In Search of Ruthenium(II) Complexes Based on Tridentate Polypyridine Ligands that Feature Long-lived Room-Temperature Luminescence: The Multichromophore Approach

摘要

Within the field of inorganic photochemistry, there is considerable interest in the design of ruthenium(II) complexes based on tridentate ligands that exhibit long-lived metal-to-ligand charge-transfer (MLCT) excited states.~[1] Indeed, ruthenium(II) polypyridyl complexes play outstanding roles in fields connected to solar-energy conversion and the storage of light and/or electronic information at the molecular level.~[2] The prototype of this class of compounds, [Ru(bpy)_3]~[2] (bpy=2,2'-bipyridine), has been one of the most studied metal-containing species in the last two decades.~[2a,3] However, its homologous compound [Ru(tpy)_2]~(2+) for several reasons: 1) [Ru(bpy)_3]~(2+) is a mixture of DELTA and LAMBDA enantiomers; 2) monosubstitution of bpy ligands introduces fac and mer isomerism, so that polynuclear arrays based on the [Ru(bpy)_3]~(2+) motif are rarely pure species; 3) a linear arrangemetn of such [Ru(bpy)_3]~(2+) chroophores, useful for the design of moledular wires and consequently vectorial energy and electron migration, is difficult to obtain. These problems can indeed be overcome by the use of tridentate, tpy-type polypyridine ligands. However, the photophysical properties of the [Ru(tpy)_2]~(2+) ion and its derivatives are much less useful than thsoe of the [Ru(bpy)_3]~(2+) ion, essentially because the [Ru(tpy)_2]~(2+) ion has a short excited-state lifetime at room temperature.~[4]