Research ArticleExperimental and Theoretical Studies on the Structure andPhotoluminescent Properties of New Mononuclear andHomodinuclear Europium(III) 120573-Diketonate Complexes
Joatildeo P Martins1 Pablo Martiacuten-Ramos12
Pedro Chamorro-Posada3 Pedro S Pereira Silva1 Jesuacutes Martiacuten-Gil4
Salvador Hernaacutendez-Navarro4 and Manuela Ramos Silva1
1CFisUC Department of Physics University of Coimbra Rua Larga 3004-516 Coimbra Portugal2Higher Polytechnic School of Huesca University of Zaragoza Carretera de Cuarte sn 22071 Huesca Spain3Signal Theory Communications and Telematics Engineering Department ETSIT University of ValladolidCampus Miguel Delibes Paseo Belen 15 47011 Valladolid Spain4Advanced Materials Laboratory ETSIIAA University of Valladolid Avenida de Madrid 44 34004 Palencia Spain
Correspondence should be addressed to Manuela Ramos Silva manuelapolluxfisucpt
Received 19 April 2015 Accepted 10 June 2015
Academic Editor Jorg Fink
Copyright copy 2015 Joao P Martins et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Two novel europium(III) complexes a monomer and a homodimer with 1-(4-chlorophenyl)-444-trifluoro-13-butanedione(Hcbtfa) and 5-chloro-110-phenanthroline (cphen) ligands formulated as [Eu(cbtfa)
3(cphen)] and [Eu
2(cbtfa)
4(cphen)
2(CH3O)2]
have been synthesized Their structures have been elucidated by X-ray diffraction and their absorption and emission propertieshave been studied in the solid state The experimental data has then been used to test the recently released LUMPAC software apromising tool which can facilitate the design ofmore efficient lanthanide light-conversionmolecular devices by combining groundstate geometry excited state energy and luminescent properties calculations
1 Introduction
The development of strategies for the design of highlyluminescent lanthanide coordination complexes is of crucialimportance with a view to a wide range of technologicalapplications which encompass for example organic-lightemitting diodes (OLEDs) luminescent probes in biomedicalassays time resolved microscopy luminescent sensors forchemical species or coatings for photovoltaics [1 2] Suchstrategies aimed at optimizing the quantum yields and otherrelevant properties ultimately depend on gaining a betterinsight on the correlation of those properties with structuraldata and the combination of experimental and theoreticalcharacterization resources is deemed as a very promisingapproach
In the particular case of Eu(III)-based light-conversionmolecular devices (LCMDs) the application of theoretical
chemistry methods to analyse the changes in structuralparameters bond energies and other properties of thelanthanide complexes as a function of ligand typesmdashin orderto boost their luminescence quantum yieldmdashhas been arecurrent theme in the literature from the pioneering workof de Sa et al back to 2000 [3] to the work of Freire et al [4ndash6] or to the more recent and comprehensive approaches offor example Lima et al [7]
Amongst the different theoretical models available thesemiempirical Sparkle [6] model is particularly attractive forthe determination of ground state geometries since it canattain a similar accuracy to that achieved by ab initioECP fullgeometry optimization calculations with significantly lowerCPU times [8ndash10] However the prediction of luminescentproperties (such as singlet and triplet energy states intensityparameters energy transfer and back-transfer rates radiativeand nonradiative rates and quantum efficiencies or quantum
Hindawi Publishing CorporationAdvances in Condensed Matter PhysicsVolume 2015 Article ID 205047 11 pageshttpdxdoiorg1011552015205047
2 Advances in Condensed Matter Physics
O
O
FF
F
Cl
NN
Cl
OOF
FF
Cl
Eu
O
O
FF
F
Cl
(a)
O
O
FF
F
Cl
NN
Cl
OOF
FF
Cl
Eu O
O
FF
F
Cl
N N
Cl
O OF
FF
Cl
Eu
O
O
H3C
H3C
(b)
Figure 1 Chemical structures of complex 1 (a) and complex 2 (b)
yields) from the optimized ground state geometries couldbe regarded as an unresolved matter due to the lack ofconvenient software toolsThis situation has recently changeddue to release of the free and user-friendly LUMPAC software[11] which covers these calculations in its third module
Encouraged by the first results published by the groupwho developed the software [12 13] we have hereby assessedLUMPAC for the theoretical study of two closely relatedEu3+ complexes a monomer and a homodinuclear complexin which the Eu3+ ion(s) is(are) coordinated by the same120573-diketonate (Hcbtfa) and the same diimide (cphen) Thechosen 120573-diketonate Hcbtfa is a more halogenated variantof 444-trifluoro-1-phenyl-13-butanedione (btfa) which hasbeen deemed as one of the best possible choices in termsof maximizing the Eu3+ luminescence quantum yield [7]In fact an analogous monomeric complex with Hcbtfaand bathophenanthroline [Eu(cbtfa)
3(bath)] [14] recently
attained a quantum efficiency of ca 60 and was successfullytested as chromophore for cost-effective OLEDs
In this study the synthesis X-ray structure and lumi-nescent properties of the aforementioned two novel Eu3+-based materials are reported and this data has then beenused as a reference in order to evaluate the suitability ofthe semiempirical calculation methods for predicting theequilibrium energy configuration the electronic properties(resorting to INDOS-CIS method) and the luminescentproperties of the complexes making use of the differentmodules of LUMPAC software
2 Experimental and Computational Methods
21 Materials and Synthesis All reagents and solventsemployed were commercially available and used without fur-ther purification All the procedures for complex preparationwere carried out under nitrogen and using dry reagents toavoid the presence of water and oxygen so as to avoid metalphotoluminescence (PL) quenching issues
Tris(14-chlorophenyl-444-trifluoro-13-butanedionate)mono(5-chloro-110-phenanthroline) europium(III) com-plex 1 (Figure 1(a)) was obtained as follows under stir-ring Eu(NO
3)3sdot5H2O (1mmol 999 purum CAS number
63026-01-7 Sigma Aldrich) was mixed with 14-chloro-phenyl-444-trifluoro-13-butanedione (3mmol 97 pu-rum CAS number 18931-60-7 Sigma Aldrich) in methanol(20mL) and a potassium methylate solution (3mmol 95purum CAS number 865-33-8 Sigma Aldrich) in methanolwas added to neutralize the mixture KNO
3was removed by
decanting and 5-chloro-110-phenanthroline (1mmol 98purum CAS number 4199-89-7 Sigma Aldrich) was finallyaddedThemixture was heated to 75∘C and stirred overnightthen washed with 14-dioxane and finally dried in vacuumto give the product in 90ndash95 yield (based on Eu) Crystalssuitable for X-ray analysis were obtained by slow evaporationof a methanol-dioxane solution at room temperature (RT)
ropium(III) complex 2 (Figure 1(b)) was obtained as a by-product of aforementioned synthesis procedure
22 X-Ray Crystallographic Analysis For the determinationof the two crystal structures presented in this paper sin-gle crystals were glued to glass fibres and mounted on aBruker APEX II diffractometer In both cases diffractiondata was collected at room temperature 293(2) K usinggraphite monochromated MoKa (120582 = 071073 A) radiationAbsorption corrections were made using SADABS [18] Thestructures were solved by direct methods using SHELXS-97 and refined anisotropically (non-H atoms) by full-matrixleast-squares on 1198652 using the SHELXL-97 program [19]PLATON [20] was used for analyzing the structure and forfigure plotting All the tested crystals of complex 1 were foundto be ill-formed and unstable during the few hours of thedata collections To be able to refine a sensible molecularmodel the whole arsenal of SHELXL restraints had to be used(ISOR DFIX FLAT and SIMU) The final model is just anapproximate model good enough to be used as a startingpoint for the semiempirical methods Atomic coordinatesthermal parameters and bond lengths and angles have beendeposited at the Cambridge Crystallographic Data Centre(CCDC) Any request to the CCDC for this material shouldquote the full literature citation and the reference numbersCCDC 1057047-1057048
Advances in Condensed Matter Physics 3
Figure 2 Structural diagram of complex 1 tris(14-chlorophenyl-444-trifluoro-13-butanedionate) mono(5-chloro-110-phenanthroline)europium(III) H atoms have been omitted for clarity reasons
23 Spectroscopic Measurements Optical absorption andphotoluminescence spectra of thematerials weremeasured atroom temperatureThe 285ndash800 nm range absorption spectrawere recordedwith a Cary 4000Varian spectrophotometer inpowder form Photoluminescence spectra of the materialsmdashin powdermdashwere obtained at room temperature using amod-ular spectrophotometer Horiba-Jobin-Yvon SPEX Fluorolog3 All spectra have been corrected by the spectral response ofthe experimental setups
24 Computational Methods Using the experimental crys-tallographic data as an initial guess the ground stategeometries were obtained using the SparklePM6 [21 22]and SparklePM7 [23 24] models implemented in theMOPAC2012 software [25 26] using periodic boundaryconditions One unit cell for each of the complexes wasemployed in the calculations by setting the keywordMERS =(1 1 1) Geometry optimizationswere performed for isolatedcomplexes as well Additionally the corresponding vibra-tional frequencies were computed for the PM6 optimizedgeometries for the two complexes in the gas phase Noimaginary vibrational frequencies were found for any ofthe geometries confirming that the results obtained cor-responded to true ground states These computations wereperformed on aDebian Linux serverwith fourAMDOpteron16 Core processors and 128GB of memory and a Linuxoperating system
The electronic spectra for each of the optimized struc-tures were calculated using the ORCA electronic structurepackage [27 28] via the intermediate neglect of differentialoverlapspectroscopic (INDOS) method and configuration
interaction with singles (CIS) [29ndash31] replacing the Eu3+ions with point charges as described by de Andrade et al[32 33] Version 301 was used for calculations invoked usingLUMPAC 10 distribution
The geometry optimization and the analysis of electronictransitions using the INDOS-CIS method are integrated ina user-friendly manner in the first and second modulesrespectively of LUMPAC software ecosystem The thirdmodule is a unique feature of LUMPAC and permits cal-culating the Judd-Ofelt intensity parameters [34] and theestimation of metal-ligand energy transfer and back-transferrates [35] the radiative and nonradiative emission ratestheoretical quantum efficiency and emission quantum yield[36] Calculations within LUMPACmodules were performedusing aWindows 8 Toshiba Satellite Core i5 laptop computer
The theoretical Judd-Ofelt parameters are determined byadjusting the charge factors and polarizabilities to reproducethe experimental values In this calculation it is requiredto provide the coordination polyhedron of the system asinput For the highly symmetric binuclear complex theanalyses have been performed by independently treating thetwo europium ions with their corresponding coordinationpolyhedra as in the individual polyhedron method reportedby Dutra et al [13]
3 Results and Discussion
31 Structural Description In the mononuclear complexcomplex 1 the Eu3+ ions are coordinated by three negativelycharged 120573-diketonate ligands and a neutral ancillary NN-donor moiety (Figure 2 Table 1) There are two symmetry
4 Advances in Condensed Matter Physics
Table 1 Crystal data and structure refinement for the mononuclear and the homodinuclear Eu3+ complexes
Complex Complex 1 Complex 2Empirical formula C42H22Cl4EuF9N2O6 C66H40Cl6Eu2F12N4O10
Formula weight 111538 179364Temperature (K) 293(2) 293(2)Wavelength (A) 07107 07107Crystal system Triclinic TriclinicSpace group P-1 P-1119886 (A) 13246(5) 102575(11)119887 (A) 18252(7) 129224(15)119888 (A) 21081(8) 150618(16)120572 (∘) 98241(8) 72179(6)120573 (∘) 99461(11) 80460(6)120574 (∘) 108751(10) 84813(6)Volume (A3) 4654(3) 18727(4)119885 4 1Calculated density (g cmminus3) 1592 1590Absorption coefficient (mmminus1) 1659 1958119865(000) 2192 880120579 range for data collection 167ndash2587∘ 144ndash2580∘
