An Organic Host–Guest System Producing Room‐Temperature Phosphorescence at the Parts‐Per‐Billion Level

• Published in: Angewandte Chemie International Edition Vol. 60; no. 31; pp. 16970 - 16973
• Main Authors: Chen, Biao, Huang, Wenhuan, Nie, Xiancheng, Liao, Fan, Miao, Hui, Zhang, Xuepeng, Zhang, Guoqing
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 26.07.2021
• Edition: International ed. in English
• Subjects: binary doping system; Coupling (molecular); Cryogenic temperature; donor–acceptor systems; Excitons; Fluorescence; host–guest systems; Medical imaging; Optoelectronics; Organic chemistry; parts per billion; Phosphorescence; Photodynamic therapy; Phthalimide; Phthalimides; Polymer films; Polymers; room-temperature phosphorescence; Spin-orbit interactions; Supramolecular compounds
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202106204

Manipulation of long‐lived triplet excitons in organic molecules is key to applications including next‐generation optoelectronics, background‐free bioimaging, information encryption, and photodynamic therapy. However, for organic room‐temperature phosphorescence (RTP), which stems from triplet excitons, it is still difficult to simultaneously achieve efficiency and lifetime enhancement on account of weak spin–orbit coupling and rapid nonradiative transitions, especially in the red and near‐infrared region. Herein, we report that a series of fluorescent naphthalimides—which did not originally show observable phosphorescence in solution, as aggregates, in polymer films, or in any other tested host material, including heavy‐atom matrices at cryogenic temperatures—can now efficiently produce ultralong RTP (ϕ=0.17, τ=243 ms) in phthalimide hosts. Notably, red RTP (λRTP=628 nm) is realized at a molar ratio of less than 10 parts per billion, demonstrating an unprecedentedly low guest‐to‐host ratio where efficient RTP can take place in molecular solids. A series of fluorescent naphthalimides, which did not originally show observable phosphorescence, can now efficiently produce ultralong room‐temperature phosphorescence (RTP) in phthalimide hosts. In particular, red RTP is realized by doping at a guest‐to‐host ratio at the 10 parts‐per‐billion (ppb) level.