As shown in Fig. 1, absorption peak of adsorbed dye onto photoanode is broader than the absorption peak of Siahkooti dye extract with a shift to the higher wavelengths (a clear red shift of the absorption peak from 539 to 550 nm), which may indicate dye adsorption onto the TiO2 nanoparticles. This red shift in the absorption maxima would also directly reflect the attachment of dye molecules to the surface of TiO2, and may increase the absorption of light by the TiO2 nanoparticles in the visible region due to the binding of anthocyanins present in the dye extract to the oxide surface [23]. The presence of carbonyl and hydroxyl groups in the anthocyanin molecules (Fig. 2), bound to the surface of TiO2 porous film, is in favor to facilitate the photoelectric conversion effect [17].