Non-linear polamzabilities of conjugated chains: regular polyenes, solitons, and polarons

Melo, Celso P. de; Silbey, R.

doi:10.1016/0009-2614(87)80482-7

Cited by 111 publications

(17 citation statements)

References 23 publications

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“…[1][2][3][4][5] In this paper we present experimental results obtained in an ongoing study of conjugated molecules; specifically all-trans polyenes, cyanines, and modified cyanines. The impetus for this work comes from a theoretical study by Rustagi and coworkers [2] in which a simple free-electron model of the x-system of a conjugated, nonalternating-bond molecule was used to compute low-frequency third-order electronic hyperpolarizabilities (Y's) for symmetric linear cyanines.…”

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confidence: 99%

Nonresonant Third-Order Nonlinear Polarizability in Linear Conjugated Molecules

1987

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Crude pictures relating molecular features and enhancement of nonresonant second-order hyperpolarizability have been known and successfully utilized in selection and preparation of materials for nonlinear-optical applications for over a decade.On the other hand, other than the requirement of "electron delocalization", such a useful picture does not exist for nonresonant third-order hyperpolarizability.In pursuit of such a picture, and to obtain a better view of the range of hyperpolarizability magnitudes which might be obtainable, simple linear conjugated molecules have been synthesized and characterized.Liquid solutions of these model compounds were studied using recently developed high precision optical third harmonic generation techniques.Results of these characterizations and a new addition to the picture of structure-property relationships are reported. IN1RODUCTIONIn the past several years there has been considerable interest in the linear and nonlinear optical properties of conjugated molecules as model compounds in the study of conjugated polymers. [1][2][3][4][5] In this paper we present experimental results obtained in an ongoing study of conjugated molecules; specifically all-trans polyenes, cyanines, and modified cyanines. The impetus for this work comes from a theoretical study by Rustagi and coworkers [2] in which a simple free-electron model of the x-system of a conjugated, nonalternating-bond molecule was used to compute low-frequency third-order electronic hyperpolarizabilities (Y's) for symmetric linear cyanines.A spatially periodic perturbing potential was introduced to represent the alternating-bond structure of simple all-trans polyenes, and a limitedrange perturbing potential was used to model symmetrically aza-substituted cyanines.Both of these perturbations act to increase the anharmonicity of the molecule's representative effective-oscillator; the bond alternation acts to reduce polarizability as well.Qualitatively it was seen that increasing polarizability (0t) enhances y and increasing anharmonicity enhances y.For moderate conjugation lengths, Rustagi's calculations predicted that y-Ka7/ 3 . The "anharmonicity factor", K, is an indicator of the intrinsic anharmonicity of polarizability in the a-system, being smallest in symmetric cyanines and largest in polyenes.According to these calculations, despite extensive delocalization, the X-electrons of symmetric cyanines are polarized as nearly perfect harmonic oscillators, the cyanines having low y's in spite of their high polarizabilities. The anharmonicity, K, can be increased by perturbing the structure, for example by a spatially periodic potential used to mimic bond alternation in polyenes, but in this case little is gained because the perturbation substantially lowers ct. On the other hand, if a structural modification can increase the anharmonicity factor without much affecting a, the value of y will certainly be significantly enhanced.Rustagi's computations showed symmetric aza substitution of cyanines to be such a modification.

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confidence: 99%

Nonresonant Third-Order Nonlinear Polarizability in Linear Conjugated Molecules

1987

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“…In addition, other theoretical studies have dealt with the influence of charged defects on the nonlinear optical properties of polyacetylene [6][7][8][9][10][11][12][13]. In a previous investigation, de Melo and Silbey [6] have shown that the polarizabilities of PA chains are particularly affected by the presence of charged conformational defects.…”

Section: Introductionmentioning

confidence: 99%

13C chemical shifts of polyacetylene chains with charged conformational defects: A GIAO–DFT study

Colherinhas¹,

Fonseca²,

Castro³

2011

Chemical Physics Letters

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“…11 Substantial enhancements of the optical nonlinearities were found to result from charged doping on polyenic chains. [8][9][10] For a finite polyenic chain, charged doping gives rise to an ionized molecule with distorted molecular structure. The structural distortions are localized for long polyenic chains, and the bond lengths profile resembles that of a charged topological soliton in polyacetylene.…”

Section: Introductionmentioning

confidence: 99%

“…1,2 Understanding of the structure-property relations for the NLO responses provides guidelines for the design of novel molecular and polymeric NLO materials. It was known that the NLO properties of conjugated molecules and polymers are sensitive to many factors such as the conjugation length, 3-5 donor and acceptor substitutions, 6,7 and the presence of defects [8][9][10] or dopants. 11 Substantial enhancements of the optical nonlinearities were found to result from charged doping on polyenic chains.…”

Section: Introductionmentioning

confidence: 99%

Bond-length-alternation and the hyperpolarizabilities of a charged soliton in polyenic chains

Wong

2003

The Journal of Chemical Physics

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Nonlinear optical responses of a charged soliton were studied using a model charged polyenic chain. It was found that simple derivative relations exist between the spatial profile of the bond-length-alternation and the profiles of the real-space description of the linear polarizability and the first and second hyperpolarizabilities of the chain. These relations can be understood if the soliton is assumed to undergo a sliding translational motion under the influence of an external electric field.

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Non-linear polamzabilities of conjugated chains: regular polyenes, solitons, and polarons

Cited by 111 publications

References 23 publications

Nonresonant Third-Order Nonlinear Polarizability in Linear Conjugated Molecules

Nonresonant Third-Order Nonlinear Polarizability in Linear Conjugated Molecules

13C chemical shifts of polyacetylene chains with charged conformational defects: A GIAO–DFT study

Bond-length-alternation and the hyperpolarizabilities of a charged soliton in polyenic chains

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