Theoretical study on excited state structures and charge transfer characteristics of 2,2′-bipyridine, pyridine-imidazole ligands and their complexes

The excited state structures and charge transfer characteristics of 2,2'-bipyridine and the compounds with 2-pyridine group have been investigated for designing novel luminescent materials. All systems possess quinoid form in the excited states. Because the strong intramolecular charge transfer leads to the electrostatic interaction, the quinoid form characteristics of pyridine-imidazole is more obvious. The characteristics of bond length alternation are relative to the magnitude of charge transfer. The charge transition, which plays an important role in spectroscopic property, mainly originates from the ligand for both the free ligands and the complexes. Metal atom limits the change of geometry of complex and increases the luminescent intensity.