DTIC ADA519170: High-Extinction Ruthenium Compounds for Sunlight Harvesting and Hole Transport

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Inorg. Chem. 2008, 47, 7062-7064
High-Extinction Ruthenium Compounds for Sunlight Harvesting and
Hole Transport
Aaron Staniszewski,† William B. Heuer,*,‡ and Gerald J. Meyer*,†
Departments of Chemistry and Materials Science and Engineering, Johns Hopkins UniVersity,
400 North Charles Street, Baltimore, Maryland 21218, and Chemistry Department,
United States NaVal Academy, Annapolis, Maryland 21402
ReceivedJanuary29,2008
The compounds Ru(bpy)(BTL)(PF) and Ru(deeb)(BTL)(PF), Scheme1
2 62 2 62
wherebpyis2,2′-bipyridine,deebis4,4′-(CHCO)-bpy,andBTL
2 5 22
g is 9′-[4,5-bis(cyanoethylthio)]-1,3-dithiol-2-ylidene]-4′,5′-diazafluo-
or
s. rene, were found to have very high extinction coefficients in the
c
a
bs.h visible region. In an acetonitrile solution, the extinction of
u1
http://pc80017 4R7u0(dnemeb.)T2(wBoTLq)u(aPsFi-6r)e2vwearssib(cid:1)le)ox4id4a0ti0o0n(wa1v0e0s0,EM1/-21)cm+-01.8a8tλan)d
EMY on September 4, 2009 | arch 26, 2008 | doi: 10.1021/i +qiocotnooubb-1amassli.geen1p0arrt6.ovvu1neeumdVMddnd,ycwLivheawiieaCtlndhrardlsgOsΦuse4psa-/featon)rccufaeetninrr0rtodrsro.eos3fnevcctior(eetorrnipelspeei0xichb.ce2olp(ieltetFerfoococdirtnrp+erjoe5d/es0lr3)utyct.ai2ctteett.eAsi5.eo,tlInecnoτ,hcr-rtae4Er)4rog1ap0ner7csn2t)ne°e5miCrrniasn,t-toltisiivgca.1ehT.oT6tissOfheota2aiVxlsatc,ewrmistcwaiaetwehtemtilaoalrsaeelns-, aopdwcRrolfiuieisltc(cohroabourtfpevtitthohyedeenne).r2ne(iibdinnBTupmTemthyhxeL-aacdn)ptei(yotssPthshlpeFyieeoon6pcf)leryi2tr2unrrgao0tieyhdss0eyc(wc0nBolo0eipTnucl0ilvomLcMeam)(rsIsp-laIaiio1)nogdundcacemnnoarddosi-rvssre1eads.d7phmtioinroTvbxeawehcltieilnweoupslndio.arteowrhWcespofeeeumitxrnhnrttpteiecieencoitnsriecuosntnaientodopllayynsf-l
DM asustainedphotocurrentwasobservedwithamaximumincident
AVAL ACADate (Web): painhbjeoscototripnot-natonf-rccoeumrrseapnetscientrfgafilcewieeenxrcceyiteiondf gs0to.a4ot.ed.Tahgerepehmoteonctu,rrceonntsaisctteionnt wanitdh gTcahnrioOadur2gpptehshoiftntrooarfienbllsemficnestrdraiohnrcaeghvreteeompamoilcsreatoesldobmpehoeeetrnrhoeouqindsu.san.Tnahtniefioecydriyelbsdtyaslsfliopnreecint(ratoensrafctaoacpsieiac)l
d by US Nublication Coordination compounds that efficiently harvest solar dwiatThsihoerle-c2lie-gnyatlnliyddencoeof]m-i4nm′t,e5ur′ne-idsctia,atze9ad′fl-[ui4no,r5e-Inbneiosr(agcbaybnarniecoveiCtahtheyedlmthiaisost)r]yB-1Tf,L3o-r,
ade P energy are of great importance in inorganic chemistry. applications in supramolecular chemistry.8 The preparative
o
wnl Rutheniumtris(bipyridine)hasattractedmuchinterestinthis procedure employed here was similar and involved a
Do regardwithmetal-to-ligandcharge-transfer(MLCT)absorp- phosphite-mediatedcouplingtothe“dafo”bpyligandshown
tion bands in the visible region and a molar extinction in Scheme 1. Coordination to cis-Ru(bpy) (Cl) or cis-
2 2
coefficient ((cid:1)) of about 15000 M-1 cm-1.1 Substitution on Ru(deeb) Cl (wheredeebis4,4′-(C H CO ) -bpy),isolation,
2 2 2 5 2 2
thebipyridineringsand/orcoordinationofnonchromophoric and purification yielded the desired Ru(bpy) (BTL)2+ and
2
ligands allow the absorption to be tuned throughout the Ru(deeb) (BTL)2+ compounds usually as PF - salts. 1H
2 6
visibleandnear-IRregionswithmodestextinctioncoefficient NMR, elemental analysis, and spectroscopic data were
changes.2–6 In contrast, natural and synthetic organic pig- consistent with the proposed formulations.
