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 t hat a substantial change in dipole moment (\Delta mu\ = 6.7 +/- 1 D) a ccompanies ground state to ''singlet'' metal-to-ligand charge transfer (MLCT) excited-state formation. The change is nearly identical to tha t reported for the 2,2'-bipyridine analogue (Oh; et al. J. Am. Chem. S ec. 1989, 111, 1130). Since both species lack ground-state dipole mome nts, the finite values for Delta mu 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, wi th an alternative ''delocalized'' charge transfer excited-state interp retation suggested by time-resolved resonance Raman studies of the tri s(phenanthroline) complex.