Thermally activated delayed fluorescence emitters with oxygen-bridged triarylborane acceptors for pure blue organic light emitting diodes

Two donor-acceptor (D-A) type pure blue thermally activated delayed fluorescent (TADF) emitters have been synthesized by integrating two oxygen-bridged triarylborane acceptors with different phenyl rings substitution sites with 10,10-diphenyl-5,10-dihydrodibenzo[b,e][1,4]azetidine (PASi). These emitters successfully keep the rapid reverse intersystem crossing rates characteristic of D-A type TADF materials, while incorporating the shortrange charge transfer (SRCT) properties of oxygen-bridged triarylborane acceptors to amplify non-radiative transition processes. Organic light-emitting diode (OLED) devices based on these pure blue emitters show that each maximum external quantum efficiency (EQEmax) of the pPhBO-PASi and mPhBO-PASi devices are 20.4 % and 15.3 %, respectively. More encouragingly, the efficiency roll-off of the device improves with the increase of doping concentration. This work provides a simple and feasible molecular design strategy to design pure blue TADF emitters.