Electron transfer in colloidal TiO 2 semiconductors sensitized by hypocrellin A

Abstract

The electron transfer from singlet states of hypocrellin A (HA) to colloidal TiO 2 nanometer-sized particles has been examined by absorption, fluorescence quenching, fluorescence lifetime measurements, laser flash photolysis and pulse radiolysis techniques. Adsorption of HA onto the surface of TiO 2 particles extended its absorption spectrum further into the visible region, and the apparent association constant ( K app) for the association between HA and colloidal TiO 2 was 3600 (mol/l) −1 determined by fluorescence quenching method. Fluorescence lifetime measurement was used to elucidate the process of electron transfer from the singlet state of HA to conduction band of TiO 2 ( K et=4.26×10 9 s −1). Laser flash photolysis and pulse radiolysis studies demonstrated formation of the radical cation of HA.