Electron transfer in colloidal TiO2 semiconductors sensitized by hypocrellin A

The electron transfer from singlet states of hypocrellin A (HA) to colloidal TiO2 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 TiO2 particles extended its absorption spectrum further into the visible region, and the apparent association constant (K-app) for the association between HA and colloidal TiO2 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 TiO2 (K-et = 4.26 X 10(9) s(-1)). Laser flash photolysis and pulse radiolysis studies demonstrated formation of the radical cation of HA. (C) 2002 Elsevier Science Ltd. All rights reserved.