Visible-LightResponsiveAzobenzeneandCholesterolBased Liquid Crystalsas EfficientSolid-StateSolar−ThermalFuels

Abstract

olar−thermalfuels(STFs)basedon photoresponsivemolecules,whichcanharvestandstoresolarenergyby theconfigurationalchangeof moleculesandcan releaseit in the formof heaton demand,havebeeninvestigatedrecently.So far,azobenzenehas beenthe mostwidelystudiedmoleculefor theseapplications.However,untilnow,onlysolidand liquidderivativesofazobenzenehavebeenexploredwhichsufferfromseverallimitations.Here,we are reportingfor the firsttimevisible-lightresponsiveSTFsbasedon liquidcrystals(LCs).We havepreparedaseriesof compoundsbasedon azobenzeneandcholesterolwithvaryingspacerandortho-substitutionon azobenzene.All of thesederivativesexhibitenantiotropicchiralnematic(N*)mesophases.Moreover,theyshowedexcellentphotostability,photocyclability,and longhalf-lifetimesofcis-states.We havefurtherevaluatedthe thinfilmsof thesecompoundsfor charging,i.e.,transtocisconversionundersolarirradiationusingvariousbandpassfilters,andalsostudiedthe kineticsof the conversion.Thesecompoundsexhibiteda maximumchargingof up to 70%for the derivativewithortho-fluoroazobenzene.Thechargedthinfilmswerefurtherevaluatedfor theirheatreleasepropertiesby infrared(IR)thermalimaging.Themaximumheatreleaseobservedwasaround5.4°C fromthe surroundingtemperaturewhichwassignificantlyhigheras comparedto similarlysubstitutedazobenzene-basedderivativewithouta LC phase