Room‐Temperature Phosphorescence Enhanced by Narrowing Down ΔEST through Tuning Excited States Energy Levels

• Published in: Advanced optical materials 2022-10, Vol.10 (20), p.n/a
• Main Authors: Liang, Dong, Jia, Ji‐Hui, Yang, Mingxue, Cai, Xian‐Bao, Yu, Rongmin, Lu, Can‐Zhong
• Format: Article
• Language: English
• Subjects: Energy gap; intersystem crossing; Materials science; Molecular energy levels; Molecular structure; Optics; Phosphorescence; Room temperature; room temperature phosphorescence; thermally activated delayed fluorescence
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202201130

In this work, two spiro‐type compounds are investigated with similar molecular structure and stacking structure. By simply altering the acceptor's heteroatoms, a strategy to enhance room temperature phosphorescence (RTP) performance is presented. The intersystem crossing process  can effectively be accelerated by reducing the energy gap between the singlet and triplet states (ΔEST) through adjusting the molecular energy level. Besides, thermally activated delayed fluorescence (TADF) is emerging in dilute solution due to such small ΔEST. This is helpful for deeply understanding the mechanism of competition in different radiative decay pathways (RTP and TADF). Through investigating two donor‐acceptor molecules with similar geometry and packing structure, a method can be put forward to enhance the room temperature phosphorescence performance through reducing ΔEST by tuning excited states level. When small ΔEST is obtained, reverse intersystem crossing process is also accelerated. Not only can phosphorescence be enhanced, but also thermally activated delayed fluorescence is induced.