ELECTROABSORPTION SPECTROSCOPY OF MOLECULAR INORGANIC-COMPOUNDS

Electroabsorption spectroscopy is known to report directly on the chan ges in dipole moment and molecular polarizability accompanying electro nic excited state formation. Because ground-state/excited-state dipole moment changes can be equated with effective one-electron transfer di stances, experimental electroabsorption spectroscopy holds exceptional promise as a methodology for investigating light-induced charge trans fer processes within inorganic systems. A survey of the available stud ies, including metal-to-ligand charge transfer, ligand-to-metal charge transfer and localized and delocalized 'intervalence' charge transfer studies, is presented. Also surveyed are electroabsorption studies ai med at illuminating selected molecular nonlinear optical responses. A general observation from electroabsorption studies has been that exper imentally determined one-electron transfer distances are less than sim ple geometric descriptions would predict. Mononuclear transition-metal systems have proven to be good models for unravelling the complicatin g effects of ground-state localization and many-electron polarization. The capability of electroabsorption spectroscopy to resolve fundament al questions relating to electronic localization and delocalization ha s been highlighted in a series of studies in bridged dinuclear and tri s(diimine) systems. The available electroabsorption data have also bee n used to reassess a number of molecular charge-transfer related param eters such as the electronic coupling energies and solvent reorganizat ion energies. Very recent studies of putative octupolar complexes and donor-acceptor porphyrinic structures have highlighted the utility of electroabsorption spectroscopy for evaluating second-order nonlinear o ptical response mechanisms and for providing detailed information abou t state-specific contributions to overall molecular hyperpolarizabilit ies.