Center for Exploitation of Solar Energy &

Department of Chemistry, University of Copenhagen

Smart Materials & Structures, Las vegas, 15-17.6.2015

Tetrathiafulvalene-Fused Radiaannulenes and -Extended Tetrathiafulvalenes

– Towards New Electrochromic Materials

Mogens Brøndsted Nielsen

Electrochromic Materials

- Reversibly changing color by electrochemical redox reactions

…. Redox-active molecules

Electrochromic Materials

- On/off switching of NIR absorptions?

Optical attenuator: device used to reduce the power level of an optical signal,

usually working by absorbing the light

Telecommunication industry: wavelengths of 1300 and 1550 nm

Both anodically and cathodically NIR-coloring materials are ideally needed

-Conjugated organic molecules

Wurster’s Blue

Wurster redox system: aromatic in reduced form

Blue color

N

N

N

N

N

N

- e

+ e

- e

+ e

Mixed Valence (MV)

fully delocalized

Tetrathiafulvalene (TTF)

S

S

S

S

S

S

S

S

S

S

S

S

TTF

- e

+ e

- e

+ eS S

S S

Mixed Valence (MV)

fully delocalized

Weitz redox system: aromatic in oxidized form

Tetrathiafulvalene

Some applications of TTF:

e-

e-

e-

Mixed valence

conduction

TTF / TTF•+

Properties can be tuned byintroduction of -spacer orsubstituents R

S

S

S

S

S

S

S

S

S

S

S

S

TTF

- e

+ e

- e

+ eS S

S S

Mixed Valence (MV)

fully delocalized

• Redox-active unit in supramolecular chemistry… molecular sensors, switches, and devices

• Redox-active unit in molecular electronics

• Mixed valence (TTF/TTF•+) organic conductors

• Electrochromic materials

Tetrathiafulvalene (TTF)

S

S

S

S

S

S

S

S

S

S

S

S

TTF

- e

+ e

- e

+ eS S

S S

Mixed Valence (MV)

fully delocalized

312 (369) nm

580 nm

390 nm

Radical Cation Absorptions

S

S S

S

S

S S

SMeS

MeS

SMe

SMe

S S

S S+

+

+

M.-B.S. Kirketerp, L.A.E. Leal, D. Varsano,A. Rubio, T.J.D. Jørgensen, K. Kilså,M.B. Nielsen, S.B. Nielsen, Chem. Commun. 2011, 47, 6900-6902.

Robin and Day Classification of Two-Center Redox Systems

Class III Cyclic Voltammogram

D D D DD D- e

+ e

- e

+ e

+ 2+Class III: Eox > 0.2 V

fully delocalized

Mixed Valence (MV)

Robin and Day Classification of Two-Center Redox Systems

Class I Class III Cyclic Voltammogram

D D

D D D DD D

Eox = Eox2 Eox1

- 2e

+ 2e

- e

+ e

- e

+ e

+ 2+

Class I: D

Class III:

D 2+ Eox ≈ 0 V (35 mV)

Eox > 0.2 V

Mixed Valence (MV)

fully delocalized

Robin and Day Classification of Two-Center Redox Systems

D D

D D D D D

D D D DD D

Eox = Eox2 Eox1

- 2e

- e

+ e

+ 2e

- e

+ e

- e

+ e

- e

+ e

+D

+ 2+

2+

Class I: D

Class II:

Class III:

D 2+ Eox ≈ 0 V (35 mV)

Eox ≈ 0 - 0.2 V

Eox > 0.2 V

Mixed Valence (MV)

fully delocalized

Class I Class III Cyclic Voltammogram

Electronic coupling: None

Potential Energy Surfaces for Electron Transfer in MV Systems

J. Hankache, O. S. Wenger, Chem. Rev. 2011, 111, 5138-5178.

Class IIClass I Class III

Weak

Broad NIR absorption

Strong

Narrow NIR absorption

Intermolecular MV Species – TTFTTF+

Figure 4. Spectral changes attendant upon the addition of neutral TTF to

the 5.8 mM solution of TTF+•CB- in CH2Cl2 at 22 C. TTF concentration

(bottom to top): 0, 44, 88, 141, 200, and 250 mM. Inset: Linear dependence

of ln KCT on 1/T.

