Orange-red organic light emitting diodes with high efficiency and low efficiency roll-off: boosted by a fused acceptor composed of pyrazine and maleimide

The strategy to develop orange-red thermally activated delayed fluorescent (TADF) materials for highperformance organic light-emitting diodes (OLEDs) with both high maximum external quantum efficiencies (EQEsmax) and low efficiency roll-off, is ongoing pursued yet challenging. Herein, two efficient orange-red TADF emitters, T-DMAC-PPyM and P-DMAC-BPyM, with a new acceptor fused by pyrazine and maleimide, were designed and synthesized. Notably, the highly twisted conformation of P-DMAC-BPyM can inhibit the close pi-pi stacking, so as to reduce exciton quenching, while the "locked" biphenyl bridge can enhance the molecular rigidity, thus reducing the non-radiative decay associated with intramolecular rotation. Consequently, P-DMACBPyM exhibits outstanding electroluminescent performance with a remarkably high EQEmax of 26.0% and an impressively low efficiency roll-off (EQE100 is 21.7%; EQE1000 is 18.3%), which are among the best results for orange-red TADF OLEDs.