Computational Studies on the Electronic Structures and Absorption Spectra of Cu-based Dye Sensitizer

We studied the description of charge-transfer excitations in [CuL₂]⁺ (L=6,6′-dimethyl-2,2′-bipyridine-4,4′-bis(propenoic acid)) dye sensitizer. This dye was studied using density functional theory (DFT), and the electronic absorption spectrum was investigated via time-dependent DFT (TD-DFT) with several hybrid functional, both in the gas phase and in acetonitrile solution. We also have investigated HOMO and LUMO levels in gas and solvent phases for these dyes. The HOMOLUMO transition describes all lowest singlet excited states. We performed TDDFT calculations at the B3LYP/6-31G(d) level of theory. Solvation effects were included by the conductor-like polarizable continuum model (CPCM ). The excitation in the range 500-800 nm of absorption spectra confirms metal-to-ligand charge-transfer (MLCT) transitions. The results of this work suggest that the copper complexes are effective as sensitizers for DSSCs and they can replace ruthenium (II) complexes.