Long-lived MLCT excited states-Ru-II complexes with a helical bis-phen ligand.

The synthesis of a new Ru-II complex [Ru(L-1)(4,7-dpphen)](2+), bearing a tetradentate bis-1,10-phenanthroline ligand L-1, is described. X-ray crystal structure analysis shows that the tetradentate ligand L, coils around the metal and occupies both axial and two of the equatorial positions of the complex. H-1 NMR studies clearly indicate that the complex has C-2 symmetry in solution. The room temperature luminescence properties of [Ru(L-1)(4,7-dpphen)](2+) have been studied, as have those of the related complex [Ru(L,)(4,4'-dmbp)](2+). For both complexes, the luminescence quantum yields and lifetimes are three to ten times higher than those of [Ru(bpy)(3)](2+). These unusual results are explained by the geometrical constraints imposed by the tetradentate ligands L-1 and L-2 in their respective complexes, resulting in an effective decoupling between the (MLCT)-M-3 and (MC)-M-3 excited states.