Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
J Phys Chem B. 2017 Feb 2;121(4):835-842. doi: 10.1021/acs.jpcb.6b05959. Epub 2017 Jan 20.
The role of different solvent environments in determining the behavior of molecules in solution is a fundamental aspect of chemical reactivity. We present an approach for exploring the influence of solvent properties on condensed-phase dynamics using ultrafast transient absorption spectroscopy in supercritical CO. Using supercritical CO permits adjustment of the density, by varying the temperature and pressure, whereas varying the concentration or identity of a second solvent, the cosolvent, in a binary mixture allows for adjustments of the degree of interaction between the solute and the solvent. Salicylidene aniline, a prototypical excited-state intramolecular proton-transfer system, is the subject of this study. In this system, the decay rate of the transient absorption signal decreases as the fraction of the cosolvent (for both 1-propanol and cyclohexane) increases. The decay rate also decreases with an increase in the viscosity of the mixture, but the effect is much larger for the 1-propanol cosolvent than for cyclohexane. These observations illustrate that the decay rate of the photoexcited salicylidene aniline depends on more than just the solvent viscosity, suggesting that properties such as polarity also play a role in the dynamics.
不同溶剂环境在决定溶液中分子行为方面的作用是化学反应性的一个基本方面。我们提出了一种使用超临界 CO 中的超快瞬态吸收光谱研究溶剂性质对凝聚相动力学影响的方法。使用超临界 CO 可以通过改变温度和压力来调整密度，而在二元混合物中改变第二溶剂（共溶剂）的浓度或种类则可以调整溶质和溶剂之间的相互作用程度。本研究的主题是水杨醛苯胺，一种典型的激发态分子内质子转移体系。在该体系中，瞬态吸收信号的衰减速率随着共溶剂（对于 1-丙醇和环己烷）分数的增加而降低。衰减速率也随着混合物粘度的增加而降低，但对于 1-丙醇共溶剂的影响比环己烷大得多。这些观察结果表明，光激发水杨醛苯胺的衰减速率不仅取决于溶剂粘度，还表明极性等性质也在动力学中起作用。
