Greener protocol for one pot synthesis of coumarin styryl dy

Anewmethodforsynthesizingnovelcoumarinstyryldyesbasedon2-(1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)ethylidene)malononitrileisproposedbyaneco-friendlyapproachinasinglepotusingadeepeutecticsolvent(DES).TheDESischeaperandbiodegradableandservesthedualroleofcatalystaswellassolvent.Theapproachprovidesanenvironment-friendlypathway,simpleprocedure,mildconditions,andexcellentyieldsofnovelstyryldyes.ReactionusingDESrequireslesserreactiontimethanconventionalmethod.Itiseasytoseparateproductafterreaction.DEScanberecycledseveraltimeswithoutlosingitsactivity.Thesenoveldyesshowgoodthermalstabilityandbrilliant uorescence.Theycan ndpotentialapplicationsin uorescentchemosensorsandlasertechnologyetc.

Ó2012ElsevierLtd.Allrightsreserved.

1.Introduction

Coumarinsareattractiveandversatilemoleculesthat ndapplicationsinvarious eldslikemedicine,perfumery,dyes,pigments,opticalbrightners,lasers,opticaldatastoragedevices,solarcells,etc.[1].Recently,coumarinshavebeenattractingmuchattentioninelectronicandphotonicapplications[2e5]duetotheirinherentphotochemicalcharacteristics,reasonablestabilityandsolubilityinvariousorganicsolvents.Manycoumarinderivativeshavebeencommercializedasblue-greenlaserfor uorescentlabels, uorescentprobes[6e8]andenzymaticmeasurements[9].Theyexhibitintense uorescenceonsubstitutionofvariousfunc-tionalgroupsatdifferentpositions[10].Hueand uorescencepropertiesofcoumarinscanbealteredbysubstitutingdifferentfunctionalgroupslikeamino,hydroxyandmethoxyatthe3-or7-position.Modi cationoftheelectron-acceptingabilityofthesubstituentat3-positionespeciallyimprovesthe uorescencepropertiesofthecoumarins.

Cyanocoumarinsareofconsiderableinterestaspotentialbuildingblocksfornitrogen-containingheterocyclicsystems[11].Thermalstabilityisoneoftheimportantcriteriarequiredformanyelectronicandphotonicapplications,asorganicmaterialswithgoodthermalstabilityincreasethestabilityandlifetimeofthe

*Correspondingauthor.Tel.:þ9133612708;fax:þ912233611020.E-mailaddress:gsshankarling@(G.S.

Shankarling).0143-7208/$eseefrontmatterÓ2012ElsevierLtd.Allrightsreserved./10.1016/j.dyepig.2012.12.001

devices.Classicalroutesforsynthesisofcoumarinsandcyanocou-marinsincludethePechmann,Knoevenagel,Perkin,ReformatskyandWittigcondensationreactions[12,13].Knoevenagelconden-sationisoneofthesimplestandmostcommonlyusedmethodsforthesynthesisofcoumarinoritsderivatives.Tomaketheseclassicalreactionsef caciousseveralvariationsintermsofcatalystandreactionconditionshavebeenintroduced[14].However,theclassicmethodsincludingKnoevenagelcondensationsufferfromthemultipleproblemsofexpensivecatalyst,laboriousmulti-stepprocedures,longreactiontime,highreactiontemperatureandenvironmentalpollution,aswell[11].

Inthiseraofdyestuffchemistry,theimprovementofreactionef ciency,avoidanceoftoxicreagents,minimizationofwaste,andtheresponsibleutilizationofresourceshavebecomecrucialobjectives.Inthisregard,deepeutecticsolvents(DESs)havegainedmoreimportanceinbiocatalysis,syntheticorganicchemistry,electroplating,dye-sensitizedsolarcellsetc.thanothertoxicimidazolium-basedionicliquids.Deepeutecticsolventsaretypesofionicliquidspreparedasmixturesoftwoormorecomponents,whichformaeutecticwithameltingpointmuchlowerthanthatoftheindividualcomponents.Thesearemoltensaltsthatinteractbytheformationofhydrogenbondsormetalhalidebonds.Theyhavepropertiessimilartothoseofanionicliquidbutarefreeofmanydisadvantages(likeexpenseandhandling-dif culty)associatedwithotherionicliquids.Manyionicliquidsreportedinliteratureleavehazardousmaterialsintheenvironment.Theirtoxicityissimilartoorhigherthanthatoforganicsolvents[15,16].Incontrast,

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