Universal blue emitters for high efficiency thermally activated delayed fluorescence and fluorescent organic light-emitting diodes

Two blue-emitting materials with a planar indolo[3,2,1-jk]carbazole (ICz) acceptor and diphenylamine or acridine donor were developed as universal blue emitters for thermally activated delayed fluorescence (TADF) and conventional fluorescence. The incorporation of two strong donors and a phenyl group on the ICz acceptor resulted in two blue emitters. The influence of donor groups on the photophysical and electroluminescent properties of emitters was investigated for TADF and fluorescence. The diphenylamine donor substituted emitter demonstrated sky blue emission with a maximum external quantum efficiency (EQE) of 5.6% as a fluorescence emitter and a very high EQE of 30.4% as a TADF emitter. Whereas, the acridine donor-derived emitter showed deep blue emission with a maximum EQE of 4.4% as a fluorescence emitter and 17.0% as a TADF emitter. In particular, the diphenylamine donor-derived emitter offered a longer lifetime than the conventional pyrene-based emitter as well as the improved EQE. Therefore, the ICz derived blue emitters can be universally used as the fluorescent emitter in the TADF and fluorescence organic light-emitting diodes.