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Research ArticleA High Molar Extinction Coefficient Ru(II) ComplexFunctionalized with cis-Dithiocyanato-bis-(9-anthracenyl-10-(2-methyl-2-butenoic acid)-110-phenanthroline)Potential Sensitizer for Stable Dye-Sensitized Solar Cells

Adewale O Adeloye and Peter A Ajibade

Department of Chemistry Faculty of Science and Agriculture University of Fort Hare Private Bag X1314 Alice 5700 South Africa

Correspondence should be addressed to Peter A Ajibade pajibadeufhacza

Received 12 November 2013 Revised 5 February 2014 Accepted 5 February 2014 Published 28 April 2014

Academic Editor Mengqing Xu

Copyright copy 2014 A O Adeloye and P A Ajibade This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

New heteroleptic ruthenium(II) complex was formulated as [Ru(L1)2(NCS)

2] where L

1= 9-anthracenyl-10-(2-methyl-2-butenoic

acid)-110-phenanthroline was synthesized and its photophysical properties were studied and compared to previously reportedanalogue complex containing no anthracene moiety [Ru(L

2)2(NCS)

2] L2= (2-methyl-2-butenoic acid)-110-phenanthroline The

two complexes though exhibit very strongmolar extinction coefficient values however [Ru(L1)2(NCS)

2] shows better characteristic

broad and intense metal-to-ligand charge transfer (MLCT) absorption band and higher molar absorptivity coefficient at (120582max =

522 nm 120576 = 660 times 104Mminus1 cmminus1) than that of [Ru(L2)2(NCS)

2] complex (120582max = 446 nm 120576 = 482 times 104Mminus1 cmminus1) At

room temperature long wavelength emissions with strong intensity ratio centered at 660 nm were recorded for [Ru(L1)2(NCS)

2]

complex with a bathochromic shift (120582em = 700 nm) for [Ru(L2)2(NCS)

2] complex It was shown that the luminescence wavelength

characteristic of the complexes may be a function relating to the increasing length of 120587-conjugation andor molecular weight Apreliminary cyclic voltammetry of [Ru(L

1)2(NCS)

2] complex also exhibits good electroredox activity with oxidation potential of

about 104V significantly better than other Ru(II) polypyridine complexes containing bidentate ligands

1 Introduction

The search for efficient solar energy conversion devicesis an important area of research [1ndash7] Among all majorconstituents vital to dye-sensitized solar cells (DSCs) photo-sensitizers are responsible for light harvesting while suitablephotoanodes redox couples and counter electrodes areutilized to achieve efficient charge separation collectionand transportation The major challenge of this emergenttechnology is to integrate each of the components into ahighly efficient single photonic device [8ndash15] Recently anorder of magnitude increase in solar energy conversion effi-ciencies at dye-sensitized photoelectrochemical cells has beenrealized [16ndash22] This breakthrough was accomplished byattaching ruthenium polypyridyl complexes to high surfacearea titanium dioxide TiO

2electrodes when operating as

photoanodes in a photoelectrochemical cells these materialsefficiently convert visible light to electricity [23 24] Researchon artificial photosynthetic devices based on this technologyprovides an opportunity to directly convert light energy intoelectricity on a molecular level Since it is expected thatmost inorganic charge transfer complexes possess uniqueground and excited state properties it is not surprising tofind that solar energy conversion efficiencies are dependenton the nature of the molecular dye sensitizer Rutheniumpolypyridine complexes are widely used as photosensitizersin covalently linked multicomponent systems Their photo-physical properties make them ideal candidates as buildingblocks for the design of supramolecular species performingcomplex light induced functions [25ndash28] These complexesoffer desirable redox properties excited-state reactivity lumi-nescent emission and excited-state lifetimes [29ndash36]

Hindawi Publishing CorporationJournal of SpectroscopyVolume 2014 Article ID 869363 10 pageshttpdxdoiorg1011552014869363

2 Journal of Spectroscopy

Previous study has shown that metal-to-ligand chargetransfer (MLCT) sensitizers with positive metal-based oxi-dation potentials have the disadvantage of exhibiting highenergy absorption bands which only harvest a fractionof visible light [25 26] For complexes of the type cis-Ru(LL)

2X2(where LL is bidentate polypyridine ligands and X

is ancillary ligands) intenseMLCTabsorption bands are oftenobserved from 400 to 600 nm with negligible absorptionat longer wavelengths [22] The MLCT absorption can beextended to lower energy by appropriate substituent changesin the chromophoric ligands or by decreasing the d120587-120587lowastbackbonding donation of the nonchromophoric ligands Theeffect of these changes on the photophysical properties ofmetal polypyridine complexes has been the subject of severalinvestigations which have given fundamental insight intothe factors which govern radiative and nonradiative decayprocesses of excited states [25 26]

In an attempt to extend the spectral sensitivity ofdye molecules towards the red we have designed a newcis-Ru(LL)

2-(X)2polypyridine complex based on the lig-

and 5-(9-anthracenyl-10-(trans-2-methyl-2-butenoic acid)-110-phenanthroline) with extended 120587lowast accepting orbitals atlower energy and the photophysical properties compared tothe previously reported heteroleptic Ru(II) complex of 5-(trans-2-methyl-2-butenoic acid)-110-phenanthroline ligand[37] The photoelectrochemical characteristics exhibited bythe complex are rationalized in terms of spectroscopicaland photophysical properties measured in fluid solutionAs envisaged enhanced spectral response was found forcomplex containing anthracenyl functionality as comparedto that without anthracene However of particular relevancein the context of this report in relation to our previousstudies and reports on the increasing number of anthracenefunctionality in a particular ruthenium polypyridyl complexin which molar extinction coefficient values are reduceddue to molecular aggregation [38ndash40] On the basis of thiswe set out to investigate and discuss the photophysical andelectrochemical properties of a new-type monoanthracenylfunctionalized phenanthroline heteroleptic ruthenium(II)complex in relation to its potential use as a photosensitizerfor application in the dye-sensitized solar cells (DSSCs) andother optoelectronic devices

2 Results and Discussion

21 Chemistry Scheme 1 (indashiii) shows the stepwise syn-thetic pathways for L

1and L

2and outlines the chemistry

of the present study 910-Dibromoanthracene 2-methyl-2-butenoic acid and 110-phenanthroline are the starting mate-rials for 1 and 2 9-Bromo-10-(2-methyl-2-butenoic acid)-anthracene (1) was obtained when 910-dibromoanthraceneand 2-methyl-2-butenoic acid were refluxed in a ben-zenedichloromethane mixture under basic condition usingtriethylamine potassium hydroxide and palladium carbideProduct 2 was obtained by the initial introduction ofrequired bromine functions on 110-phenanthroline underan environmentally benign condition as reported by Vyasand coworkers [41] L

1and L

2were synthesized following

slightmodifications of established procedures reported in theliterature [40] The synthesis of L

1essentially follows two

major reaction steps the initial synthesis of a 2-methyl-2-butenoic acid functionalized anthracenyl group followed by apalladium cross-catalyzed reaction of two halide compoundsThis reaction was aided by the use of an equivalent volumeratio of dichloromethane-benzene as solvent to overcome thepoor solubility of anthracenyl derivatives in common organicsolvents such as methanol and chloroform It was foundthat this reaction could be reversed by first reaction of thehalogenated polypyridine with 910-dibromoanthracene anda subsequent dehydrohalogenation reaction with 2-methyl-butenoic acid L

2was obtained by one-step nucleophilic

aromatic substitution reaction of the bromide group ofproduct 2 with 2-methyl-2-butenoic acid The synthesis ofthe metal precursor [RuCl

2(dmso)

4] [42] and the complexes

[Ru(L1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] followed the general

synthetic route shown in Scheme 1 (iv and v) Sequentialsubstitution of the DMSO coordinating ligand from themetal precursor led to formation of intermediate complex[Ru(L

119909)2Cl2] (L119909= L1or L2) which was not isolated

Final reaction was carried out with chloride exchange withthiocyanate group [43]

