Electroabsorption Studies of Metal-to-Ligand Charge Transfer in Ru(phenanthroline)(3)(2+): Evidence for Intrinsic Charge Localization in the Initially Formed Excited State.

Electroabsorption studies of ruthenium(II) tris(phenanthroline) show that a substantial change in dipole moment (|Delta&mgr;| = 6.7 +/- 1 D) accompanies ground state to "singlet" metal-to-ligand charge transfer (MLCT) excited-state formation. The change is nearly identical to that reported for the 2,2'-bipyridine analogue (Oh; et al. J.Am. Chem. Soc. 1989, 111, 1130). Since both species lack ground-state dipole moments, the finite values for Delta&mgr; are diagnostic of intrinsic charge localization in the excited states. The nominally triplet transition for the phenanthroline complex also involves the formation of a charge localized state. The combined results are inconsistent, therefore, with an alternative "delocalized" charge transfer excited-state interpretation suggested by time-resolved resonance Raman studies of the tris(phenanthroline) complex.