Resonance Raman Studies of Solvent Dynamics in Solvatochromic Systems

McHale得到了实验物理化学计划的支持，该计划旨在阐明溶剂动力学对溶致变色分子光谱的影响。该程序包括(1)测量低温玻璃的吸收、发射和共振拉曼光谱，以便分离分子内对线宽的贡献；(2)使用溶剂同位素异构体来分离室温溶剂中对吸收、发射和共振拉曼光谱的动态影响；(3)测量作为溶剂同位素替代的荧光产量和寿命，以便获得玻璃和液态溶液中的辐射和非辐射衰减率。这些策略将能够提取溶剂诱导的消相函数，从而提取溶剂光谱密度。需要解决的问题包括辐射和非辐射驰豫速率对溶剂同位异体的敏感性，将溶剂响应视为独立于溶质电子态的有效性，溶剂诱导电子退相可能依赖于振动模，以及溶剂分子内模式在电子退相中的作用。溶解在液体溶剂中的分子表现出受周围环境中的溶剂分子影响很大的行为。这些相互作用是复杂的，目前仍未得到很好的理解。该项目的结果将有助于弥合理论预测和实际系统之间在理解溶液动力学方面的差距。这项工作的基本见解可以改善与生物化学有关的电子转移过程的描述，以及与材料科学有关的非线性光学性质的分子模型。

McHale is supported by the Experimental Physical Chemistry Program for studies to elucidate solvent dynamical influences on the optical spectra of solvatochromic molecules. The program includes (1) measuring absorption, emission, and resonance Raman spectra in low-temperature glass, in order to isolate the intramolecular contribution to the linewidth, (2) employing solvent isotopomers to isolate solvent dynamical effects on absorption, emission, and resonance Raman spectra in room temperature solvents, and (3) determining fluorescence yields and lifetimes as a function of solvent isotopic substitution in order to obtain radiative and nonradiative decay rates in glass and liquid phase solutions. These strategies will enable the extraction of the solvent-induced dephasing function, and hence the solvent spectral density. Issues to be addressed include the sensitivity of radiative and nonradiative relaxation rates to solvent isotopomer, the validity of treating solvent response as independent of the solute electronic state, the possible dependence of solvent-induced electronic dephasing on vibrational mode, and the role of solvent intramolecular modes in electronic dephasing. Molecules dissolved in liquid solvents exhibit behaviors that are much affected by the solvent molecules in the surrounding environment. These interactions are complex and still not understood well at this time. Results from this project will help to bridge the gap between theoretical predictions and real systems in understanding solution dynamics. Fundamental insights from this work could improve both the description of electron transfer processes relevant to biochemistry and the molecular models for nonlinear optical properties relevant to materials science.