22 Infrared Spectra The FT-IR spectra of the startingmaterials the ligands and the complex showed certaincharacteristic absorption bands that were compared andassigned on careful comparisonDue to structural similaritiesbetween the ligand and the complex a strong band in theregion 3479ndash3055 cmminus1 was found This gave indication ofthe presence of an OminusH group possibly from the carboxylicacid moiety This band however shifted to higher frequencyat 3551 cmminus1 in the complex (Figure 1) The vibration fre-quency bands between 3479 and 3237 cmminus1 may be dueto presence of 120572- 120573-unsaturated carboxylic acid andoraromaticCminusHstretching characteristics of themoleculesTheband at 2928 cmminus1 shows the presence of CminusH stretchingof methyl groups The complex shows a broad absorptionfrequency at 2104 cmminus1 for stretch vibrational modes due tothe N-coordinated 120592 (CN) This band is reduced in intensitycompared to the band at 926 cmminus1 due to 120592(CS) The bandsat 1971 1638 cmminus1 1309 and 1256 cmminus1 were assigned to the120592(C=O) and 120592(CndashO) stretching of carboxylic acid groupsrespectively The singlet sharp band at 1617 cmminus1 is assignedto the aromatic CndashN stretch vibration with the two bandsat 1459 and 1438 cmminus1 due to ring stretching modes of theligands A comparison of the infrared spectra of L1 and 910-dibromoanthracene showed that a strong vibrational band inthe former was conspicuously absent in the latter confirmingthe loss of CndashBr bond and the formation of CndashC bondlinkages of the anthracenyl group Furthermore the CndashCbond linkage between anthracene and phenanthroline wasaffirmed by the absorption frequency at 804 cmminus1 Peaks inthe region at 747 and 730 cmminus1 demonstrate the existence offour adjacent hydrogen atoms common to L1 and complex[Ru(L

1)2(NCS)

2] All vibrational peaks in the region are

found to be relatively weak and broad in the complex whichmay be ascribed to the loss of crystallinity and the broad

Journal of Spectroscopy 3

Br

Br

Br

Br

BR

+

+

+

H

H

N

N NN

NN N

N

NN

CH3

CH3

CH3

CH3

COOH

HOOC

HOOC

HOOC

CH2Cl2ndashC6H6(50)

CH2Cl2 C6H6(50)

PdC ET3N KOH 12 h

Br

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

COOH

COOH

COOH

COOH

COOH

COOHMeOH rt 20h

MeOH PdC

KOH Et3N 8h

(i)

(ii)

(iii)

(iv)

(v)

(a)

(b)

(1)

(1)

(2)

(i)

(ii)

H3C

H3C

H3C

H3C

H3C

[RuCl3(H2O)] + 4 (CH3)2SO[RuCl2((CH3)2SO)4]

[RuCl2((CH3)2SO)4]

Yellow powder

Yellow powder

(L2)

(L1)

(1) Reflux100∘C 10min

(2) Washed in acetone

Ru

Ru

N

N

N N

N

NN

N

N N

N

N

C

CC

CS

S

S

S

(ii) DMF reflux 120∘C 8h

PdC Et3N KOH 12h


(i) 2(L2) + 2NH4NCS

(i) 2(L2) + 2NH4NCS

chromatography

HBrH2O2 (1 1)

ndash

Scheme 1 Synthetic pathways for ligands L1and L

2and complexes [Ru(L

1)2(NCS)

2] and [Ru(L

2)2(NCS)

2]

distribution of the anthracene chain length [36] The weakabsorption frequencies at 475 and 404 cmminus1 respectivelyshow the coordination of nitrogen atoms of the ancillaryligands to ruthenium central metal atom [44]

23 NMR Spectroscopy The 1H-NMR of L1 due to molecularsymmetry showed five major signals at the aromatic region at120575 918 (d J = 32Hz) 823 (d J = 72Hz) 777 (s) 762 (ddJ = 44 80Hz) and 697 (d J = 72Hz) these peaks were

assigned to the phenanthroline and anthracene protons Thetwo signals in the aliphatic region at 120575 181 (t CH

3) and 123

(t CH3) were unambiguously assigned to the trans-methyl

protons of the carboxylic acid group (Figure 2) The 13Cspectrum peaks of the L1 ligand (Figure 3) showed importantdiagnostic peaks depicting the presence of phenanthrolineanthracene and the 2-dimethyl substituted 120572- 120573-unsaturatedcarboxylic acid At the aromatic region a peak at 120575 15028was tentatively assigned to the C=O of the acidic group


T (

)

355148

347936

341460

323723

292598

210404

197163

163824

161753

145993

143822

130476125659

115629109060

102699

92653

80403

74774

73017

62281

5792947506

40418

400

0

3600

320

0

2800

2400

2000

1800

1600

1400

1200

1000 800

600

3700

Figure 1 FT-IR spectrum of [Ru(L1)2(NCS)

2] complex in KBr

123

4123

2

1786

180

3182

5214

6

6965

6983

7258

76037614

7623

7634

7773

822

3824

1

9178

9186

9 8 7 6 5 4 3 2

(ppm)

Figure 2 1H NMR spectrum of L1 in CDCl3

andor the C=N of the phenanthroline framework Increasein the 120587-bond conjugation in molecules is known to causeupfield shifts for all types of carbonyl compounds due tostrong electron density delocalization [45]The reduced peaksignals at 120575 14619 13925 and 12861 ppm were assignedto the quaternary carbon atoms Three strong peaks at 12057513598 12650 and 12306 ppm were assigned to the methinegroups of the ligand At the aliphatic region the two methylgroups showed conspicuous peaks at 120575 1442 and 1174 ppmGood 1H and 13C-NMR spectra resolutions were difficultto obtain for the corresponding [Ru(L

1)2(NCS)

2] complex

However in the aromatic region of the 1H-NMR it wasobserved that the two major symmetric signals assigned tothe anthracene protons dominate the spectrum at 120575 859 (dd J= 48 72Hz) and 763 (dd J = 28 68Hz) the phenanthrolineproton peak signals were found at a very much reducedintensity (Figure 4) The aliphatic region of the spectrumhowever gave interesting information with the presence offour downfield singlet peak signals at 120575 295 288 217 and204 ppm which were assigned to the methyl signals of thecarboxylic acid groups The reason for the splitting intofour different singlet peaks is unclear at the moment butit could be inferred that the two outer anchoring ligandsin the complex possibly have different spatial orientation as

15027

614

6196

139253

135970

128609

126469

123059

77348

77031

76713

14522

11736

180 160 140 120 100 80 60 40 20 0

(ppm)

Figure 3 13C NMR spectrum of L1 in CDCl3

12 10 8 6 4 2 minus0

(ppm)

8603

8594

8585

8578

7646

7639

7629

7621

7257

5295

2953

288

1

216

7203

8

000

2

Figure 4 1H NMR spectrum of [Ru(L1)2(NCS)

2] complex

opposed to the symmetry found in a single (L1) ligand before

complexation

24 Electronic Absorption and Emission Spectra

241 Electronic Absorption Spectroscopy The UV-Visabsorbance and emission spectra of complex[Ru(L

1)2(NCS)

2] were recorded at room temperature in

aerated DMF solution and are shown in Figures 5 6 and7 respectively The complex exhibits a very broad andintense metal-to-ligand charge (MLCT) absorption bandthroughout the visible region of the spectrum (430ndash700 nm)characteristics of many other ruthenium(II) polypyridylcomplexes which can be assigned to electronic transitionsfrom the RuII based t

2g orbital to the ligand based 120587lowast orbitals

Themolar extinction coefficient of [Ru(L1)2(NCS)

2] complex

centered at its maximum 522 nm is 660 times 104Mminus1 cmminus1about 73 larger than that of [Ru(L

2)2(NCS)

2] (482 times

104Mminus1 cmminus1) with a blue shift at 446 nm The anthracenylnature of the complex exhibits multiple distinct vibronicpeaks for the intraligand (120587 rarr 120587lowast) charge transfer transitionscharacteristics of anthracene derivatives at 348 365 383and 405 nm These bands enhance the oscillator strengthin the blue and green portions of the spectrum relative to[Ru(L

2)2(NCS)

2] complex These features have also been

found as ameans of improving light absorption cross sectionsat higher energy in similar complexes [46] In addition thehigher absorption coefficient of the [Ru(L

1)2(NCS)

2]


0

05

1

15

2

300 400 500 600 700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)

[Ru(L1)2(NCS)2][Ru(L2)2(NCS)2]

Figure 5 Comparison of the UV-V is absorption spectrum of[Ru(L

1)2(NCS)

2] (solid line) with [Ru(L

2)2(NCS)

2] (dash line) at

a concentration of 1 times 10minus3Mminus1 in DMF solution showing effect ofextended 120587-conjugation using anthracene

complex consequently allows a thinner nanocrystallineTiO2film to avoid the decrease of the mechanical strength

A thinner film also facilitates the electrolyte diffusion andreduces the recombination possibility of the light-inducedcharges during transportation [47] The molar extinctioncoefficients of the two complexes descend steadily towardslonger wavelengths Noticeably the complexes show acommon weak shoulder in the near infrared region at918 nm (120576 = 5734Mminus1 cmminus1) and general broad bands inthe region of 965ndash1022 nm (Figure 6) these absorptionbands are attributed to the 3MLCT triplet state excitationof the ruthenium(II) polypyridine complexes [39 48]The intense absorption band in the UV region around280ndash300 nm (not shown) was assigned to the intraligand120587 rarr 120587

lowast transitions of L1and L

2ligands The lower-energy

absorption in the two complexes may have been enhanceddue to the presence of the electron withdrawing nature of thecarboxylic groups which lowers the energy of the 120587lowast orbitalof the phenanthroline ligands and a further stability of thecomplexes provided by the trans nature of the methyl groups[49]