ments also absorb solar photons but with extinctions that Figure 1 shows the UV–visible absorption spectrum in a
CH CN solution. The inset displays the concentration
*Towhomcorrespondenceshouldbeaddressed.E-mail:[email protected] 3
(W.B.H.),[email protected](G.J.M.). dependence of the Ru(deeb)2(BTL)(PF6)2 compound. The
†JohnsHopkinsUniversity. normalized absorption spectra were concentration-indepen-
‡UnitedStatesNavalAcademy.
(1) Kalyanasundaram,K.PhotochemistryofPolypyridineandPorphyrin
Complexes;AcademicPress:London,1992. (5) Jiang,K.-J.;Xia,J.-b.;Masaki,N.;Noda,S.;Yanigada,S.Inorg.Chim.
(2) Wang,P.;Klein,C.;Humphry-Baker,R.;Zakeeruddin,S.M.;Gratzel, Acta2008,361,783.
M.J.Am.Chem.Soc.2005,127,808. (6) Karthikeyan,C.S.;Peter,K.;Wietasch,H.;Thelakkat,M.Sol.Energy
(3) Chen, C.-Y.; Wu, S.-J.; Wu, C.-G.; Chen, J.-G.; Ho, K.-C. Angew. Mater.Sol.Cells2007,91,432.
Chem.2006,45,5822. (7) Hasselman,G.M.;Watson,D.F.;Stromberg,J.;Bocian,D.F.;Holten,
(4) Jang, S.-R.; Lee, C.; Choi, H.; Ko, J. K.; Lee, J.; Vittal, R.; Kim, D.;Lindsey,J.S.;Meyer,G.J.J.Phys.Chem.B2006,110,25430.
K.-J.Chem.Mater.2006,18,5604. (8) Baudron,S.A.;Hosseini,M.W.Inorg.Chem.2006,45,5260.
7062 InorganicChemistry, Vol.47,No.16,2008 10.1021/ic800171hCCC:$40.75 2008AmericanChemicalSociety
PublishedonWeb03/26/2008
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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
High-Extinction Ruthenium Compounds for Sunlight Harvesting and
5b. GRANT NUMBER
Hole Transport
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
5e. TASK NUMBER
5f. WORK UNIT NUMBER
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United States Naval Academy (USNA),Chemistry REPORT NUMBER
Department,Annapolis,MD,21402
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COMMUNICATION
Figure 1. Absorption spectra of Ru(deeb)2(BTL)(PF6)2 (solid line) and
Ru(bpy)2(BTL)(PF6)2(dashedline)inneatacetonitrile.Theinsetshowsthe
concentrationdependenceoftheRu(deeb)2(BTL)(PF6)2absorbanceat470nm.
Thebest-fitlineyieldedanextinctioncoefficientof44300M-1cm-1.
dent,andmultiplemeasurementsyielded(cid:1))44000(1000
g M-1cm-1atλ)470nm.Thecorrespondingbpycompound
s.or showedpropertiessimilartothoseofthedeebanalogue(cid:1))
c
bs.ah 32000 ( 2000 M-1 cm-1 at λ ) 468 nm. The free BTL
pu71 ligand has an extinction coefficient of 34700 M-1 cm-1 at
4, 2009 | http://10.1021/ic8001 4Tpti1ooh6unensnv9dmisosinibbsultethcoedamibBdspTonlrioLcptatlaitioebgndsaonswrdpbietalchisgtrowhuvtmeealrlplopaafprsetphRciienuagbrfuliytnhtbBereanTyliiLuogmnaadnn(dI4dI5)tRr0cauonnmmsfi--.
