An indolo[3,2,1- jk ]carbazole-fused multiple resonance-induced thermally activated delayed fluorescence emitter for an efficient narrowband OLED.

By inserting a tricoordinate B atom into an indolo[3,2,1- jk ]carbazole precursor, an efficient fused multiple resonance-induced thermally activated delayed fluorescence emitter was prepared, which exhibits a narrowband emission and a considerable reverse intersystem crossing rate. The corresponding organic light-emitting diode displays an external quantum efficiency of 27.2% with a suppressed efficiency roll-off.