Publications Repository - Gdańsk University of Technology

Thefeatureof abundantandenvironmentallyfriendlyheavyatoms(HAs)like bromineto acceleratespin-forbiddentransitionsin organicmoleculeshas beenknownforyears.In combinationwiththe easinessof incorporation,brominederivativesof organicemittersshowingthermallyactivateddelayedfluorescence(TADF)emergeas a cheapand efficientsolutionforthe slowreverseintersystemcrossing(rISC)problemin suchemittersand strongefficiencyroll-offof all-organiclight-emittingdiodes(OLEDs).Here,we presenta comprehensivephotophysicalstudyof atri-PXZ-TRZemitterreportedpreviouslyanditshexabromoderivativeshowinga remarkableenhancementof rISCof up to 9 timesand a shortlifetimeof delayedfluorescenceof 2μs. Analysisof the key molecularvibrationsand TADFmechanismindicatesalmostcompeteblockageof the spin-fliptransitionbetweenthe charge-transferstatesof differentmultiplicity3CT→1CT.In sucha case,rISCas well as its enhancementby the HA is realizedvia the3LE→1CT transition,where3LE is the tripletstatelocalizedon the samebrominatedphenoxazinedonorinvolvedin the formationof the1CT state.Interestingly,the spin−orbitcoupling(SOC)withtwo other3LE statesis negligiblebecausethey are localizedon differentdonorsand not involvedin1CT. Weconsiderthis as an exampleof an additional“localization”criterionthat completesthe well-knownEl Sayedrule on the differentnatureof statesfor nonzeroSOC.The applicativepotentialof sucha hexabromoemitteris testedin a “hyperfluorescent”systemcontaininga red fluorescentdopant(tetraphenyldibenzoperiflanthene,DBP)as an acceptorof Försterresonanceenergytransfer,affordinga narrow-bandred-emittingsystem,withmostof the emissionin the submicroseconddomain.In fact, the fabricatedredOLEDdevicesshowremarkableimprovementof efficiencyroll-offfrom2−4 timesdependingon the luminance,mostlybecauseofthe increaseof the rISCconstantrate and the decreaseof the overalldelayedfluorescencelifetimethanksto the HA effect.

Authors

• mgr Michał Mońka,
• Szymon Gogoc,
• Karol Kozakiewicz,
• Vladyslav Ievtukhov link open in new tab ,
• Daria Grzywacz,
• mgr inż. Olga Ciupak link open in new tab ,
• Aleksander Kubicki,
• prof. dr hab. Piotr Bojarski,
• Przemysław Data,
• Illia E. Serdiuk