Theory of electroabsorption spectroscopy in poly-nuclear Ru complexes

Electroabsorption spectroscopy is a powerful experimental technique for the study of the charge transfer states of inorganic molecules. From the difference between the near IR-vis spectra, with and without the application of an electric field, it is possible to extract the value of the variation of dipole moment and polarizability in the transition between the ground and the first few low lying excited states of mono- and poly-nuclear ligand-bridged transition metal complexes. How these quantities and the difference spectra themselves can be obtained by theoretical methods is the subject of the present review. After a brief outline of the experiments and of the background theory which is used to obtain the relevant parameters from the measured difference spectra, the two-state electronic model and its connections to electroabsorption spectra are discussed. The inclusion of selected nuclear degrees of freedom and electronic correlation effects in the computation of line-shape profiles are then examined. This is done within the framework of simple model Hamiltonians which may be applied to the study of the optical properties of the various members of a class of Ruligand poly-nuclear complexes, as well as by the use of extensive ab initio multireference CI calculations.