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 1 coils around the metal and occupies both axial and two of the equatorial positions of the complex. 1 H 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 2 )(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 3 MLCT and 3 MC excited states. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)