The fluorescence spectra of 9-anthrol during the sol−gel−xerogel transitions of 13 systems containing different silicon and aluminum ratios and catalysts have been observed at a constant temperature (300 K) as a function of the sol−gel reaction time. Fluorescence decay curves for typical xerogel samples also have been observed. 9-Anthrol in the sol−gel systems showed four different fluorescence bands originating from the hydrogen-bonded, the complex, the ion pair, and the anion form species. Continuous light irradiation of the xerogels at 360 nm led to an increase in the fluorescence at 480 nm. These findings indicate that anthrone transforms to 9-anthrol by the photoinduced intermolecular proton transfer in these matrixes. The most effective and remarkable tautomerization occurred in the Si:Al = 90:10 system, and it was concluded that this photochromic behavior occurs by the photoinduced proton transfer from a proton at the surface Brønsted acid site on the −O−Si−O−Al−O− network to the anthrone molecule.

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The fluorescence and fluorescence-excitation spectra of 1-naphthol during sol to gel to xerogel transitions of a mixed solution comprising silicon and aluminum alkoxides (Si : Al = 94 : 6) catalyzed by a small amount of NaOH aqueous solution have been observed as a function of time. During the reaction of the system, the spectrum shifted to the red in the first stage and shifted to the blue in the next stage. This behavior reflects the changes of polarity and microviscosity of the matrix surrounding the doped 1-naphthol molecules during the sol to gel to xerogel transitions of the mixed metal alkoxide. The gelation occurred at 10 d. On the other hand, the most remarkable red-shift in the fluorescence spectrum was observed at 9 d. Comparing the fluorescence and fluorescence-excitation spectra of 1-naphthol in typical solvents with those of the sol–gel process, it has become apparent that a part of the doped 1-naphthol molecules in the ground state form a contact ion pair on the surface in cages of the prepared gel.

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