Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ*-featured excited states
Yanju Luo, Kai Zhang, Zhenming Ding, Ping Chen, Xiaomei Peng, Yihuan Zhao, Kuan Chen, Chuan Li, Xujun Zheng, Yan Huang, Xuemei Pu, Yu Liu, Shi‐Jian Su, Xiandeng Hou, Zhiyun Lu
Abstract
Abstract The harvesting of ‘hot’ triplet excitons through high-lying reverse intersystem crossing mechanism has emerged as a hot research issue in the field of organic light-emitting diodes. However, if high-lying reverse intersystem crossing materials lack the capability to convert ‘cold’ T 1 excitons into singlet ones, the actual maximum exciton utilization efficiency would generally deviate from 100%. Herein, through comparative studies on two naphthalimide-based compounds CzNI and TPANI, we revealed that the ‘cold’ T 1 excitons in high-lying reverse intersystem crossing materials can be utilized effectively through the triplet-triplet annihilation- mediated high-lying reverse intersystem crossing process if they possess certain triplet-triplet upconversion capability. Especially, quite effective triplet-triplet annihilation- mediated high-lying reverse intersystem crossing can be triggered by endowing the high-lying reverse intersystem crossing process with a 3 ππ*→ 1 nπ* character. By taking advantage of the permanent orthogonal orbital transition effect of 3 ππ*→ 1 nπ*, spin–orbit coupling matrix elements of ca. 10 cm −1 can be acquired, and hence ultra-fast mediated high-lying reverse intersystem crossing process with rate constant over 10 9 s −1 can be realized.