Solitons in finite- and infinite-length negative-defect trans-polyacetylene and the corresponding Brooker (polymethinecyanine) cations. II. Charge density wave

Craw, J. S.; Reimers, Jeffrey R.; Bacskay, George B.; Wong, Adrian T.; Hush, Noel S.

doi:10.1016/0301-0104(92)80025-q

Cited by 51 publications

(50 citation statements)

References 18 publications

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“…It has been proposed [14] that the value |∆q µ | may be considered a parameter of the "ionicity" of the bond between two neighbouring atoms µ and µ+1. Taking the relationship between the calculated electron densities and NMR signals into consideration, [15] we can also write a similar function for the alternation of the experimentally observed characteristics δ µ ( 13 C) [Equation (2)].…”

Section: Nmr Signalsmentioning

confidence: 99%

“…It has been proposed [14] that the alternation amplitude (∆q µ ) calculated by Equation (1) as the difference in electron densities at neighbouring atoms (q µ and q µ+1 , correspondingly) is a more suitable parameter with which to analyse the influence of the molecular topology and asymmetry on the shape and location of the charge wave.…”

Section: Nmr Signalsmentioning

confidence: 99%

“…On going to the monomethine cyanine 3a, the nature of the charge distribution does not change in principle: substantial alternation of the electron density at the neighbouring carbon atoms over all the cyanine chromophore (Kuhn's chain) is observed, as it is typical for polymethine dyes. [14][15][16][17][18][19] For the experimental confirmation of the character of charge distribution in the chromophore one can use NMR chemical shifts, such as δ µ ( 13 C), which are correlated with quantum-chemically accessible electron density values (q µ ) in atoms. [15] The obtained experimentally measured 13 C NMR chemical shifts and the calculated charges on the carbon atoms are collected in Table 2.…”

Section: Nmr Signalsmentioning

confidence: 99%

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Studies of 2‐Azaazulenium Derivatives: The Natures of Electron Transitions in the 2‐Azaazulenium Cation and in Monomethine Cyanine Dyes Bearing 2‐Azaazulenium Moieties as Terminal Groups

2009

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A series of novel monomethine cyanine dyes derived from 2‐azaazulene have been synthesized. Combined spectral and quantum‐chemical investigations of their molecular geometries and of their electronic structures and the natures of their lowest electron transitions have been performed. The analysis results obtained by ab initio and semiempirical methods, together with experimental data obtained from absorption and 13C NMR spectra, have shown that there is practically no difference between the charge distributions over the π‐electron systems in the ground state in a reference 2‐azaazulenium salt and in monomethine cyanines bearing 2‐azaazulene as a terminal group, because these are not dependent on the relative locations of molecular orbitals. However, the spectral properties of – and correspondingly the natures of electron transitions in – the chromophores of the salt and of the monomethine cyanine are drastically different, due to the different mechanisms of frontier molecular orbital generation. Similar differences in properties in ground and excited states are observed for unsymmetrical monomethine cyanines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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Section: Nmr Signalsmentioning

confidence: 99%

Section: Nmr Signalsmentioning

confidence: 99%

Section: Nmr Signalsmentioning

confidence: 99%

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Studies of 2‐Azaazulenium Derivatives: The Natures of Electron Transitions in the 2‐Azaazulenium Cation and in Monomethine Cyanine Dyes Bearing 2‐Azaazulenium Moieties as Terminal Groups

2009

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“…When the charge carrier is introduced into a highly polarized -conjugated system it can localize in the form of a charge wave (known as polaron), which induces changes of the molecular geometry leading to further stabilization [11][12][13][14]. These changes are sometimes referred to as a solitonic wave of alternating bond lengths, also known as a geometrical or topological soliton.…”

mentioning

confidence: 98%

Symmetry breaking in cationic polymethine dyes, part 1: Ground state potential energy surfaces and solvent effects on electronic spectra of streptocyanines

