Photophysical and photochemical behavior of nitro complexes of ruthenium(II)

Abstract

For ruthenium(II) complexes of the type cis-Ru(bpy)[sub 2](X)-(Y), where bpy is 2,2[prime]-bipyridine or a related polypyridyl ligand and X and Y are monodentate ligands, the properties of the Ru-(II) [yields] bpy, metal-to-ligand charge transfer (MLCT) excited states can be varied systematically by changing the nonchromophoric ligands or the substituents on the polypyridyl ligands. A complication is an instability toward ligand loss which occurs following MLCT excitation and thermally activated population of metal-centered, ligand field or dd states. Although this photochemistry has been used synthetically, it is the major limitation to the potential use of the MLCT excited state of these complexes as luminescence probes and in driving photoinduced electron or energy transfer. The authors report here the results of an initial investigation on the ground and excited state properties of the complexes cis-Ru(bpy)[sub 2](NO[sub 2])(X) (X = NO[sub 2], CN) and cis-[Ru(bpy)[sub 2](NO[sub 2])(py)][sup +], which contain the nitro ligand. We were interested in investigating the excited state properties of these complexes given, (1) the extensive ground-state chemistry that exists for the nitro and related nitrosyl ligands, (2) the possible existence of solvent dependent spectroscopic and photophysical properties which would allow the excited states to be used as probes formore » different environments, (3) the possible role of reversible NO[sub 2]- to NO[sup +] interconversion, on excited state behavior (eq 1), and (4) a continuing interest is establishing the electronic influence of different chromophoric and ancillary ligands on excited state properties including their effect on the relative energies of MLCT and dd states.« less