Phosphorescence of Benzophenone in Sol-Gel Silica

The phosphorescence spectra of benzophenone (BP) were studied in tetramethoxysilane (TMOS) sol-gel systems at 77 K. The phosphorescence spectra ascribed to solvent-free benzophenone (f-BP), aggregated benzophenone (a-BP), and a benzophenone-water complex (w-BP) were observed in these systems. The results showed that the spectra varied with the BP concentration and sol-gel conditions, such as the water/TMOS ratios, catalyst, and the various sol-gel reaction stages. The w-BP phosphorescence lifetimes showed a single-exponential decay of 8 ms in sol systems and a double-exponential decay of 8-12 ins and 31 ms in xerogel systems. The longer lifetime component corresponds to a w-BP complex hydrogen bonded with silanol groups. These changes are discussed in terms of the sol-gel structure and surface adsorption effects.