Index ranges minus16 lt ℎ lt 10 minus22 lt 119896 lt 18 minus16 lt 119897 lt 25 minus11 lt ℎ lt 12 minus15 lt 119896 lt 15 minus16 lt 119897 lt 18Reflections collected 20295 33633Independent reflections 3654 4769Completeness to 2120579 = 51∘ 89 98Refinement method Full-matrix LS on 1198652 Full-matrix LS on 1198652
Datarestraintsparameters 160252991181 70480452Goodness-of-fit on 1198652 0978 0980Final R indices [119868 gt 2120590(119868)] 119877 = 01169 119908119877 = 01820 119877 = 00436 119908119877 = 00792119877 indices (all data) 119877 = 02894 119908119877 = 02159 119877 = 01012 119908119877 = 01097Largest difference peak and hole minus18011623 minus06931076
independent complexes in the unit cell The coordinationspheres of these monomers consist in a square antiprismaticgeometry Table 2 summarizes the Eu-N and Eu-O distancesfor both complexes in the unit cell affected by large exper-imental uncertainties Nevertheless all of them are withinthe normal ranges reported in the literature [17 37] Bothmonomers show heavy disorder particularly evident for theCF3groups of the cbtfa ligands and for the Cl substitute
of the phenanthroline The structure contains large solventaccessible voids
Complex 2 (Figure 3 Table 1) corresponds to a dimericvariation of complex 1 in which the Eu3+ ions are bridgedby two methanolate ions Each Eu3+ ion is coordinated bytwo negatively charged 120573-diketonate (cbtfa) ligands a neutraldiimide ligand (cphen) and the two bridging methanolateions Complex 2 crystallizes in a triclinic centrosymmetriccell with the center of symmetry lying in the middle pointof the dimer There is one dimer per unit cell
Coordination distances are within the normal rangesreported in the literature [14 17 37] and the sameapplies to the bite angles with values close to 70∘ forthe O Eu O angles and of ca 60∘ for the N Eu Nangle The coordination sphere corresponds to a square
antiprism The Eu3+ ions are at a distance of 3742 A withinthe dimer
No conventional H-bonds were found joining the dimersThe packing seems to be influenced by 120587 120587 interactions(Figure 4) Neighboring phenanthroline rings are at 4143 Adistances (centroid-to-centroid) with a slippage of 2089 A
The low crystallinity of the bulk synthesized materialin which the single crystals of complexes 1 and 2 weremixed with more amorphous material prevented a reliabledetermination of the proportions of complex 1 and complex2 by means of X-ray powder diffraction
32 Modeling of the Structures by Semiempirical Methods Acomparison of the unit cell parameters obtained for the PM6and PM7 predicted structures (eg Figure 5) versus thoseof the SC-XRD data is summarized in Table 3 The percenterrors are below 5 in all cases (generally below 2) Theyare similar for both Hamiltonians in the case of complex 1while the estimation with PM7 is slightly better in the case ofcomplex 2 for all parameters except for the 119888 value (which inturn leads to an incorrect volume estimation)
The Eu-N and Eu-O distances and some selected anglesin the ground state geometries of the monomer and the
dimer (using either the PM6 or the PM7 Hamiltonian withperiodic boundary conditions) are compared with those of
the actual structures obtained from SC-XRD data in Table 4The distance values obtained using the PM7 Hamiltonian areremarkably closer to the experimental average values thanthose attained with the PM6 Hamiltonian in all cases Thisis particularly obvious for the Eu-O distances in the dimerwhile in the PM6 case they are very similar in all cases (witha significant error for the bridging methanol bonds) PM7Hamiltonian gives a much more accurate estimation anddistinguishes between the bonds associatedwith cbtfa ligandsand those corresponding to bridging methanol moleculesRegarding the angle values the percent errors are signifi-cantly higher than those for the bond lengths but PM7 errorsare consistently lower than those for PM6
This is in agreement with the observationsmade byDutraet al [24] a significant increase in accuracy has been achievedin PM7 after relatively minor changes were made to theapproximations and after proxy reference data functions rep-resenting noncovalent interactions were introduced leadingto a reduction of errors in PM7 geometries by over one-thirdrelative to those of PM6 On the other hand PM7 methodcan showworse convergence properties when compared withPM6 as it was reported in [10]
33 Luminescent Properties The experimental excitationspectrum for the mixture of the monomer and the dimer isdepicted in Figure 6(a) It exhibits a maximum at 355 nmwhich can be assigned to the electronic transitions from theground state level (120587) 119878
0to the excited level (120587lowast) 119878
1of the
cbtfa organic ligand [14 15 39ndash41] according to Figure 7Thepredicted absorption spectra for the gas phase geometriesoptimized with the SparklePM6 method calculated usingthe INDOS-CIS procedure are also shown Gabedit software
Table 3 Comparison of the unit cell parameters for PM6 and PM7 predicted structures In parentheses for the experimental values standarddeviation is shown for theoretical values percent error is indicated
Table 4 Comparison of the experimental and calculated average Eu-N and Eu-O distances (in A) and selected angles (in ∘) for themononuclear (monomer 1) and the homodinuclear Eu3+ complexes In parentheses for the experimental values standard deviation is shownfor theoretical values percent error is indicated
Table 5 Comparison of theoretical (for complex 1 and complex 2) and experimental values (for similar Eu3+ complexes reported in theliterature) of the intensity parameters (Ω
120582) radiative (119860 rad) and nonradiative (119860nrad) emission rates and quantum yields (120578)
Compound Intensity parameters (10minus20 cm2)119860 rad (s
Figure 5 Comparison of the SparklePM6 (blue) and SparklePM7(green) optimized geometries with the X-ray geometry (red) ofcomplex 2 (software used for visualization VMD version 191 [38])
[42] has been used for the representation of the spectra fromthe calculated data As expected there is a hypsochromic shiftfor the lowest predicted transition (versus the experimentalone) as it is usually the case in this type of calculations [3]
Upon excitation of the organic ligands in the UV regionefficient indirect excitation of Eu3+ is attained via antennaeffect [43] Figure 6(b) shows the experimental photolumi-nescence spectrum in which the characteristic narrow emis-sion bands of Eu3+ corresponding to the intraconfigurational5D0rarr 7FJ (119869 = 0ndash4) transitions appear The five expected
peaks for the 5D0rarr 7F
0ndash4 transitions (namely 5D0rarr 7F
0
(sim580 nm) 5D0rarr 7F
1(sim591 nm) 5D
0rarr 7F
2(sim614 nm)
5D0rarr 7F
3(sim651 nm) and 5D
0rarr 7F
4(sim692 nm)) [44] can
be identified (see Figure 7)The emission bands at ca 580 and 651 nm are weak
since their corresponding transitions 5D0rarr 7F
03are
forbidden both in magnetic and electric dipole schemes [47]The intensity of the emission band at 593 nm is stronger andindependent of the coordination environment because the
corresponding transition 5D0rarr 7F
1is of magnetic charac-
ter In contrast the 5D0rarr 7F
2transition is an induced elec-
tric dipole transition and its corresponding intense emissionat 613 nm is very sensitive to the coordination environment[47] This very intense 5D
0rarr 7F
2peak responsible for the
brilliant red emission of the complex indicates that the ligandfield surrounding the Eu3+ ion is highly polarizable
With regard to the monochromaticity (R) that is theintensity ratio of the electric dipole transition to themagneticdipole transition (redorange ratio) the obtained value is 172This indicates that the CIE chromaticity coordinates for thecomplex should be very close to saturated red emission [48]and that the Eu3+ coordination is consistent with a local sitewithout inversion [49ndash51]
The lifetime measurements for the mixture of themonomer and the dimer (not shown) do not correspond toa monoexponential decay curve which is consistent with thepresence of two slightly different coordination environmentsfor the Eu3+ ion in complex 1 and complex 2 The estimatedaverage 120591 value would be close to 700 120583s in the same rangeas the lifetimes reported for similar complexes with cbtfaand btfa ligands 754120583s for [Eu(cbtfa)
3(bath)] [14] 670 120583s for
[Er(btfa)3(phen)] [15 52] and 750120583s [Eu(btfac)
3(dmbipy)]
[53]
34 Theoretical Modeling of the Luminescent Properties withLUMPAC By using LUMPAC lanthanide luminescence soft-ware package [11ndash13] singlet and triplet excited state energiesfor the lanthanide containing systems were obtained fromINDOS-CIS ORCA [27] calculations From the experi-mental emission spectrum and estimated lifetime valueJudd-Ofelt intensity parameters radiative and nonradiativeemission rates and quantum efficiencies were also calculatedThe isolated complex ground state geometries have been usedin the calculations As discussed above the two Eu3+ ions incomplex 2 have been treated individually and are describedas Eu1 and Eu1a in Table 5
The estimated singlet (3682740 cmminus1 for the monomerand 3694560 cmminus1 for the dimer) is higher than that of thecbtfa ligand (30675 cmminus1 [16]) but would be a reasonable
8 Advances in Condensed Matter Physics
Abso
rptio
n (a
u)
Wavelength (nm)300 400 500 600 700
ExperimentalCalculated complex 1
Calculated complex 2
(a)
Wavelength (nm)
PL em
issio
n (a
u)
550 600 650 700
5D0 rarr7F0
5D0 rarr7F2
5D0 rarr7F1
5D0 rarr7F3
5D0 rarr7F4
(b)
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Figure 1 Chemical structures of complex 1 (a) and complex 2 (b)
yields) from the optimized ground state geometries couldbe regarded as an unresolved matter due to the lack ofconvenient software toolsThis situation has recently changeddue to release of the free and user-friendly LUMPAC software[11] which covers these calculations in its third module
Encouraged by the first results published by the groupwho developed the software [12 13] we have hereby assessedLUMPAC for the theoretical study of two closely relatedEu3+ complexes a monomer and a homodinuclear complexin which the Eu3+ ion(s) is(are) coordinated by the same120573-diketonate (Hcbtfa) and the same diimide (cphen) Thechosen 120573-diketonate Hcbtfa is a more halogenated variantof 444-trifluoro-1-phenyl-13-butanedione (btfa) which hasbeen deemed as one of the best possible choices in termsof maximizing the Eu3+ luminescence quantum yield [7]In fact an analogous monomeric complex with Hcbtfaand bathophenanthroline [Eu(cbtfa)
3(bath)] [14] recently
attained a quantum efficiency of ca 60 and was successfullytested as chromophore for cost-effective OLEDs
In this study the synthesis X-ray structure and lumi-nescent properties of the aforementioned two novel Eu3+-based materials are reported and this data has then beenused as a reference in order to evaluate the suitability ofthe semiempirical calculation methods for predicting theequilibrium energy configuration the electronic properties(resorting to INDOS-CIS method) and the luminescentproperties of the complexes making use of the differentmodules of LUMPAC software
2 Experimental and Computational Methods
21 Materials and Synthesis All reagents and solventsemployed were commercially available and used without fur-ther purification All the procedures for complex preparationwere carried out under nitrogen and using dry reagents toavoid the presence of water and oxygen so as to avoid metalphotoluminescence (PL) quenching issues
Tris(14-chlorophenyl-444-trifluoro-13-butanedionate)mono(5-chloro-110-phenanthroline) europium(III) com-plex 1 (Figure 1(a)) was obtained as follows under stir-ring Eu(NO
