Dimerization of xanthene dyes in sol–gel titania films

Abstract

Dye-dispersing titania gel films were prepared by the sol−gel method using the titanium alkoxide solutions containing the xanthene dyes; i.e., fluorescein, eosin Y, rhodamine 110, and rhodamine 123.Dimerization of the xanthene dyes in the films, depending on their concentrations, and their photoinduced electron transfer processes to the titania gels were investigated by spectroscopic and photoelectric techniques. The dye having a higher dimerization constant in solution formed a higher amount of the dimer in the titania gel.There was only a slight difference between the photoelectric conversion efficiencies of the monomer and dimer. The titanium species were coordinated to the carboxylate of the dyes.The dimers as well as the monomers were encapsulated in the narrow spaces of the gel films and strongly interacted with the surrounding titania matrix in the dye-dispersing titania gel films. The dye having a more nucleophilic carboxylate oxygen was easier to form the coordination complex with the titanium species. The dye-titania interaction played an important role in the 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

“…In our previous study, such shift was also observed in the fluorescein-dispersing titania due to the fluorescein-titania complex formation [20,24], whereas eosin Y weakly interacted with the titanium species due to its lower electron affinity than zinc [20,23,39].…”

“…The compounds in such materials exhibit a more efficient light harvesting and fluorescence because they are finely dispersed in the amorphous or nanosized crystalline matrices compared to the conventional dye-adsorbing materials [20][21][22][23]. Therefore, it is expected that such films exhibit a higher function, stability, and performance in various applications.…”

“…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].…”

“…Eosin Y, one of the xanthene dyes, was used as the photosensitizer. This dye can more strongly interact with the zinc species although it weakly interacted with the titanium species in a previous study [20,23]. The photoinduced electron transfer and transport properties of the dye-dispersing ZnO precursor films were investigated by spectroscopic and electrochemical measurements in order to evaluate the electronic interaction between the dye and zinc compared to the dye-dispersing titania systems.…”

“…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].…”