Stark spectroscopy of mixed-valence systems

Abstract

Many mixed-valence systems involve two or more states with different electric dipole moments whose magnitudes depend upon the charge transfer distance and the degree of delocalization; these systems can be interconverted by excitation of an intervalence charge transfer transition. Stark spectroscopy involves the interaction between the change in dipole moment of a transition and an electric field, so the Stark spectra of mixed-valence systems are expected to provide quantitative information on the degree of delocalization. In limiting cases, a classical Stark analysis can be used, but in intermediate cases the analysis is much more complex because the field affects not only the band position but also the intrinsic bandshape. Such non-classical Stark effects lead to widely different bandshapes. Several examples of both classes are discussed. Because electric fields are applied to immobilized samples, complications arise from inhomogeneous broadening, along with other effects that limit our ability to extract unique parameters in some cases. In the case of the radical cation of the special pair in photosynthetic reaction centres, where the mixed-valence system is in a very complex but structurally well-defined environment, a detailed analysis can be performed.

M2δ to ligand π-conjugation: testbeds for current theories of mixed valence in ground and photoexcited states of molecular systems

“…Stark spectroscopy allows for the change in dipole moment between the ground and excited state to be determined. [56][57][58][59][60][61][62][63][64] For the oxalate bridged compounds of both Mo and W, the change in dipole moment is negligible. However, upon increasing the length of the bridge from oxalate to 1,4-terephthalate the Stark spectra indicate a more substantial change in dipole moment, which is found to be greater for the molybdenum complex than for the tungsten complex.…”

Electronic States of Tris(bipyridine) Ruthenium(II) Complexes in Neat Solid Films Investigated by Electroabsorption Spectroscopy

“…In their microscopic model of electroabsorption, the interaction with the modulating electric field is explicitly included in the Hamiltonian, and only the input parameters are defined and estimated in terms of molecular wave functions. Some progress has been as well achieved in taking into account the vibronic coupling mechanism in EA behavior of poly-nuclear Ru complexes of mixed valence properties, although the more tractable description is at best restricted here to one electronic transition coupled to one or two vibrational modes [ 39 , 40 ].…”

Mixed valence: origins and developments

“…Barbara's investigations of intervalence absorption of both ground and excited states using femto-second spectroscopy (Reid et al 1995) takes us into a new and fascinating time-domain, with concomitant questions arising concerning the definition of localization and refinement of the concept (see also Lu et al 1995). In the present meeting, Boxer also discusses the use of Stark spectroscopy to probe IT transitions in systems near the class 2/3 borderline (Silverman et al 2008).…”