Electron Transfer Process in Fluorescein-Dispersing Titania Gel Films Observed by Time-Resolved Fluorescence Spectroscopy

Transient absorption spectroscopy is generally used to study the photoinduced electron transfer process in the dye–titania systems. Time-resolved fluorescence spectroscopy is more sensitive than transient absorption spectroscopy. Fluorescein-dispersing titania gel films were prepared by a sol–gel process and steam treatment using a titanium alkoxide solution containing fluorescein. The photoinduced electron transfer process in the films was investigated by steady state and time-resolved fluorescence measurements. The fluorescence quenching efficiency increased with an increase in the steam treatment time due to the dye–titania complex formation. The titanium species were coordinated to the carboxylate of the fluorescein species during the steam treatment based on an FTIR analysis. The dye–titania complex formation played an important role in the electron injection from the dye to the titania conduction band.