SYNTHETIC MANIPULATION OF EXCITED-STATE DECAY PATHWAYS IN A SERIES OFRUTHENIUM(II) COMPLEXES CONTAINING BIPYRAZINE AND SUBSTITUTED BIPYRIDINE LIGANDS

A series of heteroleptic complexes, Ru(bpz)(2)L(2+) (where bpz = 2,2'- bipyrazine and L is 2,2'-bipyridine (bpy), 4,5'-diazafluorene (daf), 5 -monomethyl-2,2'-bipyridine (mmb) or 4,4'-dimethyl-2,2'-bipyridine (dm b)) is studied, wherein the donor strength of the ''spectator'' ligand (L) is systematically increased. Attention is focused on the temperat ure dependence of the lifetimes of the lowest lying (3)MLCT states in order to reveal the relative contributions from two independent therma lly activated decay pathways. One involves a high lying ligand field s tate ((3)dd), while the other is associated with population of a so-ca lled ''fourth'' 3MLCT state which is only slightly (<1000 cm(-1)) more energetic than the lowest energy manifold. The results show that the relative importance of each pathway is dictated by the donor strength of the spectator ligand and that in the cases of Ru(bpz)(2)(bpy)(2+) a nd Ru(bpz)(2)(mmb)(2+) both pathways participate in the overall decay.