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Proton transfer from the excited state of 8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt to surrounding water molecules is used as a sensitive fluorimetric method for following directly and in detail the kinetics of water consumption during the early stages of teh tetramethylorthosilicate sol-gel polymerization process. Changes in water/silane ratio and in pH were found to affect markedly the kinetic behavior of water consumption.

We report the use of photophysical probes for studying the sol/gel transition of silicon tetra-alkoxide undergoing hydrolysis and condensation-polymerization, for studying the properties of the final silica gel glass, and for studying the formation of reversed-phase organic silica gel glasses during hydrolysis of phenyl and ethyl trimethoxysilanes. Pyrene fluorescence and excimerization process were used to probe, stage by stage, the dynamics of the structural changes that occur during the sol to wet gel to dry gel transitions and to probe the effects of parameter changes such as pH, water/silane ratio and alkoxy groups. Unlike adsorption on silica surfaces, pyrene trapped in the silica glass shows monomeric emission only. Structural oscillations are observed upon addition of surface active agent. To the best of our knowledge, this is the first far-from-equilibrium dissipative structure, in which a polymeric system oscillates. We also report the uses of the final gel glass as a novel room-temperature trap of organic molecules. The possibility to trap an organic molecule in inorganic glass opens many new opportunities and applications, two of which are reported: (a) Room temperature phosphorescence is obtained for a number of molecules, e.g., pyrene. (b) The first organic-dye (spiropyrane)/inorganic glass (SiO2) photochromic material is described.

It is unnecessary to add alcohol to a polymerizing silicon tetramethoxide-H2O sol-gel system as a co-solvent. The alcohol released during the reaction is sufficient to convert the initially biphasic system into a homogeneous one, resulting in the usual highly transparent, porous xerogel. We suggest that the alcohol-free sol-gel system may replace in many cases the traditional H2O-alcohol-alkoxide system