Photoelectrochemistry in colloidal systems: Interfacial electron transfer between colloidal TiO 2 and thionine in acetonitrile

Abstract

When adsorbed on a colloidal TiO 2 semiconductor suspension, the thiazine dye thionine exhibited a red shift in its absorption and emission spectra. The apparent association constant for the association of TiO 2 colloid and thionine in acetonitrile was determined to be 2.75 × 10 5 M −1. Reversible photoelectrochemical reduction of thionine was observed when the colloidal TiO 2 suspension in acetonitrile containing thionine was subjected to band gap illumination (λ < 380 nm). The interfacial electron transfer between colloidal TiO 2 and thionine in acetonitrile was investigated by means of steady photolysis and nanosecond laser flash photolysis techniques. The quantum yield for the photoelectrochemical reduction of thionine to semithionine was determined to be 0.1. The dependence of the photoelectrochemical production of semithionine on thionine concentration, the acidity of the medium and the intensity of excitation was examined.