Ternary donor–acceptor phosphine oxide hosts with peculiar high energy gap for efficient blue electroluminescence

Abstract

Ternary donor (D)–acceptor (A)–acceptor (A) molecules are commonly considered as low triplet (T₁) energy systems for specific applications. In this work, exception to this behavior was observed in a triangle-shaped D–A–A molecule PCImbPO with unusually high triplet energy of 3.0 eV. Profiting from the enhanced D–A electronic coupling, electron injecting and transporting ability of PCImbPO was dramatically improved with negligible influences on its highest occupied molecular orbital (HOMO) characteristics. Its particular T₁ configuration adjustment further gives rise to the separated frontier MO and T₁ locations, beneficial to suppress quenching effects. By utilizing PCImbPO as host in blue phosphorescent organic light-emitting diodes (PHOLEDs) and thermally activated delayed fluorescence devices, impressively high external quantum efficiency of 22% and 12% were achieved, respectively. This work established a new understanding of high-energy-gap complicated D–A systems.