DFT study of the effect of different metals on structures and electronic spectra of some organic-metal compounds as sensitizing dyes

Ruthenium polypyridined-derivative complexes are used in dye-sensitized solar cell DSSC] as a light to current conversion sensitizer. In order to lower the cost of the DSSC the normal transition metals were used to replace the noble metal ruthenium, and some compounds ML₂L′] (M = Pt, Fe, Ni, Zn; L = isonicotinic acid, L′ = maleonitriledithiolate, I = PtL₂L′, II = FeL₂L′, III = NiL₂L′, IV = ZnL₂L′) were selected as the replacement. The geometries, electronic structures and optical absorption spectra of these compounds have been studied by using density functional theory (DFT) calculation at the B3LYP/LANL2DZ, B3P86/LANL2DZ, B3LYP/GEN level of theory. All the geometric parameters are close to the experimental values. The HOMOs are mainly on the maleonitriledithiolate groups mixed with fewer characters of the metal atom, the LUMOs are mainly on the two pyridine ligands. This means that the electron transition is attributed to the LLCT. The maximum absorptions of complexes are found to be at 351 nm, 806 nm for compound I, and 542 nm for compound II. The maximum absorptions of complexes are found to be at 884 nm for compound III, and 560 nm for compound IV. This means that those compounds may be as a suitable sensitizer for solar energy conversion applications.