Electronic structures and spectroscopic properties of rhenium (I) tricarbonyl photosensitizer: [Re(4,4′-(COOEt)2-2,2′-bpy)(CO)3py]PF6

The ground state and lowest triplet-state structures of [Re(4,4′-(COOEt)2-2,2′-bpy)(CO)3py]PF6 photosensitizer (bpy = bipyridine, py = pyridine) have been studied with density functional theory (DFT). Time-dependent density functional theory (TD-DFT) was carried out to predict the photophysical properties of the photosensitizer. The effects of the solvents were evaluated using the conductor-like polarizable continuum (CPCM) method in dichloromethane, chloroform, acetonitrile, acetone, ethanol and dimethylsulfoxide. The electronic transition energies computed with BLYP, MPWPW91, B3LYP and MPW1PW91 functionals are compared with the experimental spectra. Based on the calculated excited energies, the experimental absorption maximum is assigned as metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) mixed transition, and the luminescence originates from the lowest triplet state that is ascribed as the mixed transition of MLCT/LLCT.