, S.; Milic, A.; Miljevic, B.; Nabi, M. N.; Zare, A.; Bottle, S. E.; Brown, R. J.; Ristovski, Z. D., Influence of oxygen content of the certain types of biodiesels on particulate oxidative potential. Sci. Total Environ. 2016, 545-546, 381-388.
85. Miljevic, B.; Fairfull-Smith, K. E.; Bottle, S. E.; Ristovski, Z. D., The application of profluorescent nitroxides to detect reactive oxygen species derived from combustion-generated particulate matter: Cigarette smoke. A case study. Atmos. Environ. 2010, 44 (18), 2224-2230.
C H A P T E R E I G H T
P a g e | 248
86. Miljevic, B.; Heringa, M. F.; Keller, A.; Meyer, N. K.; Good, J.; Lauber, A.; DeCarlo, P. F.; Fairfull-Smith, K. E.; Nussbaumer, T.; Burtscher, H.; Prevot, A. S. H.; Baltensperger, U.; Bottle, S. E.; Ristovski, Z. D., Oxidative Potential of Logwood and Pellet Burning Particles Assessed by a Novel Profluorescent Nitroxide Probe. Environ. Sci. Technol. 2010, 44 (17), 6601-6607.
87. Simpson, E. M.; Ristovski, Z. D.; Bottle, S. E.; Fairfull-Smith, K. E.; Blinco, J. P., Modular design of profluorescent polymer sensors. Polym. Chem. 2015, 6 (15), 2962-2969.
88. Stevanovic, S.; Miljevic, B.; Eaglesham, G. K.; Bottle, S. E.; Ristovski, Z. D.; Fairfull-Smith, K. E., The Use of a Nitroxide Probe in DMSO to Capture Free Radicals in Particulate Pollution. Eur. J. Org. Chem. 2012, 2012 (30), 5908-5912.
89. Stevanovic, S.; Miljevic, B.; Surawski, N. C.; Fairfull-Smith, K. E.; Bottle, S. E.; Brown, R.; Ristovski, Z. D., Influence of oxygenated organic aerosols on oxidative potential of diesel and biodiesel particulate matter. Environ. Sci. Technol. 2013, 47 (14), 7655-7662.
90. Stevanovic, S.; Ristovski, Z. D.; Miljevic, B.; Fairfull-Smith, K. E.; Bottle, S. E., Application of profluorescent nitroxides for measurements of oxidative capacity of combustion generated particles. Chem. Ind. Chem. Eng. Q. 2012, 18 (4/2), 653-659.
91. Surawski, N. C.; Miljevic, B.; Ayoko, G. A.; Elbagir, S.; Stevanovic, S.; Fairfull-Smith, K. E.; Bottle, S. E.; Ristovski, Z. D., Physicochemical Characterization of Particulate Emissions from a Compression Ignition Engine: The Influence of Biodiesel Feedstock. Environ. Sci. Technol. 2011, 45 (24), 10337-10343.
92. Surawski, N. C.; Miljevic, B.; Roberts, B. A.; Modini, R. L.; Situ, R.; Brown, R. J.; Bottle, S. E.; Ristovski, Z. D., Particle Emissions, Volatility, and Toxicity from an Ethanol Fumigated Compression Ignition Engine. Environ. Sci. Technol. 2010, 44 (1), 229-235.
93. Sleiman, M.; Destaillats, H.; Gundel, L. A., Solid-phase supported profluorescent nitroxide probe for the determination of aerosol-borne reactive oxygen species. Talanta 2013, 116 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1033-1039.
94. Ballesteros, O. G.; Maretti, L.; Sastre, R.; Scaiano, J. C., Kinetics of Cap Separation in Nitroxide-Regulated "Living" Free Radical Polymerization: Application of a Novel Methodology Involving a Prefluorescent Nitroxide Switch. Macromolecules 2001, 34 (18), 6184-6187.
95. Moad, G.; Shipp, D. A.; Smith, T. A.; Solomon, D. H., Measurements of primary radical concentrations generated by pulsed laser photolysis using fluorescence detection. J. Phys. Chem. A 1999, 103 (33), 6580-6586.
96. Turro, N. J.; Lem, G.; Zavarine, I. S., A Living Free Radical Exchange Reaction for the Preparation of Photoactive End-Labeled Monodisperse Polymers. Macromolecules 2000, 33 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 9782-9785.
97. Colwell, J. M.; Blinco, J. P.; Hulbert, C.; Fairfull-Smith, K. E.; Bottle, S. E., A Profluorescent Azaphenalene Nitroxide for Nitroxide-Mediated Polymerization. Aust. J. Chem. 2011, 64 (4), 426-432.
98. Colwell, J. M.; Nikolic, M. A. L.; Bottle, S. E.; George, G. A., Sensitive luminescence techniques to study the early stages of polymer oxidation. Polym. Degrad. Stab. 2013, 98 (12), 2436-2444.
C H A P T E R E I G H T
P a g e | 249
99. Colwell, J. M.; Walker, J. R.; Blinco, J. P.; Micallef, A. S.; George, G. A.; Bottle, S. E., Profluorescent nitroxides: Thermo-oxidation sensors for stabilised polypropylene. Polym. Degrad. Stab. 2010, 95 (10), 2101-2109.
100. Moghaddam, L.; Blinco, J. P.; Colwell, J. M.; Halley, P. J.; Bottle, S. E.; Fredericks, P. M.; George, G. A., Investigation of polypropylene degradation during melt processing using a profluorescent nitroxide probe: A laboratory-scale study. Polym. Degrad. Stab. 2011, 96 (4), 455-461.
101. Blinco, J. P.; Keddie, D. J.; Wade, T.; Barker, P. J.; George, G. A.; Bottle, S. E., Profluorescent nitroxides: Sensors and stabilizers of radical-mediated oxidative damage. Polym. Degrad. Stab. 2008, 93 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 1613-1618.
102. Coenjarts, C.; Garcia, O.; Llauger, L.; Palfreyman, J.; Vinette, A. L.; Scaiano, J. C., Mapping photogenerated radicals in thin polymer films: Fluorescence imaging using a prefluorescent radical probe. Journal of the American Chemical Society 2003, 125 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 620-621.
103. Aspee, A.; Garcia, O.; Maretti, L.; Sastre, R.; Scaiano, J. C., Free Radical Reactions in Poly(methyl methacrylate) Films Monitored Using a Prefluorescent Quinoline-TEMPO Sensor. Macromolecules 2003, 36 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 3550-3556.
104. Blinco, J. P. The synthesis and application of novel profluorescent nitroxides as probes for polymer degradation. PhD, 2008.
105. Keddie, D. J.; Fairfull-Smith, K. E.; Bottle, S. E., The palladium-catalyzed copper-free Sonogashira coupling of isoindoline nitroxides: a convenient route to robust profluorescent carbon-carbon frameworks. Org. Biomol. Chem. 2008, 6 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 3135-3143.
106. Blinco, J. P.; McMurtrie, J. C.; Bottle, S. E., The first example of an azaphenalene pro-fluorescent nitroxide. Eur. J. Org. Chem. 2007, (28), 4638-4641.
107. Gerlock, J. L.; Zacmanidis, P. J.; Bauer, D. R.; Simpson, D. J.; Blough, N. V.; Salmeen, I. T., Fluorescence detection of free radicals by nitroxide scavenging. Free Radical Res. Commun. 1990, 10 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 119-21.
108. Danko, M.; Chmela, S.; Hrdlovic, P., Photochemical stability and photostabilizing efficiency of anthracene/hindered amine stabilizers in polymer matrices. Polym. Degrad. Stab. 2002, 79 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 333-343.
109. Bognar, B.; Osz, E.; Hideg, K.; Kalai, T., Synthesis of new double (spin and fluorescence) sensor reagents and labels. J. Heterocycl. Chem. 2006, 43 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 81-86.
110. Blinco, J. P.; Fairfull-Smith, K. E.; Micallef, A. S.; Bottle, S. E., Highly efficient, stoichiometric radical exchange reactions using isoindoline profluorescent nitroxides. Polym. Chem. 2010, 1 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1009-1012.
C H A P T E R E I G H T
P a g e | 250
111. Chattopadhyay, S. K.; Das, P. K.; Hug, G. L., Photoprocesses in diphenylpolyenes. 2. Excited-state interactions with stable free radicals. Journal of the American Chemical Society 1983, 105 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 6205-10.
112. Kaiser, R. D.; London, E., Location of Diphenylhexatriene (DPH) and Its Derivatives within Membranes: Comparison of Different Fluorescence Quenching Analyses of Membrane Depth. Biochemistry 1998, 37 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 8180-8190.
