Arylamine-Modified Thiazoles as Donor-Acceptor Dyes: Quantum Chemical Evaluation of the Charge-Transfer Process and Testing as Ligands in Ruthenium(II) Complexes

A series of new 4-hydroxy-1,3-thiazole-based chromophores bearing different arylamine components (triarylamines, carbazole, and phenothiazine) as electron donors and azaheterocycle components (pyridine, pyrazine and pyrimidine) as electron-acceptor moieties have been synthesized. Elaborate quantum chemical calculations were carried out with two selected compounds to identify the natures of the HOMO/LUMO transition and of the intramolecular charge-transfer state. The electrochemical properties were investigated: the dyes show reversible first oxidation and reduction peaks, with the former strongly dominated by the type of arylamine. The donor moieties were synthesized under BuchwaldHartwig conditions. Several of the presented X-ray structures provide deeper insight into the geometries of the ligands. The bidentate nature of the chromophores makes them suitable as ligands in transition metal complexes. The corresponding ruthenium(II) polypyridine complexes Ru(dmbpy)2(L)(PF6)2 (dmbpy = 4,4'-dimethyl-2,2'-bipyridine) were successfully synthesized for seven of the ligands. The MLCT bands in these complexes are significantly broadened, resulting in improved light-harvesting efficiencies.