Novel Ru(Ii)/Os(Ii)-Exchange Homo- And Heterometallic Polypyridyl Complexes With Effective Energy Transfer

Two novel homometallic Ru-Ru and heterometallic Ru-Os dimers and trimers, [M-II(bpy)(2)(4-tpy-4 '-methyl-2,2 '-bipyridine)M-II(tpy)](4+) and [M-II(bpy)(2)](4-tpy-4 '-tpy-2,2 '-bipyridine)(M-II(tpy))(2)](6+), have been first prepared and characterized. Electrochemical properties of the metal-based reversible oxidation and ligand-based reduction are measured. Spectroscopic analysis of these complexes exhibits for every Ru- or Os-based subunit an individual intense absorption spectrum extended over the entire UV and visible region. The heteronuclear complexes [Ru-II(bpy)(2)(4-tpy-4 '-methyl-2,2 '-bipyridine)Os-II(tpy)](4+), [Ru-II(bpy)(2)](4-tpy-4 '-tpy-2,2 '-bipyridine)(Os-II(tpy))(2)](6+), and [Os-II(bpy)(2)](4-tpy-4 '-tpy-2,2 '-bipyridine)(Ru-II(tpy))(2)](6+) display a weak emission spectrum in the near-infrared region (NIR). The luminescence of the polynuclear assemblies is quantitatively quenched, by intramolecular energy transfer to the lower-lying metal-to-ligand charge transfer ((MLCT)-M-3) and metal-centered ((MC)-M-3) state of the Os(II)-based center or Ru(II)-terpyridine moiety at room temperature.