Thioxanthone-containing blue thermally activated delayed fluorescent emitter

Abstract Accelerating reverse intersystem crossing (RISC) without sacrificing fast radiative decay is effective in suppressing efficiency roll‐off (eRO) in thermally activated delayed fluorescence (TADF)‐based organic light‐emitting diodes. We here report a TADF emitter, CC‐TXO‐I, combining a bicarbazole donor (CC) and a sulfur‐containing acceptor (TXO). The CC is used to accelerate radiative decay via moderate donor‐acceptor torsion angle, and the TXO is expected to provide fast RISC by the heavy atom effect of sulfur. We successfully realized very large rate constants for RISC ( k RISC ) of ~10 7 s −1 , and eROs were improved by increasing both k RISC and rate constants of radiative decays.