Electroabsorption spectroscopy of charge transfer states of transition metal complexes

The use of electroabsorption spectroscopy to determine the dipole-moment changes that occur in the metal-to-ligand, ligand-to-metal, and metal-to-metal charge-transfer transitions in mononuclear and binuclear transition metal complexes is reviewed. The ground-excited state dipole-moment differences are much smaller than expected for the transfer of unit electronic charge between the donor and acceptor centers. The results are discussed in terms of a model in which two factors, electron delocalization and polarization of the acceptor, donor or bridging ligand electrons in response to the changed charge on the metal centers, are considered to be primarily responsible for the relatively small dipole-moment changes. The implications of the results for electronic coupling elements and reorganization energies are also discussed. (C) 1998 Elsevier Science S.A. All rights reserved.