A theoretical study of near-IR-vis electroabsorption spectroscopy (Stark effect) for the Creutz-Taube ion, a pyrazine-bridged mixed-valence Ru dimer, and for its homovalent +4 analogue is presented. A vibronic model that takes into account correlation effects is considered for the calculation of absorption line shape profiles, also in the presence of an external static electric field. The model also incorporates the orientation of molecules with respect to the applied field and the polarization of the incident light and accounts for the essential features of the difference spectra that have been observed experimentally.