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

Efficient reverse intersystem crossing (RISC) is an important process for thermally activated delayed fluorescence (TADF) to suppress efficiency roll-off in organic LEDs (OLEDs). Enhancing spin-orbit coupling is effective for fast RISC and 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- Me pi , Phox- MeO pi , and MeO3 Ph- FMe pi . The three emitters showed large RISC rate constants exceeding 106 s-1. The Phox- Me pi -based OLED exhibited higher maximum external quantum efficiency (EQEmax = 10.0%) compared to the Phox- MeO pi -based OLED (EQEmax = 6.7%).