The role of isomeric effects on the luminescence lifetimes and electrochemistry of oligothienyl-bridged dinuclear tris(2,2′-bipyridine)ruthenium(II) complexes

The luminescence lifetimes (in CH3CN at room temperature) and electrochemical potentials (in CH3CN) of a range of mono- and bis(bidentate) 2,2'-bipyridine-capped oligo-thiophene-bridged Run complexes based on the 6-(2-thienyl)-2,2'-bipyridine and 4-(2-thienyl)-2,2'-bipyridine motifs have been measured. The redox potentials occurred in a very narrow range and showed only small shifts from that of [Ru(bpy)(3)](2+), which indicates that the inductive effects of the substituents on the 2,2'-bipyridine ligands are very similar across this series. In the complexes that incorporated a bithiophene moiety the oxidation of the bithienyl group occurred at higher potentials than the metal-centered Ru-III/II oxidation. No or very weak interaction between the metal cores in the dinuclear complexes was observed. It was found that the luminescence lifetimes of the complexes where the attachment point of the oligothiophene bridge is in the 4-position of a 2,2'-bipyridine ligand were extended compared to [Ru(bPY)(3)](2+), whereas the luminescence was very short-lived (<30ns) or completely quenched in the complexes where the oligothiophene bridge was attached in the 6-position. The difference in lifetimes is probably due to steric interactions between the thienyl bridge and the auxiliary bipyridyl ligands, resulting in disturbances in coordination symmetry of the metal core. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)