S. V. Rosokha, J. K. Kochi, J. Am. Chem. Soc. 2007, 129, 828-838.

[TTF•TTF+]:

Kas = 6.0 M-1

Class II:

(2310 x max)1/2 = FWHM

[TTF+•TTF+]:

Kas = 0.6 M-1

Figure 2. Temperature-dependent absorption of 1.3 mM solutions of

TTF+•CB- in acetone, showing reversible interconversion between the

electronic spectrum of the monomer M (prevailing at room temperature)

and the dimer D (at low temperature). Temperature (in C, from bottom to

top at 740 nm): 22, - 40, - 55, - 63, - 70, - 78, - 85, and - 90. Inset:

Low-energy range of the absorption at high concentrations of TTF+·CB-

(λ ) 2 mm, 22 C). Concentration of TTF+•CB- (in mM, bottom to top):

0, 4.7, 6.2, 9.3, 13, and 19.

S. V. Rosokha, J. K. Kochi, J. Am. Chem. Soc. 2007, 129, 828-838.

-Dimer of Two TTF Radical Cations

D D

S

S S

S S

S S

S

SS

S S

• Redox properties?

• Optical properties of oxidized species?

• Interactions between redox centers?

Outline

Tetrathiafulvalene (TTF) – Acetylene Macrocycles

S

S

S

S

S

S

S

SEtS

EtS SEt

SEt

iPr3Si SiiPr3

S

S S

S

S S

S S

SS

RR

R

RR

R iPr3Si SiiPr3

TTF-Radiaannulene

Cross-conjugated cyclic core

S S

TTF-Dehydroannulene

Linearly conjugated cyclic core

How do the TTFs interact?

Synthesis of TTF-Dehydroannulenes

A. S. Andersson, K. Kilså, T. Hassenkam, J.-P. Gisselbrecht, C. Boudon, M. Gross,M. B. Nielsen, F. Diederich, Chem. Eur. J. 2006, 12, 8451.

K. Lincke, M. A. Christensen, F. Diederich, M. B. Nielsen, Helv. Chim. Acta 2011, 94, 1743-1753.

by Hay Couplings

S

S S

S

S

S

S S

S

SS

S

RR

R

R R

R

R = Pr, Hex, SEt

S

S

S

S

R

R

45-70%

Si(i-Pr)3

Si(i-Pr)3

1) Bu4NF, THF

S

S

S

S

R

R

2) CuCl, TMEDA

CH2Cl2, air

No - stacking interactions

The molecule does not seem either to associate in solution

X-Ray Crystal Structure

-0.50 -0.25 0.00 0.50 0.75 1.00

-4.0x10-5

-2.0x10-5

0.0

2.0x10-5

4.0x10-5

6.0x10-5

Cu

rre

nt

(A)

0.25

Potential (V)

Electrochemistry

S

S

S

S

S

SS

S

EtS SEt

S S

S S

SEt

SEtEtS

EtS

CH2Cl2 + 0.1 M Bu4NPF6

+1 +3

+6

Spectroelectrochemistry

M M+

M3+

M6+

MV absorption

CH2Cl2 + 0.1 M Bu4NPF6

S

S S

S

S

S

S

SS

S

EtS SEt

S S

SEt

SEtEtS

EtS

S

SS

S

S

S S

S

EtS

EtS SEt

SEt

(i-Pr)3Si Si(i-Pr)3

Si(i-Pr)3(i-Pr)3Si

S

S

S

SEtS

EtS I

I

(i-Pr)3Si Si(i-Pr)3

Pd(PPh3)4, CuI

iPr2NH10%

Synthesis of TTF-Radiaannulene

K. Lincke, A. F. Frellsen, C. R. Parker, A. D. Bond,O. Hammerich, M. B. Nielsen, Angew. Chem. 2012,

51, 6099-6102 .

by Sonogashira Couplings

A fused Weitz/Wurster-type redox system has been prepared by fusing a central

expanded radiaannulene core with two tetrathiafulvalene units. The system

formally gains H ! ckel aromaticity by either oxidation (6p-dithiolium units) or

reduction (14p-octadehydroannulene unit) and can exist in several redox states

with characteristic UV/Vis/IR absorptions. More about this system can be found in

the Communication by M. Brøndsted Nielsen and co-workers (DOI : 10.1002/

anie.201202324).

