Differentiating Solvation Mechanisms at Polar Solid/Liquid Interfaces

Resonance enhanced second harmonic generation (SHG) has been used to identify solvation mechanisms at different solid/liquid interfaces. Solvation interactions are characterized as being either nonspecific and averaged over the entire solute cavity or specific, referring to localized, directional interactions between a solute and its surroundings. SHG spectra report the electronic structure of solutes adsorbed to silica/organic solvent interfaces, and different solutes are chosen to probe either interfacial polarity or interfacial hydrogen bond donating/accepting opportunities. SHG results show that interfacial polarity probed by p-nitroanisole depends sensitively on solvent structure, whereas hydrogen bonding interactions probed by indoline are insensitive to solvent identity and instead are dominated by the hydrogen bond donating properties of the polar silica substrate. The bulk solvation interactions were modeled with a series of ab initio calculations that characterized solute electronic structure within a dielectric continuum and in the presence of explicit, individual solvent molecules. Collectively, these measurements and calculations create a comprehensive picture of how solvation mechanisms vary at different polar, solid surfaces.