Novel Carbazol-Pyridine-Carbonitrile Derivative as Excellent Blue Thermally Activated Delayed Fluorescence Emitter for Highly Efficient Organic Light-Emitting Devices

A novel blue thermally activated delayed fluorescence (TADF) emitter, CPC (2,6-di(9H-carbazol-9-yl)-4-phenylpyridine-3,5-dicarbonitrile), was designed and synthesized. By directly linking carbazole (to serve as electron-donor) and pyridine-3,5-dicarbonitrile (to serve as electron-acceptor), and distributing cyanogroups and carbazole groups at the para-position of pyridine core, CPC successfully achieves an extremely small singlet-triplet splitting and fairish photoluminescence quantum yield, thus can act as the highly efficient blue TADF emitter. The optimized organic light-emitting diode (OLED) based on 13 wt % CPC doped in mCP (1,3-bis(9H-carbazol-9-yl)benzene) host exhibits maximum current efficiency, power efficiency, and external quantum efficiency of 47.7 cd A(-1), 42.8 lm W-1, and 21.2%, respectively, which are the best results in reported blue TADF-based devices up to date and even comparable with the best reported blue phosphorescent OLEDs.