An Apparent Angle Dependence for the Nonradiative Deactivation of Excited Triplet States of Sterically Constrained, Binuclear Ruthenium(II) Bis(2,2‘:6‘,2‘ ‘-terpyridine) Complexes

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 110; no. 32; pp. 9880 - 9886
• Main Authors: Benniston, Andrew C, Harriman, Anthony, Li, Peiyi, Patel, Pritesh V, Rostron, James P, Sams, Craig A
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.08.2006
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp061059g

The photophysical properties are reported for a series of binuclear ruthenium(II) bis(2,2‘:6‘,2”-terpyridine) complexes built around a geometrically constrained, biphenyl-based bridge. The luminescence quantum yield and lifetime increase progressively with decreasing temperature, but the derived rate constant for nonradiative decay of the lowest-energy triplet state depends on the length of a tethering strap attached at the 2,2‘-positions of the biphenyl unit. Since the length of the strap determines the dihedral angle for the central C−C bond, the rate of nonradiative decay shows a pronounced dependence on angle. The minimum rate of nonradiative decay occurs when the dihedral angle is 90°, but there is a maximum in the rate when the dihedral angle is about 45°. This effect does not appear to be related to the extent of electron delocalization at the triplet level but can be explained in terms of variable coupling with a low-frequency vibrational mode associated with the strapped biphenyl unit.