Photosensitization of colloidal TiO2 nanoparticles with phycocyanin pigment.

Bluish phycocyanin is a water soluble pigment having strong visible light absorption at 615 nm. The dynamics of photoinduced electron injection from phycocyanin to colloidal TiO(2) nanoparticles has been studied by absorption, FT-IR, steady state and time-resolved fluorescence spectroscopic methods. The phycocyanin adsorbed on the surface of colloidal TiO(2) nanoparticles, the apparent association constant (K(app)) for the association between colloidal TiO(2) nanoparticles and phycocyanin was measured from both absorption changes (K(app)=4.01x10(2) M(-1)) and fluorescence quenching data (K(app)=5.20x10(2) M(-1)). The value of K(app) obtained from the data of fluorescence quenching matches with that determined from the absorption spectral changes. The good agreement between these values of K(app) highlighted the validity of assumption proposed for the association between phycocyanin and colloidal TiO(2) nanoparticles. The free energy change (DeltaG(et)) for electron injection has been calculated by applying Rehm-Weller equation. Electron injection from excited state phycocyanin into the conduction band of TiO(2) is suggested.