Influences of Acid on Molecular Forms of Fluorescein and Photoinduced Electron Transfer in Fluorescein‐Dispersing Sol–Gel Titania Films

Abstract

Fluorescein-dispersing titania gel films were prepared by the acid-catalyzed sol−gel reaction using a titanium alkoxide solution containing fluorescein.The molecular forms of fluorescein in the films, depending on its acid-base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate-like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e., the dye-titania complex.This result indicated that the dianion form was the most favorable for formation of the dyetitania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye-titania complex formation played an important role in the electron injection from the dye to the titania conduction band.

Interaction between dye and zinc in the dye-dispersing ZnO films prepared by a wet process

“…This result indicated that the interaction between some acetate and zinc was enhanced by the hot water molecules although most of the acetate evaporated [20,24,26]. Acetate existing between the zinc hydroxide interlayers was difficult to remove.…”

“…The values slightly changed after the 60-min treatment, although they decreased to lower than one-third in the previous titania system [20,26]. The peaks were shifted in the longer wavelength direction by the steam treatment, indicating the possibility of the dye-zinc complex formation.…”

“…The steam treatment enhanced the fluorescein dye-titania surface complex formation in our previous study [20,24,26]. However, eosin Y weakly interacted with the titanium species even after steam treatment, because the oxygen atoms of its carboxyl and quinone-like groups are less nucleophilic than those of fluorescein and more difficult to form the coordination complex with metal species [20,23].…”

“…Xanthene dyes as laser dyes are available materials for utilizing photoenergy due to their high absorption and fluorescence efficiencies in various visible light regions [32]. It was reported that the hydrothermal treatment of a dye-dispersing amorphous titania film remarkably improved the photoelectric conversion efficiency due to not only its crystallization but also the dye-titanium complex formation [20][21][22][23][24][25][26][27][28][29][30][31].…”

“…The organic dye-dispersing titania gel is suited for the dye-titania complex formation because the dye molecules with carbonyl and/or carboxyl groups are encapsulated in the narrow spaces of the gel [20][21][22][23][24][25][26]. The xanthene dye-dispersing titania gel was prepared without heating from a titanium alkoxide sol containing the dye molecules by the sol-gel method [27][28][29][30][31].…”