Spectroscopic characterization of porphyrin-doped sol-gel-derived matrices

Absorption and fluorescence spectra were measured for metal free (HTSPP) an d zinc (ZnTSPP) sulfonated porphyrins in SiO2 and TiO2 matrices produced by the sol-gel technique. These are compared to correspondent data obtained f or the two porphyrins in ethanol at different pH values. In the silica medi um (acidic), HTSPP is diprotonated and forms aggregates. This effect is fou nd to be reversed on exposure to ammonia vapor and occurs to a much lower d egree in titania matrices. This is possibly because of the smaller amount o f solvent retained in the pore structure. The main effect of incorporating ZnTSPP in sol-gel-derived matrices is demetallation, although to a lesser e xtent than in acidic solution.