Synthesis and study of the light absorbing, redox and photophysical properties of Ru(II) and Os(II) complexes of 4,7-diphenyl-1,10-phenanthroline containing the polyazine bridging ligand 2,3-bis(2-pyridyl)pyrazine

Abstract

Monometallic light absorbing complexes of the form [(Ph 2phen) 2M(dpp)] 2+ (M = Os(II) or Ru(II), Ph 2phen = 4,7-diphenyl-1,10-phenanthroline, dpp = 2,3-bis(2-pyridyl)pyrazine) have been synthesized. The coupling of Ph 2phen to Ru and Os complexes with polyazine bridging ligands will allow for the incorporation of these chromophores into supramolecular assemblies. The spectroscopic, redox and photochemical properties were studied. The complexes exhibit overlapping 1MLCT (metal-to-ligand charge transfer) transitions in their electronic absorbance spectroscopy with lowest energy peaks at 444 nm and 494 nm for [(Ph 2phen) 2Ru(dpp)] 2+ and [(Ph 2phen) 2Os(dpp)] 2+, respectively. An intense 3MLCT absorption for the Os complex centered at ca. 650 nm is also observed. The redox properties show significantly different reversible one electron metal oxidations, E 1 / 2 ox = 1.39 V and 1.02 V vs. Ag/AgCl for the Ru and Os complexes, respectively. Each complex displays three reversible reductions based on each polyazine ligand. The photophysical properties show strong 3MLCT emissions centered at 697 and 800 nm for the Ru and Os complexes, respectively.