The effects of pendant vs. fused thiophene attachment upon the luminescence lifetimes and electrochemistry of tris(2,2′-bipyridine)ruthenium(II) complexes

The electrochemical and photophysical properties for a range of tris(2,2'-bipyridine)ruthenium(II) complexes in which a thiophene substituent is attached to one of the bipyridine ligands by either a pendant or a fused mode have been determined. The fused mode of attachment eliminates torsional movement between the thiophene unit and the chelating bipyridine, thereby offering optimal overlap between the pi-systems of the chelating unit and the attached thiophene unit. The electrochemical properties of these complexes were found to be similar; however, the luminescence lifetimes and intensities (in CH3CN at room temperature) were found to be correlated to the mode of attachment. The longest luminescence lifetime was observed for the complex [Ru(bPy)(2)(4-(thiophen-2-yl)-2,2'-bipyridinel](2+) (3000 ns), as compared to the prototypic [Ru(bpy)(3)](2+), (1745 ns). This complex also had the highest quantum yield (0.045). In the four isomeric complexes, where the thiophene ring was fused to the b or c face of the pyridine ring, the lifetimes fell in the interval 2751510 ns, and the quantum yield ranged between 0.0047 and 0.014. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).