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 π-expanded acceptor and electron-donor phenoxazine (PXZ), namely PXZ-BIP, shows a high maximum external quantum efficiency (η ext,max ) of 21% with CIE coordinates of (0.21, 0.37). These results have clearly demonstrated that PXZ-BIP exhibits the highest η ext,max among imidazole-based fluorescent sky-blue OLEDs. The corresponding imidazophenanthridine derivative, with a less π-expanded acceptor, shows inferior OLED performances, with a η 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.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics