Research progress in the field of photochromic delayed fluorescent materials by Professor Yan Dongpeng of Beijing Normal University

In recent years, intelligent response luminescent materials have attracted extensive attention of researchers, which have important application value in the fields of information security, data recording and storage devices Mechanochemical luminescent materials are a kind of materials which change the photophysical properties such as wavelength, intensity and lifetime of luminescent under the action of external forces (such as shearing, grinding, scraping, etc.) This process can be caused by the change of weak intermolecular forces (hydrogen bond, C-H ··· π, π - π) under the action of external forces, which can be recovered by solvent fumigation or heat treatment Therefore, a reasonable balance of the different forces between molecules is the key to the design of mechanochemical materials Up to now, most of the intelligent light-emitting systems are based on the traditional fluorescence or phosphorescence mechanism There are few reports about the mechanochemical delayed fluorescence (MCDF) materials involving the energy conversion between singlet and triplet states Recently, Professor Yan Dongpeng's research group of School of chemistry, Beijing Normal University, based on the research work of three-wire state regulation of phosphorescent materials (NAT Commun., 2018, 9, 2798; angel Chem Int ed 2017, 56, 7853; chem SCI 2017, 8, 590; Chem SCI 2016, 7, 4519), and the two-dimensional layered micro / nano size metal organic hybrid material (mcdf-1) with force-induced delayed fluorescence discoloration was successfully prepared In the aspect of microstructure, the research group selected 9-anthranilic acid (9-AC) and benzimidazole (BIM) as ligands to construct various weak intermolecular forces, and also realized the delayed fluorescence luminescence performance; in the aspect of macro morphology, the research group constructed the micro/ Nano size two-dimensional layered metal organic hybrid materials, this design is mainly based on the weak force between the two-dimensional layered material monolayers, the molecular layer will appear slip and deformation under the action of external force, which is conducive to change the force between the chromophores and the arrangement formula, so as to achieve the performance of force-induced color change In the process of friction, the luminescent center of the material can be changed from 9-AC / BIM exciplex to 9-AC / 9-AC exciplex, so as to realize the mechanochemical phenomenon of delayed fluorescence from blue to green The color change can be restored by CH3CN solvent fumigation, and the transformation of mcdf-1 and its solvate configuration can also be realized In addition, it can be inferred from the temperature dependent luminescence spectrum of the material before and after the force-induced reaction that there is a redistribution of the energy of the single excited state and the triple excited state in the process of the force-induced response Therefore, a new idea of constructing two-dimensional layered micro / nano size force-induced delayed fluorescence response materials based on the interaction of exciplexes and exciplexes is proposed This work was supported by 973 program, National Natural Science Foundation and Beijing Natural Science Foundation The research results were published on advanced science, a comprehensive publication of Wiley press (DOI: 10.1002/advs.201801187) Professor Yan Dongpeng and Professor Wang Kezhi of Beijing Normal University are co correspondents, and Dr Yang Yongsheng is the first author of the paper.