Size exclusion chromatography

SS

S

S

S

SS

S

Si(i-Pr)3(i-Pr)3Si

(i-Pr)3Si Si(i-Pr)3

EtS

EtS

SE

t

SE

t

Si(i-Pr)3(i-Pr)3Si

S

SS

S

EtS

EtSS

S

S

S SEt

SEt

Si(i-Pr)3(i-Pr)3Si

Si(i-Pr)3(i-Pr)3Si

MALDI MS

-3 -2 -1 0 1

-0.04

-0.02

0.00

-0.04

0.02

-0.02

0.00

-0.06

0.02

-0.04

-0.02

0.00

0.02

0.04-3 -2 -1 0 1

E/V

5

I/A

8

9

S

SS

S

S

S S

S

EtS

EtS SEt

SEt

(i-Pr)3Si Si(i-Pr)3

Si(i-Pr)3(i-Pr)3Si

S

SS

S

S

S S

S

EtS

EtS SEt

SEt

Si(i-Pr)3(i-Pr)3Si

S

S

S

SEtS

EtSSi(i-Pr)3

Si(i-Pr)3

Cyclic Voltammograms

+1+2

+2

+4

+1

+2

+4

9000 8000 7000 4000 3000 2000 1000

A

6000 5000

/cm-1

Neutral

Monocation

2250 2200 2100 2050

A

2150

/cm-1

7000

/nm

2000

FWHM = 2131 cm-1

Theory – Class II:

(2310 x max)1/2 = 3125 cm-1

Spectroelectrochemistry

S

SS

S

S

S S

S

EtS

EtS SEt

SEt

(i-Pr)3Si Si(i-Pr)3

Si(i-Pr)3(i-Pr)3Si

Radical cation: low-energy MV absorption

Si(i-Pr)3(i-Pr)3Si

S S

S S

BuS

BuS

S S

S S

SBu

SBu

S

S

S

S

BuS

BuS

S S

S S

SBu

SBu

Si(i-Pr)33(i-Pr) Si

S S

S S

BuS

BuS

S S

S S

SBu

SBu

Spectroelectrochemisty of Bis-TTFs

M M+M2+

MV absorptionMV absorption

MV absorption: short distance or cyclic structure

BJOC 2015, 11, 930-948.

-2 0 1-1

V vs Fc+/Fc

Cyclic voltammogram:

+1

+2

+4

-2

Mixed valence state:

max ca. 2250 nm

Neutral core: NICS()zz = -8.4 ppm

Dianion core: NICS()zz = -33.2 ppm

Gain in aromaticity (Wurster type)

6 redox statesS S

S S

S S

S SEtS

EtS SEt

SEt

(i-Pr)3Si Si(i-Pr)3

Si(i-Pr)3(i-Pr)3Si

-1

0

14

K. Lincke, A. F. Frellsen, C. R. Parker, A. D. Bond,O. Hammerich, M. B. Nielsen, Angew. Chem. Int. Ed.

2012, 51, 6099-6102 .

Hückel 4n+2

300 500 900 1100

A

700

/nm

Neutral

Monoanion

Neutral regenerated

Spectroelectrochemistry – Generation of Monoanion

S

SS

S

S

S S

S

EtS

EtS SEt

SEt

(i-Pr)3Si Si(i-Pr)3

Si(i-Pr)3(i-Pr)3Si

CT(neutral

compound)

S S

S

SS

S

S S

S

SS

S

SEtEtS

SEt

SEt

EtS

EtS

BC

E / eV (electrochemistry)

S S

S S

EtS

EtS

S S

S S

SEt

SEt

Si(i-Pr)3(i-Pr)3Si

Si(i-Pr)3(i-Pr)3Si

A

(i-Pr)3Si Si(i-Pr)3

S

SS

S S

SS

S

EtS

EtS SEt

SEt

HOMO-LUMO Gap Comparison of Neutral Compounds

1.9

1.85

1.8

1.75

1.7

1.65

1.6

1.55

1.5

1.45

1.4

1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9

E

/eV

(U

V-V

is)

A

B

C

HOMO

LUMO

ABC

D D

SS

S S

• Redox properties?

• Optical properties of oxidized species?

