Acceptor Modulation for Blue and Yellow TADF Materials and Fabrication of All-TADF White OLED

4,4'-(4-Phenylpyridine-2,6-diyl)dibenzonitrile (PyDCN) was designed to reduce electron-withdrawing strength and to decentralize the unsaturated N atoms relative to triazine. PyDCN was used as acceptor to construct thermally activated delayed fluorescence (TADF) emitters PyDCN-PXZ and PyDCN-DMAC with phenoxazine (PXZ) and 9,9-dimethyl-9,10-dihydroacridine (DMAC) as electron donors. The relatively high radiative transition rate constants (kF) in the order of 107 s-1, high photoluminescence quantum yields of 80-90%, and balanced charge transportation were detected for both TADF emitters. PyDCN-DMAC exhibited electroluminescence (EL) with peak at 472 nm and CIE values of (0.17, 0.26), more approaching to real blue in comparison with most of DMAC based sky-blue TADF analogues. High external quantum yield (ηext) of 25.6% was obtained for PyDCN-DMAC doped organic light-emitting diode (OLED). PyDCN-PXZ exhibited green EL with a ηext of 26.9% at 519 nm in doped OLED. Its non-doped yellow OLED also revealed a moderate ηext of 18.2% at a peak of 557 nm. Furthermore, PyDCN-DMAC was used as the blue host emitter to fabricate single-emitting-layer all-TADF white OLED in combination with a yellow home-made TADF emitter PP-PXZ, which exhibited a maximum ηext of 18.5% with CIE coordinates of (0.38, 0.44) and excellent color stability.