3)3sdot5H2O (1mmol 999 purum CAS number
63026-01-7 Sigma Aldrich) was mixed with 14-chloro-phenyl-444-trifluoro-13-butanedione (3mmol 97 pu-rum CAS number 18931-60-7 Sigma Aldrich) in methanol(20mL) and a potassium methylate solution (3mmol 95purum CAS number 865-33-8 Sigma Aldrich) in methanolwas added to neutralize the mixture KNO
3was removed by
decanting and 5-chloro-110-phenanthroline (1mmol 98purum CAS number 4199-89-7 Sigma Aldrich) was finallyaddedThemixture was heated to 75∘C and stirred overnightthen washed with 14-dioxane and finally dried in vacuumto give the product in 90ndash95 yield (based on Eu) Crystalssuitable for X-ray analysis were obtained by slow evaporationof a methanol-dioxane solution at room temperature (RT)
ropium(III) complex 2 (Figure 1(b)) was obtained as a by-product of aforementioned synthesis procedure
22 X-Ray Crystallographic Analysis For the determinationof the two crystal structures presented in this paper sin-gle crystals were glued to glass fibres and mounted on aBruker APEX II diffractometer In both cases diffractiondata was collected at room temperature 293(2) K usinggraphite monochromated MoKa (120582 = 071073 A) radiationAbsorption corrections were made using SADABS [18] Thestructures were solved by direct methods using SHELXS-97 and refined anisotropically (non-H atoms) by full-matrixleast-squares on 1198652 using the SHELXL-97 program [19]PLATON [20] was used for analyzing the structure and forfigure plotting All the tested crystals of complex 1 were foundto be ill-formed and unstable during the few hours of thedata collections To be able to refine a sensible molecularmodel the whole arsenal of SHELXL restraints had to be used(ISOR DFIX FLAT and SIMU) The final model is just anapproximate model good enough to be used as a startingpoint for the semiempirical methods Atomic coordinatesthermal parameters and bond lengths and angles have beendeposited at the Cambridge Crystallographic Data Centre(CCDC) Any request to the CCDC for this material shouldquote the full literature citation and the reference numbersCCDC 1057047-1057048
Advances in Condensed Matter Physics 3
Figure 2 Structural diagram of complex 1 tris(14-chlorophenyl-444-trifluoro-13-butanedionate) mono(5-chloro-110-phenanthroline)europium(III) H atoms have been omitted for clarity reasons
23 Spectroscopic Measurements Optical absorption andphotoluminescence spectra of thematerials weremeasured atroom temperatureThe 285ndash800 nm range absorption spectrawere recordedwith a Cary 4000Varian spectrophotometer inpowder form Photoluminescence spectra of the materialsmdashin powdermdashwere obtained at room temperature using amod-ular spectrophotometer Horiba-Jobin-Yvon SPEX Fluorolog3 All spectra have been corrected by the spectral response ofthe experimental setups
24 Computational Methods Using the experimental crys-tallographic data as an initial guess the ground stategeometries were obtained using the SparklePM6 [21 22]and SparklePM7 [23 24] models implemented in theMOPAC2012 software [25 26] using periodic boundaryconditions One unit cell for each of the complexes wasemployed in the calculations by setting the keywordMERS =(1 1 1) Geometry optimizationswere performed for isolatedcomplexes as well Additionally the corresponding vibra-tional frequencies were computed for the PM6 optimizedgeometries for the two complexes in the gas phase Noimaginary vibrational frequencies were found for any ofthe geometries confirming that the results obtained cor-responded to true ground states These computations wereperformed on aDebian Linux serverwith fourAMDOpteron16 Core processors and 128GB of memory and a Linuxoperating system
The electronic spectra for each of the optimized struc-tures were calculated using the ORCA electronic structurepackage [27 28] via the intermediate neglect of differentialoverlapspectroscopic (INDOS) method and configuration
interaction with singles (CIS) [29ndash31] replacing the Eu3+ions with point charges as described by de Andrade et al[32 33] Version 301 was used for calculations invoked usingLUMPAC 10 distribution
The geometry optimization and the analysis of electronictransitions using the INDOS-CIS method are integrated ina user-friendly manner in the first and second modulesrespectively of LUMPAC software ecosystem The thirdmodule is a unique feature of LUMPAC and permits cal-culating the Judd-Ofelt intensity parameters [34] and theestimation of metal-ligand energy transfer and back-transferrates [35] the radiative and nonradiative emission ratestheoretical quantum efficiency and emission quantum yield[36] Calculations within LUMPACmodules were performedusing aWindows 8 Toshiba Satellite Core i5 laptop computer
The theoretical Judd-Ofelt parameters are determined byadjusting the charge factors and polarizabilities to reproducethe experimental values In this calculation it is requiredto provide the coordination polyhedron of the system asinput For the highly symmetric binuclear complex theanalyses have been performed by independently treating thetwo europium ions with their corresponding coordinationpolyhedra as in the individual polyhedron method reportedby Dutra et al [13]
3 Results and Discussion
31 Structural Description In the mononuclear complexcomplex 1 the Eu3+ ions are coordinated by three negativelycharged 120573-diketonate ligands and a neutral ancillary NN-donor moiety (Figure 2 Table 1) There are two symmetry
4 Advances in Condensed Matter Physics
Table 1 Crystal data and structure refinement for the mononuclear and the homodinuclear Eu3+ complexes
Complex Complex 1 Complex 2Empirical formula C42H22Cl4EuF9N2O6 C66H40Cl6Eu2F12N4O10
Formula weight 111538 179364Temperature (K) 293(2) 293(2)Wavelength (A) 07107 07107Crystal system Triclinic TriclinicSpace group P-1 P-1119886 (A) 13246(5) 102575(11)119887 (A) 18252(7) 129224(15)119888 (A) 21081(8) 150618(16)120572 (∘) 98241(8) 72179(6)120573 (∘) 99461(11) 80460(6)120574 (∘) 108751(10) 84813(6)Volume (A3) 4654(3) 18727(4)119885 4 1Calculated density (g cmminus3) 1592 1590Absorption coefficient (mmminus1) 1659 1958119865(000) 2192 880120579 range for data collection 167ndash2587∘ 144ndash2580∘
Index ranges minus16 lt ℎ lt 10 minus22 lt 119896 lt 18 minus16 lt 119897 lt 25 minus11 lt ℎ lt 12 minus15 lt 119896 lt 15 minus16 lt 119897 lt 18Reflections collected 20295 33633Independent reflections 3654 4769Completeness to 2120579 = 51∘ 89 98Refinement method Full-matrix LS on 1198652 Full-matrix LS on 1198652
Datarestraintsparameters 160252991181 70480452Goodness-of-fit on 1198652 0978 0980Final R indices [119868 gt 2120590(119868)] 119877 = 01169 119908119877 = 01820 119877 = 00436 119908119877 = 00792119877 indices (all data) 119877 = 02894 119908119877 = 02159 119877 = 01012 119908119877 = 01097Largest difference peak and hole minus18011623 minus06931076
independent complexes in the unit cell The coordinationspheres of these monomers consist in a square antiprismaticgeometry Table 2 summarizes the Eu-N and Eu-O distancesfor both complexes in the unit cell affected by large exper-imental uncertainties Nevertheless all of them are withinthe normal ranges reported in the literature [17 37] Bothmonomers show heavy disorder particularly evident for theCF3groups of the cbtfa ligands and for the Cl substitute
of the phenanthroline The structure contains large solventaccessible voids
Complex 2 (Figure 3 Table 1) corresponds to a dimericvariation of complex 1 in which the Eu3+ ions are bridgedby two methanolate ions Each Eu3+ ion is coordinated bytwo negatively charged 120573-diketonate (cbtfa) ligands a neutraldiimide ligand (cphen) and the two bridging methanolateions Complex 2 crystallizes in a triclinic centrosymmetriccell with the center of symmetry lying in the middle pointof the dimer There is one dimer per unit cell
Coordination distances are within the normal rangesreported in the literature [14 17 37] and the sameapplies to the bite angles with values close to 70∘ forthe O Eu O angles and of ca 60∘ for the N Eu Nangle The coordination sphere corresponds to a square
antiprism The Eu3+ ions are at a distance of 3742 A withinthe dimer
No conventional H-bonds were found joining the dimersThe packing seems to be influenced by 120587 120587 interactions(Figure 4) Neighboring phenanthroline rings are at 4143 Adistances (centroid-to-centroid) with a slippage of 2089 A
The low crystallinity of the bulk synthesized materialin which the single crystals of complexes 1 and 2 weremixed with more amorphous material prevented a reliabledetermination of the proportions of complex 1 and complex2 by means of X-ray powder diffraction
32 Modeling of the Structures by Semiempirical Methods Acomparison of the unit cell parameters obtained for the PM6and PM7 predicted structures (eg Figure 5) versus thoseof the SC-XRD data is summarized in Table 3 The percenterrors are below 5 in all cases (generally below 2) Theyare similar for both Hamiltonians in the case of complex 1while the estimation with PM7 is slightly better in the case ofcomplex 2 for all parameters except for the 119888 value (which inturn leads to an incorrect volume estimation)
The Eu-N and Eu-O distances and some selected anglesin the ground state geometries of the monomer and the
dimer (using either the PM6 or the PM7 Hamiltonian withperiodic boundary conditions) are compared with those of
the actual structures obtained from SC-XRD data in Table 4The distance values obtained using the PM7 Hamiltonian areremarkably closer to the experimental average values thanthose attained with the PM6 Hamiltonian in all cases Thisis particularly obvious for the Eu-O distances in the dimerwhile in the PM6 case they are very similar in all cases (witha significant error for the bridging methanol bonds) PM7Hamiltonian gives a much more accurate estimation anddistinguishes between the bonds associatedwith cbtfa ligandsand those corresponding to bridging methanol moleculesRegarding the angle values the percent errors are signifi-cantly higher than those for the bond lengths but PM7 errorsare consistently lower than those for PM6
This is in agreement with the observationsmade byDutraet al [24] a significant increase in accuracy has been achievedin PM7 after relatively minor changes were made to theapproximations and after proxy reference data functions rep-resenting noncovalent interactions were introduced leadingto a reduction of errors in PM7 geometries by over one-thirdrelative to those of PM6 On the other hand PM7 methodcan showworse convergence properties when compared withPM6 as it was reported in [10]
33 Luminescent Properties The experimental excitationspectrum for the mixture of the monomer and the dimer isdepicted in Figure 6(a) It exhibits a maximum at 355 nmwhich can be assigned to the electronic transitions from theground state level (120587) 119878
0to the excited level (120587lowast) 119878
1of the
cbtfa organic ligand [14 15 39ndash41] according to Figure 7Thepredicted absorption spectra for the gas phase geometriesoptimized with the SparklePM6 method calculated usingthe INDOS-CIS procedure are also shown Gabedit software
Table 3 Comparison of the unit cell parameters for PM6 and PM7 predicted structures In parentheses for the experimental values standarddeviation is shown for theoretical values percent error is indicated
Table 4 Comparison of the experimental and calculated average Eu-N and Eu-O distances (in A) and selected angles (in ∘) for themononuclear (monomer 1) and the homodinuclear Eu3+ complexes In parentheses for the experimental values standard deviation is shownfor theoretical values percent error is indicated
Table 5 Comparison of theoretical (for complex 1 and complex 2) and experimental values (for similar Eu3+ complexes reported in theliterature) of the intensity parameters (Ω
120582) radiative (119860 rad) and nonradiative (119860nrad) emission rates and quantum yields (120578)