113. Sato, S.; Tsunoda, M.; Suzuki, M.; Kutsuna, M.; Takido-uchi, K.; Shindo, M.; Mizuguchi, H.; Obara, H.; Ohya, H., Synthesis and spectral properties of polymethine-cyanine dye-nitroxide radical hybrid compounds for use as fluorescence probes to monitor reducing species and radicals. Spectrochim Acta A Mol Biomol Spectrosc 2009, 71 (Copyright (C) 2016 U.S. National Library of Medicine.), 2030-9.
114. Sato, S.; Suzuki, M.; Soma, T.; Tsunoda, M., Synthesis and properties of umbelliferone-nitroxide radical hybrid compounds as fluorescence and spin-label probes. Spectrochim. Acta, Part A 2008, 70A (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 799-804.
115. Bueno, C.; Mikelsons, L.; Maretti, L.; Scaiano, J. C.; Aspee, A., Photophysical properties of the prefluorescent nitroxide probes QT and C343T. Photochem. Photobiol. 2008, 84 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1535-1542.
116. Hrdlovic, P.; Chmela, S.; Danko, M.; Sarakha, M.; Guyot, G., Spectral Properties of Probes Containing Benzothioxanthene Chromophore Linked with Hindered Amine in Solution and in Polymer Matrices. J. Fluoresc. 2008, 18 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 393-402.
117. Goto, A.; Scaiano, J. C.; Maretti, L., Photolysis of an alkoxyamine using intramolecular energy transfer from a quinoline antenna - towards photo-induced living radical polymerization. Photochem. Photobiol. Sci. 2007, 6 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 833-835.
118. Morrow, B. J.; Keddie, D. J.; Gueven, N.; Lavin, M. F.; Bottle, S. E., A novel profluorescent nitroxide as a sensitive probe for the cellular redox environment. Free Radical Biol. Med. 2010, 49 (1), 67-76.
119. Kalai, T.; Hideg, E.; Jeko, J.; Hideg, K., Synthesis of paramagnetic BODIPY dyes as new double (spin and fluorescence) sensors. Tetrahedron Lett. 2003, 44 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 8497-8499.
120. Kalai, T.; Hideg, K., Synthesis of new, BODIPY-based sensors and labels. Tetrahedron 2006, 62 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 10352-10360.
121. Kollar, J.; Hrdlovic, P.; Chmela, S., Synthesis and spectral characteristics of substituted 1,8-naphthalimides: Intramolecular quenching by mono-nitroxides. J. Photochem. Photobiol., A 2009, 204 (2-3), 191-199.
122. Gallas, K.; Knall, A.-C.; Scheicher, S. R.; Fast, D. E.; Saf, R.; Slugovc, C., A Modular Approach Towards Fluorescent pH and Ascorbic Acid Probes Based on Ring-Opening Metathesis Polymerization.
C H A P T E R E I G H T
P a g e | 251
Macromol. Chem. Phys. 2014, 215 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 76-81.
123. Sylvester, P. D.; Ryan, H. E.; Smith, C. D.; Micallef, A. S.; Schiesser, C. H.; Wille, U., Perylene-based profluorescent nitroxides for the rapid monitoring of polyester degradation upon weathering: An assessment. Polym. Degrad. Stab. 2013, 98 (10), 2054-2062.
124. Hunger, W. H. a. K., Industrial Organic Pigments. A Wiley Company: 1997.
125. Huang, C.; Barlow, S.; Marder, S. R., Perylene-3,4,9,10-tetracarboxylic Acid Diimides: Synthesis, Physical Properties, and Use in Organic Electronics. Journal of Organic Chemistry 2011, 76 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 2386-2407.
126. Wescott, L. D.; Mattern, D. L., Donor-σ-Acceptor Molecules Incorporating a Nonadecyl-Swallowtailed Perylenediimide Acceptor. Journal of Organic Chemistry 2003, 68 (26), 10058-10066.
127. Wuerthner, F., Perylene bisimide dyes as versatile building blocks for functional supramolecular architectures. Chem. Commun. (Cambridge, U. K.) 2004, (14), 1564-1579.
128. Serin, J. M.; Brousmiche, D. W.; Frechet, J. M. J., Cascade energy transfer in a conformationally mobile multichromophoric dendrimer. Chem. Commun. (Cambridge, U. K.) 2002, (22), 2605-2607.
129. An, Z.; Yu, J.; Jones, S. C.; Barlow, S.; Yoo, S.; Domercq, B.; Prins, P.; Siebbeles, L. D. A.; Kippelen, B.; Marder, S. R., High electron mobility in room-temperature discotic liquid-crystalline perylene diimides. Adv. Mater. (Weinheim, Ger.) 2005, 17 (21), 2580-2583.
130. Jones, B. A.; Facchetti, A.; Wasielewski, M. R.; Marks, T. J., Tuning Orbital Energetics in Arylene Diimide Semiconductors. Materials Design for Ambient Stability of n-Type Charge Transport. Journal of the American Chemical Society 2007, 129 (49), 15259-15278.
131. Ford, W. E.; Kamat, P. V., Photochemistry of 3,4,9,10-perylenetetracarboxylic dianhydride dyes. 3. Singlet and triplet excited-state properties of the bis(2,5-di-tert-butylphenyl)imide derivative. J. Phys. Chem. 1987, 91 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 6373-80.
132. Choi, J.; Sakong, C.; Choi, J.-H.; Yoon, C.; Kim, J.-P., Synthesis and characterization of some perylene dyes for dye-based LCD color filters. Dyes Pigm. 2011, 90 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 82-88.
133. Langhals, H., Synthesis of highly pure perylene fluorescent dyes in large scale amounts - specific preparation of atropic isomers. Chem. Ber. 1985, 118 (11), 4641-45.
134. Boehm, A.; Arms, H.; Henning, G.; Blaschka, P. Aromatic derivatives of 3,4,9,10-perylenetetracarboxylic acids, dianhydrides, and diimides, their preparation and their use. DE19547209A1, 1997.
135. Hill, Z. B.; Rodovsky, D. B.; Leger, J. M.; Bartholomew, G. P., Synthesis and utilization of perylene-based n-type small molecules in light-emitting electrochemical cells. Chem. Commun. (Cambridge, U. K.) 2008, (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 6594-6596.
C H A P T E R E I G H T
P a g e | 252
136. Wurthner, F.; Sautter, A.; Schilling, J., Synthesis of diazadibenzoperylenes and characterization of their structural, optical, redox, and coordination properties. J. Org. Chem. 2002, 67 (Copyright (C) 2011 U.S. National Library of Medicine.), 3037-44.
137. Bottle, S. E.; Chand, U.; Micallef, A. S., Hydrogen abstraction from unactivated hydrocarbons using a photochemically excited isoindoline nitroxide. Chem. Lett. 1997, (9), 857-858.
138. Giroud, A. M.; Rassat, A., Nitroxides. LXXX. Synthesis of mono- and dinitroxide radicals derived from isoindoline. Bull. Soc. Chim. Fr. 1979, (1-2, Pt. 2), 48-55.
139. Griffiths, P. G.; Moad, G.; Rizzardo, E.; Solomon, D. H., Synthesis of the radical scavenger 1,1,3,3-tetramethylisoindolin-2-yloxyl. Aust. J. Chem. 1983, 36 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 397-401.
140. Bolton, R.; Gillies, D. G.; Sutcliffe, L. H.; Wu, X., An EPR and NMR study of some tetramethylisoindolin-2-yloxyl free radicals. Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry (1972-1999) 1993, (11), 2049-52.
141. Reid, D. A.; Bottle, S. E.; Micallef, A. S., The synthesis of water soluble isoindoline nitroxides and a pronitroxide hydroxylamine hydrochloride UV-VIS probe for free radicals. Chem. Commun. (Cambridge) 1998, (Copyright (C) 2015 American Chemical Society (ACS). All Rights Reserved.), 1907-1908.
142. Micallef, A. S.; Bott, R. C.; Bottle, S. E.; Smith, G.; White, J. M.; Matsuda, K.; Iwamura, H., Brominated isoindolines: precursors to functionalized nitroxides. Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry (1972-1999) 1999, (Copyright (C) 2015 American Chemical Society (ACS). All Rights Reserved.), 65-72.
143. Jayawardena, V. C.; Fairfull-Smith, K. E.; Bottle, S. E., Improving the Yield of the Exhaustive Grignard Alkylation of N-Benzylphthalimide. Aust. J. Chem. 2013, 66 (6), 619-625.
