New J. Chem. 2009, 33, 1320-1323

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A‘‘reverseinterrupter’’:thenovelmoleculardesignofa uorescentphotochromicDTE-basedbipyridinew

VincentAubert,aElenaIshow,bFatimaIbersiene,aAbdouBoucekkine,a

miMetivier,bKeitaroNakatani,bJ.A.GarethWilliams,cLoicToupet,dRe

roniqueGuerchais*aandHubertLeBozec*aVe

Received(inMontpellier,France)23rdDecember2008,Accepted30thJanuary2009FirstpublishedasanAdvanceArticleontheweb12thFebruary2009DOI:10.1039/b823113c

Downloaded by Jiangxi Science and Technology Normal University on 09 January 2013Published on 12 February 2009 on | doi:10.1039/B823113C

Anoriginaldesignofa uorescentdithienylethene(DTE)-basedbipyridine,wheredonor(D)andacceptor(A)groupsarelocatedonthesamethiopheneringoftheDTEunit,isreported;innon-polarsolvents,UVorvisibleexcitationtriggersaphoto-chromicreaction,disruptingtheconjugationandquenchingthe uorescence.

Fluorescentswitchingsystemscontainingphotochromicmoleculeshaveattractedsigni cantattentiononaccountoftheirpotentialusesasopticalmemorymediaandphoto-switchabledevices.1Mostsystemso eringthephotomodulationofluminescenceinvolveaphotochromecovalentlylinkedtoanorganic2ormetal–organic3 uorophore,whereintheluminescenceisregulatedbyanintramolecularenergytransferfromtheexcited uorophoretothephotochromicunit.Incontrast,littleattentionhasbeendevotedtoluminescentphotoswitchesbasedondonor–bridge–acceptor(D–p–A)derivatives,inwhichthephotochromicunitisapartofthep-conjugatedbridge.4

Wehavepreviouslyshownthat2,20-bipyridinesfeaturingp-donor-conjugatedsubstituentsaregoodbuildingblocksfortheconstructionofmetalcomplexeswithverylargenon-linearopticalresponsesandinterestingluminescentproperties,whicharegovernedbystrongintra-ligandchargetransfer(ILCT)transitions.5Inthecourseofourcontinuingexplora-tionofsuchsystemsandthesearchforthephotomodulationoftheseproperties,wehaverecentlyincorporatedadithienyl-ethene(DTE)unitintoadonor-substitutedstyrylbipyridineligand,allowingthepreparationofthe rstexampleofmetal-containingphotochromicbipyridineligandsdisplayingane cientswitchingoftheNLOresponses(Scheme1(a)).6

However,thesefreebipyridineligands,inwhichthedonor(D)andacceptor(A)groupsarelocatedateachendoftheDTEunit,arenotemissiveunderambientconditions,neitherintheopennorclosedforms.Thus,asanalternativewaytoobtaina uorescentphotoswitch,wesoughttodesignapush–pullchromophorefeaturingDandAmoietieslocatedatthe2-and5-positionsofthesamethiopheneringoftheDTEunit(Scheme1(b)),ratherthanthembeinglocatedontwodi erentthiophenerings.4,7Inthisso-called‘‘reverseinterrupter’’,p-conjugationbetweenAandDise cientonlywhentheDTEunitisinitsopenform(‘‘ON’’state),whereasintheclosedringisomer(‘‘OFF’’state),theformationofatetrahedralsp3centerattheC2carbondisconnectstheDandApartsofthemolecule.Inthesesystems,itwasanticipatedthattheruptureoftheintramolecularchargetransferaccom-panyingthephotoisomerizationprocesswouldallowmodula-tionoftheemissionpropertiesofthechromophore.

Asa rstapproach,wewishtodiscloseourpreliminaryresultsinthesynthesis,andphotochromicandphotophysicalstudiesofreverseinterrupter1,containingdimethylamino-phenylandvinylbipyridinemoietiesastheDandAendgroups,respectively(Scheme2).WeshowthatthephotochromicreactioncanbetriggereduponexcitationwithUVandvisiblelight.Inaddition,thisprocess,whichcanitselfbeswitchedonoro accordingtothepolarityofthesolvent,allowsane cientmodulationofthe uorescence.

Substituted4,40-vinyl-2,20-bipyridinederivativesareaccessibleviaaWadsworth–Emmonsreactionofbipyridine-bis(phosphonate)7andtheappropriatealdehydeinthepresenceofabase.Wehaveusedthisapproachtopreparecompound1(Scheme3).Thetwodistinctthienylfragments,3and4,were rstpreparedindependently.Thep

-dimethylaminophenyl

a

SciencesChimiquesdeRennesUMR6226,CNRS-Universite´deRennes1,CampusdeBeaulieu,35042Rennes,France.

E-mail:lebozec@univ-rennes1.fr,veronique.guerchais@univ-rennes1.fr;Fax:+33223236939;Tel:+33223236544b

LaboratoiredePhotophysiqueetPhotochimieMole´culaire,UMRCNRS8531,ENSCachan,94235Cachan,Francec

DepartmentofChemistry,UniversityofDurham,SouthRoad,Durham,UKDH13LEd

GroupeMatie`reCondense´e,UMR6626CNRS,Universite´deRennes1,CampusdeBeaulieu,35042Rennes,France

wElectronicsupplementaryinformation(ESI)available:Experimentalproceduresandcharacterizations,detailsofthecrystallographicstruc-tureof1(o,o),DC640444.ForESIandcrystallographicdatainCIForotherelectronicformatseeDOI:10.1039/b823113c

Scheme1Schematicrepresentationofnormal(a)and‘‘reverse’’(b)push–pullinterrupters.

1320|NewJ.Chem.,2009,33,1320–1323

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