Electronic structures and spectral properties of rhenium (I) tricarbonyl cyclopenta[b]dipyridine complexes containing different aromatic ring groups

The ground geometries, frontier molecular orbitals, and absorption properties of [Re(CO)3(cpen-dpy)Cl] (cpen-dpy = cyclopenta[b]dipyridine) functionalized with different aromatic ring groups were theoretically studied. The introduction of different moieties insignificantly changed the geometric parameters of the complexes. However, the molecular orbital energy levels of the complexes with aromatic ring groups were strongly affected by the solvent molecules. The lowest lying absorption bands of all complexes had HOMO → LUMO transition configurations that resulted in the ligand-to-ligand charge transfer character. The results showed that all complexes displayed a comparative higher sensitivity within the long wavelength range with stronger oscillator strength, which can be beneficial to more efficient absorption of the solar spectrum. The calculated ionization potential and electron affinity revealed that the balanced transport of electrons and holes of 1 was more accessible, whereas 4 possessed good hole-transfer abilities.