Difluoroboron-Enabled Thermally Activated Delayed Fluorescence

A new series of tetracoordinated boron-enabled thermally activated delayed fluorescence (TADF) materials with a donor-acceptor BF₂-type framework were designed and conveniently synthesized. Difluoroboron plays a critical role and acts as a key to coordinate with the latent acceptor of the 2-(4-phenylpyridin-2-yl)phenol (PPyPOH) moiety to realize TADF. TADF materials are air-stable and have a high photoluminescence quantum yield of up to 99%. NOBF2-Cz- and NOBF2-DPCz-doped blue OLEDs demonstrated EQEs of 11.0% with CIE coordinates of (0.14, 0.16) and 15.8% with (0.14, 0.28) and high brightness of 6761 and 19383 cd/m² could be achieved, respectively. Moreover, the blue OLED doped with NOBF2-DPCz and the green OLED doped with NOBF2-DMAC achieved operational lifetimes at 50% of initial luminance (L₀ = 500 cd/m²), LT₅₀, of 54 and 920 h, respectively. This work indicates that these tetracoordinated difluoroboron molecules can act as efficient and stable TADF materials for OLED applications.