• Interactions between redox centers?

Outline

S

S S

S S

S S

S

CH2Cl2 + 0.1 M NBu4PF6

Potentials vs Fc+/Fc

-0.25 0.00 0.25 0.75 1.00 1.25

-5.0x10-5

0.0

5.0x10-5

Curr

en

t (A

)

0.50

Potential (V)

ox

10 cycles

E = +0.72 V

Me3Si SiMe3

S

S

CO2Me

SMeO2C

CO2MeS

MeO2C

Me3Si SiMe3

S

S

CO2Me

SMeO2C

CO2MeS

MeO2C

Me

Me

Electrochemistry – Cyclic Voltammetry

Independent

redox centers

(Class I)

J. Am. Chem. Soc. 2014, 47, 16497−16507.

S S

S S

R R

RR'

S S

S S

R R

R R

- 2e

+ 2e

F.G. Brunetti, J.L. López, C. Atienza, N. Martín,J. Mater. Chem. 2012, 22, 4188-4205.

Potential Inversion

E2 < E1

C. A. Christensen,A. S. Batsanov, M. R. Bryce, J. Am. Chem. Soc. 2006, 128, 10484-10490.

Rigid Cyclophane

Intermediate radical cation

Extended TTFs

S

S S

S

TTF

S S

S S

S

S

S

S S

S

S

S

TTF2+S S

R R

RR

S S

S S

R R

R R

S S

S S

S S

S S

S S

S S

TTF +

S S

Intermediate?

Fully delocalized?

Indenofluorene-extended TTF

S S

S S

BuS SBu

O

BuS SBu

S S

SBuBuS

O

O

SS

S

BuS

BuS

P(OEt)3, 23%

S

S

BuS

BuS

O

P(OMe)2

NaHMDS, THF

69%

Synthesis ofIndenofluorene-Extended TTF

J. Mater. Chem. 2014, 2, 10428-10438.

0.8 0.6 0.4 0.2 0.0 -0.2

-30

-20

-10

10

20

ic-1/(

Am

M-1)

E/V 1.2 1.0

-10

-8

-6

-4

00

-2

2

4

i(

A)

0.8 0.6

E (V vs. Ag)

CH2Cl2 (0.1 M Bu4NPF6); Potentials vs Fc+/Fc

1 mM

0.06 mM

21 oC

-5.5 oC

0.25 mM

Cyclic Voltammetry

Concentrationdependence

21

16

10

3.5

-5.5

Temperature dependence

0.4 0.2

Intermolecular interactions

S S

S S

S S

S S

S S

S S

BuS SBu

BuS SBu

BuS SBu

BuS SBu

BuS SBu

BuS SBu

- e

+ e

- e

+ e

-30

-25

-20

-15

-10

-5

0

5

10

15

i/

A

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1

E/V

experimental

simulated

d2+ + e- c·+

c·+ + e- n

[c-c]2+ + e- [n-c]·+

[n-c]·+ + e- [n-n]

c·+ + c·+ n + d2+

c·+ + n [n-c]·+

[n-c]·+ + c·+ [c-c]2+ + n

[n-c]·+ + d2+ [c-c]2+ + c·+

c·+ + c·+ [c-c]2+

n + n [n-n]

redox-1

redox-2

redox-3

redox-4

Eq.-1

Eq.-2

Eq.-3

Eq.-4

Eq.-5

Eq.-6

n + [n-c]·+c·+ + [n-n]Eq.-7

c·+ + [n-c]·+d2+ + [n-n]Eq.-8

S S

SBu

Complexes:

neutral – neutral

neutral – cation

cation – cation

BuS

n

Simulation ofCyclic Voltammogram

S S

BuS

c+

SBu

S S

BuS

d2+

SBu

BuS SBu BuS SBu BuS SBu

S S S S S S

Spectroelectrochemistry

Relative intensities of low-energy

absorptions are concentration dependent

M M+M2+

/ nm

J. Mater. Chem. 2014, 2, 10428-10438.

M M+M2+

M+

M:M+

M+:M+

M+

M+:M+

S S

S S

BuS SBu

BuS SBu

Spectroelectrochemistry

MV Dimer:Kas = 7.8 x 104 M-1

-Dimer:Kas = 1.8 x 104 M-1

[TTF•TTF+]: Kas = 6.0 M-1

[TTF+•TTF+]: Kas = 0.6 M-1

S. V. Rosokha, J. K. Kochi, J. Am. Chem. Soc. 2007, 129, 828-838

After 10% conversion

After 90% conversion

Ottle cell

Progression from yellow to blue solution upon oxidation

(neutral to dication)