144. Thomas, K.; Chalmers, B. A.; Fairfull-Smith, K. E.; Bottle, S. E., Approaches to the Synthesis of a Water-Soluble Carboxy Nitroxide. Eur. J. Org. Chem. 2013, 2013 (5), 853-857.
145. Keddie, D. J.; Johnson, T. E.; Arnold, D. P.; Bottle, S. E., Synthesis of profluorescent isoindoline nitroxides via palladium-catalysed Heck alkenylation. Org. Biomol. Chem. 2005, 3 (14), 2593-8.
146. Manley-King, C. I.; Bergh, J. J.; Petzer, J. P., Inhibition of monoamine oxidase by C5-substituted phthalimide analogues. Bioorg. Med. Chem. 2011, 19 (16), 4829-4840.
147. Chalmers, B. A.; Morris, J. C.; Fairfull-Smith, K. E.; Grainger, R. S.; Bottle, S. E., A novel protecting group methodology for syntheses using nitroxides. Chem. Commun. (Cambridge, U. K.) 2013, 49 (88), 10382-10384.
148. Bottle, S. E.; Gillies, D. G.; Hughes, D. L.; Micallef, A. S.; Smirnov, A. I.; Sutcliffe, L. H., Synthesis, single crystal X-ray structure and W-band (95 GHz) EPR spectroscopy of a new anionic isoindoline aminoxyl: synthesis and characterization of some derivatives. Perkin 2 2000, (Copyright (C) 2015 American Chemical Society (ACS). All Rights Reserved.), 1285-1291.
149. Blinco, J. P.; Hodgson, J. L.; Morrow, B. J.; Walker, J. R.; Will, G. D.; Coote, M. L.; Bottle, S. E., Experimental and Theoretical Studies of the Redox Potentials of Cyclic Nitroxides. Journal of Organic
C H A P T E R E I G H T
P a g e | 253
Chemistry 2008, 73 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 6763-6771.
150. Bahr, J. L.; Yang, J.; Kosynkin, D. V.; Bronikowski, M. J.; Smalley, R. E.; Tour, J. M., Functionalization of carbon nanotubes by electrochemical reduction of aryl diazonium salts: A bucky paper electrode. Journal of the American Chemical Society 2001, 123 (27), 6536-6542.
151. Kaupp, G.; Herrmann, A.; Schmeyers, J., Waste-free chemistry of diazonium salts and benign separation of coupling products in solid salt reactions. Chem.--Eur. J. 2002, 8 (Copyright (C) 2013 American Chemical Society (ACS). All Rights Reserved.), 1395-1406.
152. Fairfull-Smith, K. E.; Debele, E. A.; Allen, J. P.; Pfrunder, M. C.; McMurtrie, J. C., Direct Iodination of Isoindolines and Isoindoline Nitroxides as Precursors to Functionalized Nitroxides. Eur. J. Org. Chem. 2013, 2013 (22), 4829-4835.
153. Schareina, T.; Zapf, A.; Maegerlein, W.; Mueller, N.; Beller, M., A state-of-the-art cyanation of aryl bromides: a novel and versatile copper catalyst system inspired by nature. Chem. - Eur. J. 2007, 13 (21), 6249-6254.
154. Dincalp, H.; Avcibasi, N.; Icli, S., Spectral properties and G-quadruplex DNA binding selectivities of a series of unsymmetrical perylene diimides. J. Photochem. Photobiol., A 2007, 185 (Copyright (C) 2010 American Chemical Society (ACS). All Rights Reserved.), 1-12.
155. Robb, M. J.; Newton, B.; Fors, B. P.; Hawker, C. J., One-Step Synthesis of Unsymmetrical N-Alkyl-N'-aryl Perylene Diimides. Journal of Organic Chemistry 2014, 79 (13), 6360-6365.
156. Pasaogullari, N.; Icil, H.; Demuth, M., Symmetrical and unsymmetrical perylene diimides: Their synthesis, photophysical and electrochemical properties. Dyes Pigm. 2005, 69 (Copyright (C) 2010 American Chemical Society (ACS). All Rights Reserved.), 118-127.
157. Rotstein, B. H.; Mourtada, R.; Kelley, S. O.; Yudin, A. K., Solvatochromic Reagents for Multicomponent Reactions and their Utility in the Development of Cell-Permeable Macrocyclic Peptide Vectors. Chem.--Eur. J. 2011, 17 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 12257-12261, S12257/1-S12257/47.
158. Hamel, M.; Simic, V.; Normand, S., Fluorescent 1,8-naphthalimides-containing polymers as plastic scintillators. An attempt for neutron-gamma discrimination. React. Funct. Polym. 2008, 68 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 1671-1681.
159. Kasha, M., Collisional perturbation of spin-orbital coupling and the mechanism of fluorescence quenching. A visual demonstration of the perturbation. J. Chem. Phys. 1952, 20, 71-4.
160. Davidson, R. S.; Bonneau, R.; Joussot-Dubien, J.; Trethewey, K. R., Intramolecular quenching of the excited singlet state of a naphthyl group by halogeno substituents. Chem. Phys. Lett. 1980, 74 (2), 318-20.
161. Martinho, J. M. G., Heavy-atom quenching of monomer and excimer pyrene fluorescence. J. Phys. Chem. 1989, 93 (18), 6687-92.
162. Dreeskamp, H.; Pabst, J., Thermally assisted and heavy-atom assisted intersystem crossing in meso-substituted anthracenes. Chem. Phys. Lett. 1979, 61 (2), 262-5.
C H A P T E R E I G H T
P a g e | 254
163. Coulson, D. R., Tetrakis(triphenylphosphine)palladium(0). Inorg. Synth. 1990, 28 (Reagents Transition Met. Complex Organomet. Synth.), 107-9.
164. Wurthner, F.; Stepanenko, V.; Chen, Z.; Saha-Moller, C. R.; Kocher, N.; Stalke, D., Preparation and characterization of regioisomerically pure 1,7-disubstituted perylene bisimide dyes. J. Org. Chem. 2004, 69 (Copyright (C) 2011 U.S. National Library of Medicine.), 7933-9.
165. Ahrens, M. J.; Sinks, L. E.; Rybtchinski, B.; Liu, W.; Jones, B. A.; Giaimo, J. M.; Gusev, A. V.; Goshe, A. J.; Tiede, D. M.; Wasielewski, M. R., Self-Assembly of Supramolecular Light-Harvesting Arrays from Covalent Multi-Chromophore Perylene-3,4:9,10-bis(dicarboximide) Building Blocks. Journal of the American Chemical Society 2004, 126 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 8284-8294.
166. Dubey, R. K.; Efimov, A.; Lemmetyinen, H., 1,7- And 1,6-Regioisomers of Diphenoxy and Dipyrrolidinyl Substituted Perylene Diimides: Synthesis, Separation, Characterization, and Comparison of Electrochemical and Optical Properties. Chem. Mater. 2011, 23 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 778-788.
167. Chan, K. S.; Li, X. Z.; Lee, S. Y., Ligand-Enhanced Aliphatic Carbon-Carbon Bond Activation of Nitroxides by Rhodium(II) Porphyrin. Organometallics 2010, 29 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 2850-2856.
168. Doyle, M. P.; Bryker, W. J., Alkyl nitrite-metal halide deamination reactions. 6. Direct synthesis of arenediazonium tetrafluoroborate salts from aromatic amines, tert-butyl nitrite, and boron trifluoride etherate in anhydrous media. Journal of Organic Chemistry 1979, 44 (9), 1572-4.
169. Snow, A. W.; Foos, E. E., Conversion of alcohols to thiols via tosylate intermediates. Synthesis 2003, (4), 509-512.
170. Ikeda, H.; Nishikawa, S.; Yamamoto, Y.; Ueno, A., Homotropic cooperativity of cyclodextrin dimer as an artificial hydrolase. J. Mol. Catal. A: Chem. 2010, 328 (1–2), 1-7.
171. Shahid, M.; Srivastava, P.; Misra, A., An efficient naphthalimide based fluorescent dyad (ANPI) for F- and Hg2+ mimicking OR, XNOR and INHIBIT logic functions. New J. Chem. 2011, 35 (8), 1690-1700.
172. Sowers, M. A.; McCombs, J. R.; Johnson, J. A.; Wang, Y.; Paletta, J. T.; Rajca, A.; Morton, S. W.; Dreaden, E. C.; Hammond, P. T.; Boska, M. D.; Ottaviani, M. F., Redox-responsive branched-bottlebrush polymers for in vivo MRI and fluorescence imaging. Nat Commun 2014, 5, 5460.
