Theoretical studies of natural pigments relevant to dye-sensitized solar cells

As dye-sensitizers in DSSCs, natural cyanidin, crocetin and phycocyanobilin have been studied using density functional theory (DFT) at the B3LYP/6-31G(d) and B3LYP/6-31+G(d) levels. Ground state geometries, electronic transition energies and oxidation potentials are reported. The HOMO → LUMO transition describes all lowest singlet excited states. The ground state oxidation potentials are calculated to be 0.86 V, 1.72 V and 1.14 V (vs. a normal hydrogen electrode, NHE), respectively, and the excited state oxidation potentials are −1.86 V, −2.6 V and −1.6 V (vs. NHE), respectively. Deprotonation order is determined by calculating proton affinities at different sites.