Intramolecular Noncovalent Interactions Facilitate Thermally Activated Delayed Fluorescence (TADF)

• Published in: The journal of physical chemistry letters Vol. 10; no. 12; pp. 3260 - 3268
• Main Authors: Chen, Xian-Kai, Bakr, Brandon W, Auffray, Morgan, Tsuchiya, Youichi, Sherrill, C. David, Adachi, Chihaya, Bredas, Jean-Luc
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20-06-2019
• Subjects: Chemistry; Materials Science; Physics; Science & Technology - Other Topics
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.9b01220

In the conventional molecular design of thermally activated delayed fluorescence (TADF) organic emitters, simultaneously achieving a fast rate of reverse intersystem crossing (RISC) from the triplet to the singlet manifold and a fast rate of radiative decay is a challenging task. A number of recent experimental data, however, point to TADF emitters with intramolecular π–π interactions as a potential pathway to overcome the issue. Here, we report a comprehensive investigation of TADF emitters with intramolecular π···π or lone-pair···π noncovalent interactions. We uncover the impact of those intramolecular noncovalent interactions on the TADF properties. In particular, we find that folded geometries in TADF molecules can trigger lone-pair···π interactions, introduce a n → π* character of the relevant transitions, enhance the singlet–triplet spin–orbit coupling, and ultimately greatly facilitate the RISC process. This work provides a robust foundation for the molecular design of a novel class of highly efficient TADF emitters in which intramolecular noncovalent interactions play a critical function.