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 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%).

Keywords

• organic light-emitting diodes
• thermally activated delayed fluorescence
• reverse intersystem crossing
• charge transfer excited states
• locally excited states
• triarylborane compounds