CHARACTERISTIC CHANGES IN THE FLUORESCENCE-SPECTRA OF 1-NAPHTHOL AT THE GELATION POINT DURING THE SOL-GEL-XEROGEL TRANSITIONS

The fluorescence spectra of I-naphthol were observed during the sol-gel-xerogel transitions of two different systems as a function of time; one is in the silicon and titanium (Si:Ti = 4500:1) binary systems involving no catalysts and the silicon and lithium (Si:Li = 99:1) binary systems involving HCl as the catalyst. During the first stage of the sol-gel reaction of the l-naphthol system, the fluorescence spectra mainly originated from the broad (i)L(a) state. The fluorescence spectrum originating from the anionic species at around 470 nm increased as the reaction proceeded. It was found that the fluorescence spectra originating from the anionic species of l-naphthol drastically decreased in both systems just after gelation. These findings indicate that it becomes difficult for the dissociation of the excited state of I-naphthol to give a dissociative proton to the surrounding matrix. The fluorescence-excitation spectra for the Si/Ti system indicated that the main route for the excited state of I-naphthol to form a dissociative proton is through the excited state of the contact ion pair, while the main route in the Si/Li system is via the direct excitation of the neutral l-naphthol and its dissociation. The observed changes in the fluorescence spectra of l-naphthol in these sol-gel systems provide a sensitive means to monitor changes during the sol-gel transition process.