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 π‐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′‐bipyridine}]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 275–1510 ns, and the quantum yield ranged between 0.0047 and 0.014. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)