Triarylborane-based thermally activated delayed fluorescence materials with an efficient reverse intersystem crossing

Abstract

Efficient reverse intersystem crossing (RISC) is an important process for thermally activated delayed fluorescence (TADF) to suppress efficiency roll-off in organic light-emitting diodes (OLEDs). Enhancing spin-orbit coupling is effective for fast RISC, which is achieved by mediating a locally excited triplet state when RISC occurs between charge transfer states. Here, we experimentally confirmed that efficient RISC occurred in triarylborane-based TADF emitters named Phox-Meπ, Phox-MeOπ, and MeO3Ph-FMeπ. The three emitters showed large rate constants of RISC exceeding 106 s−1. Phox-Meπ-based OLEDs exhibited higher maximum external quantum efficiency (EQEmax = 10.0%) compared to Phox-MeOπ-based OLED (EQEmax = 6.7%).