Photochemistry and Photophysics of Bis(terpyridyl) Complexes of Ru(II) in Fluid Solution. Evidence for the Formation of an η2-Diphenylterpyridine Complex

Article abstract of DOI:10.1021/ja00291a009

The photochemical and photophysical properties of Ru(dpt)2(2+), where dpt denotes 6,6''-diphenyl-2,2':6',2''-terpyridine, are described.The absorption maximum occurs at 477 nm in CH2Cl2 and is ascribed to a metal-to-ligand charge-transfer band.Excitation at 477 nm yields little or no detectable emission in CH2Cl2 at room temperature or in a 4:1 EtOH/MeOH glass at 77 K.Upon irradiation in CH2Cl2 at 25 deg C with added SCN(1-), Ru(dpt)(2+) undergoes photoanation.The quantum yield for the reaction is (4.0+/-0.5)E-3.Several possible structures for the photoproduct are considered, and on the basis of the available data, it is formulated as Ru(dpt)(η²-dpt)(NCS)(1+).The photophysical properties of Ru(dpt)2(2+) are compared with other Ru(II) bis(terpyridyl) complexes, and we conclude that the extremly short lifetimes of these complexes can not be explained by solvent interactions with the metal center.A kinetic scheme is proposed in which nonradiative decay occurs via a d-d excited state which is prone to undergo ligand substitution processes.The model is used to explain the disparate behavior of three different complexes of Ru(II) involving terpyridine-based ligands.