173. Giacobbe, E. M.; Mi, Q.; Colvin, M. T.; Cohen, B.; Ramanan, C.; Scott, A. M.; Yeganeh, S.; Marks, T. J.; Ratner, M. A.; Wasielewski, M. R., Ultrafast intersystem crossing and spin dynamics of photoexcited perylene-3,4:9,10-bis(dicarboximide) covalently linked to a nitroxide radical at fixed distances. Journal of the American Chemical Society 2009, 131 (10), 3700-3712.
174. Colvin, M. T.; Giacobbe, E. M.; Cohen, B.; Miura, T.; Scott, A. M.; Wasielewski, M. R., Competitive Electron Transfer and Enhanced Intersystem Crossing in Photoexcited Covalent TEMPO-Perylene-3,4:9,10-bis(dicarboximide) Dyads: Unusual Spin Polarization Resulting from the Radical-Triplet Interaction. J. Phys. Chem. A 2010, 114 (4), 1741-1748.
C H A P T E R E I G H T
P a g e | 255
175. Dyar, S. M.; Margulies, E. A.; Horwitz, N. E.; Brown, K. E.; Krzyaniak, M. D.; Wasielewski, M. R., Photogenerated Quartet State Formation in a Compact Ring-Fused Perylene-Nitroxide. J. Phys. Chem. B 2015, Ahead of Print.
176. Handa, N. V.; Shirtcliff, L. D.; Lavine, B. K.; Powell, D. R.; Berlin, D. K., 1,6- And 1,7-regioisomers of perylene tetracarboxylic dianhydride and diimide: The effects of neutral bay substituents on the electrochemical and structural properties. Phosphorus, Sulfur Silicon Relat. Elem. 2014, 189 (6), 738-752.
177. Nagao, Y., Synthesis and properties of perylene pigments. Prog. Org. Coat. 1997, 31 (1-2), 43-49.
178. Gosztola, D.; Niemczyk, M. P.; Svec, W.; Lukas, A. S.; Wasielewski, M. R., Excited Doublet States of Electrochemically Generated Aromatic Imide and Diimide Radical Anions. J. Phys. Chem. A 2000, 104 (28), 6545-6551.
179. Yang, J.-X.; Wang, X.-L.; Wang, X.-M.; Xu, L.-H., The synthesis and spectral properties of novel 4-phenylacetylene-1,8-naphthalimide derivatives. Dyes Pigm. 2005, 66 (1), 83-87.
180. Choppawa, T.; Sukwattanasinitt, M.; Sahasithiwat, S.; Ruangpornvisuti, V.; Rashatasakhon, P., Substituent effect on quantum efficiency in 4-aryloxy-N-(2',6'-diisopropylphenyl)-1,8-naphthalimides: Experimental and computational investigations. Dyes Pigm. 2014, 109, 175-180.
181. Berlman, I. B., Handbook of Fluorescence Spectra of Aromatic Molecules. 2nd ed. Academic: 1971; p 473 pp.
182. Jimenez, A. J.; Spanig, F.; Rodriguez-Morgade, M. S.; Ohkubo, K.; Fukuzumi, S.; Guldi, D. M.; Torres, T., A tightly coupled bis(zinc(II) phthalocyanine)-perylenediimide ensemble to yield long-lived radical ion pair states. Org. Lett. 2007, 9 (13), 2481-4.
183. Zhao, Y.; Wasielewski, M. R., 3,4:9,10-perylenebis(dicarboximide) chromophores that function as both electron donors and acceptors. Tetrahedron Lett. 1999, 40 (39), 7047-7050.
184. Aubry, J.-M.; Pierlot, C.; Rigaudy, J.; Schmidt, R., Reversible Binding of Oxygen to Aromatic Compounds. Acc. Chem. Res. 2003, 36 (9), 668-675.
185. Sanguineti, A.; Sassi, M.; Turrisi, R.; Ruffo, R.; Vaccaro, G.; Meinardi, F.; Beverina, L., High Stokes shift perylene dyes for luminescent solar concentrators. Chem. Commun. (Cambridge, U. K.) 2013, 49 (16), 1618-1620.
186. Colwell, J. M.; Khan, J. H.; Will, G.; Fairfull-Smith, K. E.; Bottle, S. E.; George, G. A.; Trueman, A., Prognostic tools for lifetime prediction of aircraft coatings: paint degradation. Adv. Mater. Res. 2010, 138 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 137-149.
187. Lussini, V. C.; Blinco, J. P.; Fairfull-Smith, K. E.; Bottle, S. E., Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability. Chem. - Eur. J. 2015, 21 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 18258-18268.
188. Celina, M.; George, G. A., Heterogeneous and homogeneous kinetic analyses of the thermal oxidation of polypropylene. Polym. Degrad. Stab. 1995, 50 (1), 89-99.
C H A P T E R E I G H T
P a g e | 256
189. Kishore, R. S. K.; Ravikumar, V.; Bernardinelli, G.; Sakai, N.; Matile, S., Rapid and mild synthesis of functionalized naphthalenediimides. Journal of Organic Chemistry 2008, 73 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 738-740.
190. Gallo, R.; Pegoraro, M.; Severini, F.; Ipsale, S.; Nisoli, E., Degradation of outdoor exposed poly(1-trimethylsilyl)-1-propyne. Polym. Degrad. Stab. 1997, 58 (3), 247-250.
191. Sato, S.; Ishiba, Y.; Wada, T.; Kanehashi, S.; Matsumoto, S.; Matsumoto, H.; Nagai, K., Hydrophilic molecular sieve surface layer formation in hydrophobic poly(1-trimethylsilyl-1-propyne) membranes. J. Membr. Sci. 2013, 429, 364-372.
192. Nagai, K.; Masuda, T.; Nakagawa, T.; Freeman, B. D.; Pinnau, I., Poly[1-(trimethylsilyl)-1-propyne] and related polymers: synthesis, properties and functions. Prog. Polym. Sci. 2001, 26 (5), 721-798.
193. Nakade, K.; Nagai, Y.; Ohishi, F., Photodegradation of some ethylene-norbornene random copolymers. Polym. Degrad. Stab. 2010, 95 (12), 2654-2658.
194. Perrin, D. D.; Armarego, W. L. F., Purification of Laboratory Chemicals (Second Edition). Pergamon Press: Oxford, 1980; p 580.
195. Haines, C.; Chen, M.; Ghiggino, K. P., The effect of perylene diimide aggregation on the light collection efficiency of luminescent concentrators. Sol. Energy Mater. Sol. Cells 2012, 105, 287-292.
196. Tang, T.; Qu, J.; Muellen, K.; Webber, S. E., Molecular Layer-by-Layer Self-Assembly of Water-Soluble Perylene Diimides through π-π and Electrostatic Interactions. Langmuir 2006, 22 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 26-28.
197. Marcon, R. O.; Dos Santos, J. G.; Figueiredo, K. M.; Brochsztain, S., Characterization of a Novel Water-Soluble 3,4,9,10-Perylenetetracarboxylic Diimide in Solution and in Self-Assembled Zirconium Phosphonate Thin Films. Langmuir 2006, 22 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 1680-1687.
198. Khodzhaeva, V. L.; Zaikin, V. G., Fourier transform infrared spectroscopy study of poly(1-trimethylsilyl-1-propyne) aging. J. Appl. Polym. Sci. 2007, 103 (4), 2523-2527.
199. Morliere, N.; Vallieres, C.; Perrin, L.; Roizard, D., Impact of thermal ageing on sorption and diffusion properties of PTMSP. J. Membr. Sci. 2006, 270 (1-2), 123-131.
200. Monthly mean daily global solar exposure, Brisbane. Bureau of Meteorology, Commonwealth of Australia: 2015.
201. Dabrowska, D.; Kot-Wasik, A.; Namiesnik, J., Stability studies of selected polycyclic aromatic hydrocarbons in different organic solvents and identification of their transformation products. Pol. J. Environ. Stud. 2008, 17 (1), 17-24.
202. Lee, R. F.; Gardner, W. S.; Anderson, J. W.; Blaylock, J. W.; Barwell-Clarke, J., Fate of polycyclic aromatic hydrocarbons in controlled ecosystem enclosures. Environ. Sci. Technol. 1978, 12 (7), 832-8.
203. Starannikova, L.; Khodzhaeva, V.; Yampolskii, Y., Mechanism of aging of poly[1-(trimethylsilyl)-1-propyne] and its effect on gas permeability. J. Membr. Sci. 2004, 244 (1-2), 183-191.
C H A P T E R E I G H T
P a g e | 257
204. Yang, J.-X.; Cui, J.; Long, Y.-Y.; Li, Y.-G.; Li, Y.-S., Synthesis of cyclic olefin polymers with high glass transition temperature by ring-opening metathesis (Co)Polymerization and subsequent hydrogenation. J. Polym. Sci., Part A: Polym. Chem. 2014, 52 (18), 2654-2661.
