Resonant-surface second-harmonic generation studies of phenol derivatives at air/water and hexane/water interfaces

Resonant-surface second-harmonic generation and surface tension measurements have been used to study the adsorption of p-nitrophenol, phenol and p-propylphenol at the air/water and hexane/water interfaces at full monolayer coverage. The determining forces defining the angle of orientation of the moieties are the solute-solvent interactions at both interfaces. In particular, we observed the screening effect of the hexane phase on the solute-water interactions. Surface tension measurements performed on these interfaces showed that the number of molecules per unit surface at full coverage follows from the angle of orientation. From a wavelength analysis of the SH response of the monolayers, we are led to the conclusion that partial hydration of the aromatic rings of phenol and p-propylphenol occurs at both the air/water and the hexane/water interfaces, whereas p-nitrophenol remains largely within the water phase at both interfaces.