Compound Intensity parameters (10minus20 cm2)119860 rad (s
Figure 5 Comparison of the SparklePM6 (blue) and SparklePM7(green) optimized geometries with the X-ray geometry (red) ofcomplex 2 (software used for visualization VMD version 191 [38])
[42] has been used for the representation of the spectra fromthe calculated data As expected there is a hypsochromic shiftfor the lowest predicted transition (versus the experimentalone) as it is usually the case in this type of calculations [3]
Upon excitation of the organic ligands in the UV regionefficient indirect excitation of Eu3+ is attained via antennaeffect [43] Figure 6(b) shows the experimental photolumi-nescence spectrum in which the characteristic narrow emis-sion bands of Eu3+ corresponding to the intraconfigurational5D0rarr 7FJ (119869 = 0ndash4) transitions appear The five expected
peaks for the 5D0rarr 7F
0ndash4 transitions (namely 5D0rarr 7F
0
(sim580 nm) 5D0rarr 7F
1(sim591 nm) 5D
0rarr 7F
2(sim614 nm)
5D0rarr 7F
3(sim651 nm) and 5D
0rarr 7F
4(sim692 nm)) [44] can
be identified (see Figure 7)The emission bands at ca 580 and 651 nm are weak
since their corresponding transitions 5D0rarr 7F
03are
forbidden both in magnetic and electric dipole schemes [47]The intensity of the emission band at 593 nm is stronger andindependent of the coordination environment because the
corresponding transition 5D0rarr 7F
1is of magnetic charac-
ter In contrast the 5D0rarr 7F
2transition is an induced elec-
tric dipole transition and its corresponding intense emissionat 613 nm is very sensitive to the coordination environment[47] This very intense 5D
0rarr 7F
2peak responsible for the
brilliant red emission of the complex indicates that the ligandfield surrounding the Eu3+ ion is highly polarizable
With regard to the monochromaticity (R) that is theintensity ratio of the electric dipole transition to themagneticdipole transition (redorange ratio) the obtained value is 172This indicates that the CIE chromaticity coordinates for thecomplex should be very close to saturated red emission [48]and that the Eu3+ coordination is consistent with a local sitewithout inversion [49ndash51]
The lifetime measurements for the mixture of themonomer and the dimer (not shown) do not correspond toa monoexponential decay curve which is consistent with thepresence of two slightly different coordination environmentsfor the Eu3+ ion in complex 1 and complex 2 The estimatedaverage 120591 value would be close to 700 120583s in the same rangeas the lifetimes reported for similar complexes with cbtfaand btfa ligands 754120583s for [Eu(cbtfa)
3(bath)] [14] 670 120583s for
[Er(btfa)3(phen)] [15 52] and 750120583s [Eu(btfac)
3(dmbipy)]
[53]
34 Theoretical Modeling of the Luminescent Properties withLUMPAC By using LUMPAC lanthanide luminescence soft-ware package [11ndash13] singlet and triplet excited state energiesfor the lanthanide containing systems were obtained fromINDOS-CIS ORCA [27] calculations From the experi-mental emission spectrum and estimated lifetime valueJudd-Ofelt intensity parameters radiative and nonradiativeemission rates and quantum efficiencies were also calculatedThe isolated complex ground state geometries have been usedin the calculations As discussed above the two Eu3+ ions incomplex 2 have been treated individually and are describedas Eu1 and Eu1a in Table 5
The estimated singlet (3682740 cmminus1 for the monomerand 3694560 cmminus1 for the dimer) is higher than that of thecbtfa ligand (30675 cmminus1 [16]) but would be a reasonable
8 Advances in Condensed Matter Physics
Abso
rptio
n (a
u)
Wavelength (nm)300 400 500 600 700
ExperimentalCalculated complex 1
Calculated complex 2
(a)
Wavelength (nm)
PL em
issio
n (a
u)
550 600 650 700
5D0 rarr7F0
5D0 rarr7F2
5D0 rarr7F1
5D0 rarr7F3
5D0 rarr7F4
(b)
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Figure 2 Structural diagram of complex 1 tris(14-chlorophenyl-444-trifluoro-13-butanedionate) mono(5-chloro-110-phenanthroline)europium(III) H atoms have been omitted for clarity reasons
23 Spectroscopic Measurements Optical absorption andphotoluminescence spectra of thematerials weremeasured atroom temperatureThe 285ndash800 nm range absorption spectrawere recordedwith a Cary 4000Varian spectrophotometer inpowder form Photoluminescence spectra of the materialsmdashin powdermdashwere obtained at room temperature using amod-ular spectrophotometer Horiba-Jobin-Yvon SPEX Fluorolog3 All spectra have been corrected by the spectral response ofthe experimental setups
24 Computational Methods Using the experimental crys-tallographic data as an initial guess the ground stategeometries were obtained using the SparklePM6 [21 22]and SparklePM7 [23 24] models implemented in theMOPAC2012 software [25 26] using periodic boundaryconditions One unit cell for each of the complexes wasemployed in the calculations by setting the keywordMERS =(1 1 1) Geometry optimizationswere performed for isolatedcomplexes as well Additionally the corresponding vibra-tional frequencies were computed for the PM6 optimizedgeometries for the two complexes in the gas phase Noimaginary vibrational frequencies were found for any ofthe geometries confirming that the results obtained cor-responded to true ground states These computations wereperformed on aDebian Linux serverwith fourAMDOpteron16 Core processors and 128GB of memory and a Linuxoperating system
The electronic spectra for each of the optimized struc-tures were calculated using the ORCA electronic structurepackage [27 28] via the intermediate neglect of differentialoverlapspectroscopic (INDOS) method and configuration
interaction with singles (CIS) [29ndash31] replacing the Eu3+ions with point charges as described by de Andrade et al[32 33] Version 301 was used for calculations invoked usingLUMPAC 10 distribution
The geometry optimization and the analysis of electronictransitions using the INDOS-CIS method are integrated ina user-friendly manner in the first and second modulesrespectively of LUMPAC software ecosystem The thirdmodule is a unique feature of LUMPAC and permits cal-culating the Judd-Ofelt intensity parameters [34] and theestimation of metal-ligand energy transfer and back-transferrates [35] the radiative and nonradiative emission ratestheoretical quantum efficiency and emission quantum yield[36] Calculations within LUMPACmodules were performedusing aWindows 8 Toshiba Satellite Core i5 laptop computer
The theoretical Judd-Ofelt parameters are determined byadjusting the charge factors and polarizabilities to reproducethe experimental values In this calculation it is requiredto provide the coordination polyhedron of the system asinput For the highly symmetric binuclear complex theanalyses have been performed by independently treating thetwo europium ions with their corresponding coordinationpolyhedra as in the individual polyhedron method reportedby Dutra et al [13]
3 Results and Discussion
31 Structural Description In the mononuclear complexcomplex 1 the Eu3+ ions are coordinated by three negativelycharged 120573-diketonate ligands and a neutral ancillary NN-donor moiety (Figure 2 Table 1) There are two symmetry
4 Advances in Condensed Matter Physics
Table 1 Crystal data and structure refinement for the mononuclear and the homodinuclear Eu3+ complexes
Complex Complex 1 Complex 2Empirical formula C42H22Cl4EuF9N2O6 C66H40Cl6Eu2F12N4O10
Formula weight 111538 179364Temperature (K) 293(2) 293(2)Wavelength (A) 07107 07107Crystal system Triclinic TriclinicSpace group P-1 P-1119886 (A) 13246(5) 102575(11)119887 (A) 18252(7) 129224(15)119888 (A) 21081(8) 150618(16)120572 (∘) 98241(8) 72179(6)120573 (∘) 99461(11) 80460(6)120574 (∘) 108751(10) 84813(6)Volume (A3) 4654(3) 18727(4)119885 4 1Calculated density (g cmminus3) 1592 1590Absorption coefficient (mmminus1) 1659 1958119865(000) 2192 880120579 range for data collection 167ndash2587∘ 144ndash2580∘
Index ranges minus16 lt ℎ lt 10 minus22 lt 119896 lt 18 minus16 lt 119897 lt 25 minus11 lt ℎ lt 12 minus15 lt 119896 lt 15 minus16 lt 119897 lt 18Reflections collected 20295 33633Independent reflections 3654 4769Completeness to 2120579 = 51∘ 89 98Refinement method Full-matrix LS on 1198652 Full-matrix LS on 1198652
Datarestraintsparameters 160252991181 70480452Goodness-of-fit on 1198652 0978 0980Final R indices [119868 gt 2120590(119868)] 119877 = 01169 119908119877 = 01820 119877 = 00436 119908119877 = 00792119877 indices (all data) 119877 = 02894 119908119877 = 02159 119877 = 01012 119908119877 = 01097Largest difference peak and hole minus18011623 minus06931076
independent complexes in the unit cell The coordinationspheres of these monomers consist in a square antiprismaticgeometry Table 2 summarizes the Eu-N and Eu-O distancesfor both complexes in the unit cell affected by large exper-imental uncertainties Nevertheless all of them are withinthe normal ranges reported in the literature [17 37] Bothmonomers show heavy disorder particularly evident for theCF3groups of the cbtfa ligands and for the Cl substitute
of the phenanthroline The structure contains large solventaccessible voids
Complex 2 (Figure 3 Table 1) corresponds to a dimericvariation of complex 1 in which the Eu3+ ions are bridgedby two methanolate ions Each Eu3+ ion is coordinated bytwo negatively charged 120573-diketonate (cbtfa) ligands a neutraldiimide ligand (cphen) and the two bridging methanolateions Complex 2 crystallizes in a triclinic centrosymmetriccell with the center of symmetry lying in the middle pointof the dimer There is one dimer per unit cell
Coordination distances are within the normal rangesreported in the literature [14 17 37] and the sameapplies to the bite angles with values close to 70∘ forthe O Eu O angles and of ca 60∘ for the N Eu Nangle The coordination sphere corresponds to a square
antiprism The Eu3+ ions are at a distance of 3742 A withinthe dimer
No conventional H-bonds were found joining the dimersThe packing seems to be influenced by 120587 120587 interactions(Figure 4) Neighboring phenanthroline rings are at 4143 Adistances (centroid-to-centroid) with a slippage of 2089 A
The low crystallinity of the bulk synthesized materialin which the single crystals of complexes 1 and 2 weremixed with more amorphous material prevented a reliabledetermination of the proportions of complex 1 and complex2 by means of X-ray powder diffraction
32 Modeling of the Structures by Semiempirical Methods Acomparison of the unit cell parameters obtained for the PM6and PM7 predicted structures (eg Figure 5) versus thoseof the SC-XRD data is summarized in Table 3 The percenterrors are below 5 in all cases (generally below 2) Theyare similar for both Hamiltonians in the case of complex 1while the estimation with PM7 is slightly better in the case ofcomplex 2 for all parameters except for the 119888 value (which inturn leads to an incorrect volume estimation)
The Eu-N and Eu-O distances and some selected anglesin the ground state geometries of the monomer and the
dimer (using either the PM6 or the PM7 Hamiltonian withperiodic boundary conditions) are compared with those of
the actual structures obtained from SC-XRD data in Table 4The distance values obtained using the PM7 Hamiltonian areremarkably closer to the experimental average values thanthose attained with the PM6 Hamiltonian in all cases Thisis particularly obvious for the Eu-O distances in the dimerwhile in the PM6 case they are very similar in all cases (witha significant error for the bridging methanol bonds) PM7Hamiltonian gives a much more accurate estimation anddistinguishes between the bonds associatedwith cbtfa ligandsand those corresponding to bridging methanol moleculesRegarding the angle values the percent errors are signifi-cantly higher than those for the bond lengths but PM7 errorsare consistently lower than those for PM6
