Synthesis, Photophysical, and Electrochemical Properties of RuII Polypyridyl Complexes Bridged with two Tetrapodal Symmetric and one Asymmetric Ligands

Two symmetric tetrapodal ligands L1–2 and one asymmetric tetrapodal ligand L3 based on 4,5-diazafluoren have been synthesized and characterized. Ligands L1–2 formed by the condensation of pentaerythrityl tetratosylate with 4,5-diazafluoren-9-oxime and 9-(4-hydroxy)phenylimino-4,5-diazafluorene, respectively. L3 was prepared by two steps, 9-(4-hydroxy)phenylimino-4,5-diazafluorene reacted with pentaerythrityl tetratosylate affording 1,1′,1"-tris[(4,5-diazafluoren-9-ylimino)phenoxymethyl]-1"′-(p-tosyloxymethyl)-methane, which reacted with 4,5-diazafluoren-9-oxime affording the asymmetric ligand L3. Three tetranuclear RuII complexes [(bpy)8L1–3Ru4](PF6)8 (bpy = bipyridine) were obtained by the reaction of Ru(bpy)2Cl2·2H2O with ligands L1–3. Spectroscopic studies of these complexes exhibit metal-to-ligand charge transfer absorptions at 440–445 nm and emissions at 575–579 nm. The electrochemical behaviors of these complexes are consistent with one RuII-based oxidation couple and three ligand-centered reduction couples.