Fluorescence quenching of meso-tetrakis (4-sulfonatophenyl) porphyrin by colloidal TiO2

A stable colloidal TiO2 has been prepared. The interaction of meso-tetrakis (4-sulfonatophenyl) porphyrin (TSPP) with colloidal TiO2 was studied by absorption and fluorescence spectroscopy. Upon excitation of its absorption band, the fluorescence emission of TSPP was quenched by colloidal TiO2. The bimolecular quenching rate constant (kq) is 1.78 × 1011 M−1 s−1. The porphyrin can participate in the quenching process by injecting electrons from its excited states into the conduction band of TiO2. The quenching mechanism is discussed on the basis of the quenching rate constant as well as the reduction potential of the colloidal TiO2. Rehm-Weller equation was applied for the calculation of free energy change (ΔGet).