242 Emission Study The emission spectra of[Ru(L

1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] are displayed in

Figure 7 Upon excitation into the 1LC and 1MLCT bands(470 nm) both complexes display appreciable luminescenceat room temperature An emission wavelength maximumcentered at 660 nm was recorded for [Ru(L

1)2(NCS)

2] It

is interesting to note the red shift in emission wavelengthmaximum centered at 700 nm for [Ru(L

2)2(NCS)

2] As

observed in the absorption spectra the emission spectrashow no shoulders indicating probably the existence of onlyone emitting state and nondistortion of molecular structuresin the two complexes However overall emission wavelengthsshow an inverse relationship with increase in absorptionwavelength maxima This may be explained in terms ofthe energy gap between the ground and the lowest excitedstates which monotonically increases as the extent of chargetransfer of the electronic ground state decreases The results

0

005

01

015

700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)


Figure 6 Comparison of the lowest energy absorption bandsof [Ru(L

1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] complexes detected in

the near infrared region of 900ndash1022 nm (120576 = 570 minus 780 times103Mminus1 cmminus1)

0

200

400

600

800

1000

1200

630 650 670 690 710 730

Emiss

ion

inte

nsity

(au

)

Wavelength (nm)


Figure 7 Comparison of the emission spectrum of[Ru(L

1)2(NCS)


2)2(NCS)

2] (dash line)

at a concentration of 1 times 10minus3Mminus1 in DMF solution showing effectof extended 120587-conjugation using anthracene

may also be ascribed to the molecular size of the complexesIt has been reported that as the molecular size increasesthrough the extended 120587-conjugation the density of thestates will increase thus providing more effective couplingchannels between the ground and photon-allowed states[50 51] It is well known that conjugated functional organicmolecules are useful for the study of electron transport atthe molecular scale and that the use of fused-ring systemsis a powerful and practical approach The energy of the LCexcited states depends on intrinsic properties of the ligandssuch as the HOMO-LUMO energy gap and the singlet-tripletsplitting The intense emission is a significant contribution


[Ru(L1)2(NCS)2]

II

III

I

minus15 minus1 minus05 0 05 1 15Potential (V versus Ag|AgCl)

60120583A

(a)

II

IIII


60120583A

SQW of [Ru (L1)2(NCS)2]

(b)

Figure 8 Cyclic and square wave voltammograms (a and b) for [Ru(L2)2(NCS)

2] complex at 1 times 10minus3M in freshly distilled DMF containing

01M TBABF4supporting electrolyte Step potential is 5mV amplitude is 60mV versus Ag|AgCl and frequency is 10Hz Scan rate is 100m

Vsminus1 versus Ag|AgCl

to the excited state from an interaction between the metald-orbital and the ligand 120587-systems [52]

25 Electrochemical Study The cyclic and square wavevoltammograms of the complex [Ru(L

1)2(NCS)

2] were

examined in the potential range +15 to minus15 V and at a scanrate 50mVsdotsminus1 using Ag|AgCl electrode in DMF solvent with01M tetrabutylammonium hexafluorophosphate as support-ing electrolyte (Figure 8(a)) The voltammograms display theRu2+Ru3+ couple at positive potential and ligand based onreduction couples at negative potential A reversible one-electron oxidation peak at E

12= +104V (process III) was

attributed to Ru2+Ru3+ wave couple which was found ata slightly reduced potential (sim+014V) in the square wavevoltammogram (Figure 8(b)) The reason for the observedshift in potential could not be adequately accounted forthough the possibility of instrumental error is not pre-cluded [40 49] In comparison the highly efficient Ru(II)DSC sensitizers commonly possess Ru2+Ru3+ potentialsclose to or greater than ca +09V while maintaining asizeable over potential versus IminusI

3

minus couple to ensure thefast regeneration of the oxidized sensitizer [53 54] Tocircumvent this limitation one possible solution is to attach astrong electron-withdrawing group onto the ancillary so thatoxidation potentials can be adequately controlled [55] Oneidentified irreversible oxidation peak process II was observedat +058V this was ascribed to the ring oxidation of eitherthe phenanthroline or anthracene andor a contributionfrom the carboxylate ions present in the complex At thenegative potential pseudoirreversible wave was observed atminus089V for process I The more positive reduction potentialmay be assigned to the contribution from the liganddue toan additional (C=C) conjugative 120587-bond as found in thestructure of anthracene since the ligand contains the electron

withdrawing ndashCOOH group of the anchoring ligand beingresponsible for lowering the LUMO levels

3 Experimental

31 Materials and General Physical Measurements Allchemical and reagents were analytically pure and usedwithout further purification 5-Bromo-110-phenanthrolineand 5-(9-bromoanthracene)-110-phenanthroline weresynthesized as described in the literature [41] 5-(9-Anthracenyl-10-(trans-2-methyl-2-butenoic acid)-110-phenanthroline) (L

1) and 5-(trans-2-methyl-2-butenoic

acid)-110-phenanthroline (L2) were synthesized by

the literature procedure [38] with slight modifications(Scheme 1) All thin layer chromatography (TLC) analyseswere done with aluminium sheet precoated with normalphase silica gel 60 F

254(Merck 020mm thickness) unless

otherwise stated The TLC plates were developed usingany of the following solvent systems solvent systemA dichloromethane-methanol (9 1) solvent system Bdichloromethane-methanol (7 3) solvent system C diethylether-methanol (1 1) Gel filtration was performed usingSephadex LH-20 previously swollen in specified solvent(s) prior to loading of extract onto the column (35 cm times85 cm) Melting points were determined using a Gallenkampelectrothermal melting point apparatus Microanalyses (CH N and S) were carried out with a Fisons elementalanalyzer and infrared spectra were obtained with KBrdiscs or nujol on a Perkin Elmer System 2000 FT-IRSpectrophotometer UV-Vis and fluorescence spectra wererecorded in a 1 cm path length quartz cell on a Perkin ElmerLambda 35 spectrophotometer and Perkin Elmer Lambda45 spectrofluorometer respectively 1H- and 13C-NMRspectra were run on a Bruker EMX 400MHz spectrometerfor 1H and 100MHz for 13C The chemical shift values


were reported in parts per million (ppm) relative to (TMS)as internal standard Chemical shifts were reported for theligands and complex with respect to CDCl

3at 120575c 7700 and 120575H

CDCl3at 726 Electrochemical experiment was performed

using a PGSTAT 302 Autolab potentiostat (EcoChemieUtrecht The Netherlands) driven by the general purposeelectrochemical system data processing software (GPESsoftware version 49) A conventional three-electrode systemwas used The working electrode was a bare glassy carbonelectrode (GCE) Ag|AgCl wire and platinum wire wereused as the pseudo-reference and auxiliary electrodesrespectively The potential response of the Ag|AgCl pseudo-reference electrode was less than the Ag|AgCl (3M KCl)by 0015 plusmn 0003V Prior to use the electrode surface waspolished with alumina on a Buehler felt pad and rinsed withexcess Millipore water All electrochemical experiments wereperformed in freshly distilled dry DMF containing TBABF

4

as supporting electrolyte

32 Synthesis of 5-(9-Anthracenyl-10-(trans-2-Methyl-2-butenoic acid)-110-phenanthroline) (L

1) 5-Bromo-110-

phenanthroline (1 g 386mmol) and 9-bromo-10-(2-methyl-2-butenoic acid)-anthracene (137 g 386mmol) weredissolved in benzene-dichloromethane (70mL vv 1 1)followed by the addition of Et

3N (1mL) KOH (027 g

482mmol) and palladium-carbide (005 g) The reactionwas carried out under reflux for 12 h at temperature 110ndash120∘C Colour yellow crystalline solid Melting point167ndash169∘C percentage yield 140 g 59 IR (KBr) ]maxcm

minus13427 3055 2979 2924 2552 1966 1871 1802 1579 15581453 1417 1304 1255 1140 1089 1040 994 926 756 654 619579 1H-NMR (CDCl

3) 120575 918 (d J = 32Hz) 823 (d J =

72Hz) 777 (s) 762 (dd J = 44 80Hz) 697 (d J = 72Hz)181 (t CH

3) 123 (t CH

3) 13C-NMR (CDCl

3) 120575 15028

14619 13925 13597 12861 12649 12304 1442 and 1174Elemental analysis calculated H 488 C 8172 and N 616required H 471 C 8160 and N 631 Molecular formulaC31H22N2O2

