Theoretical investigation on the electronic structures and spectroscopic properties as well as the features as dyes in dye-sensitized solar cells of quinonoid containing Re(I) complexes

A series of Re(I) model complexes with the bidentate N<^>O type ligand (N<^>O = 2,5-bis(4'-(isopropyl)anilino)-1,4-benzoquinone) involving quinone group, which are expressed as [Re-2(CO)(6)(N<^>O)L-2] (L = 4-dimethylaminopyridine) 1, [Re(CO)(3)(N<^>O) L] (L = 4-dimethylaminopyridine a1; 4-carboxylicpyridine a2; ethynyl b1; phenol b2), and [Re(CO)(2)(N<^>O) L] (L = 4,4'-dicarboxyl-2,2'-bipyridine (N<^>N)) c1, have been investigated by means of the density functional theory (DFT) in combination with time-dependent DFT (TDDFT) to explore their electronic structures and spectroscopic properties as well as the features as dyes in dye-sensitized solar cells (DSSCs). The geometry structure optimization results in the ground state at PBE1PBE/[LanL2DZ, 6-311G(d)] level revealed that Re(I) in all the model complexes exhibited the distorted octahedral coordination conformation. The frontier molecular orbitals of the complexes were effectively tuned on the energy level and energy gaps through introducing the ligands or ancillary group with different pi-donating ability. TD/DFT calculations uncovered that all the mononuclear complexes displayed absorptions and emissions both in the visible light region. The comprehensive results including ionization potential (IP) and electron affinity (EA) along with the reorganization energy (lambda) properties indicated that a2 and c1 had the advantage to act as the charge transfer material. The calculated light harvest efficiency (LHE) and the negative difference of free energy (-Delta G(inject)) value of similar to 0.5 and 0.7 eV, respectively for a2 and c1 suggested that the two complexes were promising candidates as dyes in DSSCs. (C) 2018 Elsevier B.V. All rights reserved.