ber oi: bpy MLCT transitions. The higher extinction for the
md
pte08 | Ru(deeb)2(BTL)2+ compound was expected because it is
Se20 known that substituents with low-lying π orbitals (such as
MY on ch 26, acraonmeanthicasn,ceestMersL,CcTarbeoxxtiynlcictioacnidcso,eoffircuinesnattsurraetleadtivoergtaoniucns-)
DEMar substitutedbpy.10–12Interestingly,4and4′disubstitutionof Figure2.Absorptiondifferencespectrumobserved1µsafterpulsed532.5
AVAL ACADate (Web): 2asul,s2bo′s-tabiltilupotywiroienddiinfnoerthbieninc5dreianansgdetso5′m(cid:1)peosmsoioptirooernosue.1sf1fne,1ac2ntiTovcherelyysetsatthlelarinngerToduoiOpess2 n°CaCbmHsoa3lCinrgpdNhtit(oaBentx)rccoaihontaamcnthigotoeenrmemodpfoetRnorauitat(oudrnreeeaed.nbToa)h2ct(re5Byi4sTn0tsLaeln)lt(imPnineF.p6T)a2irOt(AB2)tshihninonwfiesalmtaasicinentg0ol.ne1iwtMrialveLeailCten-lOg4t4h0/
Nn thin films from an acetonitrile solution.
ownloaded by US Publicatio fbTRoywurT(coRdhyeeucqel(ruibbeca)pd2svyo(ioB-x)rltTe(paBvLrmoeT)rmp(LsPeie)rbF(ttrlPi6eye)F2si,ono)Exf0,i1td/.2Eh1ae)tMicoo+)nLm0iwC+p.8ola08Ouv.n8e4a/sd5nasdcVwew+teoevr1nree.eir1tsroc6uihblseVasrefs,aeroacvrlnrtueeoddtriciooezfnnneosdeer. iwocRmofuamms(adpeeexrrseisipsbeneed)gcd2l(tieenoBdfT0ptf.Lrh1ooe+rMd)Tou/TxicLOitidiO2Cia(z2els(eO-sedi)4-g,/s1)Cn3e.eHnTadsn3hiCdtetioNztwheraereeaapscknuohdlsataiebatrdigsnvoeieenr-lpsaetetbhcipsoetaronoarrappnitnpteiienodtahnTresanitnOreaecat2deer,
D (Fc+/0). The2first oxida6ti2on1i/s2 assigned to the BDT ligand 520 nm was assigned to the oxidized dithioline ligand.14
Thus,within10nsoflightexcitation,anelectronisinjected
and the second to the ruthenium(II) metal center. Our
intoTiO andtheholeistranslatedfromthemetalcenterto
inabilitytoresolvethemetal-centeredoxidationforthebpy 2
thedithioline-containingBTLligand.Thedrivingforcefor
compoundprobablystemsfrominsolubilityoftheoxidized
hole transfer after injection is -280 mV but was slightly
product. Both compounds showed an irreversible reduction
at E ∼ -1.6 V versus Fc+/0. Attempts to obtain the uphill from the MLCT excited state, which presumably
pr
explainswhyitwasnotobservedinafluidsolution(Figure
absorption spectra of the reduced and oxidized forms were
2A). We note that, after electron injection by the N3
frustrated by sample decomposition.
sensitizer,cis-Ru(dcb) (NCS) , a similar hole transfer from
The compounds were only weakly emissive at room tem- 2 2
ruthenium(III) to the thiocyanate ligands has been pro-
perature with excited-state lifetimes near our instrumental
response,τ<10ns.At-40°CinCHCN,alonger-livedstate
3
wasobservedwithspectroscopicpropertiescharacteristicofan (10) Damrauer,N.H.;McCusker,J.K.J.Phys.Chem.A1999,103,8440.
(11) Argazzi,R.;Bignozzi,C.A.;Heimer,T.A.;Castellano,F.N.;Meyer,
MLCT excited state (Figure 2). The excited state decayed to
G.J.Inorg.Chem.1994,33,5741–5749.
thegroundstatewithfirst-orderkinetics,τ)25ns. (12) Liu,Y.;DeNicola,A.;Reiff,O.;Ziessel,R.;Schanze,K.S.J.Phys.
Chem.A2003,107,3476.