205. Liu, M. O.; Lin, H.-F.; Yang, M.-C.; Lai, M.-J.; Chang, C.-C.; Feng, M.-C.; Shiao, P.-L.; Chen, I.-M., Thermal oxidation and molding feasibility of cycloolefin copolymers (COCs) with high glass transition temperature. Polym. Degrad. Stab. 2006, 91 (7), 1443-1447.
206. Yang, T. C. K.; Lin, S. S. Y.; Chuang, T.-H., Kinetic analysis of the thermal oxidation of metallocene cyclic olefin copolymer (mCOC)/TiO2 composites by FTIR microscopy and thermogravimetry (TG). Polym. Degrad. Stab. 2002, 78 (3), 525-532.
207. Bauer, D. R., Predicting in-service weatherability of automotive coatings: a new approach. J. Coat. Technol. 1997, 69 (864), 85-96.
208. Laycock, B.; Nikolic, M.; Colwell, J. M.; Gauthier, E.; Halley, P.; Bottle, S.; George, G., Lifetime prediction of biodegradable polymers. Prog. Polym. Sci. 2017, 71, 144-189.
209. Pickett, J. E.; Gardner, M. M., Reproducibility of Florida weathering data. Polym. Degrad. Stab. 2005, 90 (3), 418-430.
210. Yang, X. F.; Vang, C.; Tallman, D. E.; Bierwagen, G. P.; Croll, S. G.; Rohlik, S., Weathering degradation of a polyurethane coating. Polym. Degrad. Stab. 2001, 74 (2), 341-351.
211. Zhang, G.; Pitt, W. G.; Goates, S. R.; Owen, N. L., Studies on oxidative photodegradation of epoxy resins by IR-ATR spectroscopy. J. Appl. Polym. Sci. 1994, 54 (4), 419-27.
212. Bagheri, R.; Darvishi, R., Study of the effect of natural weathering on degradation of Polypropylene/starch filled polymer containing photo initiators by spectroscopic methods. International Journal of Plastics Technology 2015, 19 (1), 56-67.
213. Jansson, A.; Moller, K.; Hjertberg, T., Chemical degradation of a polypropylene material exposed to simulated recycling. Polym. Degrad. Stab. 2004, 84 (2), 227-232.
214. Nikolic, M. A. L.; Gauthier, E.; Colwell, J. M.; Halley, P.; Bottle, S. E.; Laycock, B.; Truss, R., The challenges in lifetime prediction of oxodegradable polyolefin and biodegradable polymer films. Polym. Degrad. Stab. 2017, 145, 102-119.
215. Azuma, Y.; Takeda, H.; Watanabe, S.; Nakatani, H., Outdoor and accelerated weathering tests for polypropylene and polypropylene/talc composites: A comparative study of their weathering behavior. Polym. Degrad. Stab. 2009, 94 (12), 2267-2274.
216. Bauer, D. R., Interpreting weathering acceleration factors for automotive coatings using exposure models. Polym. Degrad. Stab. 2000, 69 (3), 307-316.
217. Bauer, D. R., Global exposure models for automotive coating photo-oxidation. Polym. Degrad. Stab. 2000, 69 (3), 297-306.
218. Bauer, D. R., Application of failure models for predicting weatherability in automotive coatings. ACS Symp. Ser. 1999, 722 (Service Life Prediction of Organic Coatings), 378-395.
C H A P T E R E I G H T
P a g e | 258
219. Martin, J. W.; Nguyen, T.; Byrd, E.; Dickens, B.; Embree, N., Relating laboratory and outdoor exposures of acrylic melamine coatings I. Cumulative damage model and laboratory exposure apparatus. Polym. Degrad. Stab. 2001, 75 (1), 193-210.
220. George, G. A.; Celina, M.; Vassallo, A. M.; Cole-Clarke, P. A., Real-time analysis of the thermal oxidation of polyolefins by FT-IR emission. Polym. Degrad. Stab. 1995, 48 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 199-210.
221. Rouillon, C.; Bussiere, P. O.; Desnoux, E.; Collin, S.; Vial, C.; Therias, S.; Gardette, J. L., Is carbonyl index a quantitative probe to monitor polypropylene photodegradation? Polym. Degrad. Stab. 2016, 128 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 200-208.
222. Mielewski, D. F.; Bauer, D. R.; Gerlock, J. L., The role of hydroperoxides in the photooxidation of crosslinked polymer coatings. Polym. Degrad. Stab. 1991, 33 (1), 93-104.
223. Wiles, D. M.; Scott, G., Polyolefins with controlled environmental degradability. Polym. Degrad. Stab. 2006, 91 (7), 1581-1592.
224. Gijsman, P.; Gitton-Chevalier, M., Aliphatic amines for use as long-term heat stabilizers for polypropylene. Polym. Degrad. Stab. 2003, 81 (Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.), 483-489.
225. Vasile, C., Handbook of Polyolefins, Second Edition. CRC Press: 2000.
226. Morris, J. C.; McMurtrie, J. C.; Bottle, S. E.; Fairfull-Smith, K. E., Generation of Profluorescent Isoindoline Nitroxides Using Click Chemistry. Journal of Organic Chemistry 2011, 76 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 4964-4972.
227. Lussini, V. C.; Colwell, J. M.; Fairfull-Smith, K. E.; Bottle, S. E., Profluorescent nitroxide sensors for monitoring photo-induced degradation in polymer films. Sensors and Actuators B: Chemical 2017, 241, 199-209.
228. Pilar, J.; Michalkova, D.; Sedenkova, I.; Pfleger, J.; Pospisil, J., NOR and nitroxide-based HAS in accelerated photooxidation of carbon-chain polymers; Comparison with secondary HAS: An ESRI and ATR FTIR study. Polym. Degrad. Stab. 2011, 96 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 847-862.
229. Lussini, V. C.; Blinco, J. P.; Fairfull-Smith, K. E.; Bottle, S. E., Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability. Chemistry 2015, (Copyright (C) 2015 U.S. National Library of Medicine.).
230. Wilkinson, F.; Abdel-Shafi, A. A., Mechanism of Quenching of Triplet States by Oxygen: Biphenyl Derivatives in Acetonitrile. The Journal of Physical Chemistry A 1997, 101 (30), 5509-5516.
231. McGarvey, D. J.; Szekeres, P. G.; Wilkinson, F., The efficiency of singlet oxygen generation by substituted naphthalenes in benzene. Evidence for the participation of charge-transfer interactions. Chem. Phys. Lett. 1992, 199 (3), 314-319.
232. Grewer, C.; Brauer, H.-D., Mechanism of the Triplet-State Quenching by Molecular Oxygen in Solution. The Journal of Physical Chemistry 1994, 98 (16), 4230-4235.
C H A P T E R E I G H T
P a g e | 259
233. Olea, A. F.; Wilkinson, F., Singlet Oxygen Production from Excited Singlet and Triplet States of Anthracene Derivatives in Acetonitrile. The Journal of Physical Chemistry 1995, 99 (13), 4518-4524.
234. DeRosa, M. C.; Crutchley, R. J., Photosensitized singlet oxygen and its applications. Coord. Chem. Rev. 2002, 233–234, 351-371.
235. Tanaka, N.; Barashkov, N.; Heath, J.; Sisk, W. N., Photodegradation of polymer-dispersed perylene di-imide dyes. Appl. Opt. 2006, 45 (16), 3846-3851.
236. Dinçalp, H.; Içli, S., Photoinduced electron transfer-catalyzed processes of sulfoamino perylene diimide under concentrated sun light. Solar Energy 2006, 80 (3), 332-346.
237. Erten, S.; Alp, S.; Icli, S., Photooxidation quantum yield efficiencies of naphthalene diimides under concentrated sun light in comparisons with perylene diimides. Journal of Photochemistry and Photobiology A: Chemistry 2005, 175 (2–3), 214-220.
238. Dinçalp, H.; Kızılok, Ş.; İçli, S., Targeted Singlet Oxygen Generation Using Different DNA-Interacting Perylene Diimide Type Photosensitizers. J. Fluoresc. 2014, 24 (3), 917-924.
239. Rabek, J. F.; Ranby, B., Role of singlet oxygen in photo-oxidative degradation and photostabilization of polymers. Polym. Eng. Sci. 1975, 15 (1), 40-3.
240. Enko, B.; Borisov, S. M.; Regensburger, J.; Baumler, W.; Gescheidt, G.; Klimant, I., Singlet oxygen-induced photodegradation of the polymers and dyes in optical sensing materials and the effect of stabilizers on these processes. J. Phys. Chem. A 2013, 117 (36), 8873-82.
