Enhancing reverse intersystem crossing rate of red thermally activated delayed fluorescence emitters by simultaneously involving locally excited triplet states from donor and acceptor segments

•Developing red TADF emitters by simultaneously employing polycyclic large-conjugation donor and acceptor units.•The first example of delicate management of 3LED and 3LEA for constructing a high-performance red TADF emitter.•DBBPZ-IDPZ delivers fast kRISC and high PLQY of 98.1% thanks to the joint contribution of 3LED and 3LEA.•DBBPZ-IDPZ based OLED affords an improved EQE of 26.0 %, peaking at 628 nm.