33 Synthesis of 5-(trans-2-Methyl-2-butenoic acid)-110-phenanthroline (L

2) 5-Bromo-110-phenanthroline (10 g

386mmol) and trans-2-methyl-2-butenoic acid (039 g386mmol) were dissolved in MeOH (40mL) in a 250mLflask Et

3N (10mL) and palladium carbide (0050 g) were

added and the mixture was refluxed for 8 h at a temperaturebetween 110 and 120∘C Colour white-pink crystalline solidpercentage yield 074 g 53 melting point ND IR (KBr]maxcm

minus1) 3419 3032 2929 1694 1652 1619 1589 15611506 1420 1385 1343 1256 1219 1140 1093 1080 10371015 843 766 734 769 625 and 530 1H-NMR (CDCl

3) 120575

1133 (br OH) 898 (t J = 40Hz 2H H-2 9) 792 (d J =80Hz 2H H-4 7) 745 (s 1H H-6) 735 (2d J = 44Hz2H H-38) 168 (s 3H CH

3) and 159 (d J = 68Hz 3H

CH3) 13C-NMR (CDCl

3) 120575 17283 15039 15030 14630

14621 13879 13613 12881 12872 12668 12659 1232712319 1474 and 1214 Elemental analysis calculated H 507C 7337 and N 1007 required H 499 C 7364 and N 1023Molecular formula C

17H14N2O2

34 Synthesis of cis-Dithiocyanato-bis-5-(9-anthracenyl-10-(trans-2-methyl-2-butenoic acid)-110-phenanthrolyl) Ruthe-nium(II) Complex [Ru(L

1)2(NCS)

2] In a 250mL flask

[RuCl2(dmso)

4] (005 g 011mmol) was dissolved in NN-

dimethylformamidemethod mixture (80mL 1 5 vv) fol-lowed by the addition of ligand L

1(010 g 122mmol) The

mixture was refluxed initially at 120∘C for 12 h in the darkand excess of NH

4NCS (017 g 220mmol) Colour dark-

brown solid melting point gt260∘C percentage yield 079 g25 IR (KBr) ]maxcm

minus1 3551 3479 3414 3237 29282104 1971 1638 1617 1459 1448 1304 1265 1156 10901026 926 804 747 730 622 579 475 and 404 UV-Vis(120582maxnm 120576 = times104Mminus1 cmminus1 DMF) 348 (1170) 365 (1727)383 (2362) 405 (2123) 437 (507) and 522 (659) Emissionwavelength (120582exc = 500 nm 120582em = 660 nm) Selected 1H-NMR data (CDCl

3) 120575 859 (dd J = 48 72Hz) 763 (dd J

= 28 68Hz) 295 (s CH3) 288 (s CH

3) 217 (s CH

3) and

204 (s CH3) 13C-NMR (CDCl

3) ND Cyclic voltammetry

data Ru2+Ru3+ = +104 V Eanodic = +058V Ecathodic =minus089V Elemental analysis calculated H 394 C 6825 N744 and S 569 required H 422 C 6855 N 776 and S 591Molecular formula RuC

64H44N6O4S2

35 Synthesis of cis-Dithiocyanato-bis-5-(trans-2-methyl-2-butenoic acid)-110-phenanthrolyl Ruthenium(II) Complex[Ru(L

2)2(NCS)

2] In a 250mL flask [RuCl

2(dmso)

4] (044 g

090mmol) was dissolved in NN-dimethylformamide(40mL) followed by the addition of ligand L

2(050 g

179mmol) The mixture was refluxed initially at 120∘C for2 h in the dark and excess of NH

4NCS (027 g 359mol)

was added and the same procedure as described above wasfollowed Colour orange solid melting point 201ndash204∘Cpercentage yield 038 g 38 IR (KBr) ]maxcm

minus1 34233058 2926 2856 2086 2058 1978 1631 1427 13841221 1205 1147 1056 879 844 773 721 621 and 559UV-Vis (120582maxnm 120576 = times104Mminus1 cmminus1 DMF) 416 (449)446 (482) Emission wavelength (120582exc = 500 nm 120582em =700 nm) 1H-NMR (CDCl

3) 120575 877 (d J = 80Hz 4H) 838

(s 2H) 808 (d J = 48Hz 4H) 776 (dd J = 52 80Hz 4H)and 340 (s 6H) Selected aromatic 13C-NMR data (CDCl

3)

15362 14813 13769 13133 12892 and 12717 Elementalanalysis calculated H 365 C 5588 N 1086 and S 829required H 332 C 5595 N 1051 and S 859 Molecularformula RuC

36H28N6O4S2

4 Conclusions

With the growing research in the different sections of DSSCincluding sensitizers we have designed synthesized andcharacterized a new ligand 5-(9-anthracenyl-10-(2-methyl-2-butenoic acid)-110-phenanthroline (L

1) and its ruthe-

nium(II) complex [Ru(L1)2(NCS)

2] using FT-IR 1H NMR

and elemental analysis The photophysical properties of thecomplex when compared with previously reported analogue[Ru(L

2)2(NCS)

2] complex containing no anthracenyl func-

tionality were found to show higher molar extinction coef-ficient and shifting of the wavelength maximum to the red asthese were attributed to the extension of 120587-bond conjugation


in the molecule In terms of emission characteristic howeverthe wavelength of the complex [Ru(L

1)2(NCS)

2] was blue-

shifted due to the sizemolecular weight as more conjugatedbonds are introduced

By comparison of the electroredox property of the com-plex [Ru(L

1)2(NCS)

2] to other reported Ru(II) polypyridyl

complexes used as photosensitizers for dye-sensitized solarcells (DSSCs) applications the complex showed a goodelectroredox property The Ru2+Ru3+ oxidation potential(Eox

o) is measured as 104V (versus AgCl) which is largerthan that of the IminusI

3

minus redox potential (sim035V versus NHE)It has been revealed that oxidation potentials provide first-hand information on whether newly developed dyes canbe efficiently regenerated by the IminusI

3

minus redox couple [56ndash58] Particularly for this molecule further work is ongoingin our laboratory to establish the solar-to-electrical energyconversion efficiency (120578) in the dye-sensitized solar cells(DSSCs) However due to 120587-electron cloud overlaps inanthracene derivatives the molecule could be useful in otherapplications including organic electroluminescence materialfor biosensitizers and display devices such as organic lightemitting diode (OLED) organic thin film transistor (OTFT)wearable display photochromic agents and electronic paper

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Financial support from the South African National EnergyResearch Institute (SANERI) and Govan Mbeki ResearchCentre University of Fort Hare Alice South Africa is highlyappreciated

References

[1] M A Fox and M Chanon Photoinduced Electron TransferElsevier Amsterdam The Netherlands 1988

[2] M Gratzel Heterogeneous Photochemical Electron TransferCRC Press Boca Raton Fla USA 1989

[3] O U Yoping G Chen J Yin G-A O Yu and S H Liuldquo2Rotaxane based on terpyridyl bimetal ruthenium complexesand 120573-cyclodextrin as organic sensitizer for dye-sensitized solarcellsrdquo Journal of Coordination Chemistry vol 64 no 17 pp3062ndash3067 2011

[4] B C OrsquoRegan and J R Durrant ldquoKinetic and energeticparadigms for dye-sensitized solar cells moving from the idealto the realrdquo Accounts of Chemical Research vol 42 no 11 pp1799ndash1808 2009

[5] H J Snaith ldquoEstimating the maximum attainable efficiency indye-sensitized solar cellsrdquo Advanced Functional Materials vol20 no 1 pp 13ndash19 2010

[6] A Harriman M Hissler A Khatyr and R Ziessel ldquoThephotophysical properties of hybrid metal complexes containingboth 221015840-bipyridine and 2210158406101584021015840-terpyridine unitsrdquo EuropeanJournal of Inorganic Chemistry no 5 pp 955ndash959 2003

[7] V Duprez M Biancardo H Spanggaard and F CKrebs ldquoSynthesis of conjugated polymers containingterpyridine-ruthenium complexes photovoltaic applicationsrdquoMacromolecules vol 38 no 25 pp 10436ndash10448 2005

[8] C W Hsu S T Ho K L Wu Y Chi S H Liu and P T ChouldquoRu(II) sensitizers with a tridentate heterocyclic cyclometalatefor dye-sensitized solar cellsrdquo Energy amp Environmental Sciencevol 5 no 6 pp 7549ndash7554 2012

[9] L M Goncalves V de zea Bermudez H A Ribeiro and A MMendes ldquoDye-sensitized solar cells a safe bet for the futurerdquoEnergy amp Environmental Science vol 1 no 6 pp 655ndash667 2008