Electrocrystallization

Solvent: PhCl + counter electrolyte

S S

EtS SEt

S S

SEtEtS

a) b) c)

Cation•TaF6

Cation•PF6 Cation•Dication•(BF4)1.5 Cation•TaF6

J. Mater. Chem. 2014, 2, 10428-10438.

Conductances of Salts S S

S S

EtS SEt

SEtEtS

IFTTF

semiconductors

CAN WE ENHANCE THE CATION ASSOCIATIONS?

Incorporation of Fused Thiophene Units

S

S

BuS

BuS

O

P(OMe)2

S

S

S

S

S

BuS

SBu

S

SBu

SBu

S

S

O

O

S

SS

S

S

S

BuS

SBu

BuS

SBu

S

S

O

O

SS

S

S

RSS

SR SR

SRSO O

NaHMDS, THF

65%

R = Et (67%) R = Bu (64%)

S

S

BuS

BuS

O

P(OMe)2

NaHMDS, THF

40%

S

S

RS

RS

O

P(OMe)2

NaHMDS, THF

RSC Adv. 2015, 5, 49748-49751.

SS

S S

S

BuS

SBu SBu

SBu

Differential Pulse Voltammograms

S

SS

S

S

S

BuS

SBu

BuS

SBu

S

S

S

S

S

S

BuS

SBu

SBu

MV Dimer:

Kas = 1.8 x 104 M-1

-Dimer:

Kas = 2.8 x 103 M-1

Associations increase

(by one order

of magnitude)

SBu

RSC Adv. 2015, 5, 49748-49751.

SS

S S

S

BuS

SBu SBu

SBu

Differential Pulse Voltammograms

Oxidation Potentials

+0.14 V, +0.31 V

+0.32 V, +0.60 V

+0.09 V, +0.33 VS

S

S

S

S

S

BuS

SBu

SBu

SBu

S

SS

S

S

S

BuS

SBu

BuS

SBu

Linear conjugation

Cross-conjugation

(weakest donor)

SS

S

S

BuS S

SBu SBu

SBu

S

SS

S

S

S

BuS

SBu

SBu

S

S

S

S

S

S

BuS

BuS

SBu

SBu

SBu

Spectroelectrochemistry M M+M2+

Conclusions

S

S

S

S

S

SS

S

R R

S S

R

RR

R

S S

S S

S S

S SEtS

EtS SEt

SEt

iPr3Si SiiPr3

S S

TTF-Acetylene Macrocycles

Strong charge-transfer chromophores

Multiple redox states with distinct optical properties – molecules can both be oxidized and reduced

Interactions between TTFs are enforced

in the cyclic structures in comparison

to acyclic ones (MV absorptions of radical cations)

S S

S S

BuS SBu

SBuBuS

Indenofluorene-Extended TTFs

Strong associations between cations- Tectons for self-assembly

Broad UV-Vis-NIR absorptions

Thiophene units enhance donor strength

significantly when redox centers are

connected in linearly conjugated

pathway

S

S

S

S

S

S

BuS

SBu

SBu

SBu

iPr3Si SiiPr3

Combined Weitz and Wurster type redox system

University of Copenhagen:

Past and present group members:

Dr. Christian R. Parker

Dr. Mikkel A. Christensen

Dr. Karsten JennumDr. Marco Santella

Dr. Kasper Lincke

Dr. Søren Lindbæk Broman Dr. Virginia MazzantiPeter Bæch Abrahamsen

Emil GlibstrupMads Mansø

Huixin Jiang

Anders F. Frellsen

Cecilie L. Andersen

Prof. O. HammerichProf. Henrik G. Kjaergaard

Assoc. Prof. Thomas J. SørensenDr. Eduardo Della PiaDr. Theis Brock-NannestadT. J. Morsing

University of Oregon:

Prof. Michael M. Haley Gabriel E. Rudebusch

Acknowledgements

Villum Foundation