Tu Yujie, Liu Junkai, Zhang Haoke, Peng Qian, Lam Jacky W Y, Tang Ben Zhong
Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction and Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
Angew Chem Int Ed Engl. 2019 Oct 14;58(42):14911-14914. doi: 10.1002/anie.201907522. Epub 2019 Aug 27.
Restriction of intramolecular motion (RIM), as the working mechanism of aggregation-induced emission (AIE), cannot fully explain some heteroatom-containing systems. Now, two excited states are taken into account and a mechanism, restriction of access to dark state (RADS), is specified to elaborate RIM and complete the picture of AIE mechanism. A nitrogen-containing molecule named APA is chosen as a model compound; its weak fluorescence in solution is ascribed to the easy access from the bright (π,π*) state to the close-lying dark (n,π*) state. By either metal complexation or aggregation, the dark state is less accessible due to restriction of the molecular motion leading to the dark state and elevation of the dark state energy, thus the bright state emission is restored. RADS is powerful in elucidating the AIE effect of molecules with excited states favoring non-radiative decay, including overlap-forbidden states such as (n,π*) and CT states, spin-forbidden triplet states, and so on.
分子内运动受限（RIM）作为聚集诱导发光（AIE）的作用机制，无法完全解释一些含杂原子体系。现在，考虑到两个激发态，并提出了一种机制，即暗态可达性受限（RADS），以详细阐述RIM并完善AIE机制的全貌。选择一种名为APA的含氮分子作为模型化合物；其在溶液中的弱荧光归因于从亮态（π，π*）到紧邻暗态（n，π*）的容易跃迁。通过金属络合或聚集，由于导致暗态的分子运动受限以及暗态能量升高，暗态的可达性降低，从而恢复了亮态发射。RADS在阐明具有有利于非辐射衰变激发态的分子的AIE效应方面很有效，包括（n，π*）和CT态等重叠禁戒态、自旋禁戒三重态等等。
