Anthocyanins from various plants give different sensitizing performances [23]. Siahkooti dye extract shows an absorption in the wavelength range 450–600 nm, so it can be considered as an efficient sensitizer for wide band gap semiconductors. The exhibited absorption peak around 539 nm in visible region may be due to the absorption of anthocyanin pigments (Fig. 1a). After the immersion of the TiO2-coated electrode (photoanode) in the Siahkooti extract, observable color of TiO2 film turned to deep purple by the natural dye. Fig. 1b shows the UV–Vis absorption peaks of natural dye adsorbed onto TiO2 film which is located at 550 nm.