A Series of Imidazo[1,2-f ]phenanthridine-Based Sky-Blue TADF Emitters Realizing EQE of over 20%

摘要

Although imidazole derivatives are promising as blue fluorescent emitters in organic light-emitting devices (OLEDs), the corresponding blue thermally activated delayed fluorescence (TADF) emitter is rarely explored. In this study, a series of imidazo[1,2-f]phenanthridine-based TADF materials in the blue to sky-blue region is developed. The resultant benzimidazole (BIP)-based TADF materials, with pi-expanded acceptor and electron-donor phenoxazine (PXZ), namely PXZ-BIP, shows a high maximum external quantum efficiency (eta(ext,max)) of 21% with CIE coordinates of (0.21, 0.37). These results have clearly demonstrated that PXZ-BIP exhibits the highest eta(ext,max) among imidazole-based fluorescent sky-blue OLEDs. The corresponding imidazophenanthridine derivative, with a less pi-expanded acceptor, shows inferior OLED performances, with a eta(ext,max) of 5.9% and CIE of (0.19, 0.30). This study provides a critical molecular design to realize high-efficiency TADF materials based on imidazole derivatives.