This is ascribed to the particular anthocyanin contained in each three natural dyes with their corresponding chemical structures cyaniding, aurantinidin and rosinidin respectively as shown in Fig. 3. The slight difference in the absorption kmax of the three natural dyes is due to the positioning and the number of the hydroxyl group. Carbonyl and hydroxyl groups in the anthocyanin molecule make the electron transfer through binding to the surface of a porous TiO2 film