Pulsed-lightexcitationofaRu(deeb) (BTL)/TiO thinfilm
2 2 (13) Rothenberger,G.;Fitzmaurice,D.;Grätzel,M.J.Phys.Chem.1992,
96,5983.
(9) Zhu, Q.-Y.; Bian, G.-Q.; Dai, J.; Jia, D.-X.; Zhang, J.-S.; Guo, L. (14) Torrance, J. B.; Scott, B. A.; Welber, B.; Kaufman, F. B.; Seiden,
Inorg.Chim.Acta2003,351,177. P.E.Phys.ReV.B1979, 19,730.
Inorganic Chemistry, Vol. 47, No. 16, 2008 7063
COMMUNICATION
Ru(deeb)(BTL)2+*andRu(bpy)(BTL)2+*atroomtemperature
2 2
inafluidsolutionareconsistentwiththepresenceoflow-lying
ligand-field (LF) states.1 Previous studies of ruthenium(II)
bipyridyl“dafo”compoundshaveshownthatthebridgeopens
the bite angle between the pyridyl nitrogens, which thereby
reduces the metal-nitrogen σ overlap and stabilizes the LF
states.21,22Wehavepreviouslypresentedcompellingevidence
that MLCT deactivation by LF states in ruthenium and iron
sensitizerscanlowertheelectroninjectionyieldsintoTiO.23–25
2
One method by which this can be avoided is to utilize
coordination compounds that have LF states at much higher
energy,suchasthosebasedonosmium(II).1
Inconclusion,aruthenium(II)bipyridinedithiolinecompound
withanotablyhighextinctioncoefficientinthevisibleregion
was found to photoinject electrons into TiO and support
2
Figure3.IPCEandabsorptancespectrumofaRu(deeb)2(BTL)/TiO2thin intramolecular hole transfer away from the ruthenium center.
film.Thephotocurrentactionspectrumwasmeasuredin0.50MLiIand WhiledistinctintraligandandMLCTabsorptionswereapparent
0.50 M I2/acetonitrile, while the absorptance spectrum was measured in in the electronic spectrum of Ru(deeb)(BTL)2+, the photo-
org 0.1MLiClO4/acetonitrile. physicalandelectron-transferbehaviorn2earroomtemperature
acs. posed.15 Hole transfer to more weakly coupled electron onnanosecondandlongertimescaleswasconsistentwiththe
ubs.1h donors has been demonstrated at sensitized interfaces.16–18 presence of a single MLCT excited state. The approach of
http://pc80017 staItreraindjieacntcioendaantaddheomleotnrastnrsafteerdwthearet tthheesyaimeledsfofro5r3e2x.c5itaendd- ucotielifzfiicnigenitnstraanlidgapnrdomcohtaergheolteratnrsafnesrfetroweanshasunccceesesxfutiln.cTtiohne
4, 2009 | 10.1021/i 4ac1t7inonmmetelirgshthtaetxalcliotawtiaobns.olWuteemheaavseuredmeveenltoopfedthethqiunanfitulmm drpeiuptrhrsieuoseleidnnetaaplipvgriaaonbadlceshabolrtifedrginnianttrgiovdtehutecoi3nthgaencmdono3jr′uepgtoarsateidtdiiotignorsnoaoulfpabsnidpinywrtiihddeienl4ye
September 2008 | doi: aeyxnietaillndyc(sstii)so,nfhrocoomweefvfidecarit,eanretliqtkhueairtetahscakctnosomhwpolawendnigeesincohfFatirhggeuerctehraa2nnBsgf.ee1r9i,ndTtahhtaee apcnrryodsdt4ua′clltpiinooensiTtioioOfnse.fifHfilmcigisehnoterxastloitnelacrnrtiaoctnievlselesgnesboiatmiszeeedrtrsioewnsowuthiltdihneninneharebrnleeannttholye-
