Electrochemistry and spectroelectrochemistry of polypyridine ligands: A theoretical approach

The 2,3-bis(2′-pyridyl)pyrazine (2,3-dpp) and 2,5-bis(2′-pyridyl)pyrazine (2,5-dpp) have been successfully used as bridging ligands for building up ruthenium (II) and osmium (II) polypyridyl redox and luminescent active dendrimers. Such ligands have been herein investigated by ab initio and DFT theoretical calculations both in gas phase and with the solvent effect. The different molecular conformations exhibited by 2,3-dpp, which depend on whether it is free or coordinated to one or two metal centres, have been explored by performing the scan of the potential energy surface. The spectra of the neutral and the radical anion species of the relevant conformers have been calculated at DFT and semiempirical level of the theory. The results have been assessed by correlating them with electrochemical and UV-Vis-NIR spectroelectrochemical experimental ones, obtained in highly aprotic and dry conditions.