Researchers at Tianjin Normal University have developed an inclusion co-crystal strategy using Tröger’s base molecular boxes to achieve thermally activated delayed fluorescence, according to a study published in Nature Communications. The method uses non-covalent through-space charge transfer inside supramolecularly engineered confined environments that bind aromatic guest molecules.
The research team synthesized electron-rich molecular box hosts designated as TB[2], incorporating both mesomeric (meso-TB[2]) and racemic (race-TB[2]) forms. From a group of six electron-withdrawing cyanobenzenes, these hosts selectively encapsulated 1,3,5-benzenetricarbonitrile (BTN) and 1,2,4,5-tetracyanobenzene (TCNB). This selective binding yielded three distinct 1:1 binary inclusion charge-transfer co-crystals stabilized by multiple non-covalent interactions.
Luminescence properties differed according to the balance of charge transfer strength and host-guest complexation. The BTN@meso-TB[2] and BTN@race-TB[2] co-crystals generated tunable yellow-green and bright cyan thermally activated delayed fluorescence emission due to strong host-guest complexation paired with weak through-space charge transfer interactions. In contrast, TCNB@meso-TB[2] showed almost no luminescence because strong intermolecular charge transfer promoted non-radiative decay.
The study was authored by Yuan Wang, Kun Liu, Ya Li, Zhe Zheng, Yuna Shang, Bin Li, Hongming He, and Chunju Li at the university's Academy of Interdisciplinary Studies on Intelligent Molecules. Yongxu Hu of Tianjin University assisted with organic light-emitting diode testing. Research funding was provided by the National Natural Science Foundation of China under grants 22571233, 22201213, and 22301218, and the Natural Science Foundation of Tianjin City under grants 23JCZDJC00660 and 25JCQNJC00500.
