Photoprocesses of molecules encapsulated in porous solids XI: Excited state dynamics of proflavine and photosensitization of TiO2 in nanoporous materials

Abstract

Photosensitization of titanium dioxide (TiO2) encapsulated in the nanoporous materials of different pore size using proflavine dye as the sensitizer was studied using steady state and time resolved fluorescence spectral techniques. The titanium dioxide encapsulated nanoporous materials was prepared by ion exchange method and were characterized by UV–visible diffuse reflectance spectra, ICP-OES, BET and powder XRD techniques. The observed results show that TiO2 were encapsulated in the nanochannels and nanocavities of the host materials. The photophysical properties of proflavine are found to be influenced by the pore size and the Si/Al ratio of the host materials. Photosensitization of TiO2 in the host by proflavine was inferred from the decreased stead state fluorescence intensity of the dye molecule. In the case of the dye encapsulated TiO2 loaded ZSM-5, fluorescence intensity decreases with red shifted emission maximum. Excitation of proflavine in presence of TiO2 nanoparticles leads to protonation of proflavine in the excited state as confirmed in ultrafast time resolved fluorescence and decay associated spectral studies. On the other hand, no protonated proflavine was detected when zeolite-Y and MCM-41 were used as the host material.