Polarities of sol-gel-derived ormosils and of their interfaces with solvents

The effective polarities of a series of organically modified sol-gel silicas and of their interfaces were probed using the solvatochromic dye E_T(30) (2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate). The series of materials was obtained by copolymerizing, in various proportions, of methyltrimethoxy-, vinyltrimethoxy-, propyltrimethoxy-, isobutyltrimethoxy- and phenyltrimethoxysilanes with tetramethoxysilane. The various doped Ormosils are solvatochromic toward organic solvents such as various alcohols and toluene. Trends in the polarity variation as a function of the monomer type, of its proportion, and of the solvent at the interface were identified and are discussed. These materials can be used as solvent sensors.