Electron oscillation effects in the vibrational spectra of tetracyanoquinodimethane ion radical salts

Anderson, George R.; Devlin, J. Paul

doi:10.1021/j100578a013

Cited by 47 publications

(5 citation statements)

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“…Due to the coupling to the CT transition, the out-of-phase q i modes are both infrared and Raman active and their frequencies are lowered with respect to those of Q i . , In addition, for the out-of-phase q i modes, the electron oscillation and therefore the dipole moment and polarizability changes are predominantly perpendicular to the molecular plane. This polarization of the infrared bands has been confirmed by experiments on oriented CT complexes ,− but has not, to our knowledge, been confirmed for the corresponding Raman bands. Finally, it is important to note that the frequencies of the strong infrared absorption bands for viologen radical cations that have been attributed to vibronic activation of the A g ring modes 47-50 are identical with those of the lower energy bands attributed to the dimer in the resonance Raman spectra …”

Section: Resultsmentioning

confidence: 58%

Dimerized π-Complexes in Self-Assembled Monolayers Containing Viologens: An Origin of Unusual Wave Shapes in the Voltammetry of Monolayers

et al. 1996

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A direct comparison of the self-assembly on Au and Ag of thiol and disulfide derivatives of viologens bearing long n-alkyl chains was made in order to ascertain the relative efficiency of monolayer formation for each type of functionality. The structures of the two derivatives that were studied can be written as CH3V2+(CH2)12SH and [CH3V2+(CH2)12S]2 for the thiol and disulfide, respectively, where V2+ represents the viologen (i.e. N,N‘-dialkyl-4,4‘-bipyridinium) redox group. In contrast to the behavior of n-alkane thiols and di-n-alkyl disulfides, which adsorb to give very nearly the same surface coverage and interfacial properties, these two viologen derivatives exhibit different saturation surface coverages of 1.8 × 10-10 mol cm-2 for the disulfide and 4.5 × 10-10 mol cm-2 for the thiol, as determined from the charge for exhaustive reduction and reoxidation of the viologen redox groups. In addition, monolayers of the thiol derivative that had very high surface coverages exhibited very sharply peaked cyclic voltammetric responses that are attributed to very strong interactions between the one-electron-reduced cation radicals in the monolayer, a phenomenon that does not occur in monolayers prepared from pure samples of the disulfide derivative. Vibrational spectroscopic examination of these monolayers under conditions in which this unique voltammetric response is observed revealed the presence of vibrational spectroscopic signatures of viologen dimer formation. Specifically, surface Raman spectroscopy (including surface-enhanced Raman, surface resonance Raman, and surface-enhanced resonance Raman) was used to demonstrate that the lateral interaction of the cation radical viologen redox groups in these monolayers results in the formation of π complex dimers. The presence of these dimers is correlated with the very sharply peaked cyclic voltammetric responses. The Raman bands due exclusively to the dimer are assigned to the out-of-phase coupling combination of the totally symmetric ring modes of the component cation radicals in the dimer.

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Section: Resultsmentioning

confidence: 58%

Dimerized π-Complexes in Self-Assembled Monolayers Containing Viologens: An Origin of Unusual Wave Shapes in the Voltammetry of Monolayers

et al. 1996

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“…This model was extended to include multiple single-site modes , and solvent effects, and its consequences were explored in terms of predicted line shapes of IT bands and postulated “tunneling” far-infrared absorptions, which subsequently were shown not to exist in the Creutz−Taube ion and it was claimed that this model successfully accounts for vibronic enhancement of symmetric TCNQ normal modes in organic linear-chain conductors, − which were typically analyzed using adapted linear-response theory.…”

Section: Introductionmentioning

confidence: 99%

Vibronic Participation of the Bridging Ligand in Electron Transfer and Delocalization: New Application of a Three-State Model in Pyrazine-Bridged Mixed-Valence Complexes of Trinuclear Ruthenium Clusters

Londergan

Kubiak

2003

J. Phys. Chem. A

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The importance of the bridging ligand in mediating electronic communication and delocalization between charge centers in near-delocalized mixed-valence complexes is investigated in the specific context of pyrazine-bridged, hexanuclear ruthenium complexes that display electron-transfer rates on the order of 1011−1012 s-1, as observed by partial coalescence of infrared bands. It is shown that a three-state vibronic model explicitly including the electronic and vibrational participation of the bridging ligand is needed to account for infrared and resonance Raman evidence of vibronic activity in symmetric modes of the bridging pyrazine ligand. The specific molecular orbital and normal-mode basis for this application of the three-state model is presented using experimental observations and density functional calculations on model trinuclear ruthenium clusters. An important conclusion of the application of this model is that infrared activity of symmetric bridging ligand modes in mixed-valence complexes is not a reliable indicator of electronic asymmetry on the vibrational time scale. The three-state model is shown to qualitatively reproduce the “tunability” of electronic communication observed in these complexes. The central importance of such a direct consideration of the bridging ligand in similar near-delocalized or delocalized complexes (like the well-known Creutz−Taube ion) is re-emphasized in this study.

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“…The increase in intensity of these bands with doping may result from coupling of the vibrational modes with oscillations of the charge carriers in the doped polymer (22). This vibration-charge carrier coupling enhances the absorbance for the coupled-vibration and has been shown to be operative in a number of electronically conductive organic solids (23)(24).…”

mentioning

confidence: 99%

Infrared investigations of pristine, doped and partially doped polypyrrole

1992

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Electron oscillation effects in the vibrational spectra of tetracyanoquinodimethane ion radical salts

Cited by 47 publications

References 4 publications

Dimerized π-Complexes in Self-Assembled Monolayers Containing Viologens: An Origin of Unusual Wave Shapes in the Voltammetry of Monolayers

Dimerized π-Complexes in Self-Assembled Monolayers Containing Viologens: An Origin of Unusual Wave Shapes in the Voltammetry of Monolayers

Vibronic Participation of the Bridging Ligand in Electron Transfer and Delocalization: New Application of a Three-State Model in Pyrazine-Bridged Mixed-Valence Complexes of Trinuclear Ruthenium Clusters

Infrared investigations of pristine, doped and partially doped polypyrrole

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