Solvatochromism in a Near-Critical Solution:  A Direct Correlation with Local Solution Structure

• Published in: The journal of physical chemistry. B 1998-09, Vol.102 (38), p.7455-7461
• Main Author: Adams, John E
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp9816059

Although many studies of supercritical fluid solutions have been interpreted in terms of solute−solvent clustering, no work directly relating microscopic solution structure to solvatochromism measurements has been described previously. Here we report a simulation of a model supercritical fluid solution that directly yields the information required for the calculation of solvatochromic shifts, the density dependence of which mirrors the general behavior (that the most rapid change in the spectral shift with increasing solution density is found in the subcritical regime) reported in numerous experiments. Our calculations also confirm that it is the extent of population of the first solvent shell that most strongly influences the solute's spectroscopy (i.e., “direct” solvation effects dominate the spectral shift) and that even a rather small simulation yields an adequate description of the local solvation environment. However, the wide distribution of local environments does require that special attention be paid to adequate configuration averaging. We discuss the implications of this work with regard to the popular physical cluster picture of solvation in a near-critical fluid.