Molecular Vibration Studies of Quasi-One-Dimensional Organic Charge-Transfer Compounds

Bozio, Renato; Pecile, Cesare

doi:10.1007/978-94-009-9067-8_9

Cited by 29 publications

(24 citation statements)

References 73 publications

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“…Thus, the vibration within the CT complex will be strongly coupled to the charge transfer transition, leading to the e−mv coupling originally described by Ferguson and Matsen . This kind of e−mv interaction in CT complexes has been very well studied in a variety of quasi-one-dimensional organic charge transfer crystals by Pecile and co-workers and Rice and co-workers …”

Section: Resultsmentioning

confidence: 83%

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: 83%

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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“…The calculations were carried out using a tetragonal supercell of 20ϫ20ϫ15 a.u. 3 containing one molecule. In all calculations the molecule had been electrostatically decoupled from its periodic images as described in Ref.…”

Section: Computational Detailsmentioning

confidence: 99%

“…Although a majority of the CT complexes crystallize in this latter insulating mixed-stack structure, research interest has mainly been focused on the segregated compounds as they can exhibit a high electrical conductivity. [1][2][3] But more recently, the discovery of the so-called neutral-to-ionic phase transition has renewed interest in the mixed-stack compounds. 4 For a long time, the underlying assumption has been that mixed-stack complexes can only be either completely neutral or completely ionic.…”

Section: Introductionmentioning

confidence: 99%

First-principles molecular-dynamics simulations for neutralp-chloranil and its radical anion

et al. 1996

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The neutral p-chloranil ͑2,3,5,6-tetrachloro-p-benzoquinone͒ and its radical anion have been extensively studied using the Car-Parrinello projector augmented wave method, which is an all-electron electronic structure method for first-principles molecular dynamics based on the local density approximation of density functional theory. Frequencies and eigenmodes are derived by fitting a system of harmonic oscillators to the moleculardynamics trajectories. The dependence of the bond lengths and vibrational frequencies on the molecular ionicity is discussed, and the electron affinity, Coulomb repulsion, and the spin-splitting parameter of p-chloranil are also derived. ͓S0163-1829͑96͒05318-0͔

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“…It consists of a broad envelope with several peaks and troughs as a fine structure. This is a typical shape for the infrared absorption spectrum in this region for TTF-based low-dimensional organic conductors, which has been associated with the electron−molecular vibrations coupling (EMVC) effect. , The mechanism of this effect can be described as an electron oscillation between the adjacent molecules with overlapping partially occupied MO (dimers) induced by the molecular vibrations. In such compounds, the totally symmetrical CC and CS bonds stretching modes have the highest EMVC constants. , In the presence of EMVC these normally infrared-inactive A g modes become infrared-active for the light polarized in the direction of the dimer axis.…”

Section: Resultsmentioning

confidence: 95%

Experimental Evidence of the Symmetry Breakdown in 4,8-Diethoxy-2,7-bis(benzo-1‘,3‘-dithiol-2‘-ylidene)-1,3,5,7-tetrathia-s-indacene Compounds

et al. 1997

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The visible-near-IR absorption spectra of a bis(TTF) molecule, 4,8-diethoxy-2,7-bis(benzo-1′,3′-dithiol-2′ylidene)-1,3,5,7-tetrathia-s-indacene (1), and of the corresponding monocationic species 1 •+ generated by chemical or electrochemical oxidation are reported. IR and Raman studies of 1 and the derived 1 x PF 6 salt and ESR studies of 1 •+ are described. The results of this experimental investigation are compared with those of semiempirical calculations performed using the PM3 or AM1 modeling and simulation programs, and of a normal coordinate analysis. This comparison affords additional evidence for a symmetry breakdown in radical cations based on such bis(TTF) systems. An asymmetrical spin density distribution in the 1 •+ radical cation is also confirmed by ESR measurements.

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Molecular Vibration Studies of Quasi-One-Dimensional Organic Charge-Transfer Compounds

Cited by 29 publications

References 73 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

First-principles molecular-dynamics simulations for neutralp-chloranil and its radical anion

Experimental Evidence of the Symmetry Breakdown in 4,8-Diethoxy-2,7-bis(benzo-1‘,3‘-dithiol-2‘-ylidene)-1,3,5,7-tetrathia-s-indacene Compounds

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