Lee Sebok, Jen Myungsam, Jang Taehyung, Lee Gisang, Pang Yoonsoo
Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61005, Republic of Korea.
Sci Rep. 2022 Apr 21;12(1):6557. doi: 10.1038/s41598-022-10565-6.
The structural changes during the intramolecular charge transfer (ICT) of nitroaromatic chromophores, 4-dimethylamino-4'-nitrobiphenyl (DNBP) and 4-dimethylamino-4'-nitrostilbene (DNS) were investigated by femtosecond stimulated Raman spectroscopy (FSRS) with both high spectral and temporal resolutions. The kinetically resolved Raman spectra of DNBP and DNS in the locally-excited and charge-transferred states of the S state appear distinct, especially in the skeletal vibrational modes of biphenyl and stilbene including ν and ν. The ν of two phenyls and the ν of the central ethylene group (only for stilbene), which are strongly coupled in the planar geometries, are broken with the twist of nitrophenyl group with the ICT. Time-resolved vibrational spectroscopy measurements and the time-dependent density functional theory simulations support the ultrafast ICT dynamics of 220-480 fs with the twist of nitrophenyl group occurring in the S state of the nitroaromatic chromophores. While the ICT of DNBP occurs via a barrier-less pathway, the ICT coordinates of DNS are strongly coupled to several low-frequency out-of-phase deformation modes relevant to the twist of the nitrophenyl group.
利用具有高光谱和时间分辨率的飞秒受激拉曼光谱（FSRS）研究了硝基芳香发色团4-二甲基氨基-4'-硝基联苯（DNBP）和4-二甲基氨基-4'-硝基芪（DNS）分子内电荷转移（ICT）过程中的结构变化。DNBP和DNS在S态的局域激发态和电荷转移态的动力学分辨拉曼光谱明显不同，特别是在联苯和芪的骨架振动模式中，包括ν和ν。在平面几何结构中强烈耦合的两个苯基的ν和中心乙烯基的ν（仅对芪而言），随着硝基苯基基团在ICT过程中的扭转而被破坏。时间分辨振动光谱测量和含时密度泛函理论模拟支持了硝基芳香发色团S态中硝基苯基基团扭转发生的220-480飞秒的超快ICT动力学。虽然DNBP的ICT通过无障碍途径发生，但DNS的ICT坐标与几个与硝基苯基基团扭转相关的低频异相变形模式强烈耦合。
