Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Abstract

The solvatochromism of both absorption and emission spectra of two centro-symmetrical squaraine dyes was studied in pure solvents, dioxane–water mixtures and AOT (Aerosol OT, bis(2-ethylhexyl)sodium sulfosuccinate) reversed micelles. The shifts observed in pure solvents are relatively large and are associated with non-negligible solute–solvent polar interactions. Good empirical correlations with the π* polarity scale (a measure of the solvent dipolar character) and with the solvent proticity α scale (a measure of the solvent acidity character) were obtained. Preferential solvation by water was not observed in the dioxane–water mixtures enabling the calculation of π*, α and E_T30 polarity scale values, the latter in a good agreement with literature values. Similar trends of these parameters in AOT reversed micelles were found, but some deviations are observed at low water contents due to probe distribution at two different interfacial sites.