d by US NAVAL ACADEMY on ublication Date (Web): March 26, ttiwniWehhnnxoiaechtTttrtriheenaheocngbacextoehstsiiituenodenohslericnedzpbriteadocolnldteioioiotgnvre0etfhterfo.a5atbfiprspteamhcsuhitioufreoso4temnbott2oohtctpv0afeeuwtailirnnRleoreauemcenuxsedtn(tr,utitdofhnbtsoeechaceeferhettcdfibieato,yct)mhhu2initee(eehsiBncleewddocaToiylxeywtLfriihc(deeo)iIet(lioPhudlPz3llelCeisF4dwndE6pwe0b)a)os20esi.oerwt0ahnΦrΦIadfsMssaiitc)to)maia-pnzbl1le0eeia0alr.ctc.i1ssi2atmdnutyt.aaoiu1r-onre4oemt1nddssf. ldecceuSovooxinctwemopAhdierreiepcodncrrskloeiwctuinepunneradaoenfoytardiwcFttocseoioenonl.dmeuldobeFaepnuagar2noidensrdmvuaeaeilntds-reatid.otoobnuosnnotInnfhm.triuaa4nTreatvi,gtohs4nnhere′tde-ienoedraxaofsiutbts.itihmtuanothebbhcupolsteterirtoodsitrnvdouutasheinttctehamchokdteoirneonmsbontlihiiuwtppnseomay.elsfrereaSiddblautgiyfilnhgceelrdeahrsttunothtdosPhettdshueemNeenadtrrnihaiiiouuevdtilmsgimaeohtu(ntiaeIhvmraiIseees)lt
ade P counter electrode and 0.5 M LiI and 0.05 M I2/acetonitrile Research Fund, administered by the American Chemical
ownlo spohlouttoiocunrsr(eFnitgaucretio3n).aTnhdeambasxoirmptuamnceIPsCpEecwtraasw4e0r%e,ianngdotohde Society,forfinancialsupportofthiswork.W.B.H.acknowl-
D edges support from the Naval Academy Research Council.
agreement, consistent with injection from a single excited
state. In other words, even though there was evidence for IC800171H
RuII f deeb, RuII f BTL, and π f π* intraligand BTL
(15) Clifford,J.N.;Palomeras,E;Nazeeruddin,Md.K.;Graztel,M.;Nelson,
transitionsintheabsorptionspectrumofthiscompound,there
J.;Long,N.J.;Durrant,J.R.J.Am.Chem.Soc.2004,126,5225.
was no evidence for preferential injection from any one of (16) Argazzi,R.;Bignozzi,C.A.;Heimer,T.A.;Castellano,F.N.;Meyer,
these excited states in the regenerative solar cell. This is G.J.J.Am.Chem.Soc.1995,117,11815.
(17) Bonhote, P.; Moser, J. E.; Humphry-Baker, R.; Vlachopoulos, N.;
consistentwiththefactthatinjectionandholetransferyields Zakeeruddin,S.M.;Walder,L.;Grätzel,M.J.Am.Chem.Soc.1999,
were, within experimental error, the same with green and 121,1324.
(18) Argazzi,R.;Bignozzi,C.A.;Heimer,T.A.;Castellano,F.N.;Meyer,
blue light excitation. It is likely that the less than 0.5 G.J.J.Phys.Chem.B1997,101,2591.
photocurrentefficiencyresultsfromthepoorinjectionyields (19) Bergeron,B.V.;Kelly,C.A.;Meyer,G.J.Langmuir2003,19,8389.
inferred from the spectroscopic measurements. Rapid sen- (20) Clifford, J. N.; Palomeras, E.; Nazeeruddin, Md. K.; Graztel, M.;
Durrant,J.R.J.Phys.Chem.B2007,111,6561.
sitizer regeneration through iodide oxidation is indeed (21) (a)Wang,Y.;Rillema,D.P.Inorg.Chem.1998,1,27.(b)Wang,Y.;
expected because of the positive ground-state reduction Jackman,D.C.;Woods,C.;Rillema,D.P.J.Chem.Crystallogr.1995,
25,549.
potential.20
(22) Henderson,L.J.,Jr.;Fronczek,F.R.;Cherry,W.R.J.Am.Chem.
A complete understanding of the factors that influence the Soc.1984,106,5876.
(23) Qu,P.;Thompson,D.W.;Meyer,G.J.Langmuir2000,16,4662.
injection and hole transfer yields for Ru(deeb)(BTL)/TiO is
2 2 (24) Yang,M.;Thompson,D.W.;Meyer,G.J.Inorg.Chem.2002,41,1254.
absent.Theweakemissionandshortexcited-statelifetimeof (25) Liu,F.;Meyer,G.J.Inorg.Chem.2003,42,7351.
7064 InorganicChemistry,Vol.47,No.16,2008