Role of vibronic coupling and correlation effects on the optical properties of mixed-valent and monovalent dimer compounds: the Creutz-Taube ion and its monovalent analogs

Abstract

A three-site, three-harmonic oscillator vibronic model Hamiltonian that includes correlation effects is considered in order to study the optical absorption spectra of the Creutz-Taube ion at various values for the total charge. The model is made by a two band Hubbard Hamiltonian, plus a vibronic interaction that is linear in the nuclear coordinates. W e show that the main features of absorption spectra observed experimentally in the near-IR-visible are well reproduced by this model, as far as band position and shape are concerned. An approximate approach to the vibronic problem reveals that, in the present case, the vibronic interaction is strong and good results can be obtained only by solving the full vibronic problem.

Characterization of infrared vibrational activity in specific totally symmetric bridging modes of mixed-valence systems near the localized-to-delocalized transition

“…In the cluster dimer systems, the argument that the electron transfer dynamics are strongly coupled to the vibrational motions of the intervening pz ligand has been supported via resonance Raman spectroscopy [27,28], which revealed resonant enhancement of only totally symmetric modes of the pz bridge (especially m 8a ) accompanying excitation in the cluster-to-cluster ''intervalence'' charge transfer (IVCT) band. Those results are in qualitative agreement with a three-site/three-state vibronic model [11,[29][30][31][32] proposed for the Creutz-Taube ion and almost delocalized analogues. Here, in addition to the two charge centers or redox moieties (metal sites), Scheme 3.…”

Charge Instability in Quadrupolar Chromophores: Symmetry Breaking and Solvatochromism

“…29 Charge and structural instabilities and symmetry breaking phenomena have been quite extensively investigated in these systems as a consequence of electron-vibration coupling. [30][31][32] Here we propose the occurrence of similar phenomena in multipolar organic dyes.…”

“…The coupling between electronic and vibrational degrees of freedom indeed governs structural instabilities in a variety of extended systems with delocalized electrons and/or extended charge resonance, including polymers, charge transfer salts, and mixed valence chains. 71 Instabilities in finite molecular systems are also an active research field, 32,40,72,73 where, however, the subtle distinction between static and dynamic effects makes the problem much more complex than in extended systems. 32,55 Here we focus on the spectroscopic consequences of brokensymmetry states in quadrupolar organic dyes for NLO applications.…”

Probing the localized-to-delocalized transition

“…In the delocalized limit, a band is predicted to appear having a 0-0 energy difference of 2H ab which is coupled to symmetric vibrations and only weakly coupled to solvent (Ko & Ondrechen 1985;Ferretti et al 1995).…”