The study of the electronic structure and optical properties of natural pigments using state of the art time-dependent first-principles calculations is presented to highlight their usefulness for photo electrochemical devices. Ground state geometries, UV-vis spectra and photovoltaic properties are reported. In the family of chosen anthocyanidins, it is observed that the frontier molecular orbitals (FMOs) are mainly localized over the whole molecule with exceptions noted for Delphinidin and Petunidin, while in the anthocyanins all the FMOs are localized over the three rings of the molecule, without any contribution of the glycoside motifs. Conversely, the interaction between Cyanidin and Cyanidin 3,5-diglucoside with TiO2 as the semiconductor in its cluster and surface form was also studied using periodic density functional calculations for suitable supercell models representing the systems of interest. For the Cyanidin 3,5-diglucoside/TiO2 system the results showed that its highest occupied molecular orbital (HOMO) is located in the TiO2 bandgap and its lowest unoccupied molecular orbital (LUMO) is close to the TiO2 conduction band minimum (CB) leading to greatly enhanced visible light absorption. (C) 2016 Elsevier Ltd. All rights reserved.