EXCITED-STATE PROPERTIES OF BIS-TETRAAZAPHENANTHRENE-RU(II) DIAD COMPLEXES WITH A FERROCENYL UNIT

The excited state properties of the diad complexes Ru(tap)(2)(ppFc)(2) and Ru(bpy)(2)(ppFc)(2+) (tap, 1,4,5,8-tetraazaphenanthrene; bpy, 2, 2'-bipyridine), bearing a reducing ferrocenyl (Fc) centre on a derivat ized (pyridine)pyrazole (pp) ligand, were compared with those of the c orresponding complexes without an Fc unit. For these latter complexes, the existence of intermolecular photoelectron transfer with added fer rocene was clearly demonstrated. However, direct evidence for intramol ecular photoelectron transfer in Ru(bpy)(2)(ppFc)(2+) and Ru(tap)(2)(p pFc)(2+) could not be obtained unambiguously. Although the absence of luminescence in these diad complexes indicated the existence of this i ntramolecular process, laser flash photolysis did not allow the detect ion of a reduced complex entity in most experimental conditions. Only flash photolysis of Ru(bpy)(2)(ppFc)(2+) in water generated a long-liv ed intermediate with the characteristic spectral features of the radic al anion bpy(.-). Indirect arguments, such as the formation of a produ ct on illumination of both diad complexes, were in favour of a photore action induced by intramolecular electron transfer.