title: Energy Transfer in Rigid Ru(II)/Os(II) Dinuclear Complexes with Biscyclometalating Bridging Ligands Containing a Variable Number of Phenylene Units.
abstract: We have prepared rodlike cyclometalated Ru(II)/Os(II) dinuclear complexes, (ttp)Ru(dpb-(ph)(n)()-dpb)Os(ttp)(2+), where the biscyclometalating bridging ligands contain dipyridylbenzene fragments, dbp, separated by a variable number, n, of phenylene spacers, and the terminal ligand is a terpyridine derivative [dpbH is di-2-pyridyl-1,3-benzene, ttp is 4'-p-tolyl-2,2':6',2"-terpyridine, and n = 0-2]. The rigid bridging ligands keep the metal centers at a distance r(MM) = 11, 15.5, and 20 Å, depending on n. Photoinduced energy transfer has been investigated by luminescence spectroscopy in nitrile solvents at room temperature and at 77 K (i.e., in frozen medium). According to a classical description of the process, the energy transfer occurs in a nearly activationless regime, is governed by electronic factors, and can be described in terms of the Dexter-type mechanism. The obtained energy transfer rates roughly span 3 orders of magnitude and indicate (i) that the temperature (i.e., the state of the solvent) has a small influence on the process and (ii) that the interposed phenylene spacers are weak attenuators of intercenter electronic coupling, H [H = H(0) exp(-betar(MM)), with beta approximately 0.33 Å(-)(1)].
authors.affiliation: Istituto FRAE-CNR, Via P. Gobetti 101, 40129 Bologna, Italy, Dipartimento Chimico "G. Ciamician", Università di Bologna, Via Selmi 2, 40126 Bologna, Italy, and Laboratoire de Chimie Organo-Minerale, Université Louis Pasteur, Faculté de Chimie, 1 rue Blaise Pascal, F-67008 Strasbourg, France.
authors.forename: Francesco
authors.initials: F
authors.lastname: Barigelletti
authors.forename: Lucia
authors.initials: L
authors.lastname: Flamigni
authors.forename: Massimo
authors.initials: M
authors.lastname: Guardigli
authors.forename: Alberto
authors.initials: A
authors.lastname: Juris
authors.forename: Marc
authors.initials: M
authors.lastname: Beley
authors.forename: Sandrine
authors.initials: S
authors.lastname: Chodorowski-Kimmes
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Collin
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Sauvage