241. Araujo, J. A., Particulate air pollution, systemic oxidative stress, inflammation, and atherosclerosis. Air Quality, Atmosphere, & Health 2011, 4 (1), 79-93.
242. Paul, B. K.; Guchhait, N., A computational insight into the photophysics of a potent UV absorber Tinuvin P: Critical evaluation of the role of charge transfer interaction and topological properties of the intramolecular hydrogen bonding. Computational and Theoretical Chemistry 2011, 966 (1–3), 250-258.
243. Allen, N. S., Recent advances in the photo-oxidation and stabilization of polymers. Chem. Soc. Rev. 1986, 15 (3), 373-404.
244. Kurumada, T.; Ohsawa, H.; Yamazaki, T., Synergism of hindered amine light stabilizers and UV-absorbers. Polym. Degrad. Stab. 1987, 19 (3), 263-272.
245. Ávár, L.; Bechtold, K., Studies on the interaction of photoreactive light stabilizers and UV-absorbers. Prog. Org. Coat. 1999, 35 (1–4), 11-17.
246. Pilař, J.; Michálková, D.; Šlouf, M.; Vacková, T.; Dybal, J., Heterogeneity of accelerated photooxidation in commodity polymers stabilized by HAS: ESRI, IR, and MH study. Polym. Degrad. Stab. 2014, 103, 11-25.
247. Koch, G. H.; Thompson, N. G.; Moghissi, O.; Payer, J. H.; Varney, J. IMPACT (International Measures of Prevention, Application, and Economics of Corrosion Technologies Study; APUS310GKOCH(AP110272); NACE International: Houston, Texas, USA, 2016.
C H A P T E R E I G H T
P a g e | 260
248. Kohl, C.; Weil, T.; Qu, J.; Muellen, K., Towards highly fluorescent and water-soluble perylene dyes. Chem.--Eur. J. 2004, 10 (Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.), 5297-5310.
249. Hodgson, J. L.; Coote, M. L., Clarifying the Mechanism of the Denisov Cycle: How do Hindered Amine Light Stabilizers Protect Polymer Coatings from Photo-oxidative Degradation? Macromolecules (Washington, DC, U. S.) 2010, 43 (10), 4573-4583.
250. Colonna, G.; Pilati, T.; Rusconi, F.; Zecchi, G., Synthesis and properties of some new N,N′-disubstituted 2,5-dihydro-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrroles. Dyes Pigm. 2007, 75 (1), 125-129.
251. Celik, S.; Ergun, Y.; Alp, S., Synthesis and Spectroscopic Studies of 3,6-Diphenyl-2,5-Dihydropyrrolo[3,4-C]Pyrrole-1,4-Dion's N,N'-Dialkyl Derivatives. J. Fluoresc. 2009, 19 (5), 829-835.
252. David, J.; Weiter, M.; Vala, M.; Vynuchal, J.; Kucerik, J., Stability and structural aspects of diketopyrrolopyrrole pigment and its N-alkyl derivatives. Dyes Pigm. 2011, 89 (2), 137-143.
253. Sonar, P.; Foong, T. R. B.; Singh, S. P.; Li, Y.; Dodabalapur, A., A furan-containing conjugated polymer for high mobility ambipolar organic thin film transistors. Chem. Commun. (Cambridge, U. K.) 2012, 48 (67), 8383-8385.
254. Robeson, L. M., The upper bound revisited. J. Membr. Sci. 2008, 320 (1–2), 390-400.
255. Jiang, W.; Li, Y.; Yue, W.; Zhen, Y.; Qu, J.; Wang, Z., One-pt facile synthesis of pyridyl annelated perylene bisimides. Org. Lett. 2010, 12 (2), 228-231.
256. Choi, J.; Lee, W.; Sakong, C.; Yuk, S. B.; Park, J. S.; Kim, J. P., Facile synthesis and characterization of novel coronene chromophores and their application to LCD color filters. Dyes Pigm. 2012, 94 (1), 34-39.
257. Qian, H.; Negri, F.; Wang, C.; Wang, Z., Fully Conjugated Tri(perylene bisimides): An Approach to the Construction of n-Type Graphene Nanoribbons. Journal of the American Chemical Society 2008, 130 (52), 17970-17976.
258. Blinco, J. P.; Chalmers, B. A.; Chou, A.; Fairfull-Smith, K. E.; Bottle, S. E., Spin-coated carbon. Chem. Sci. 2013, 4 (9), 3411-3415.
C H A P T E R N I N E
P a g e | 261
9. APPENDIX
9.1. Supplementary Information for Polyaromatic Profluorescent
Nitroxide Probes with Enhanced Photostability (Chapter 3)
V. C. Lussini,[a][b] J. P. Blinco,[a] K. E. Fairfull-Smith*[a] and S. E. Bottle*[a][b]
[a] ARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School of
Chemistry, Physics and Mechanical Engineering, Faculty of Science and Engineering,
Queensland University of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001, Australia
[b] Defence Materials Technology Centre, School of Chemistry, Physics and Mechanical
Engineering, Faculty of Science and Engineering, Queensland University of Technology
(QUT), GPO Box 2434, Brisbane, QLD 4001, Australia
*Corresponding author: E-mail: [email protected] ; Fax: +61 7 3138 1804; Tel: +61 7 3138
1356
C H A P T E R N I N E
P a g e | 262
9.1.1. 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)
02 VL 74B (26 02 13).001.esp
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
12.102.930.940.930.99
1.4
0
3.7
7
6.5
66.5
7
6.7
0
6.9
46
.96
Figure 80: 1H NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)
C H A P T E R N I N E
P a g e | 263
02VL76_C_110605_CARBON_CDCL3_20150611_01
168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
65
.41
66
.69
67
.01
76
.6876
.99
77
.31
10
8.3
6
11
4.2
912
2.5
1
13
7.4
9
14
6.8
7
15
4.9
5
Figure 81: 13C NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)
Figure 82: HPLC (70% MeOH/ Water) chromatogram of 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)
C H A P T E R N I N E
P a g e | 264
9.1.2. N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104)
PROTON_CDCL3_01
8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
No
rma
lize
d I
nte
nsity
17.3511.862.892.810.990.971.020.961.050.992.01
1.2
81
.31
1.4
61
.49
3.8
1
6.9
46
.96
6.9
66
.99
6.9
97
.08
7.1
97
.21
7.4
57
.56
7.5
87
.80
7.8
27
.84
8.5
08
.52
8.7
28
.72
8.7
8
Figure 83: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-
naphthalimide (104)
C H A P T E R N I N E
P a g e | 265
CARBON_CDCL3_01
168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
No
rma
lize
d I
nte
nsity
15
.26
29
.69
31
.20
31
.70
34
.20
35
.48
50
.84
65
.54
66
.98
67
.15
76
.71
77
.03
77
.34
11
0.2
7
11
4.1
2
11
6.6
7
11
9.8
0
12
2.9
31
23
.41
12
4.0
11
26
.1112
6.5
11
27
.77
12
8.6
81
30
.10
13
2.3
31
33
.30
14
2.6
31
43
.76
14
7.8
8
14
9.9
6
15
4.0
0
16
0.4
0
16
4.7
61
65
.42
Figure 84: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-
1,8-naphthalimide (104)
Figure 85: HPLC (70% MeOH/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104)
C H A P T E R N I N E
P a g e | 266
9.1.3. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-
yloxyl-5-yloxy)-1,8-naphthalimide (105)
PROTON_CDCL3_01
8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
No
rma
lize
d I
nte
nsity
17.571.231.040.960.991.021.99
1.3
11
.33
7.0
1
7.2
67
.457.4
77.5
97
.61
7.8
7
8.5
98.7
58
.76
8.8
0
Figure 86: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-
naphthalimide (105)
C H A P T E R N I N E
P a g e | 267
Figure 87: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-
2-yloxyl-5-yloxy)-1,8-naphthalimide (105)
Figure 88: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-
1,8-naphthalimide (105)
C H A P T E R N I N E
P a g e | 268
Figure 89: Quantum Yield of fluorescence calculations for 104 and 105
9.1.4. 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)
C H A P T E R N I N E
P a g e | 269
02VL46-_120615_PROTON_CDCL3_20150612_01
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
11.512.820.920.971.00
1.4
1
3.7
83
.86
6.4
36
.44
6.5
76
.58
6.8
86
.90
Figure 90: 1H NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)
02VL46_C_120615_CARBON_CDCL3_20150612_01
160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
65
.40
66
.65
67
.02
76
.79
77
.11
77
.43
10
8.1
5
11
4.4
7
12
2.2
3
13
5.4
9
14
5.7
11
46
.35
Figure 91: 13C NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)
C H A P T E R N I N E
P a g e | 270
Figure 92: HPLC (70% MeOH/ Water) chromatogram of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)
9.1.5. 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline
tetrafluoroborate (63)
C H A P T E R N I N E
P a g e | 271
PROTON_DMSO_01
14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
12.743.361.132.00
Water