This is in agreement with the observationsmade byDutraet al [24] a significant increase in accuracy has been achievedin PM7 after relatively minor changes were made to theapproximations and after proxy reference data functions rep-resenting noncovalent interactions were introduced leadingto a reduction of errors in PM7 geometries by over one-thirdrelative to those of PM6 On the other hand PM7 methodcan showworse convergence properties when compared withPM6 as it was reported in [10]
33 Luminescent Properties The experimental excitationspectrum for the mixture of the monomer and the dimer isdepicted in Figure 6(a) It exhibits a maximum at 355 nmwhich can be assigned to the electronic transitions from theground state level (120587) 119878
0to the excited level (120587lowast) 119878
1of the
cbtfa organic ligand [14 15 39ndash41] according to Figure 7Thepredicted absorption spectra for the gas phase geometriesoptimized with the SparklePM6 method calculated usingthe INDOS-CIS procedure are also shown Gabedit software
Table 3 Comparison of the unit cell parameters for PM6 and PM7 predicted structures In parentheses for the experimental values standarddeviation is shown for theoretical values percent error is indicated
Table 4 Comparison of the experimental and calculated average Eu-N and Eu-O distances (in A) and selected angles (in ∘) for themononuclear (monomer 1) and the homodinuclear Eu3+ complexes In parentheses for the experimental values standard deviation is shownfor theoretical values percent error is indicated
Table 5 Comparison of theoretical (for complex 1 and complex 2) and experimental values (for similar Eu3+ complexes reported in theliterature) of the intensity parameters (Ω
120582) radiative (119860 rad) and nonradiative (119860nrad) emission rates and quantum yields (120578)
Compound Intensity parameters (10minus20 cm2)119860 rad (s
Figure 5 Comparison of the SparklePM6 (blue) and SparklePM7(green) optimized geometries with the X-ray geometry (red) ofcomplex 2 (software used for visualization VMD version 191 [38])
[42] has been used for the representation of the spectra fromthe calculated data As expected there is a hypsochromic shiftfor the lowest predicted transition (versus the experimentalone) as it is usually the case in this type of calculations [3]
Upon excitation of the organic ligands in the UV regionefficient indirect excitation of Eu3+ is attained via antennaeffect [43] Figure 6(b) shows the experimental photolumi-nescence spectrum in which the characteristic narrow emis-sion bands of Eu3+ corresponding to the intraconfigurational5D0rarr 7FJ (119869 = 0ndash4) transitions appear The five expected
peaks for the 5D0rarr 7F
0ndash4 transitions (namely 5D0rarr 7F
0
(sim580 nm) 5D0rarr 7F
1(sim591 nm) 5D
0rarr 7F
2(sim614 nm)
5D0rarr 7F
3(sim651 nm) and 5D
0rarr 7F
4(sim692 nm)) [44] can
be identified (see Figure 7)The emission bands at ca 580 and 651 nm are weak
since their corresponding transitions 5D0rarr 7F
03are
forbidden both in magnetic and electric dipole schemes [47]The intensity of the emission band at 593 nm is stronger andindependent of the coordination environment because the
corresponding transition 5D0rarr 7F
1is of magnetic charac-
ter In contrast the 5D0rarr 7F
2transition is an induced elec-
tric dipole transition and its corresponding intense emissionat 613 nm is very sensitive to the coordination environment[47] This very intense 5D
0rarr 7F
2peak responsible for the
brilliant red emission of the complex indicates that the ligandfield surrounding the Eu3+ ion is highly polarizable
With regard to the monochromaticity (R) that is theintensity ratio of the electric dipole transition to themagneticdipole transition (redorange ratio) the obtained value is 172This indicates that the CIE chromaticity coordinates for thecomplex should be very close to saturated red emission [48]and that the Eu3+ coordination is consistent with a local sitewithout inversion [49ndash51]
The lifetime measurements for the mixture of themonomer and the dimer (not shown) do not correspond toa monoexponential decay curve which is consistent with thepresence of two slightly different coordination environmentsfor the Eu3+ ion in complex 1 and complex 2 The estimatedaverage 120591 value would be close to 700 120583s in the same rangeas the lifetimes reported for similar complexes with cbtfaand btfa ligands 754120583s for [Eu(cbtfa)
3(bath)] [14] 670 120583s for
[Er(btfa)3(phen)] [15 52] and 750120583s [Eu(btfac)
3(dmbipy)]
[53]
34 Theoretical Modeling of the Luminescent Properties withLUMPAC By using LUMPAC lanthanide luminescence soft-ware package [11ndash13] singlet and triplet excited state energiesfor the lanthanide containing systems were obtained fromINDOS-CIS ORCA [27] calculations From the experi-mental emission spectrum and estimated lifetime valueJudd-Ofelt intensity parameters radiative and nonradiativeemission rates and quantum efficiencies were also calculatedThe isolated complex ground state geometries have been usedin the calculations As discussed above the two Eu3+ ions incomplex 2 have been treated individually and are describedas Eu1 and Eu1a in Table 5
The estimated singlet (3682740 cmminus1 for the monomerand 3694560 cmminus1 for the dimer) is higher than that of thecbtfa ligand (30675 cmminus1 [16]) but would be a reasonable
8 Advances in Condensed Matter Physics
Abso
rptio
n (a
u)
Wavelength (nm)300 400 500 600 700
ExperimentalCalculated complex 1
Calculated complex 2
(a)
Wavelength (nm)
PL em
issio
n (a
u)
550 600 650 700
5D0 rarr7F0
5D0 rarr7F2
5D0 rarr7F1
5D0 rarr7F3
5D0 rarr7F4
(b)
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Table 1 Crystal data and structure refinement for the mononuclear and the homodinuclear Eu3+ complexes
Complex Complex 1 Complex 2Empirical formula C42H22Cl4EuF9N2O6 C66H40Cl6Eu2F12N4O10
Formula weight 111538 179364Temperature (K) 293(2) 293(2)Wavelength (A) 07107 07107Crystal system Triclinic TriclinicSpace group P-1 P-1119886 (A) 13246(5) 102575(11)119887 (A) 18252(7) 129224(15)119888 (A) 21081(8) 150618(16)120572 (∘) 98241(8) 72179(6)120573 (∘) 99461(11) 80460(6)120574 (∘) 108751(10) 84813(6)Volume (A3) 4654(3) 18727(4)119885 4 1Calculated density (g cmminus3) 1592 1590Absorption coefficient (mmminus1) 1659 1958119865(000) 2192 880120579 range for data collection 167ndash2587∘ 144ndash2580∘
Index ranges minus16 lt ℎ lt 10 minus22 lt 119896 lt 18 minus16 lt 119897 lt 25 minus11 lt ℎ lt 12 minus15 lt 119896 lt 15 minus16 lt 119897 lt 18Reflections collected 20295 33633Independent reflections 3654 4769Completeness to 2120579 = 51∘ 89 98Refinement method Full-matrix LS on 1198652 Full-matrix LS on 1198652
Datarestraintsparameters 160252991181 70480452Goodness-of-fit on 1198652 0978 0980Final R indices [119868 gt 2120590(119868)] 119877 = 01169 119908119877 = 01820 119877 = 00436 119908119877 = 00792119877 indices (all data) 119877 = 02894 119908119877 = 02159 119877 = 01012 119908119877 = 01097Largest difference peak and hole minus18011623 minus06931076
independent complexes in the unit cell The coordinationspheres of these monomers consist in a square antiprismaticgeometry Table 2 summarizes the Eu-N and Eu-O distancesfor both complexes in the unit cell affected by large exper-imental uncertainties Nevertheless all of them are withinthe normal ranges reported in the literature [17 37] Bothmonomers show heavy disorder particularly evident for theCF3groups of the cbtfa ligands and for the Cl substitute
of the phenanthroline The structure contains large solventaccessible voids
Complex 2 (Figure 3 Table 1) corresponds to a dimericvariation of complex 1 in which the Eu3+ ions are bridgedby two methanolate ions Each Eu3+ ion is coordinated bytwo negatively charged 120573-diketonate (cbtfa) ligands a neutraldiimide ligand (cphen) and the two bridging methanolateions Complex 2 crystallizes in a triclinic centrosymmetriccell with the center of symmetry lying in the middle pointof the dimer There is one dimer per unit cell
Coordination distances are within the normal rangesreported in the literature [14 17 37] and the sameapplies to the bite angles with values close to 70∘ forthe O Eu O angles and of ca 60∘ for the N Eu Nangle The coordination sphere corresponds to a square
antiprism The Eu3+ ions are at a distance of 3742 A withinthe dimer
No conventional H-bonds were found joining the dimersThe packing seems to be influenced by 120587 120587 interactions(Figure 4) Neighboring phenanthroline rings are at 4143 Adistances (centroid-to-centroid) with a slippage of 2089 A
The low crystallinity of the bulk synthesized materialin which the single crystals of complexes 1 and 2 weremixed with more amorphous material prevented a reliabledetermination of the proportions of complex 1 and complex2 by means of X-ray powder diffraction
32 Modeling of the Structures by Semiempirical Methods Acomparison of the unit cell parameters obtained for the PM6and PM7 predicted structures (eg Figure 5) versus thoseof the SC-XRD data is summarized in Table 3 The percenterrors are below 5 in all cases (generally below 2) Theyare similar for both Hamiltonians in the case of complex 1while the estimation with PM7 is slightly better in the case ofcomplex 2 for all parameters except for the 119888 value (which inturn leads to an incorrect volume estimation)
The Eu-N and Eu-O distances and some selected anglesin the ground state geometries of the monomer and the
dimer (using either the PM6 or the PM7 Hamiltonian withperiodic boundary conditions) are compared with those of
the actual structures obtained from SC-XRD data in Table 4The distance values obtained using the PM7 Hamiltonian areremarkably closer to the experimental average values thanthose attained with the PM6 Hamiltonian in all cases Thisis particularly obvious for the Eu-O distances in the dimerwhile in the PM6 case they are very similar in all cases (witha significant error for the bridging methanol bonds) PM7Hamiltonian gives a much more accurate estimation anddistinguishes between the bonds associatedwith cbtfa ligandsand those corresponding to bridging methanol moleculesRegarding the angle values the percent errors are signifi-cantly higher than those for the bond lengths but PM7 errorsare consistently lower than those for PM6
This is in agreement with the observationsmade byDutraet al [24] a significant increase in accuracy has been achievedin PM7 after relatively minor changes were made to theapproximations and after proxy reference data functions rep-resenting noncovalent interactions were introduced leadingto a reduction of errors in PM7 geometries by over one-thirdrelative to those of PM6 On the other hand PM7 methodcan showworse convergence properties when compared withPM6 as it was reported in [10]
33 Luminescent Properties The experimental excitationspectrum for the mixture of the monomer and the dimer isdepicted in Figure 6(a) It exhibits a maximum at 355 nmwhich can be assigned to the electronic transitions from theground state level (120587) 119878
0to the excited level (120587lowast) 119878
1of the
cbtfa organic ligand [14 15 39ndash41] according to Figure 7Thepredicted absorption spectra for the gas phase geometriesoptimized with the SparklePM6 method calculated usingthe INDOS-CIS procedure are also shown Gabedit software
Table 3 Comparison of the unit cell parameters for PM6 and PM7 predicted structures In parentheses for the experimental values standarddeviation is shown for theoretical values percent error is indicated
Table 4 Comparison of the experimental and calculated average Eu-N and Eu-O distances (in A) and selected angles (in ∘) for themononuclear (monomer 1) and the homodinuclear Eu3+ complexes In parentheses for the experimental values standard deviation is shownfor theoretical values percent error is indicated
Table 5 Comparison of theoretical (for complex 1 and complex 2) and experimental values (for similar Eu3+ complexes reported in theliterature) of the intensity parameters (Ω