[10] J-H Yum P Chen M Gratzel and M K NazeeruddinldquoRecent developments in solid-state dye-sensitized solar cellsrdquoChemSusChem vol 1 no 8-9 pp 699ndash707 2008

[11] TW Hamann R A Jensen A B F Martinson H van Ryswykand J T Hupp ldquoAdvancing beyond current generation dye-sensitized solar cellsrdquo Energy amp Environmental Science vol 1no 1 pp 66ndash78 2008

[12] M Gratzel ldquoRecent advances in sensitized mesoscopic solarcellsrdquo Accounts of Chemical Research vol 42 no 11 pp 1788ndash1798 2009

[13] Y Luo D Li and Q Meng ldquoTowards optimization of materialsfor dye-sensitized solar cellsrdquo Advanced Materials vol 21 no45 pp 4647ndash4651 2009

[14] A Hagfeldt G Boschloo L Sun L Kloo and H PetterssonldquoDye-sensitized solar cellsrdquo Chemical Reviews vol 110 no 11pp 6595ndash6663 2010

[15] Z Ning Y Fu and H Tian ldquoImprovement of dye-sensitizedsolar cells what we know and what we need to knowrdquo Energy ampEnvironmental Science vol 3 no 9 pp 1170ndash1181 2010

[16] J DesilvestroMGratzel L Kavon JMoser and J AugustynskildquoHighly efficient sensitization of titanium dioxiderdquo Journal ofthe American Chemical Society vol 107 no 10 pp 2988ndash29901985

[17] N Vlachopoulos P Liska J Augustynski and M GratzelldquoVery efficient visible light energy harvesting and conversionby spectral sensitization of high surface area polycrystallinetitanium dioxide filmsrdquo Journal of the American ChemicalSociety vol 110 no 4 pp 1216ndash1220 1988

[18] P Liska N Vlachopoulos M K Nazeeruddin PComte and M Gratzel ldquocis-diaquabis(221015840-bipyridyl-441015840-dicarboxylate)ruthenium(II) sensitizes wide band gap oxidesemiconductors very efficiently over a broad spectral range inthe visiblerdquo Journal of the American Chemical Society vol 110no 11 pp 3686ndash3687 1988

[19] M Chandrasekharam G Rajkumar C S Rao P Y Reddyand M L Kantam ldquoChange of dye bath for sensitisationof nanocrystalline TiO

2films enhances performance of dye-

sensitized solar cellsrdquo Advances in OptoElectronics vol 2011Article ID 376369 9 pages 2011

[20] M Chandrasekharam G Rajkumar C S Rao T Suresh andP Y Reddy ldquoPhenothiazine conjugated bipyridine as ancillaryligand in Ru(II)-complexes for application in dye sensitizedsolar cellrdquo Synthetic Metals vol 161 no 15-16 pp 1469ndash14762011

[21] B-S Chen K Chen Y-H Hong et al ldquoNeutral panchro-matic Ru(ii) terpyridine sensitizers bearing pyridine pyrazolatechelates with superior DSSC performancerdquo Chemical Commu-nications no 39 pp 5844ndash5846 2009

[22] YH Jang X XinM Byun Y J Jang Z Lin andDH Kim ldquoAnunconventional route to high-efficiency dye-sensitized solar


cells via embedding graphitic thin films into TiO2nanoparticle

photoanoderdquo Nano Letters vol 12 no 1 pp 479ndash485 2012[23] T A Heimer C A Bignozzi and G J Meyer ldquoMolecular level

photovoltaics the electrooptical properties of metal cyanidecomplexes anchored to titanium dioxiderdquoThe Journal of Physi-cal Chemistry vol 97 no 46 pp 11987ndash11994 1993

[24] R Argazzi C A Bignozzi T A Heimer F N Castellano andG J Meyer ldquoEnhanced spectral sensitivity from ruthenium(II)polypyridyl based photovoltaic devicesrdquo Inorganic Chemistryvol 33 no 25 pp 5741ndash5749 1994

[25] V Balzani and F Scandola Supramolecular Photochemistry EllisHorwood Chichester UK 1991

[26] M Duati S Fanni and J G Vos ldquoA new luminescent Ru(terpy)complex incorporating a 124-triazole based 120590-donor ligandrdquoInorganic Chemistry Communications vol 3 no 2 pp 68ndash702000

[27] A Juris S Campagna V Balzani G Gremaud and A vonZelewsky ldquoAbsorption spectra luminescence properties andelectrochemical behavior of tris-heteroleptic ruthenium(II)polypyridine complexesrdquo Inorganic Chemistry vol 27 no 20pp 3652ndash3655 1988

[28] A Prasanna de Silva D B Fox T S Moody and S M WeirldquoLuminescent sensors and photonic switchesrdquo Pure and AppliedChemistry vol 73 no 3 pp 503ndash511 2001

[29] J R Winkler D G Nocera K M Yocom EBordignon and H B Gray ldquoElectron-transfer kinetics ofpentaammineruthenium(III)(histidine-33)-ferricytochrome cMeasurement of the rate of intramolecular electron transferbetween redox centers separated by 15 A in a proteinrdquo Journal ofthe American Chemical Society vol 104 no 21 pp 5798ndash58001982

[30] H Sugihara L P Singh K Sayama H Arakawa M KNazeeruddin and M Gratzel ldquoEfficient photosensitizationof nanocrystalline TiO

2films by a new class of

sensitizer cis-dithiocyanato bis(47-dicarboxy-110-phenanthroline)ruthenium(II)rdquo Chemistry Letters vol 27no 10 pp 1005ndash1006 1998

[31] T Renouard R-A Fallahpour M K Nazeeruddin et alldquoNovel ruthenium sensitizers containing functionalized hybridtetradentate ligands synthesis characterization and INDOSanalysisrdquo Inorganic Chemistry vol 41 no 2 pp 367ndash378 2002

[32] P Wang S M Zakeeruddin J E Moser et al ldquoStable newsensitizer with improved light harvesting for nanocrystallinedye-sensitized solar cellsrdquo Advanced Materials vol 16 no 20pp 1806ndash1811 2004

[33] P Wang C Klein R Humphry-Baker S M Zakeeruddinand M Gratzel ldquoA high molar extinction coefficient sensitizerfor stable dye-sensitized solar cellsrdquo Journal of the AmericanChemical Society vol 127 no 3 pp 808ndash809 2005

[34] C Y Chen S J Wu J Y Li C G Wu J G Chen and K CHo ldquoA new route to enhance the light-harvesting capability ofruthenium complexes for dye-sensitized solar cellsrdquo AdvancedMaterials vol 19 no 22 pp 3888ndash3891 2007

[35] C Klein M K Nazeeruddin P Liska et al ldquoEngineering of anovel ruthenium sensitizer and its application in dye-sensitizedsolar cells for conversion of sunlight into electricityrdquo InorganicChemistry vol 44 no 2 pp 178ndash180 2005

[36] C-Y Chen S-J Wu C-G Wu J-G Chen and K-CHo ldquoA ruthenium complex with superhigh light-harvestingcapacity for dye-sensitized solar cellsrdquo Angewandte ChemiemdashInternational Edition vol 45 no 35 pp 5822ndash5825 2006

[37] A O Adeloye ldquoSynthesis photophysical and electrochemicalproperties of a mixed bipyridyl-phenanthrolyl ligand Ru(II)heteroleptic complex having trans-2-methyl-2-butenoic acidfunctionalitiesrdquoMolecules vol 16 no 10 pp 8353ndash8367 2011

[38] AO Adeloye and P A Ajibade ldquoSynthesis and characterizationof a heteroleptic Ru(II) complex of phenanthroline containingOligo-anthracenyl carboxylic acidmoietiesrdquo International Jour-nal of Molecular Sciences vol 11 no 9 pp 3158ndash3176 2010

[39] AO Adeloye and P A Ajibade ldquoSynthesis and characterizationof a Ru(II) complex with functionalized phenanthroline lig-ands having single-double linked anthracenyl and 1-methoxy-1-buten-3-yne moietiesrdquo Molecules vol 15 no 11 pp 7570ndash75812010

[40] A O Adeloye and P A Ajibade ldquoA high molar extinction coef-ficient mono-anthracenyl bipyridyl heteroleptic ruthenium(II)complex synthesis photophysical and electrochemical proper-tiesrdquoMolecules vol 16 no 6 pp 4615ndash4631 2011

[41] P V Vyas A K Bhatt G Ramachandraiah and A V BedekarldquoEnvironmentally benign chlorination and bromination ofaromatic amines hydrocarbons and naphtholsrdquo TetrahedronLetters vol 44 no 21 pp 4085ndash4088 2003

