Photosensitization of colloidal TiO 2 nanoparticles with phycocyanin pigment

Abstract

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 = 4.01 × 10 2 M −1) and fluorescence quenching data ( K app = 5.20 × 10 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 (Δ G 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.