Xanthene dye molecules form a chelate complex with the titanium species on the titania surface in dye−titania systems. The complex formation causes a fast electron injection into the titania conduction band. In this study, simple spectroscopic and photocurrent measurements of the xanthene dye-doped titania gels prepared by the sol−gel method were conducted in order to clarify the influence of a steam treatment on the dye−titania interaction and electron transfer. The photocurrent quantum efficiency of the fluorescein-doped electrode was remarkably increased by the steam treatment compared to that of the untreated electrode consisting of an amorphous titania gel. The photocurrent action spectrum was red-shifted, and the short circuit photocurrent and open circuit voltage values increased with the steam treatment time. The steam treatment promoted the dye−titania complex formation, a negative shift in the conduction band potential of the titania, and the electron injection from the dye to the titania.

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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.

Thin sol-gel films including rhodamine B (RB) which were dip-coated using the sol-gel reaction of tetraethyl orthosilicate have been prepared as a function of time after mixing of the reaction systems. The absorption and fluorescence spectra of the individual thin films have been observed as a function of time after the preparation of the individual thin films. The relative contribution of the monomer, H-dimer, and J-dimer of RB existing in the individual thin films to the total absorption and fluorescence spectra of the individual samples was obtained as a function of time. RB molecules were encapsulated in a certain structural region (prestructure of the pores) long before the gelation point. With the progress of the sol-gel reaction, dimerization in the prepared film was gradually prevented, and the monomer RB became the preferential species. On the other hand, dimerization of RB in the thin film was pronounced just after dip-coating until the SiO 2 network was almost formed, and the dimerization was enhanced progressively with the time course of the reaction under a specific reaction condition. Water plays an important role in the dimerization process.

Thin titania gel films containing well-dispersed fluorescein dye were prepared by the sol−gel method and treated with steam to promote crystal growth of the titania particles. It is known that steam treatment converts the titania structure from amorphousness to crystalline. In the present study, such change is found to increase the rate of the photoinduced electron transfer from and to dispersed fluorescein dye molecules.