Phenazasiline/Spiroacridine Donor Combined with Methyl-Substituted Linkers for Efficient Deep Blue Thermally Activated Delayed Fluorescence Emitters.

Phenazasiline, a sp3 hybridized silicon-bridged diphenylamine, is a promising donor moiety for deep-blue TADF emitters because of its deep highest occupied molecular orbital, high triplet level of 3.1 eV, and orthogonal connection with acceptor moieties. Herein, we report highly efficient deep-blue TADF emitters composed of phenazasiline donor and triazine acceptor combined with methyl-substituted phenylene linkers. As a series of methyl-substituted linker-based TADF emitters, we also synthesized spiroacridine donor-based sky-blue TADF emitters to study the effect of methyl-substituted linkers on the photophysical properties of TADF emitters. Deeper blue emissions of TADF emitters were obtained by substituting either one or two methyl groups at the phenylene linker of TADF molecules, and a small singlet-triplet gap below 0.2 eV was maintained for efficient reverse intersystem crossing. Organic light-emitting diodes (OLEDs) with spiroacridine-based TADF emitters, TTSA and TXSA, showed external quantum efficiencies (EQEs) of 27.9 and 20.7% with sky-blue emission of Commision Internationale de L'Eclairage (CIE) color coordinates of (0.158, 0.283) and (0.154, 0.251), respectively. With phenazasiline-based TADF emitters, TTAZ and TXAZ, highly efficient deep-blue OLEDs were realized with EQEs of 23.7 and 16% with improved CIE coordinates of (0.148, 0.158) and (0.148, 0.131), respectively.