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.