Optimization of boron-containing acceptors towards high-efficiency TADF emitters: sky-blue OLEDs with external quantum efficiency of 32.6%

Two new thermally activated delayed fluorescence (TADF) molecules, 13-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-5,5-dimethyl-5,13-dihydrobenzo[4,5]thieno[3,2-c]acridine (BOBT) and 13-(4-(dimesitylboranyl)-3,5-dimethylphenyl)-5,5-dimethyl-5,13-dihydrobenzo[4,5]thieno[3,2-c]acridine (BPBT), are constructed via connecting the 5,5-dimethyl-5,13-dihydrobenzo[4,5]thieno[3,2-c]acridine (BTDMAC) donor (D) with triarylboron or oxygen-bridged cyclized boron acceptors (A), respectively. In comparison with the photoluminescence quantum yield (PLQY) of 84% for BPBT, BOBT shows a higher PLQY of 100%, due to the multi-resonance effect of the boron-oxygen skeleton. In addition, the D-A-type molecular structural characteristic endows the boron-containing BOBT emitter with a fast reverse intersystem crossing rate on the order of 10⁶ s⁻¹. The sky-blue organic light-emitting diode (OLED) employing the BOBT emitter achieves state-of-the-art device performances with a high external quantum efficiency of 32.6%.