120582) radiative (119860 rad) and nonradiative (119860nrad) emission rates and quantum yields (120578)
Compound Intensity parameters (10minus20 cm2)119860 rad (s
Figure 5 Comparison of the SparklePM6 (blue) and SparklePM7(green) optimized geometries with the X-ray geometry (red) ofcomplex 2 (software used for visualization VMD version 191 [38])
[42] has been used for the representation of the spectra fromthe calculated data As expected there is a hypsochromic shiftfor the lowest predicted transition (versus the experimentalone) as it is usually the case in this type of calculations [3]
Upon excitation of the organic ligands in the UV regionefficient indirect excitation of Eu3+ is attained via antennaeffect [43] Figure 6(b) shows the experimental photolumi-nescence spectrum in which the characteristic narrow emis-sion bands of Eu3+ corresponding to the intraconfigurational5D0rarr 7FJ (119869 = 0ndash4) transitions appear The five expected
peaks for the 5D0rarr 7F
0ndash4 transitions (namely 5D0rarr 7F
0
(sim580 nm) 5D0rarr 7F
1(sim591 nm) 5D
0rarr 7F
2(sim614 nm)
5D0rarr 7F
3(sim651 nm) and 5D
0rarr 7F
4(sim692 nm)) [44] can
be identified (see Figure 7)The emission bands at ca 580 and 651 nm are weak
since their corresponding transitions 5D0rarr 7F
03are
forbidden both in magnetic and electric dipole schemes [47]The intensity of the emission band at 593 nm is stronger andindependent of the coordination environment because the
corresponding transition 5D0rarr 7F
1is of magnetic charac-
ter In contrast the 5D0rarr 7F
2transition is an induced elec-
tric dipole transition and its corresponding intense emissionat 613 nm is very sensitive to the coordination environment[47] This very intense 5D
0rarr 7F
2peak responsible for the
brilliant red emission of the complex indicates that the ligandfield surrounding the Eu3+ ion is highly polarizable
With regard to the monochromaticity (R) that is theintensity ratio of the electric dipole transition to themagneticdipole transition (redorange ratio) the obtained value is 172This indicates that the CIE chromaticity coordinates for thecomplex should be very close to saturated red emission [48]and that the Eu3+ coordination is consistent with a local sitewithout inversion [49ndash51]
The lifetime measurements for the mixture of themonomer and the dimer (not shown) do not correspond toa monoexponential decay curve which is consistent with thepresence of two slightly different coordination environmentsfor the Eu3+ ion in complex 1 and complex 2 The estimatedaverage 120591 value would be close to 700 120583s in the same rangeas the lifetimes reported for similar complexes with cbtfaand btfa ligands 754120583s for [Eu(cbtfa)
3(bath)] [14] 670 120583s for
[Er(btfa)3(phen)] [15 52] and 750120583s [Eu(btfac)
3(dmbipy)]
[53]
34 Theoretical Modeling of the Luminescent Properties withLUMPAC By using LUMPAC lanthanide luminescence soft-ware package [11ndash13] singlet and triplet excited state energiesfor the lanthanide containing systems were obtained fromINDOS-CIS ORCA [27] calculations From the experi-mental emission spectrum and estimated lifetime valueJudd-Ofelt intensity parameters radiative and nonradiativeemission rates and quantum efficiencies were also calculatedThe isolated complex ground state geometries have been usedin the calculations As discussed above the two Eu3+ ions incomplex 2 have been treated individually and are describedas Eu1 and Eu1a in Table 5
The estimated singlet (3682740 cmminus1 for the monomerand 3694560 cmminus1 for the dimer) is higher than that of thecbtfa ligand (30675 cmminus1 [16]) but would be a reasonable
8 Advances in Condensed Matter Physics
Abso
rptio
n (a
u)
Wavelength (nm)300 400 500 600 700
ExperimentalCalculated complex 1
Calculated complex 2
(a)
Wavelength (nm)
PL em
issio
n (a
u)
550 600 650 700
5D0 rarr7F0
5D0 rarr7F2
5D0 rarr7F1
5D0 rarr7F3
5D0 rarr7F4
(b)
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
dimer (using either the PM6 or the PM7 Hamiltonian withperiodic boundary conditions) are compared with those of
the actual structures obtained from SC-XRD data in Table 4The distance values obtained using the PM7 Hamiltonian areremarkably closer to the experimental average values thanthose attained with the PM6 Hamiltonian in all cases Thisis particularly obvious for the Eu-O distances in the dimerwhile in the PM6 case they are very similar in all cases (witha significant error for the bridging methanol bonds) PM7Hamiltonian gives a much more accurate estimation anddistinguishes between the bonds associatedwith cbtfa ligandsand those corresponding to bridging methanol moleculesRegarding the angle values the percent errors are signifi-cantly higher than those for the bond lengths but PM7 errorsare consistently lower than those for PM6
This is in agreement with the observationsmade byDutraet al [24] a significant increase in accuracy has been achievedin PM7 after relatively minor changes were made to theapproximations and after proxy reference data functions rep-resenting noncovalent interactions were introduced leadingto a reduction of errors in PM7 geometries by over one-thirdrelative to those of PM6 On the other hand PM7 methodcan showworse convergence properties when compared withPM6 as it was reported in [10]
33 Luminescent Properties The experimental excitationspectrum for the mixture of the monomer and the dimer isdepicted in Figure 6(a) It exhibits a maximum at 355 nmwhich can be assigned to the electronic transitions from theground state level (120587) 119878
0to the excited level (120587lowast) 119878
1of the
cbtfa organic ligand [14 15 39ndash41] according to Figure 7Thepredicted absorption spectra for the gas phase geometriesoptimized with the SparklePM6 method calculated usingthe INDOS-CIS procedure are also shown Gabedit software
Table 3 Comparison of the unit cell parameters for PM6 and PM7 predicted structures In parentheses for the experimental values standarddeviation is shown for theoretical values percent error is indicated
Table 4 Comparison of the experimental and calculated average Eu-N and Eu-O distances (in A) and selected angles (in ∘) for themononuclear (monomer 1) and the homodinuclear Eu3+ complexes In parentheses for the experimental values standard deviation is shownfor theoretical values percent error is indicated
Table 5 Comparison of theoretical (for complex 1 and complex 2) and experimental values (for similar Eu3+ complexes reported in theliterature) of the intensity parameters (Ω
120582) radiative (119860 rad) and nonradiative (119860nrad) emission rates and quantum yields (120578)
Compound Intensity parameters (10minus20 cm2)119860 rad (s
Figure 5 Comparison of the SparklePM6 (blue) and SparklePM7(green) optimized geometries with the X-ray geometry (red) ofcomplex 2 (software used for visualization VMD version 191 [38])
[42] has been used for the representation of the spectra fromthe calculated data As expected there is a hypsochromic shiftfor the lowest predicted transition (versus the experimentalone) as it is usually the case in this type of calculations [3]
Upon excitation of the organic ligands in the UV regionefficient indirect excitation of Eu3+ is attained via antennaeffect [43] Figure 6(b) shows the experimental photolumi-nescence spectrum in which the characteristic narrow emis-sion bands of Eu3+ corresponding to the intraconfigurational5D0rarr 7FJ (119869 = 0ndash4) transitions appear The five expected
peaks for the 5D0rarr 7F
0ndash4 transitions (namely 5D0rarr 7F
0
(sim580 nm) 5D0rarr 7F
1(sim591 nm) 5D
0rarr 7F
2(sim614 nm)
5D0rarr 7F
3(sim651 nm) and 5D
0rarr 7F
4(sim692 nm)) [44] can
be identified (see Figure 7)The emission bands at ca 580 and 651 nm are weak
since their corresponding transitions 5D0rarr 7F
03are
forbidden both in magnetic and electric dipole schemes [47]The intensity of the emission band at 593 nm is stronger andindependent of the coordination environment because the
corresponding transition 5D0rarr 7F
1is of magnetic charac-
ter In contrast the 5D0rarr 7F
2transition is an induced elec-
tric dipole transition and its corresponding intense emissionat 613 nm is very sensitive to the coordination environment[47] This very intense 5D
0rarr 7F
2peak responsible for the
brilliant red emission of the complex indicates that the ligandfield surrounding the Eu3+ ion is highly polarizable
With regard to the monochromaticity (R) that is theintensity ratio of the electric dipole transition to themagneticdipole transition (redorange ratio) the obtained value is 172This indicates that the CIE chromaticity coordinates for thecomplex should be very close to saturated red emission [48]and that the Eu3+ coordination is consistent with a local sitewithout inversion [49ndash51]
The lifetime measurements for the mixture of themonomer and the dimer (not shown) do not correspond toa monoexponential decay curve which is consistent with thepresence of two slightly different coordination environmentsfor the Eu3+ ion in complex 1 and complex 2 The estimatedaverage 120591 value would be close to 700 120583s in the same rangeas the lifetimes reported for similar complexes with cbtfaand btfa ligands 754120583s for [Eu(cbtfa)
3(bath)] [14] 670 120583s for
[Er(btfa)3(phen)] [15 52] and 750120583s [Eu(btfac)
3(dmbipy)]
[53]
34 Theoretical Modeling of the Luminescent Properties withLUMPAC By using LUMPAC lanthanide luminescence soft-ware package [11ndash13] singlet and triplet excited state energiesfor the lanthanide containing systems were obtained fromINDOS-CIS ORCA [27] calculations From the experi-mental emission spectrum and estimated lifetime valueJudd-Ofelt intensity parameters radiative and nonradiativeemission rates and quantum efficiencies were also calculatedThe isolated complex ground state geometries have been usedin the calculations As discussed above the two Eu3+ ions incomplex 2 have been treated individually and are describedas Eu1 and Eu1a in Table 5
The estimated singlet (3682740 cmminus1 for the monomerand 3694560 cmminus1 for the dimer) is higher than that of thecbtfa ligand (30675 cmminus1 [16]) but would be a reasonable
8 Advances in Condensed Matter Physics
Abso
rptio
n (a
u)
Wavelength (nm)300 400 500 600 700
ExperimentalCalculated complex 1
Calculated complex 2
(a)
Wavelength (nm)
PL em
issio
n (a
u)
550 600 650 700
5D0 rarr7F0
5D0 rarr7F2
5D0 rarr7F1
5D0 rarr7F3
5D0 rarr7F4
(b)
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Table 3 Comparison of the unit cell parameters for PM6 and PM7 predicted structures In parentheses for the experimental values standarddeviation is shown for theoretical values percent error is indicated
Table 4 Comparison of the experimental and calculated average Eu-N and Eu-O distances (in A) and selected angles (in ∘) for themononuclear (monomer 1) and the homodinuclear Eu3+ complexes In parentheses for the experimental values standard deviation is shownfor theoretical values percent error is indicated
Table 5 Comparison of theoretical (for complex 1 and complex 2) and experimental values (for similar Eu3+ complexes reported in theliterature) of the intensity parameters (Ω
120582) radiative (119860 rad) and nonradiative (119860nrad) emission rates and quantum yields (120578)
Compound Intensity parameters (10minus20 cm2)119860 rad (s
Figure 5 Comparison of the SparklePM6 (blue) and SparklePM7(green) optimized geometries with the X-ray geometry (red) ofcomplex 2 (software used for visualization VMD version 191 [38])
[42] has been used for the representation of the spectra fromthe calculated data As expected there is a hypsochromic shiftfor the lowest predicted transition (versus the experimentalone) as it is usually the case in this type of calculations [3]
Upon excitation of the organic ligands in the UV regionefficient indirect excitation of Eu3+ is attained via antennaeffect [43] Figure 6(b) shows the experimental photolumi-nescence spectrum in which the characteristic narrow emis-sion bands of Eu3+ corresponding to the intraconfigurational5D0rarr 7FJ (119869 = 0ndash4) transitions appear The five expected
