Novel Deuterated Benzothiadiazole Derivatives with Enhancing High-Lying Reverse Intersystem Crossing for High-Efficiency Organic Light-Emitting Diodes
Xiangyu Dong, Shaogang Shen, Yuanyuan Qin, Xin Xie, Zhi Pang, Honglei Gao, Guanhao Liu, Chun‐Sing Lee, Pengfei Wang, Ying Wang
Abstract
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.