The design of light-absorbent dyes with cheaper, safer, and more sustainable materials is one of the key issues for the future development of dye-sensitized solar cells (DSSCs). We report herein a theoretical investigation on a series of polypyridyl Fe(II)-based complexes of FeL2(SCN)2, [FeL3]2+, [FeL′(SCN)3]-, [FeL′2]2+, and FeL′′(SCN)2 (L = 2,2′-bipyridyl-4,4′-dicarboxylic acid, L′ = 2,2′,2″-terpyridyl-4,4′,4″-tricarboxylic acid, L″ = 4,4？-dimethyl-2,2′？:？6′,2″？:6″,2？-quaterpyridyl-4′,4″-biscarboxylic acid) by density functional theory (DFT) and time-dependent DFT (TD-DFT). Molecular geometries, electronic structures, and optical absorption spectra are predicted in both the gas phase and methyl cyanide (MeCN) solution. Our results show that polypyridyl Fe(II)-based complexes display multitransition characters of Fe？→？polypyridine metal-to-ligand charge transfer and ligand-to-ligand charge transfer in the range of 350–800？nm. Structural optimizations by choosing different polypyridyl ancillary ligands lead to alterations of the molecular orbital energies, oscillator strength, and spectral response range. Compared with Ru(II) sensitizers, Fe(II)-based complexes show similar characteristics and improving trend of optical absorption spectra along with the introduction of different polypyridyl ancillary ligands. 1. Introduction Due to the features of low cost and high conversion efficiency, dye-sensitized solar cells (DSSCs) based on organic/inorganic hybrid materials have ？attracted extensive attention as an alternative to the conventional Si-based solar cells [1–3]. As crucial light-harvesting elements in DSSCs, the photoexcited sensitizers can inject electrons from their excited states into the semiconductor conduction band, and are recharged by an electrolyte to their initial states [4–6]. Early design of sensitizers had focused on transition metal coordinated complexes because of their unique richness of electronic properties for light absorption as well as photochemical and photophysical behaviors, especially for the photoredox activities [7]. These behaviors were originated from the nature of the coordinated complexes, involving the metal-to-ligand charge transfer (MLCT) character and intervening spin-orbit coupling attached to the presence of metal cations with large atomic numbers [7]. Metal coordinated complexes also facilitate the fine tuning of electronic properties by means of the proper choice of both polypyridyl ancillary ligands and metal cations. Up to now, polypyridyl Ru(II)-based complexes are proven to be the most efficient sensitizersReferences