[42] I P Evans A Spencer and G Wilkinson ldquoDichlorote-trakis(dimethyl sulphoxide)ruthenium(II) and its use as asource material for some new ruthenium(II) complexesrdquo Jour-nal of the Chemical Society Dalton Transactions no 2 pp 204ndash209 1973

[43] C A Mitsopoulou I Veroni A I Philippopoulos and PFalaras ldquoSynthesis characterization and sensitization proper-ties of two novel mono and bis carboxyl-dipyrido-phenazineruthenium(II) charge transfer complexesrdquo Journal of Photo-chemistry and PhotobiologyA Chemistry vol 191 no 1 pp 6ndash122007

[44] J L Burmeister ldquoRecent developments in the coordinationchemistry of ambidentate ligandsrdquo Coordination ChemistryReviews vol 1 no 1-2 pp 205ndash221 1966

[45] R M Silverstein G C Bassler and T C Morrill SpectrometricIdentification of Organic Compounds John Wiley amp Sons NewYork NY USA 5th edition 1991

[46] Y Sun A C Onicha M Myahkostupov and F N CastellanoldquoViable alternative to N719 for dye-sensitized solar cellsrdquoApplied Materials and Interfaces vol 2 no 7 pp 2039ndash20452010

[47] M Guo P Diao Y-J Ren F Meng H Tian and S-MCai ldquoPhotoelectrochemical studies of nanocrystalline TiO

2co-

sensitized by novel cyanine dyesrdquo Solar Energy Materials andSolar Cells vol 88 no 1 pp 23ndash35 2005

[48] A Juris V Balzani F Barigelletti S Campagna P Belserand A von Zelewsky ldquoRu(II) polypyridine complexes photo-physics photochemistry eletrochemistry and chemilumines-cencerdquo Coordination Chemistry Reviews vol 84 pp 85ndash2771988

[49] A O Adeloye T O Olomola A I Adebayo and P A AjibadeldquoA high molar extinction coefficient bisterpyridyl homolepticRu(II) complex with trans-2- ethyl-2-butenoic acid function-ality potential dye for dye-sensitized solar cellsrdquo InternationalJournal of Molecular Sciences vol 13 no 3 pp 3511ndash3526 2012

[50] S K Lee W J Yang J J Choi C H Kim S-J Jeon and BR Cho ldquo26-bis[4-(p-dihexylaminostyryl)-styryl]anthracenederivatives with large two-photon cross sectionsrdquo OrganicLetters vol 7 no 2 pp 323ndash326 2005

[51] A P Halverson T A Elmaaty and L W Castle ldquoCom-plexes of (bpy)2Ru(II) and (Ph2bpy)2Ru(II) with a series of


thienophenanthroline ligands synthesis characterization andelectronic spectrardquo Journal of Coordination Chemistry vol 64no 21 pp 3693ndash3699 2011

[52] D M Roundhill Photochemistry and Photophysics of MetalComplexes Plenum Press New York NY USA 1993

[53] T J Meyer and M H V Huynh ldquoThe remarkable reactivityof high oxidation state ruthenium and osmium polypyridylcomplexesrdquo Inorganic Chemistry vol 42 no 25 pp 8140ndash81602003

[54] G Boschloo and A Hagfeldt ldquoCharacteristics of theiodidetriiodide redox mediator in dye-sensitized solarcellsrdquo Accounts of Chemical Research vol 42 no 11 pp1819ndash1826 2009

[55] P G Bomben T J Gordon E Schott and C P BerlinguetteldquoA trisheteroleptic cyclometalated RuII sensitizer that enableshigh power output in a dye-sensitized solar cellrdquo AngewandteChemiemdashInternational Edition vol 50 no 45 pp 10682ndash106852011

[56] D Kuang C Klein S Ito et al ldquoHigh-efficiency and stablemesoscopic dye-sensitized solar cells based on a high molarextinction coefficient ruthenium sensitizer and nonvolatileelectrolyterdquo Advanced Materials vol 19 no 8 pp 1133ndash11372007

[57] P Wang S M Zakeeruddin J E Moser M K NazeeruddinT Sekiguchi and M Gratzel ldquoA stable quasi-solid-state dye-sensitized solar cell with an amphiphilic ruthenium sensitizerand polymer gel electrolyterdquo Nature Materials vol 2 no 6 pp402ndash407 2003

[58] M Chandrasekharam G Rajkumar C S Rao T Suresh YSoujanya and P Y Reddy ldquoHigh molar extinction coefficientRu(II)-mixed ligand polypyridyl complexes for dye sensitizedsolar cell applicationrdquo Advances in OptoElectronics vol 2011Article ID 432803 11 pages 2011

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


Previous study has shown that metal-to-ligand chargetransfer (MLCT) sensitizers with positive metal-based oxi-dation potentials have the disadvantage of exhibiting highenergy absorption bands which only harvest a fractionof visible light [25 26] For complexes of the type cis-Ru(LL)

2X2(where LL is bidentate polypyridine ligands and X

is ancillary ligands) intenseMLCTabsorption bands are oftenobserved from 400 to 600 nm with negligible absorptionat longer wavelengths [22] The MLCT absorption can beextended to lower energy by appropriate substituent changesin the chromophoric ligands or by decreasing the d120587-120587lowastbackbonding donation of the nonchromophoric ligands Theeffect of these changes on the photophysical properties ofmetal polypyridine complexes has been the subject of severalinvestigations which have given fundamental insight intothe factors which govern radiative and nonradiative decayprocesses of excited states [25 26]

In an attempt to extend the spectral sensitivity ofdye molecules towards the red we have designed a newcis-Ru(LL)

2-(X)2polypyridine complex based on the lig-

and 5-(9-anthracenyl-10-(trans-2-methyl-2-butenoic acid)-110-phenanthroline) with extended 120587lowast accepting orbitals atlower energy and the photophysical properties compared tothe previously reported heteroleptic Ru(II) complex of 5-(trans-2-methyl-2-butenoic acid)-110-phenanthroline ligand[37] The photoelectrochemical characteristics exhibited bythe complex are rationalized in terms of spectroscopicaland photophysical properties measured in fluid solutionAs envisaged enhanced spectral response was found forcomplex containing anthracenyl functionality as comparedto that without anthracene However of particular relevancein the context of this report in relation to our previousstudies and reports on the increasing number of anthracenefunctionality in a particular ruthenium polypyridyl complexin which molar extinction coefficient values are reduceddue to molecular aggregation [38ndash40] On the basis of thiswe set out to investigate and discuss the photophysical andelectrochemical properties of a new-type monoanthracenylfunctionalized phenanthroline heteroleptic ruthenium(II)complex in relation to its potential use as a photosensitizerfor application in the dye-sensitized solar cells (DSSCs) andother optoelectronic devices

2 Results and Discussion

21 Chemistry Scheme 1 (indashiii) shows the stepwise syn-thetic pathways for L

1and L

2and outlines the chemistry

of the present study 910-Dibromoanthracene 2-methyl-2-butenoic acid and 110-phenanthroline are the starting mate-rials for 1 and 2 9-Bromo-10-(2-methyl-2-butenoic acid)-anthracene (1) was obtained when 910-dibromoanthraceneand 2-methyl-2-butenoic acid were refluxed in a ben-zenedichloromethane mixture under basic condition usingtriethylamine potassium hydroxide and palladium carbideProduct 2 was obtained by the initial introduction ofrequired bromine functions on 110-phenanthroline underan environmentally benign condition as reported by Vyasand coworkers [41] L

1and L

2were synthesized following

slightmodifications of established procedures reported in theliterature [40] The synthesis of L

1essentially follows two

major reaction steps the initial synthesis of a 2-methyl-2-butenoic acid functionalized anthracenyl group followed by apalladium cross-catalyzed reaction of two halide compoundsThis reaction was aided by the use of an equivalent volumeratio of dichloromethane-benzene as solvent to overcome thepoor solubility of anthracenyl derivatives in common organicsolvents such as methanol and chloroform It was foundthat this reaction could be reversed by first reaction of thehalogenated polypyridine with 910-dibromoanthracene anda subsequent dehydrohalogenation reaction with 2-methyl-butenoic acid L

2was obtained by one-step nucleophilic

aromatic substitution reaction of the bromide group ofproduct 2 with 2-methyl-2-butenoic acid The synthesis ofthe metal precursor [RuCl

2(dmso)

4] [42] and the complexes

[Ru(L1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] followed the general

synthetic route shown in Scheme 1 (iv and v) Sequentialsubstitution of the DMSO coordinating ligand from themetal precursor led to formation of intermediate complex[Ru(L

119909)2Cl2] (L119909= L1or L2) which was not isolated

Final reaction was carried out with chloride exchange withthiocyanate group [43]