peaks for the 5D0rarr 7F
0ndash4 transitions (namely 5D0rarr 7F
0
(sim580 nm) 5D0rarr 7F
1(sim591 nm) 5D
0rarr 7F
2(sim614 nm)
5D0rarr 7F
3(sim651 nm) and 5D
0rarr 7F
4(sim692 nm)) [44] can
be identified (see Figure 7)The emission bands at ca 580 and 651 nm are weak
since their corresponding transitions 5D0rarr 7F
03are
forbidden both in magnetic and electric dipole schemes [47]The intensity of the emission band at 593 nm is stronger andindependent of the coordination environment because the
corresponding transition 5D0rarr 7F
1is of magnetic charac-
ter In contrast the 5D0rarr 7F
2transition is an induced elec-
tric dipole transition and its corresponding intense emissionat 613 nm is very sensitive to the coordination environment[47] This very intense 5D
0rarr 7F
2peak responsible for the
brilliant red emission of the complex indicates that the ligandfield surrounding the Eu3+ ion is highly polarizable
With regard to the monochromaticity (R) that is theintensity ratio of the electric dipole transition to themagneticdipole transition (redorange ratio) the obtained value is 172This indicates that the CIE chromaticity coordinates for thecomplex should be very close to saturated red emission [48]and that the Eu3+ coordination is consistent with a local sitewithout inversion [49ndash51]
The lifetime measurements for the mixture of themonomer and the dimer (not shown) do not correspond toa monoexponential decay curve which is consistent with thepresence of two slightly different coordination environmentsfor the Eu3+ ion in complex 1 and complex 2 The estimatedaverage 120591 value would be close to 700 120583s in the same rangeas the lifetimes reported for similar complexes with cbtfaand btfa ligands 754120583s for [Eu(cbtfa)
3(bath)] [14] 670 120583s for
[Er(btfa)3(phen)] [15 52] and 750120583s [Eu(btfac)
3(dmbipy)]
[53]
34 Theoretical Modeling of the Luminescent Properties withLUMPAC By using LUMPAC lanthanide luminescence soft-ware package [11ndash13] singlet and triplet excited state energiesfor the lanthanide containing systems were obtained fromINDOS-CIS ORCA [27] calculations From the experi-mental emission spectrum and estimated lifetime valueJudd-Ofelt intensity parameters radiative and nonradiativeemission rates and quantum efficiencies were also calculatedThe isolated complex ground state geometries have been usedin the calculations As discussed above the two Eu3+ ions incomplex 2 have been treated individually and are describedas Eu1 and Eu1a in Table 5
The estimated singlet (3682740 cmminus1 for the monomerand 3694560 cmminus1 for the dimer) is higher than that of thecbtfa ligand (30675 cmminus1 [16]) but would be a reasonable
8 Advances in Condensed Matter Physics
Abso
rptio
n (a
u)
Wavelength (nm)300 400 500 600 700
ExperimentalCalculated complex 1
Calculated complex 2
(a)
Wavelength (nm)
PL em
issio
n (a
u)
550 600 650 700
5D0 rarr7F0
5D0 rarr7F2
5D0 rarr7F1
5D0 rarr7F3
5D0 rarr7F4
(b)
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Table 5 Comparison of theoretical (for complex 1 and complex 2) and experimental values (for similar Eu3+ complexes reported in theliterature) of the intensity parameters (Ω
120582) radiative (119860 rad) and nonradiative (119860nrad) emission rates and quantum yields (120578)
Compound Intensity parameters (10minus20 cm2)119860 rad (s
Figure 5 Comparison of the SparklePM6 (blue) and SparklePM7(green) optimized geometries with the X-ray geometry (red) ofcomplex 2 (software used for visualization VMD version 191 [38])
[42] has been used for the representation of the spectra fromthe calculated data As expected there is a hypsochromic shiftfor the lowest predicted transition (versus the experimentalone) as it is usually the case in this type of calculations [3]
Upon excitation of the organic ligands in the UV regionefficient indirect excitation of Eu3+ is attained via antennaeffect [43] Figure 6(b) shows the experimental photolumi-nescence spectrum in which the characteristic narrow emis-sion bands of Eu3+ corresponding to the intraconfigurational5D0rarr 7FJ (119869 = 0ndash4) transitions appear The five expected
peaks for the 5D0rarr 7F
0ndash4 transitions (namely 5D0rarr 7F
0
(sim580 nm) 5D0rarr 7F
1(sim591 nm) 5D
0rarr 7F
2(sim614 nm)
5D0rarr 7F
3(sim651 nm) and 5D
0rarr 7F
4(sim692 nm)) [44] can
be identified (see Figure 7)The emission bands at ca 580 and 651 nm are weak
since their corresponding transitions 5D0rarr 7F
03are
forbidden both in magnetic and electric dipole schemes [47]The intensity of the emission band at 593 nm is stronger andindependent of the coordination environment because the
corresponding transition 5D0rarr 7F
1is of magnetic charac-
ter In contrast the 5D0rarr 7F
2transition is an induced elec-
tric dipole transition and its corresponding intense emissionat 613 nm is very sensitive to the coordination environment[47] This very intense 5D
0rarr 7F
2peak responsible for the
brilliant red emission of the complex indicates that the ligandfield surrounding the Eu3+ ion is highly polarizable
With regard to the monochromaticity (R) that is theintensity ratio of the electric dipole transition to themagneticdipole transition (redorange ratio) the obtained value is 172This indicates that the CIE chromaticity coordinates for thecomplex should be very close to saturated red emission [48]and that the Eu3+ coordination is consistent with a local sitewithout inversion [49ndash51]
The lifetime measurements for the mixture of themonomer and the dimer (not shown) do not correspond toa monoexponential decay curve which is consistent with thepresence of two slightly different coordination environmentsfor the Eu3+ ion in complex 1 and complex 2 The estimatedaverage 120591 value would be close to 700 120583s in the same rangeas the lifetimes reported for similar complexes with cbtfaand btfa ligands 754120583s for [Eu(cbtfa)
3(bath)] [14] 670 120583s for
[Er(btfa)3(phen)] [15 52] and 750120583s [Eu(btfac)
3(dmbipy)]
[53]
34 Theoretical Modeling of the Luminescent Properties withLUMPAC By using LUMPAC lanthanide luminescence soft-ware package [11ndash13] singlet and triplet excited state energiesfor the lanthanide containing systems were obtained fromINDOS-CIS ORCA [27] calculations From the experi-mental emission spectrum and estimated lifetime valueJudd-Ofelt intensity parameters radiative and nonradiativeemission rates and quantum efficiencies were also calculatedThe isolated complex ground state geometries have been usedin the calculations As discussed above the two Eu3+ ions incomplex 2 have been treated individually and are describedas Eu1 and Eu1a in Table 5
The estimated singlet (3682740 cmminus1 for the monomerand 3694560 cmminus1 for the dimer) is higher than that of thecbtfa ligand (30675 cmminus1 [16]) but would be a reasonable
8 Advances in Condensed Matter Physics
Abso
rptio
n (a
u)
Wavelength (nm)300 400 500 600 700
ExperimentalCalculated complex 1
Calculated complex 2
(a)
Wavelength (nm)
PL em
issio
n (a
u)
550 600 650 700
5D0 rarr7F0
5D0 rarr7F2
5D0 rarr7F1
5D0 rarr7F3
5D0 rarr7F4
(b)
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Figure 6 (a) UV-Vis absorption spectrum and (b) photoluminescent emission spectrum in powder form for the mixture of complex 1 andcomplex 2 upon ligand-mediated excitation in the UV (120582 = 355 nm)
Ener
gy (1
03times
cmminus1)
35
30
25
20
15
10
5
0
S1
S1
T1T1
S0 S0
ISCISC
ET ET
cbtfa Eu3+ cphen
5D45G6
5D3
5D2
5D15D0
7F6
7F0
Figure 7 Scheme of the energy transfer mechanism and emissionprocessThe singlet and triplet values of Hcbtfa have been estimatedfrom those reported for Hbtfa [16 45] The singlet and tripletvalues for 5-chloro-110-phenanthroline have been taken from [46]ISC and ET stand for intersystem crossing and energy transferrespectively
estimation of the singlet of 5-chloro-110-phenanthroline(37453 cmminus1 [46]) Figure 8(a) shows the lowest unoccupiedmolecular orbital (LUMO) of complex 1 plotted using Gabe-dit software [42] with the data from MOPAC calculationsand Figures 8(b) and 8(c) depict the two lowest (almostdegenerate) unoccupied molecular orbitals of complex 2corroborating that in all cases they correspond to cphendiimide
Regarding the triplet position (estimated in2004060 cmminus1 for complex 1 and in 2017250 cmminus1 forcomplex 2) it is close to that of cphen (21142plusmn45 cmminus1 [46])and to that of the cbtfa ligand (20276 cmminus1 [16] or 21277 cmminus1[45]) so it is not possible to discern whether it correspondsto the 120573-diketonate and to the NN-donor or if both wouldplay a role in the energy transfer to the Eu3+ ion (the mostusual situation) For Eu3+ complexes with dithiocarbamateand different NN-donors (including cphen) Regulacio etal [46] suggested that the intramolecular energy transferto the emissive states of the lanthanide was predominantlyfrom the triplet state of the bidentate aromatic amine andthat there may be intramolecular energy migration from thedithiocarbamate to the bidentate aromatic ligand
In relation to the Judd-Ofelt intensity parameters Ω120582
(120582 = 2 4 and 6) they are summarized in Table 5 Itis worth noting that for the most similar complex (ie[Eu(btfa)
3(phenNO)]) the estimatedΩ
2value is pretty close
and so are the radiative and nonradiative decay rates sothe software provides a good estimation For other Eu3+complexes with different fluorinated 120573-diketonates the dif-ferences in the estimated values are as expected moreevident
4 Conclusions
Taking a 120573-diketone which is known to optimize thequantum yield of Eu3+ complexes 1-(4-chlorophenyl)-444-trifluoro-13-butanedione (Hcbtfa) and neutral diimide 5-chloro-110-phenanthroline (cphen) as coordinating lig-ands two octacoordinated complexes were synthesizeda monomer formulated as [Eu(cbtfa)
3(cphen)] and a
dimer [Eu2(cbtfa)
4(cphen)
2(CH3O)2] The experimental
Advances in Condensed Matter Physics 9
(a) (b) (c)
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Figure 8 LUMO level for complex 1 (a) and for complex 2 (b and c)
characterization data (X-ray structural elucidation UV-Visabsorption and PL emission) for a mixture of these twocomplexes was subsequently used so as to assess a recentlyreleased quantum chemistry software LUMPAC
The predicted equilibrium energy configurationscalculated by semiempirical methods (SparklePM6 andSparklePM7 Hamiltonians) showed percent errors below5 in all cases (and generally below 2) for the unit cellparameters (versus X-ray structures) thus providing a goodestimation The same applied to the distances and anglesfor the first coordination sphere (although in this caseSparklePM7 Hamiltonian attained a significantly betteraccuracy than PM6)
In relation to LUMPACrsquos second module the estimationsof the singlet and triplet obtained by INDOS-CIS methodwere remarkably good and the calculated UV-Vis absorptionspectra could be regarded as an acceptable approximation forpractical purposes
Regarding the third module the Judd-Ofelt intensityparameters radiative and nonradiative emission rates andquantum efficiencies appeared to be in good agreement withthose of similar complexes reported in the literature althoughfurther research needs to be conducted to confirm thesepreliminary findings
All considered LUMPAC software can be deemed as avery promising tool for the design of novel Ln(III) complexesgiven its computational efficiency and ease of use in additionto being free of charge
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
Pablo Martın-Ramos would like to gratefully acknowledgethe financial support of Santander Universidades throughldquoBecas Iberoamerica Jovenes Profesores e InvestigadoresEspana 2015rdquo scholarship program The authors also wishto thank Professor I R Martın and Professor V Lavın(Universidad de La Laguna) for their insightful discussions
