Construction of Blue Thermally Activated Delayed Fluorescence Materials Based on the Heptagonal Triarylamine Donor
The development of efficient blue light-emitting materials is a crucial yet challenging task in organic light-emitting diodes(OLED).Two novel blue light-emitting molecules,TRZCz-TPA and TRZ-TPA,have been designed and synthesized based on the heptagonal 9H-tripheno[b,d,f]nitrozoafluorene(TPA)donor.Their thermal stability,electrochemical properties,photophysical properties,and device performances were characterized.TRZCz-TPA and TRZ-TPA both exhibit blue emission in toluene solution with emission peaks at 455 and 440 nm,respectively.In contrast to TRZ-TPA,which exhibits through-bond charge transfer(TBCT)from the TPA donor to the diphenyltriazine(TRZ)acceptor,TRZCz-TPA,featuring two adjacent 3,6-di-tert-butylcarbazole(tBuCz)donors near the TRZ acceptor,demonstrates through-space charge transfer(TSCT)from the tBuCz donors to the TRZ acceptor.This leads to a remarkable reduction in the singlet-triplet energy gap(ΔEST)from 0.53 eV to 0.04 eV,thereby displaying thermally activated delayed fluorescence(TADF)properties.Additionally,tBuCz donor with large steric hindrance effectively suppresses aggregation-induced quenching in the aggregated state.Consequently,TRZCz-TPA achieves a photoluminescence quantum yield(PLQY)of 42.0％and a maximum external quantum efficiency(EQEmax)of 10.4％in OLED devices,significantly outperforming TRZ-TPA(PLQY=6.5％,EQEmax=3.7％).
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