Department of Chemistry, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Korea.
Int J Mol Sci. 2021 Nov 3;22(21):11926. doi: 10.3390/ijms222111926.
The intramolecular charge transfer (ICT) of 1-aminoanthraquinone (AAQ) in the excited state strongly depends on its solvent properties, and the twisted geometry of its amino group has been recommended for the twisted ICT (TICT) state by recent theoretical works. We report the transient Raman spectra of AAQ in a dimethylsulfoxide (DMSO) solution by femtosecond stimulated Raman spectroscopy to provide clear experimental evidence for the TICT state of AAQ. The ultrafast (~110 fs) TICT dynamics of AAQ were observed from the major vibrational modes of AAQ including the ν + δ and ν modes. The coherent oscillations in the vibrational bands of AAQ strongly coupled to the nuclear coordinate for the TICT process have been observed, which showed its anharmonic coupling to the low frequency out of the plane deformation modes. The vibrational mode of solvent DMSO, ν showed a decrease in intensity, especially in the hydrogen-bonded species of DMSO, which clearly shows that the solvation dynamics of DMSO, including hydrogen bonding, are crucial to understanding the reaction dynamics of AAQ with the ultrafast structural changes accompanying the TICT.
1-氨基蒽醌（AAQ）在激发态下的分子内电荷转移（ICT）强烈依赖于其溶剂性质，最近的理论工作推荐其氨基的扭曲几何形状用于扭曲 ICT（TICT）态。我们通过飞秒受激拉曼光谱报告了 AAQ 在二甲基亚砜（DMSO）溶液中的瞬态拉曼光谱，为 AAQ 的 TICT 态提供了明确的实验证据。从 AAQ 的主要振动模式包括ν+δ和ν模式观察到 AAQ 的超快（~110 fs）TICT 动力学。在 TICT 过程中与核坐标强烈耦合的 AAQ 振动带中的相干振荡已被观察到，这表明其与平面外变形模式的低频的非谐耦合。溶剂 DMSO 的振动模式ν强度降低，特别是在 DMSO 的氢键物种中，这清楚地表明 DMSO 的溶剂化动力学，包括氢键，对于理解 AAQ 的反应动力学至关重要，因为它伴随着 TICT 的超快结构变化。