22 Infrared Spectra The FT-IR spectra of the startingmaterials the ligands and the complex showed certaincharacteristic absorption bands that were compared andassigned on careful comparisonDue to structural similaritiesbetween the ligand and the complex a strong band in theregion 3479ndash3055 cmminus1 was found This gave indication ofthe presence of an OminusH group possibly from the carboxylicacid moiety This band however shifted to higher frequencyat 3551 cmminus1 in the complex (Figure 1) The vibration fre-quency bands between 3479 and 3237 cmminus1 may be dueto presence of 120572- 120573-unsaturated carboxylic acid andoraromaticCminusHstretching characteristics of themoleculesTheband at 2928 cmminus1 shows the presence of CminusH stretchingof methyl groups The complex shows a broad absorptionfrequency at 2104 cmminus1 for stretch vibrational modes due tothe N-coordinated 120592 (CN) This band is reduced in intensitycompared to the band at 926 cmminus1 due to 120592(CS) The bandsat 1971 1638 cmminus1 1309 and 1256 cmminus1 were assigned to the120592(C=O) and 120592(CndashO) stretching of carboxylic acid groupsrespectively The singlet sharp band at 1617 cmminus1 is assignedto the aromatic CndashN stretch vibration with the two bandsat 1459 and 1438 cmminus1 due to ring stretching modes of theligands A comparison of the infrared spectra of L1 and 910-dibromoanthracene showed that a strong vibrational band inthe former was conspicuously absent in the latter confirmingthe loss of CndashBr bond and the formation of CndashC bondlinkages of the anthracenyl group Furthermore the CndashCbond linkage between anthracene and phenanthroline wasaffirmed by the absorption frequency at 804 cmminus1 Peaks inthe region at 747 and 730 cmminus1 demonstrate the existence offour adjacent hydrogen atoms common to L1 and complex[Ru(L

1)2(NCS)

2] All vibrational peaks in the region are

found to be relatively weak and broad in the complex whichmay be ascribed to the loss of crystallinity and the broad


Br

Br

Br

Br

BR

+

+

+

H

H

N

N NN

NN N

N

NN

CH3

CH3

CH3

CH3

COOH

HOOC

HOOC

HOOC

CH2Cl2ndashC6H6(50)

CH2Cl2 C6H6(50)

PdC ET3N KOH 12 h

Br

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

COOH

COOH

COOH

COOH

COOH

COOHMeOH rt 20h

MeOH PdC

KOH Et3N 8h

(i)

(ii)

(iii)

(iv)

(v)

(a)

(b)

(1)

(1)

(2)

(i)

(ii)

H3C

H3C

H3C

H3C

H3C


[RuCl2((CH3)2SO)4]

Yellow powder

Yellow powder

(L2)

(L1)



Ru

Ru

N

N

N N

N

NN

N

N N

N

N

C

CC

CS

S

S

S


PdC Et3N KOH 12h


(i) 2(L2) + 2NH4NCS

(i) 2(L2) + 2NH4NCS

chromatography

HBrH2O2 (1 1)

ndash



1)2(NCS)

2] and [Ru(L

2)2(NCS)

2]




3) and 123




T (

)

355148

347936

341460

323723

292598

210404

197163

163824

161753

145993

143822

130476125659

115629109060

102699

92653

80403

74774

73017

62281

5792947506

40418

400

0

3600

320

0

2800

2400

2000

1800

1600

1400

1200

1000 800

600

3700


2] complex in KBr

123

4123

2

1786

180

3182

5214

6

6965

6983

7258

76037614

7623

7634

7773

822

3824

1

9178

9186

9 8 7 6 5 4 3 2

(ppm)



1)2(NCS)

2] complex


15027

614

6196

139253

135970

128609

126469

123059

77348

77031

76713

14522

11736

180 160 140 120 100 80 60 40 20 0

(ppm)


12 10 8 6 4 2 minus0

(ppm)

8603

8594

8585

8578

7646

7639

7629

7621

7257

5295

2953

288

1

216

7203

8

000

2


2] complex


complexation



1)2(NCS)





2] complex


2)2(NCS)

2] (482 times


2)2(NCS)



1)2(NCS)

2]


0

05

1

15

2

300 400 500 600 700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line) at








1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] are displayed in


1)2(NCS)

2] It


2)2(NCS)

2] As


0

005

01

015

700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)

2] and [Ru(L

2)2(NCS)



0

200

400

600

800

1000

1200

630 650 670 690 710 730

Emiss

ion

inte

nsity

(au

)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line)




[Ru(L1)2(NCS)2]

II

III

I


60120583A

(a)

II

IIII


60120583A


(b)







1)2(NCS)

2] were




3



3 Experimental









3at 120575c 7700 and 120575H



4



1) 5-Bromo-110-


3N (1mL) KOH (027 g


minus13427 3055 2979 2924 2552 1966 1871 1802 1579 15581453 1417 1304 1255 1140 1089 1040 994 926 756 654 619579 1H-NMR (CDCl

3) 120575 918 (d J = 32Hz) 823 (d J =


3) 123 (t CH

3) 13C-NMR (CDCl

3) 120575 15028








3) 120575


3) and 159 (d J = 68Hz 3H

CH3) 13C-NMR (CDCl

3) 120575 17283 15039 15030 14630


17H14N2O2


1)2(NCS)

2] In a 250mL flask

[RuCl2(dmso)








3) 120575 859 (dd J = 48 72Hz) 763 (dd J

= 28 68Hz) 295 (s CH3) 288 (s CH

3) 217 (s CH

3) and




64H44N6O4S2


2)2(NCS)


2(dmso)

4] (044 g


2(050 g


4NCS (027 g 359mol)



3) 120575 877 (d J = 80Hz 4H) 838


3)


36H28N6O4S2

4 Conclusions


1) and its ruthe-




2)2(NCS)





1)2(NCS)

2] was blue-



1)2(NCS)




3


3




Acknowledgments


References























































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Br

Br

Br

Br

BR

+

+

+

H

H

N

N NN

NN N

N

NN

CH3

CH3

CH3

CH3

COOH

HOOC

HOOC

HOOC

CH2Cl2ndashC6H6(50)

CH2Cl2 C6H6(50)

PdC ET3N KOH 12 h

Br

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

COOH

COOH

COOH

COOH

COOH

COOHMeOH rt 20h

MeOH PdC

KOH Et3N 8h

(i)

(ii)

(iii)

(iv)

(v)

(a)

(b)

(1)

(1)

(2)

(i)

(ii)

H3C

H3C

H3C

H3C

H3C


[RuCl2((CH3)2SO)4]

Yellow powder

Yellow powder

(L2)

(L1)



Ru

Ru

N

N

N N

N

NN

N

N N

N

N

C

CC

CS

S

S

S


PdC Et3N KOH 12h


(i) 2(L2) + 2NH4NCS

(i) 2(L2) + 2NH4NCS

chromatography

HBrH2O2 (1 1)

ndash



1)2(NCS)

2] and [Ru(L

2)2(NCS)

2]




3) and 123




T (

)

355148

347936

341460

323723

292598

210404

197163

163824

161753

145993

143822

130476125659

115629109060

102699

92653

80403

74774

73017

62281

5792947506

40418

400

0

3600

320

0

2800

2400

2000

1800

1600

1400

1200

1000 800

600

3700


2] complex in KBr

123

4123

2

1786

180

3182

5214

6

6965

6983

7258

76037614

7623

7634

7773

822

3824

1

9178

9186

9 8 7 6 5 4 3 2

(ppm)



1)2(NCS)

2] complex


15027

614

6196

139253

135970

128609

126469

123059

77348

77031

76713

14522

11736

180 160 140 120 100 80 60 40 20 0

(ppm)


12 10 8 6 4 2 minus0

(ppm)

8603

8594

8585

8578

7646

7639

7629

7621

7257

5295

2953

288

1

216

7203

8

000

2


2] complex


complexation



1)2(NCS)





2] complex


2)2(NCS)

2] (482 times


2)2(NCS)



1)2(NCS)

2]


0

05

1

15

2

300 400 500 600 700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line) at








1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] are displayed in


1)2(NCS)

2] It


2)2(NCS)

2] As


0

005

01

015

700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)

2] and [Ru(L

2)2(NCS)



0

200

400

600

800

1000

1200

630 650 670 690 710 730

Emiss

ion

inte

nsity

(au

)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line)




[Ru(L1)2(NCS)2]

II

III

I


60120583A

(a)

II

IIII


60120583A


(b)







1)2(NCS)

2] were




3



3 Experimental









3at 120575c 7700 and 120575H



4



1) 5-Bromo-110-


3N (1mL) KOH (027 g


minus13427 3055 2979 2924 2552 1966 1871 1802 1579 15581453 1417 1304 1255 1140 1089 1040 994 926 756 654 619579 1H-NMR (CDCl

