Simultaneously optimizing radiative decay and up-conversion of triphenylamine-based thermally activated delayed fluorescence emitters to achieve efficient deep-red organic light-emitting diodes

•Three TADF emitters were designed and synthesized with red to deep-red emission.•Quasi-degenerate molecular orbitals and intramolecular H-bonds are integrated.•kf and kRISC of TTPA-DCPPm are simultaneously improved.•The TTPA-DCPPm-based deep-red OLED showed an EQE of 26.5% with 640 nm emission.