Towards efficient blue aggregation-induced emission and delayed fluorescence molecules by locking the skeleton of indolocarbazole derivatives for non-doped OLEDs

Abstract

Although the design strategies for thermally activated delayed fluorescence (TADF) molecules have gradually become richer and more refined, challenges still exist in the design of such materials. Typically, the highly twisted donor (D)-acceptor (A)-type structure of TADF materials presents a challenging contradiction between the desire for a minimal singlet-triplet energy gap (ΔEST) and the pursuit of high oscillator strength/photoluminescence quantum yield (ΦPL). This study proposes an effective TADF molecular design strategy, which involves selecting a highly rigidity and planarity indolocarbazole (ICz) donor and a molecularly locked acceptor to construct molecules with a D-A-D configuration, successfully creating successfully creating emitters with high ΦPL and a small ΔEST. These molecules exhibit strong TADF and aggregation-induced emission (AIE) characteristics in nondoped films, with ΦPL exceeding 70.0 % and small ΔEST, small nonradiative transition rate constant, and larger reverse intersystem crossing constant (kRISC). Acting as excellent emitters in OLEDs, they provide efficient electroluminescence with CIEx,y=(0.148, 0.119) for 23bCzSOB and CIEx,y=(0.219, 0.463) for 23bCzTPO, with the highest current efficiency (CEmax) and external quantum efficiency (EQEmax) reaching 29.5 cd/A and 14.9 % for 23bCzSOB and 36.9 cd/A and 21.6 % for 23bCzTPO, respectively. These results indicate that the molecular design of efficient delayed fluorescence molecules is successful and promising.