Acridin-9(10H)-one based thermally activated delayed fluorescence emitter for highly efficient green OLED

Abstract

It is crucial for thermally activated delayed fluorescence (TADF) emitters to have both high photoluminescence quantum yield (PLQY) and high reverse intersystem crossing rate (kRISC). A novel TADF emitter, namely 3,6-bis(3,6-bis(diphenylamino)-9H-carbazol-9-yl)-10-phenylacridin-9(10H)-one (3,6-DPCz-AD), was designed by introducing N3,N3,N6,N6-tetraphenyl-9H-carbazole-3,6-diamine (DPCz) at 3,6-sites of the acceptor acridin-9(10H)-one (AD) by nucleophilic substitution. On the acridin-9(10H)-one ring, the sp2-hybridization of the 10-site N atom leads to high rigidity, which inhibited conformation relaxation of excited state to reduce non-radiative decay. The introduction of large conjugated diphenylamine groups at the 3,6-sites of carbazole not only facilitated the RISC by increasing intramolecular charge transfer and generating a low S1-T1 energy gap (ΔEST), but also enhanced the radiative transition by enlarging the highest occupied molecular orbital (HOMO) delocalization. As a result, even without the traditional highly distorted structure, 3,6-DPCz-AD exhibited strong TADF characteristics with high kRISC of 5.8 × 105 s−1, high kr of 3.4 × 107 s−1 and a high PLQY of 99% simultaneously. The green organic light-emitting diode (OLED) of 3,6-DPCz-AD showed both a maximum external quantum efficiency (EQEmax) of 30.1% and a power efficiency of 83.3 lm W−1. An EQE of 20.1% was still remained at a high brightness of 1000 cd m−2. This is one of the best performances for acridin-9(10H)-one based TADF emitters ever reported so far.