3) 120575 918 (d J = 32Hz) 823 (d J =


3) 123 (t CH

3) 13C-NMR (CDCl

3) 120575 15028








3) 120575


3) and 159 (d J = 68Hz 3H

CH3) 13C-NMR (CDCl

3) 120575 17283 15039 15030 14630


17H14N2O2


1)2(NCS)

2] In a 250mL flask

[RuCl2(dmso)








3) 120575 859 (dd J = 48 72Hz) 763 (dd J

= 28 68Hz) 295 (s CH3) 288 (s CH

3) 217 (s CH

3) and




64H44N6O4S2


2)2(NCS)


2(dmso)

4] (044 g


2(050 g


4NCS (027 g 359mol)



3) 120575 877 (d J = 80Hz 4H) 838


3)


36H28N6O4S2

4 Conclusions


1) and its ruthe-




2)2(NCS)





1)2(NCS)

2] was blue-



1)2(NCS)




3


3




Acknowledgments


References























































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


T (

)

355148

347936

341460

323723

292598

210404

197163

163824

161753

145993

143822

130476125659

115629109060

102699

92653

80403

74774

73017

62281

5792947506

40418

400

0

3600

320

0

2800

2400

2000

1800

1600

1400

1200

1000 800

600

3700


2] complex in KBr

123

4123

2

1786

180

3182

5214

6

6965

6983

7258

76037614

7623

7634

7773

822

3824

1

9178

9186

9 8 7 6 5 4 3 2

(ppm)



1)2(NCS)

2] complex


15027

614

6196

139253

135970

128609

126469

123059

77348

77031

76713

14522

11736

180 160 140 120 100 80 60 40 20 0

(ppm)


12 10 8 6 4 2 minus0

(ppm)

8603

8594

8585

8578

7646

7639

7629

7621

7257

5295

2953

288

1

216

7203

8

000

2


2] complex


complexation



1)2(NCS)





2] complex


2)2(NCS)

2] (482 times


2)2(NCS)



1)2(NCS)

2]


0

05

1

15

2

300 400 500 600 700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line) at








1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] are displayed in


1)2(NCS)

2] It


2)2(NCS)

2] As


0

005

01

015

700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)

2] and [Ru(L

2)2(NCS)



0

200

400

600

800

1000

1200

630 650 670 690 710 730

Emiss

ion

inte

nsity

(au

)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line)




[Ru(L1)2(NCS)2]

II

III

I


60120583A

(a)

II

IIII


60120583A


(b)







1)2(NCS)

2] were




3



3 Experimental









3at 120575c 7700 and 120575H



4



1) 5-Bromo-110-


3N (1mL) KOH (027 g


minus13427 3055 2979 2924 2552 1966 1871 1802 1579 15581453 1417 1304 1255 1140 1089 1040 994 926 756 654 619579 1H-NMR (CDCl

3) 120575 918 (d J = 32Hz) 823 (d J =


3) 123 (t CH

3) 13C-NMR (CDCl

3) 120575 15028








3) 120575


3) and 159 (d J = 68Hz 3H

CH3) 13C-NMR (CDCl

3) 120575 17283 15039 15030 14630


17H14N2O2


1)2(NCS)

2] In a 250mL flask

[RuCl2(dmso)








3) 120575 859 (dd J = 48 72Hz) 763 (dd J

= 28 68Hz) 295 (s CH3) 288 (s CH

3) 217 (s CH

3) and




64H44N6O4S2


2)2(NCS)


2(dmso)

4] (044 g


2(050 g


4NCS (027 g 359mol)



3) 120575 877 (d J = 80Hz 4H) 838


3)


36H28N6O4S2

4 Conclusions


1) and its ruthe-




2)2(NCS)





1)2(NCS)

2] was blue-



1)2(NCS)




3


3




Acknowledgments


References























































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

05

1

15

2

300 400 500 600 700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line) at








1)2(NCS)

2] and [Ru(L

2)2(NCS)

2] are displayed in


1)2(NCS)

2] It


2)2(NCS)

2] As


0

005

01

015

700 800 900 1000 1100

Abso

rban

ce (a

u)

Wavelength (nm)



1)2(NCS)

2] and [Ru(L

2)2(NCS)



0

200

400

600

800

1000

1200

630 650 670 690 710 730

Emiss

ion

inte

nsity

(au

)

Wavelength (nm)



1)2(NCS)


2)2(NCS)

2] (dash line)




[Ru(L1)2(NCS)2]

II

III

I


60120583A

(a)

II

IIII


60120583A


(b)







1)2(NCS)

2] were




3



3 Experimental









3at 120575c 7700 and 120575H



4



1) 5-Bromo-110-


3N (1mL) KOH (027 g


minus13427 3055 2979 2924 2552 1966 1871 1802 1579 15581453 1417 1304 1255 1140 1089 1040 994 926 756 654 619579 1H-NMR (CDCl

3) 120575 918 (d J = 32Hz) 823 (d J =


3) 123 (t CH

3) 13C-NMR (CDCl

3) 120575 15028








3) 120575


3) and 159 (d J = 68Hz 3H

CH3) 13C-NMR (CDCl

3) 120575 17283 15039 15030 14630


17H14N2O2


1)2(NCS)

2] In a 250mL flask

[RuCl2(dmso)








3) 120575 859 (dd J = 48 72Hz) 763 (dd J

= 28 68Hz) 295 (s CH3) 288 (s CH

3) 217 (s CH

3) and




64H44N6O4S2


2)2(NCS)


2(dmso)

4] (044 g


2(050 g


4NCS (027 g 359mol)



3) 120575 877 (d J = 80Hz 4H) 838


3)


36H28N6O4S2

4 Conclusions


1) and its ruthe-




2)2(NCS)





1)2(NCS)

2] was blue-



1)2(NCS)




3


3




Acknowledgments


References























































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


[Ru(L1)2(NCS)2]

II

III

I


60120583A

(a)

II

IIII


60120583A


(b)







1)2(NCS)

2] were




3



3 Experimental









3at 120575c 7700 and 120575H



4



1) 5-Bromo-110-


3N (1mL) KOH (027 g


minus13427 3055 2979 2924 2552 1966 1871 1802 1579 15581453 1417 1304 1255 1140 1089 1040 994 926 756 654 619579 1H-NMR (CDCl

3) 120575 918 (d J = 32Hz) 823 (d J =


3) 123 (t CH

3) 13C-NMR (CDCl

3) 120575 15028








3) 120575


3) and 159 (d J = 68Hz 3H

CH3) 13C-NMR (CDCl

3) 120575 17283 15039 15030 14630


17H14N2O2


1)2(NCS)

2] In a 250mL flask

[RuCl2(dmso)








3) 120575 859 (dd J = 48 72Hz) 763 (dd J

= 28 68Hz) 295 (s CH3) 288 (s CH

3) 217 (s CH

3) and




64H44N6O4S2


2)2(NCS)


2(dmso)

4] (044 g


2(050 g


4NCS (027 g 359mol)



3) 120575 877 (d J = 80Hz 4H) 838


3)


36H28N6O4S2

4 Conclusions


1) and its ruthe-




2)2(NCS)





1)2(NCS)

2] was blue-



1)2(NCS)




3


3




Acknowledgments


References























































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



3at 120575c 7700 and 120575H



4



1) 5-Bromo-110-


3N (1mL) KOH (027 g


minus13427 3055 2979 2924 2552 1966 1871 1802 1579 15581453 1417 1304 1255 1140 1089 1040 994 926 756 654 619579 1H-NMR (CDCl

3) 120575 918 (d J = 32Hz) 823 (d J =


3) 123 (t CH

3) 13C-NMR (CDCl

3) 120575 15028








3) 120575


3) and 159 (d J = 68Hz 3H

CH3) 13C-NMR (CDCl

3) 120575 17283 15039 15030 14630


17H14N2O2


1)2(NCS)

2] In a 250mL flask

[RuCl2(dmso)








3) 120575 859 (dd J = 48 72Hz) 763 (dd J

= 28 68Hz) 295 (s CH3) 288 (s CH

3) 217 (s CH

3) and




64H44N6O4S2


2)2(NCS)


2(dmso)

4] (044 g


2(050 g


4NCS (027 g 359mol)



3) 120575 877 (d J = 80Hz 4H) 838


3)


36H28N6O4S2

4 Conclusions


1) and its ruthe-




2)2(NCS)





1)2(NCS)

2] was blue-



1)2(NCS)




3


3




Acknowledgments


References























































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



1)2(NCS)

2] was blue-



1)2(NCS)




3


3




Acknowledgments


References























































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of































2co-
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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