Iordanov

Davis

Masunov

et al. 2009

Int J of Quantum Chemistry

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ABSTRACT:Charge localization and dynamics in conjugated organic molecules, as well as their spectral signatures are of great importance for photonic and photovoltaic applications. Intramolecular charge delocalization in polymethine dyes occurs through -conjugated bridges and contributes to the appearance of low-energy excited states that strongly influence their linear and nonlinear optical (NLO) properties. When the chain length in symmetrical cations exceeds the characteristic size of the soliton, the positive charge may localize at one of the terminal groups of the molecule and induce symmetry breaking of both the electron density distribution and molecular geometry. This charge localization is coupled with molecular vibrations and solvent effects. We investigated the mechanism of symmetry breaking in a series of cationic streptocyanines with different conjugated chain length and qualitatively predicted their electronic absorption spectra. This class of organic molecules is chosen as a model system to develop methodology which can subsequently be used to evaluate more complicated compounds for NLO applications. Our calculations show that the minimum number of vinylene groups in the conjugated chain necessary to break the symmetry of streptocyanines is eight in the gas phase and six in cyclohexane. We constructed the ground state potential energy surface (PES) in two dimensions using symmetry breaking and symmetry adapted coordinates. These were defined as the difference and the sum of the two central carbon-carbon bonds, respectively. This PES was found to have two equivalent minima for systems with symmetry breaking. The energy barrier between these two minima was estimated in the gas phase and in solution, which was taken into account by the polarizable continuum model. Charge localization in each minimum was found to be asymmetric. It is additionally stabilized by the solvent reaction field, which increases the energy barrier. The electronic absorption spectrum in solution is red shifted as compared to the gas phase. As the symmetry breaks, additional excited states with large oscillator strengths appear in the electronic spectrum. Geometry optimization and spectral predictions were also performed in a uniform external electric field in order to simulate nonequilibrium solvation effects due to the finite relaxation time of solvent molecules. Two asymmetric minima with different depths appear on the resulting PES. The lower minimum has charge localized at one of the two molecular terminal groups which is additionally stabilized by the solvent field, while the higher one has charge localized on another terminal group. This finding demonstrates the possibility that two forms with different charge distributions coexist in polar solvents. Our results suggest that nonequilibrium solvation may be a cause of absorption band broadening and splitting. This work is a first step in a larger study aimed at the analysis of the linear and nonlinear properties of long -conjugated systems of interest for NLO applications an...

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“…Thus, it was established that in a,w-dialkylamino-substituted polymethine cations or the radical-cations of polyenes, where the length of the conjugation chain exceeds the width of the soliton wave, the latter is displaced to one of the terminal groups, i.e., the symmetrical distribution of electron density in the symmetrical molecule is destroyed. At the same time with the introduction of a methoxyl group OCH 3 as terminal group the distribution of electron density and the molecular geometry remain symmetrical even with a comparatively large number of vinylene groups in the conjugation chain [2,[4][5][6][7]. The symmetry of the soliton waves is not destroyed by phenyl and other alternant carbocyclic groups in contrast to the nonalternant terminal groups, which displace the center of the soliton at a critical elongation of the polymethine chain [2,4,5].…”

Section: Linear Polymethine Systemsmentioning

confidence: 84%

Location of the charge and geometric components of soliton waves in cations of unsymmetrical conjugated systems

Kachkovskii

Ryabitskii

2008

Theor Exp Chem

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A quantum-chemical investigation into the location and form of solitons in the cations of unsymmetrical polymethine systems was undertaken. It was shown that the introduction of one terminal group (electron-donating or electron-accepting) with intrinsic level outside the energy gap of the main chromophore leads to displacement of the charge and geometric waves without substantial distortion of their form; the introduction of an amino group with a high level for the unshared electron pair is accompanied by displacement of the solitons to the end of the conjugation chain, so that half of the soliton wave projects onto the molecule. In unsymmetrical polymethine cations with two nitrous groups the geometric soliton is closer to the less basic residue; replacement of one terminal residue by a methoxy group moves the position of the soliton to the end of the chromophore. Linear polymethine systems[R 1 -(CH) m -R 2 ] z , z = 0, 1, 2 I such as polyenes, polymethine dyes, and donor-acceptor compounds continue to find wide application as highly polarized media, molecular switches or conductors in fields associated with the conversion of luminous energy [1] and also serve as suitable model compounds for the development of new theoretical concepts (e.g., see the review [2] and the references therein). Their principal characteristics are determined by the collective system of p electrons. In the case of neutral molecules the compounds are insulators with a comparatively large energy gap and with a uniform distribution of electron density on the carbon atoms in the conjugation chain. The injection of charge leads to the appearance of impurity or soliton levels in the gap [3], and a soliton-like wave of partial alternating positive and negative charges is generated on the atoms. At the same time a wave of changes in the length of the carbon-carbon bonds, which also alternate -so-called geometric or topological solitons, appears [2,4]. In unsubstituted conjugated systems both the charge and the geometric solitons are located at the center of the molecule. Earlier [2,5] it was shown that the form of the soliton waves hardly depends at all on the length of the conjugation chain, so that only the central part of the solution wave is observed in the case of short molecules. The introduction of terminal groups can lead to a significant change both in the form and in the location of the solitons. Thus, it was established that in a,w-dialkylamino-substituted polymethine cations or the radical-cations of polyenes, where the length of the conjugation chain 232 0040-5760/08/4404-0232

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Solitons in finite- and infinite-length negative-defect trans-polyacetylene and the corresponding Brooker (polymethinecyanine) cations. II. Charge density wave

Cited by 51 publications

References 18 publications

Studies of 2‐Azaazulenium Derivatives: The Natures of Electron Transitions in the 2‐Azaazulenium Cation and in Monomethine Cyanine Dyes Bearing 2‐Azaazulenium Moieties as Terminal Groups

Studies of 2‐Azaazulenium Derivatives: The Natures of Electron Transitions in the 2‐Azaazulenium Cation and in Monomethine Cyanine Dyes Bearing 2‐Azaazulenium Moieties as Terminal Groups

Symmetry breaking in cationic polymethine dyes, part 1: Ground state potential energy surfaces and solvent effects on electronic spectra of streptocyanines

Location of the charge and geometric components of soliton waves in cations of unsymmetrical conjugated systems

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