Preparation, photophysical, and electrochemical properties of two tetranuclear ruthenium(II) polypyridyl complexes containing 4,5-diazafluorene

Abstract

Two tetrapodal ligands L1 and L2 containing 4,5-diazafluorene units have been synthesized and characterized. Both ligands are composed of two kinds of nonequivalent coordinating sites: one involves the 4-(4,5-diazafluoren-9-ylimino)phenoxy moiety, and the other one involves the 2-(4,5-diazafluoren-9-ylimino)phenoxy moiety. The Ru(II) complexes [(bpy)8Ru4(L1)](PF6)8 and [(bpy)8Ru4(L2)](PF6)8 (bpy = 2,2′-bipyridine) have been obtained by refluxing Ru(bpy)2Cl2·2H2O and each ligand in 2-methoxyethanol. Both complexes exhibit metal-to-ligand charge transfer (MLCT) absorptions at around 443 nm and emission at around 574 nm. Electrochemical studies of both complexes display one Ru(II)-centered oxidation at around 1.33 V and three ligand-centered reductions.