Photochemical reactions are increasingly being used for chemical and materials synthesis, for example, in photoredox catalysis, and generally involve photoexcitation of molecular chromophores dissolved in a liquid solvent. The choice of solvent influences the outcomes of the photochemistry because solute–solvent interactions modify the energies of and crossings between electronic states of the chromophores, and they affect the evolving structures of the photoexcited molecules. Ultrafast laser spectroscopy methods with femtosecond to picosecond time resolution can resolve the dynamics of these photoexcited molecules as they undergo structural and electronic changes, relax back to the ground state, dissipate their excess internal energy to the surrounding solvent, or undergo photochemical reactions. In this Account, we illustrate how experimental studies using ultrafast lasers can reveal the influences that different solvents or cosolutes exert on the photoinduced nonadiabatic dynamics of internal conversion and intersystem crossing in nonradiative relaxation pathways. Although the environment surrounding a solute molecule is rapidly changing, with fluctuations in the coordination to neighboring solvent molecules occurring on femtosecond or picosecond time scales, we show that it is possible to photoexcite selectively only those molecular chromophores transiently experiencing specific solute–solvent interactions such as intermolecular hydrogen bonding.

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溶剂对超快光化学途径的影响

光化学反应越来越多地用于化学和材料合成，例如在光氧化还原催化中，并且通常涉及溶解在液体溶剂中的分子发色团的光激发。溶剂的选择会影响光化学的结果，因为溶质-溶剂相互作用会改变生色团电子态的能量和交叉，并且它们会影响光激发分子的演化结构。具有飞秒到皮秒时间分辨率的超快激光光谱方法可以解决这些光激发分子在经历结构和电子变化、放松回到基态、将多余的内能消散到周围溶剂或发生光化学反应时的动力学。在这个帐户中，我们说明了使用超快激光的实验研究如何揭示不同溶剂或共溶质对非辐射弛豫路径中内部转换和系统间交叉的光诱导非绝热动力学的影响。尽管溶质分子周围的环境正在迅速变化，与相邻溶剂分子的配位波动发生在飞秒或皮秒时间尺度上，但我们表明，有可能仅选择性地光激发那些瞬时经历特定溶质-溶剂相互作用的分子发色团，例如分子间氢键。