Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ-featured excited states

• Published in: Nature communications Vol. 13; no. 1; pp. 6892 - 12
• Main Authors: Luo, Yanju, Zhang, Kai, Ding, Zhenming, Chen, Ping, Peng, Xiaomei, Zhao, Yihuan, Chen, Kuan, Li, Chuan, Zheng, Xujun, Huang, Yan, Pu, Xuemei, Liu, Yu, Su, Shi-Jian, Hou, Xiandeng, Lu, Zhiyun
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12.11.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/1005/1007; 639/638/298/398; Comparative studies; Excitons; Humanities and Social Sciences; Light emitting diodes; multidisciplinary; Organic light emitting diodes; Science; Science (multidisciplinary); Spin-orbit interactions
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-34573-2

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. Here, the authors investigate naphthalimide-based compounds with cold triplet excitons utilized by triplet-triplet annihilation-mediated high-lying reverse intersystem crossing, and realize rate constant of over 10 9  s −1 with exciton utilization efficiency of 46.7% in organic light-emitting diodes.