Perylene carboxylate-modified titanium–oxide gel, a functional material with photoswitchable fluorescence properties

Abstract

A gel matrix is an appropriate medium for photoswitchable fluorescent systems, because the gel provides a wet medium for the solvent-related fluorescence emission. Although some studies have been performed on the photoswitchable fluorescence properties of dye-entrapped organo- or inorgano-gels, the gels usually act just as a matrix. We report here a new soft hybrid material, in which the inorganic TiO gel is doped with perylene tetracarboxylate (PTC). The TiO gel not only acts as a wet matrix but, more importantly, also acts as the photoactive switch or shelter. The PTC–TiO solution in ethanol is prepared by solvothermal reaction at 60 °C and 80 °C, respectively. The solution exhibits different colors and different fluorescence emission according to the reaction temperature and time, due to the different assembly of the PTC dye molecules. The solution is then gelated by a typical method for TiO₂ gels, giving a material with photoswitchable fluorescence properties. The fluorescence of the perylene moiety can be switched off and on by irradiation and oxygen blowing. The photo-induced Ti(IV)/Ti(III) redox-chromic effect is the most reasonable explanation for the fluorescence emission and extinction, because Ti(III) is detected in the photo-blackened PTC–TiO gel.