Intramolecular Energy Transfer in Covalently Linked Polypyridine Ruthenium(II)/Osmium(II) Binuclear Complexes. Ru(II)(bpy)2Mebpy(CH2)n-MebpyOs(II)(bpy)2 (n=2, 3, 5, and 7)

Article abstract of DOI:10.1246/bcsj.64.1632

A novel series of polymethylene-linked heterobinuclear complexes of polypyridine ruthenium(II)/osmium(II) complex Ru(II)(bpy)2Mebpy-(CH2)n-MebpyOs(II)(bpy)2(bpy=2,2'-bipyridine and N=2, 3, 5, and 7), 1, was prepared.The photophysical behavior was examined in various solvents.The emission spectra of 1 (excitation wavelength: 455 nm) showed a nearly complete quenching of Ru(II) -> ?^*(bpy) metal-to-ligand charge transfer (MLCT) emission and the enhancement of Os(II) -> ?^*(bpy) MLCT emission.The luminescence lifetime measurements by a time-correlated single photon-counting method provided evidence that intramolecular energy transfer is a significant pathway for the observed emission quenching.The rate constants of the intramolecular energy transfer in ethanol are 5.3 * 10⁸, 3.3 * 10⁸, 1.3 * 10⁸, and 1.0 * 10⁸ s^-1 for 1 (n=2, 3, 5, and 7), respectively.They were found to be proportional to the inverse sixth power on the center-to-center distance of the two complexes.The mechanisms is discussed in terms of the Foerster (a dipole-dipole interaction) mechanism.