References
[1] J-C G Bunzli S Comby A-S Chauvin and C D BVandevyver ldquoNew opportunities for lanthanide luminescencerdquoJournal of Rare Earths vol 25 no 3 pp 257ndash274 2007
[2] S Comby and J-C G Bunzli ldquoLanthanide near-infraredluminescence in molecular probes and devicesrdquo in OpticalSpectroscopy V K Pecharsky J C G Bunzli and K AGschneider Jr Eds pp 217ndash470 Elsevier 2007
[3] G F de Sa O L Malta C de Mello Donega et al ldquoSpectro-scopic properties and design of highly luminescent lanthanidecoordination complexesrdquo Coordination Chemistry Reviews vol196 no 1 pp 165ndash195 2000
[4] R O Freire R Q Albuquerque S A Junior G B Rocha andM E deMesquita ldquoOn the use of combinatory chemistry to thedesign of new luminescent Eu3+ complexesrdquo Chemical PhysicsLetters vol 405 no 1ndash3 pp 123ndash126 2005
[5] R O Freire F R G Silva M O Rodrigues M E de MesquitaandN B da Costa Jr ldquoDesign of europium(III) complexes withhigh quantum yieldrdquo Journal of Molecular Modeling vol 12 no1 pp 16ndash23 2005
[6] J D L Dutra I F Gimenez N B D C Junior and R OFreire ldquoTheoretical design of highly luminescent europium (III)complexes a factorial studyrdquo Journal of Photochemistry andPhotobiology A Chemistry vol 217 no 2-3 pp 389ndash394 2011
[7] N B D Lima S M C Goncalves S A Junior and A MSimas ldquoA comprehensive strategy to boost the quantum yield ofluminescence of europium complexesrdquo Scientific Reports vol 3article 2395 2013
[8] R O Freire G B Rocha R Q Albuquerque and A M SimasldquoEfficacy of the semiempirical sparkle model as compared toECP ab-initio calculations for the prediction of ligand fieldparameters of europium (III) complexesrdquo Journal of Lumines-cence vol 111 no 1-2 pp 81ndash87 2005
[9] D A Rodrigues N B da Costa Jr and R O Freire ldquoWould thepseudocoordination centre method be appropriate to describethe geometries of lanthanide complexesrdquo Journal of ChemicalInformation and Modeling vol 51 no 1 pp 45ndash51 2011
[10] P Martın-Ramos P S P Silva P Chamorro-Posada et alldquoSynthesis structure theoretical studies and luminescent prop-erties of a ternary erbium(III) complex with acetylacetone andbathophenanthroline ligandsrdquo Journal of Luminescence vol 162pp 41ndash49 2015
[11] J D L Dutra T D Bispo and R O Freire ldquoLUMPAClanthanide luminescence software efficient and user friendlyrdquo
10 Advances in Condensed Matter Physics
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
Journal of Computational Chemistry vol 35 no 10 pp 772ndash7752014
[12] J D L Dutra and R O Freire ldquoTheoretical tools for the calcula-tion of the photoluminescent properties of europium systemsmdasha case studyrdquo Journal of Photochemistry and Photobiology AChemistry vol 256 pp 29ndash35 2013
[13] J D L Dutra J W Ferreira M O Rodrigues and R OFreire ldquoTheoreticalmethodologies for calculation of Judd-Ofeltintensity parameters of polyeuropium systemsrdquo The Journal ofPhysical Chemistry A vol 117 no 51 pp 14095ndash14099 2013
[14] J P Martins P Martın-Ramos C Coya et al ldquoHighly lumines-cent pure-red-emitting fluorinated 120573-diketonate europium(III)complex for full solution-processed OLEDsrdquo Journal of Lumi-nescence vol 159 pp 17ndash25 2015
[15] C de Mello Donega S Alves Jr and G F de Sa ldquoSynthesisluminescence and quantum yields of Eu(III) mixed com-plexes with 444-trifluoro-1-phenyl-13-butanedione and 110-phenanthroline-N-oxiderdquo Journal of Alloys and Compoundsvol 250 no 1-2 pp 422ndash426 1997
[16] P P Lima R A Sa Ferreira R O Freire et al ldquoSpectroscopicstudy of a UV-photostable organic-inorganic hybrids incorpo-rating an Eu3+ 120573-diketonate complexrdquo ChemPhysChem vol 7no 3 pp 735ndash746 2006
[17] S Biju D B A Raj M L P Reddy and B M KariukildquoSynthesis crystal structure and luminescent properties ofnovel Eu3+ heterocyclic 120573-diketonate complexes with bidentatenitrogen donorsrdquo Inorganic Chemistry vol 45 no 26 pp 10651ndash10660 2006
[18] G Sheldrick SADABS University of Gottingen GottingenGermany 1996
[19] G M Sheldrick ldquoA short history of SHELXrdquo Acta Crystallo-graphica Section A Foundations of Crystallography vol 64 no1 pp 112ndash122 2007
[20] A L Spek ldquoSingle-crystal structure validationwith the programPLATONrdquo Journal of Applied Crystallography vol 36 no 1 pp7ndash13 2003
[21] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods V modification of NDDO approximations and appli-cation to 70 elementsrdquo Journal of Molecular Modeling vol 13no 12 pp 1173ndash1213 2007
[22] R O Freire and A M Simas ldquoSparklePM6 parameters forall lanthanide trications from La(III) to Lu(III)rdquo Journal ofChemical Theory and Computation vol 6 no 7 pp 2019ndash20232010
[23] J J P Stewart ldquoOptimization of parameters for semiempiricalmethods VI more modifications to the NDDO approximationsand re-optimization of parametersrdquo Journal of Molecular Mod-eling vol 19 no 1 pp 1ndash32 2013
[24] J D L Dutra M A M Filho G B Rocha R O FreireA M Simas and J J P Stewart ldquoSparklePM7 lanthanideparameters for the modeling of complexes and materialsrdquoJournal of Chemical Theory and Computation vol 9 no 8 pp3333ndash3341 2013
[25] J J P StewartMOPAC2012 Stewart Computational ChemistryColorado Springs Colo USA 2012
[26] J D C Maia G A Urquiza Carvalho C P Mangueira Jr S RSantana L A F Cabral and G B Rocha ldquoGPU linear algebralibraries and GPGPU programming for accelerating MOPACsemiempirical quantum chemistry calculationsrdquo Journal ofChemical Theory and Computation vol 8 no 9 pp 3072ndash30812012
[27] F Neese ldquoThe ORCA program systemrdquo Wiley InterdisciplinaryReviews Computational Molecular Science vol 2 no 1 pp 73ndash78 2012
[28] T Petrenko and F Neese ldquoAnalysis and prediction of absorptionband shapes fluorescence band shapes resonance Ramanintensities and excitation profiles using the time-dependenttheory of electronic spectroscopyrdquo Journal of Chemical Physicsvol 127 no 16 Article ID 164319 2007
[29] J Ridley andM Zerner ldquoAn intermediate neglect of differentialoverlap technique for spectroscopy pyrrole and the azinesrdquoTheoretica Chimica Acta vol 32 no 2 pp 111ndash134 1973
[30] M C Zerner G H Loew R F Kirchner and U T Mueller-Westerhoff ldquoAn intermediate neglect of differential overlaptechnique for spectroscopy of transition-metal complexes Fer-rocenerdquo Journal of the American Chemical Society vol 102 no2 pp 589ndash599 1980
[31] J E Ridley and M C Zerner ldquoTriplet states via intermedi-ate neglect of differential overlap benzene pyridine and thediazinesrdquo Theoretica Chimica Acta vol 42 no 3 pp 223ndash2361976
[32] A V M de Andrade R L Longo A M Simas and G F de SaldquoTheoretical model for the prediction of electronic spectra oflanthanide complexesrdquo Journal of the Chemical Society FaradayTransactions vol 92 no 11 pp 1835ndash1839 1996
[33] A V M de Andrade N B da Costa Jr O L Malta R LLongo A M Simas and G F de Sa ldquoExcited state calculationsof Europium(III) complexesrdquo Journal of Alloys and Compoundsvol 250 no 1 pp 412ndash416 1997
[34] O L Malta M A C dos Santos L C Thompson andN K Ito ldquoIntensity parameters of 4fmdash4f transitions in theEu(dipivaloylmethanate)3 1 10-phenanthroline complexrdquo Jour-nal of Luminescence vol 69 no 2 pp 77ndash84 1996
[35] O L Malta ldquoMechanisms of non-radiative energy transferinvolving lanthanide ions revisitedrdquo Journal of Non-CrystallineSolids vol 354 no 42ndash44 pp 4770ndash4776 2008
[36] O L Malta H F Brito J F S Menezes F R Goncalves eSilva C de Mello Donega and S Alves Jr ldquoExperimentaland theoretical emission quantum yield in the compoundEu(thenoyltrifluoroacetonate)32(dibenzyl sulfoxide)rdquo Chemi-cal Physics Letters vol 282 no 3-4 pp 233ndash238 1998
[37] A G Orpen L Brammer F H Allen O Kennard D G Wat-son and R Taylor ldquoSupplement Tables of bond lengths deter-mined by X-ray and neutron diffraction Part 2 Organometalliccompounds and co-ordination complexes of the d- and f-blockmetalsrdquo Journal of the Chemical Society Dalton Transactions no12 pp S1ndashS83 1989
[38] W Humphrey A Dalke and K Schulten ldquoVMD visualmolecular dynamicsrdquo Journal of Molecular Graphics vol 14 no1 pp 33ndash38 1996
[39] J-F Guo H-J Zhang L-S Fu and Q-G Meng ldquoCrys-tal structure and luminescent properties of the complex[Eu(III)(TFPB)
3bpy]rdquo Chinese Journal of Inorganic Chemistry
vol 20 no 5 pp 543ndash546 2004[40] M TMongelli andK J Brewer ldquoSynthesis and study of the light
absorbing redox and photophysical properties of Ru(II) andOs(II) complexes of 47-diphenyl-110-phenanthroline contain-ing the polyazine bridging ligand 23-bis(2-pyridyl)pyrazinerdquoInorganic Chemistry Communications vol 9 no 9 pp 877ndash8812006
[41] M A Ivanov M V Puzyk T A Tkacheva and K P BalashevldquoEffect of heterocyclic diimine ligands with donor and acceptor
Advances in Condensed Matter Physics 11
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
substituents on the spectroscopic and electrochemical proper-ties ofAu(III) complexesrdquoRussian Journal of General Chemistryvol 76 no 2 pp 165ndash169 2006
[42] A-R Allouche ldquoGabeditamdasha graphical user interface forcomputational chemistry softwaresrdquo Journal of ComputationalChemistry vol 32 no 1 pp 174ndash182 2011
[43] J-M Lehn ldquoPerspectives in supramolecular chemistrymdashfrommolecular recognition towards molecular information process-ing and self-organizationrdquo Angewandte Chemie vol 29 no 11pp 1304ndash1319 1990
[44] C Gorller-Walrand and K Binnemans ldquoSpectral intensities off-f transitionsrdquo in Handbook on the Physics and Chemistry ofRare Earths K A Gschneidner and L Eyring Eds pp 101ndash264Elsevier Amsterdam The Netherlands 1998
[45] E Stathatos P Lianos E Evgeniou and A D KeramidasldquoElectroluminescence by a Sm3+-diketonate-phenanthrolinecomplexrdquo Synthetic Metals vol 139 no 2 pp 433ndash437 2003
[46] M D Regulacio M H Pablico J A Vasquez et al ldquoLumines-cence of Ln(III) dithiocarbamate complexes (Ln = La Pr SmEu Gd Tb Dy)rdquo Inorganic Chemistry vol 47 no 5 pp 1512ndash1523 2008
[47] M H V Werts R T F Jukes and J W Verhoeven ldquoThe emis-sion spectrum and the radiative lifetime of Eu3+ in luminescentlanthanide complexesrdquo Physical Chemistry Chemical Physicsvol 4 no 9 pp 1542ndash1548 2002
[48] V Divya S Biju R L Varma and M L P Reddy ldquoHighlyefficient visible light sensitized red emission from europiumtris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](110-phenan-throline) complex grafted on silica nanoparticlesrdquo Journal ofMaterials Chemistry vol 20 no 25 pp 5220ndash5227 2010
[49] S Biju M L P Reddy A H Cowley and K V Vasudevanldquo3-Phenyl-4-acyl-5-isoxazolonate complex of Tb3+ doped intopoly-120573-hydroxybutyratematrix as a promising light-conversionmolecular devicerdquo Journal ofMaterials Chemistry vol 19 no 29pp 5179ndash5187 2009
[50] A F Kirby D Foster and F S Richardson ldquoComparison of7F119869larr 5D
119874emission spectra for Eu(III) in crystalline environ-
ments of octahedral near-octahedral and trigonal symmetryrdquoChemical Physics Letters vol 95 no 6 pp 507ndash512 1983
[51] G Ligner R Mohan S Knittel and G Duportail ldquoHypersensi-tivity of terbium and europium ions luminescence in biologicalsubstratesrdquo Spectrochimica Acta Part A Molecular Spectroscopyvol 46 no 5 pp 797ndash802 1990
[52] C D M Donega S A Junior and G F de Sa ldquoEuropium(III)mixed complexes with 120573-diketones and o-phenanthroline-N-oxide as promising light-conversion molecular devicesrdquo Chem-ical Communications no 10 pp 1199ndash1200 1996
[53] C R de Silva J R Maeyer R Wang G S Nichol and ZZheng ldquoAdducts of europium 120573-diketonates with nitrogen pp1015840-disubstituted bipyridine and phenanthroline ligands synthesisstructural characterization and luminescence studiesrdquo Inorgan-ica Chimica Acta vol 360 no 11 pp 3543ndash3552 2007
