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

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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 π , Phox- MeO π , and MeO3 Ph- FMe π . The three emitters showed large RISC rate constants exceeding 10 6 s −1 . The Phox- Me π -based OLED exhibited higher maximum external quantum efficiency (EQE max = 10.0%) compared to the Phox- MeO π -based OLED (EQE max = 6.7%).