1.4
3
2.4
8
3.7
1
7.9
07
.92
8.5
88
.60
8.6
0
Figure 93: 1H NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline tetrafluoroborate (63)
CARBON_DMSO_01
160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
No
rma
lize
d I
nte
nsity
39
.33
39
.54
39
.75
39
.95
40
.17
40
.37
40
.58
65
.38
65
.73
68
.2510
8.4
2
11
5.0
1
12
2.7
5
12
5.5
81
27
.00
13
3.4
5
14
8.0
9
15
9.0
0
Figure 94: 13C NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline tetrafluoroborate (63)
C H A P T E R N I N E
P a g e | 272
9.1.6. N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106)
PROTON_CDCL3_01
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
18.1910.543.011.121.072.001.961.080.980.970.981.00
1.2
81
.32
1.4
9
6.9
97
.17
7.1
97
.26
7.4
27
.46
7.5
77
.59
7.8
97
.98
8.0
0
8.6
08
.62
8.6
98
.71
8.8
08
.83
Figure 95: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl)-
1,8-naphthalimide (106)
C H A P T E R N I N E
P a g e | 273
02VL121_240615_CARBON_CDCL3_20150625_01
168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 0
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
No
rma
lize
d I
nte
nsity
21
.44
31
.21
31
.70
34
.22
35
.50
65
.54
67
.08
67
.24
76
.68
77
.00
77
.32
85
.74
99
.69
12
0.9
6
12
1.9
5
12
2.3
1
12
5.1
21
27
.48
12
7.7
31
28
.72
13
0.7
31
30
.83
13
1.2
11
32
.03
13
2.7
1
13
4.1
3
14
3.7
51
45
.93
14
7.0
815
0.0
3
16
4.7
41
65
.01
Figure 96: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl)-
1,8-naphthalimide (106)
Figure 97: HPLC (75% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-
tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106)
C H A P T E R N I N E
P a g e | 274
9.1.7. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-
yloxyl-5-ethynyl)-1,8-naphthalimide (107)
PROTON_CDCL3_01
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
No
rma
lize
d I
nte
nsity
15.180.970.910.972.050.941.040.99
1.2
91
.32
7.0
0
7.3
6
7.4
77.5
87
.60
7.9
17
.99
8.7
28
.73
8.8
3
Figure 98: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-
naphthalimide (107)
C H A P T E R N I N E
P a g e | 275
Figure 99: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-
2-yloxyl-5-ethynyl)-1,8-naphthalimide (107)
Figure 100: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-
ethynyl)-1,8-naphthalimide (107)
C H A P T E R N I N E
P a g e | 276
Figure 101: Quantum yield of fluorescence calculations for 106 and 107
9.1.8. N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy
diimide (117)
C H A P T E R N I N E
P a g e | 277
PROTON_CDCL3_01
9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
No
rma
lize
d I
nte
nsity
38.6822.956.035.562.002.041.710.671.271.380.840.951.53
1.2
31
.25
1.2
61
.27
1.4
3
3.7
7
6.9
46
.956.9
66
.96
7.1
27
.14
7.2
47
.43
7.4
47.5
47
.56
8.3
28
.32
8.4
08
.41
8.6
78
.67
8.6
98
.74
8.7
6
9.5
89
.59
9.6
09.6
49
.65
9.6
69
.67
Figure 102: 1H NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-
yloxy)-perylene-3,4,9,10-tetracarboxy diimide (117)
CARBON_CDCL3_01
200 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
1.0
2
29
.69
30
.93
31
.18
31
.70
34
.22
35
.48
65
.50
66
.98
67
.18
76
.69
77
.00
77
.32
11
3.1
31
18
.51
12
2.5
91
23
.56
12
4.1
11
24
.17
12
6.3
51
27
.51
12
8.7
61
28
.99
12
9.6
51
30
.63
13
2.4
21
33
.79
14
3.6
51
48
.03
15
0.1
11
54
.36
15
5.5
61
56
.63
16
3.7
41
63
.93
16
4.3
71
64
.6120
6.9
8
Figure 103: 13C NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-
5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide (117)
C H A P T E R N I N E
P a g e | 278
Figure 104: HPLC (75% THF/ Water) chromatogram of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide (117)
9.1.9. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-
tetracarboxy diimide (118)
C H A P T E R N I N E
P a g e | 279
PROTON_CDCL3_01
10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
1.2
61
.29
6.9
7
7.4
37
.55
8.7
3
9.6
6
Figure 105: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-
yloxy)-perylene-3,4,9,10-tetracarboxy diimide (118)
Figure 106: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide (118)
C H A P T E R N I N E
P a g e | 280
Figure 107: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-
yloxy)-perylene-3,4,9,10-tetracarboxy diimide (118)
Figure 108: Quantum yield of fluorescence calculations for 117 and 118
C H A P T E R N I N E
P a g e | 281
9.1.10. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy
diimide (114)
PROTON_CDCL3_01
10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
No
rma
lize
d I
nte
nsity
71.2420.232.912.522.085.364.416.951.451.94
1.2
51
.48
1.5
0
3.8
0
7.0
37
.04
7.0
47
.26
7.4
47
.477.5
07
.61
7.6
37
.63
8.7
58.7
78
.79
8.8
28
.98
10
.39
10
.41
Figure 109: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-
ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (114)
C H A P T E R N I N E
P a g e | 282
CARBON_CDCL3_01
168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
No
rma
lize
d I
nte
nsity
Figure 110: 13C NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-
ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (114)
Figure 111: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-
tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (114)
C H A P T E R N I N E
P a g e | 283
9.1.11. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-
tetracarboxy diimide (116)
PROTON_CDCL3_01
10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
No
rma
lize
d I
nte
nsity
22.712.212.321.982.164.162.03
1.2
21
.26
1.3
4
7.0
0
7.4
8
7.6
3
8.5
6
8.8
58
.98
10
.42
Figure 112: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-
ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (116)
C H A P T E R N I N E
P a g e | 284
Figure 113: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (116)
Figure 114: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-
ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (116)
C H A P T E R N I N E
P a g e | 285
9.1.12. N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-
yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-
ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115)
PROTON_CDCL3_01
10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
No
rma
lize
d I
nte
nsity
21.571.492.021.981.99
1.3
21
.33
3.8
4
6.9
97
.01
7.4
57
.49
7.6
07
.62
8.5
5
8.8
0
8.9
7
10
.42
Figure 115: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-
7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115)
C H A P T E R N I N E
P a g e | 286
Figure 116: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-
ethynyl)-7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115)
Figure 117: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-
tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-
tetracarboxy diimide (115)
C H A P T E R N I N E
P a g e | 287
Figure 118: Quantum yield of fluorescence calculations for 114, 116 and 115
9.1.13. N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-
perylene-3,4,9,10-tetracarboxyl-diimide (98)
C H A P T E R N I N E
P a g e | 288
02 VL 44- 2ND FRAC.001.esp
11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
No
rma
lize
d I
nte
nsity
1.791.838.03
1.3
2
1.5
61
.71
2.7
2
7.4
0
8.5
58
.71
Figure 119: 1H NMR spectrum of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-
tetracarboxyl-diimide (98)
Figure 120: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-
perylene-3,4,9,10-tetracarboxyl-diimide (98)
C H A P T E R N I N E
P a g e | 289
Figure 121: EPR (DCM) spectrum of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-
tetracarboxyl-diimide (98)
Figure 122: Quantum yield of fluorescence calculations for 98 and 99
C H A P T E R N I N E
P a g e | 290
9.1.14. N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-tetramethylisoindolin-2-
yl)-perylene-3,4,9,10-tetracarboxyl-diimide (99)
C H A P T E R N I N E
P a g e | 291
02 VL 44- METRAP.001.esp
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
No
