Probing the Sol-Gel Conversion in the Tetraethoxysilane/Alcohol/Water System with the Aid of Diffusion-Controlled Fluorescence Quenching

The sol-gel conversion in the tetraethoxysilane/alcohol/water system can be probed by means of the diffusion-controlled fluorescence quenching of Py* by Cu2+ ions. In the course of tetraethoxysilane hydrolysis, the viscosity of the system increases, thereby causing the quenching rate to decrease and the mean lifetime of the excited state to elongate dramatically as the system approaches the gel-point. Incorporating the equation proposed by Vogelsberger et al. (1992) for the time-dependence of the viscosity of gelating systems into the Smoluchowsky kinetic equation, an equation has been proposed to describe the observed time-dependence of the Py* lifetime. Copyright 1997 Academic Press. Copyright 1997Academic Press