Abstract
Hypocrellin B (HB), a natural pigment, when adsorbed on colloidal TiO 2 can participate in the sensitization process by injecting electrons from its excited singlet and triplet states into the conduction band of the semiconductor. Upon excitation in its absorption band, 80% of the fluorescence emission of HB could be quenched by colloidal TiO 2. Lifetime measurements and time-resolved absorption spectra gave the rate constant for the electron injection process from the excited singlet and triplet states of HB into the conduction band of the semiconductor as 6×10 8 and 1.3×10 6 s −1 , respectively. Analysis of the electron paramagnetic resonance spectra confirmed the generation of the cation radical of HB.
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