rma
lize
d I
nte
nsity
12.181.962.980.910.942.197.99
1.3
0
1.4
81
.52
2.6
92.7
12
.73
3.8
1
7.0
9
7.2
17
.27
7.3
87
.40
8.6
68
.68
8.7
48
.76
Figure 123: 1H NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-
3,4,9,10-tetracarboxyl-diimide (99)
CARBON_CDCL3_01
200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -10
Chemical Shift (ppm)
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
0.14
No
rma
lize
d I
nte
nsity
0.0
0
13
.11
21
.68
28
.28
28
.69
30
.91
64
.50
66
.17
12
2.2
9
12
7.1
51
28
.4513
0.7
6
13
3.8
2
16
2.5
8
Figure 124: 13C NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-
3,4,9,10-tetracarboxyl-diimide (99)
C H A P T E R N I N E
P a g e | 292
Figure 125: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (99)
9.1.15. N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-
yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (90)
C H A P T E R N I N E
P a g e | 293
02 VL 33 (170611).001.esp
11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
No
rma
lize
d I
nte
nsity
19.581.020.960.917.96
1.2
61
.31
1.3
4
7.0
8
7.4
87
.50
7.6
07
.62
8.7
18
.78
Figure 126: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-
3,4,9,10-tetracarboxyl-diimide (90)
02 VL 33- 2ND FRAC 13C.001.esp
200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -10 -20
Chemical Shift (ppm)
0
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
0.065
0.070
0.075
0.080
0.085
0.090
0.095
No
rma
lize
d I
nte
nsity
1.2
3
14
.33
22
.91
29
.58
29
.91
32
.14
38
.94
65
.74
67
.35
12
2.7
81
23
.47
12
3.7
1
12
7.5
41
29
.7713
1.8
81
34
.07
13
4.9
4
14
5.9
71
46
.77
16
3.7
4
Figure 127: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-
3,4,9,10-tetracarboxyl-diimide (90)
C H A P T E R N I N E
P a g e | 294
Figure 128: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-
tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (90)
Figure 129: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-
perylene-3,4,9,10-tetracarboxyl-diimide (90)
C H A P T E R N I N E
P a g e | 295
Figure 130: Quantum yield of fluorescence calculations for 90 and 92
9.1.16. N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-
diimide (92)
C H A P T E R N I N E
P a g e | 296
02 VL 33-METRAP (170611).001.esp
8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
No
rma
lize
d I
nte
nsity
19.4112.123.841.011.091.050.551.171.147.99
1.3
11
.34
1.4
9
3.8
1
7.0
47
.08
7.1
97
.21
7.2
87
.30
7.4
77
.49
7.6
07
.62
8.4
78
.49
8.5
98
.618.7
18
.73
8.7
78
.82
Figure 131: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-
perylene-3,4,9,10-tetracarboxyl-diimide (92)
CARBON_CDCL3_01
200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -10
Chemical Shift (ppm)
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
No
rma
lize
d I
nte
nsity
TMS
13
.11
21
.68
28
.35
28
.69
30
.21
30
.73
30
.91
64
.52
66
.14
12
0.8
11
21
.58
12
2.2
91
25
.39
12
6.3
21
26
.69
12
7.8
21
30
.88
13
3.9
5
16
2.6
71
63
.38
Figure 132: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-
perylene-3,4,9,10-tetracarboxyl-diimide (92)
C H A P T E R N I N E
P a g e | 297
Figure 133: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-
tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (92)
9.1.17. N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-
tetracarboxy diimide (130)
1H NMR spectrum N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide (130)
C H A P T E R N I N E
P a g e | 298
02VL136_210615_PROTON_CDCL3_20150623_01
10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
No
rma
lize
d I
nte
nsity
31.852.003.214.982.011.831.951.97
1.2
51
.26
1.2
61
.28
1.3
01
.31
1.3
1
1.5
7
6.9
26
.93
6.9
66
.97
7.0
07
.187.2
07
.26
7.2
77
.43
7.4
5
7.5
67
.58
7.6
0
8.3
38
.33
8.4
18
.68
8.6
88
.70
8.7
08
.74
8.7
68
.76
9.5
99
.60
9.6
19
.64
9.6
69
.66
9.6
8
Figure 134: 1H NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy
diimide (130)
02VL136_210615_CARBON_CDCL3_20150624_01
184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 0
Chemical Shift (ppm)
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
No
rma
lize
d I
nte
nsity
31
.18
31
.74
34
.22
35
.52
76
.68
76
.99
77
.31
11
9.3
61
19
.49
12
7.4
81
28
.79
12
9.6
41
30
.57
13
0.6
01
30
.73
13
1.6
91
33
.68
14
3.7
3
15
0.0
91
50
.11
15
5.0
51
55
.12
15
6.1
5
16
3.8
31
64
.36
Figure 135: 13C NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy
diimide (130)
C H A P T E R N I N E
P a g e | 299
Figure 136: HPLC (80% THF/ Water) chromatogram of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-
3,4,9,10-tetracarboxy diimide (130)
Figure 137: Quantum yield of fluorescence calculations for 113 and 130
C H A P T E R N I N E
P a g e | 300
9.2. Supplementary Information for Profluorescent nitroxide
sensors for monitoring the natural aging of polymer materials
(Chapter 5)
Vanessa C. Lussini,a,b John M. Colwell,a,b James P. Blinco,a Kathryn E. Fairfull-Smitha and
Steven E. Bottle*a,b
[a] ARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School of
Chemistry, Physics and Mechanical Engineering, Faculty of Science and Engineering,
Queensland University of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001, Australia
[b] Defence Materials Technology Centre, School of Chemistry, Physics and Mechanical
Engineering, Faculty of Science and Engineering, Queensland University of Technology
(QUT), GPO Box 2434, Brisbane, QLD 4001, Australia
*Corresponding author: E-mail: [email protected] ; Fax: +61 7 3138 1804; Tel: +61 7 3138
1356
C H A P T E R N I N E
P a g e | 301
Figure SI 138: Fluorescence maximum trace of aged TOPAS® films doped with PFN 116 (0.025 w%) during aging in
the laboratory (Suntest) and outdoors weathering.
C H A P T E R N I N E
P a g e | 302
Figure SI 139: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films doped with PFN-analogue 114
(0.025 wt%) with respect to radiant exposure (MJ/m2) on the rooftop.
(a) Compared to TOPAS® films containing PFN-analogue 114 + TMIO (1, 2 and 4 eqv. of 114)
(b) Compared to TOPAS® films containing PFN-analogue 1 + Tinuvin P (0.1, 0.3 and 0.5 wt%)
C H A P T E R N I N E
P a g e | 303
Figure SI 140: Relative change in UV-Vis absorbance for aged TOPAS® films doped with PFN 115 (0.025 wt%) with
respect to radiant exposure (MJ/m2) on the rooftop.
(a) Compared to TOPAS® films containing PFN-analogue 115 + TMIO (1, 2 and 4 eqv. of 115)
(b) Compared to TOPAS® films containing PFN-analogue 155 + Tinuvin P (0.1, 0.3 and 0.5 wt%)
[Type text] C H A P T E R N I N E [Type text]
P a g e | 304
Table SI 5: Summary of aged TOPAS® films doped with PFNs (0.025 wt%) and varying concentrations of
55 and 1 aged in the Suntest and aged on the rooftop.
Compou
nd # used
TMI
O
(55)*
Tinuvi
n P
(1),
wt%
Radiant
exposure
leading to
50% loss of
UV-Vis
absorbance
(MJ/m2)
Radiant
exposure
leading to an
oxidation
index above
0.003 (MJ/m2)
Radiant
exposure
leading to
maximum
fluorescence
emission
(MJ/m2)
Sunte
st
Roofto
p
Sunte
st
Roofto
p
Sunte
st
Rooftop
- 0 220 325
- 1 >800 330
- 2 >800 >800
- 4 >800 >800
- 0.1 >800 520
- 0.3 496.8 660
- 0.5 496.8 485
- 2 0.3 >800 >800
114 0 80 130 260 80
114 1 160 250 520 350
114 2 220 260 660 390
114 4 230 340 >800 460
114 0.1 140 170 360 310
[Type text] C H A P T E R N I N E [Type text]
P a g e | 305
114 0.3 230 270 340 445
114 0.5 170 320 370 470
114 2 0.3 220 520 300 690
115 0 100 100 300 95 110 100
115 1
150 140 430 120 170
Damag
ed
115 2 180 200 610 470 240 100
115 4 220 300 640 240 280 100
115 0.1 120 220 360 515 130 200
115 0.3 180 320 380 480 110 360
115 0.5 170 460 430 510 200 360
115 2 0.3 350 520 >800 600 280 430
116 0 150 260 350 465 350 330
116 1 220 360 500 500 430 370
116 2 260 430 610 490 500 360
116 4 300 480 680 420 540 300
116 0.1 360 460 680 440 >800 720
116 0.3 400 640 640 550 >800 750
116 0.5 320 640 750 520 >800 790
116 2 0.3 430 640 650 600 >800 >800
*mole equivalents relative to compound used