Novel Deuterated Benzothiadiazole Derivatives with Enhancing High-Lying Reverse Intersystem Crossing for High-Efficiency Organic Light-Emitting Diodes

Developing efficient "hot exciton" thermally activated delayed fluorescence (TADF) materials in electroluminescence has always been a significant and challenging issue. Herein, we have designed and synthesized two deuterated yellow emitters BT-2PhCz-d(10) and BT-2PhCz-d(24) based on the commonly designed hot exciton emitter BT-2PhCz to improve the exciton utilization efficiency. Transient absorption (TA) kinetic analysis showed that deuterated BT-2PhCz-d(10) and BT-2PhCz-d(24) possessed shorter delayed lifetimes and a faster high-lying reverse intersystem crossing rate constant (k(h-RISC)) than BT-2PhCz. The measured photoluminescence quantum yield (PLQY) and infrared spectrum results also experimentally confirmed that the introduction of C-D bonds played a key role in suppressing nonradiative processes. The optimized organic light-emitting diodes (OLEDs) based on these hot exciton materials exhibited a maximum external quantum efficiency (EQE) of 7.1% for BT-2PhCz, 10.0% for BT-2PhCz-d(10), and 11.8% for BT-2PhCz-d(24), respectively, corresponding to exciton utilization efficiencies of 39.3-26.2, 50.0-33.3, and 59.4-39.6%. These results confirm that the deuterated isotope effect realized the regulation of high-energy spin flip processes and nonradiative decay processes, providing a new strategy for designing high-performance hot exciton emitters.