Photosensitization of TiO2 colloid by hypocrellin B in ethanol

Hypocrellin B (HB), a natural pigment, when adsorbed on colloidal TiO2 can participate in the sensitization process by injecting electrons from its ex cited singlet and triplet states into the conduction band of the semiconduc tor. Upon excitation in its absorption band, 80% of the fluorescence emissi on of HB could be quenched by colloidal TiO2. Lifetime measurements and tim e-resolved absorption spectra gave the rate constant for the electron injec tion process from the excited singlet and triplet states of HE into the con duction band of the semiconductor as 6 x 10(8) and 1.3 x 10(6) s(-1), respe ctively. Analysis of the electron paramagnetic resonance spectra confirmed the generation of the cation radical of HE. (C) 2000 Elsevier Science B.V. All rights reserved.