Modulating the electron-donating ability of acridine donor units for orange-red thermally activated delayed fluorescence emitters.

The development of the thermally activated delayed fluorescence (TADF) emitters with orange-red emission is still lagged behind their blue, green and yellow counterparts. Recent researches to address this problem mainly focused on developing new acceptor units. There were few donor units designed especially for orange-red emitters. Herein, with the benzothiophene fused to the diphenyl acridine donor unit, a new donor moiety, namely BTDPAc, was designed and synthesized. Benefited from the strong electron-donating ability of the new donor moiety, a new TADF emitter, BTDPAc-PhNAI, shows an orange-red emission with its peak at 610 nm in dilute toluene solution. Also, with the help of the diphenyl rings of the donor unit, high photoluminescence quantum yields (ΦPL) were achieved for BTDPAc-PhNAI at a wide concentration range. Consequently, the orange-red OLED based on BTDPAc-PhNAI achieved a high external quantum efficiency (EQE) of nearly 20%, which is comparable to the state-of-art device performances with similar emission spectra.