Nonlinear optical phenomena in conjugated organic chromophores. Theoretical investigations via a π-electron formalism

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Abstract

This contribution explores the use of perturbation theory and the chemically oriented, computationally efficient PPP π-electron model Hamiltonian to describe the first three molecular hyperpolarizabilities and their interrelationships. Relationships between various nonlinear phenomena are treated as degeneracy factors, and a more general definition emerges from this analysis. Derivations of formulas describing second- to fourth-order susceptibilities are given for the monoexcited CI (MECI) and doubly excited CI (DECI) perturbation approaches, and numerical results are in good to excellent agreement with experimental values where available for a variety of second- and third-order nonlinear phenomena (second harmonic generation, frequency mixing, linear electrooptic effect, optical rectification, third harmonic generation, dc-induced second harmonic generation, degenerate four-wave mixing, Kerr effect). Additional analysis of chromophore architecture-nonlinear optical relationships reveals that the observable second-order susceptibility, βvec, is quite sensitive to intramolecular charge transfer and molecular distortions. This becomes even more pronounced in fourth-order phenomena since δiiiii is related to charge transfer in a cubic manner rather than linearly as in the case of βiii. Third-order susceptibilities, γijkl, function exactly as αij in a centrosymmetric system and are dominated by the size and shape of the electron cloud. However, in a noncentrosymmetric environment, γijkl has a more complex behavior than either αij or βijk, and charge-transfer excitations can make an important contribution.

Original languageEnglish
Pages (from-to)4325-4336
Number of pages12
JournalJournal of Physical Chemistry
Volume96
Issue number11
Publication statusPublished - 1992

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Chromophores
Harmonic generation
chromophores
Charge transfer
harmonic generations
charge transfer
formalism
magnetic permeability
Electrons
Hamiltonians
electron clouds
electrons
Four wave mixing
rectification
Electrooptical effects
Kerr effects
four-wave mixing
electro-optics
derivation
perturbation theory

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

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title = "Nonlinear optical phenomena in conjugated organic chromophores. Theoretical investigations via a π-electron formalism",
abstract = "This contribution explores the use of perturbation theory and the chemically oriented, computationally efficient PPP π-electron model Hamiltonian to describe the first three molecular hyperpolarizabilities and their interrelationships. Relationships between various nonlinear phenomena are treated as degeneracy factors, and a more general definition emerges from this analysis. Derivations of formulas describing second- to fourth-order susceptibilities are given for the monoexcited CI (MECI) and doubly excited CI (DECI) perturbation approaches, and numerical results are in good to excellent agreement with experimental values where available for a variety of second- and third-order nonlinear phenomena (second harmonic generation, frequency mixing, linear electrooptic effect, optical rectification, third harmonic generation, dc-induced second harmonic generation, degenerate four-wave mixing, Kerr effect). Additional analysis of chromophore architecture-nonlinear optical relationships reveals that the observable second-order susceptibility, βvec, is quite sensitive to intramolecular charge transfer and molecular distortions. This becomes even more pronounced in fourth-order phenomena since δiiiii is related to charge transfer in a cubic manner rather than linearly as in the case of βiii. Third-order susceptibilities, γijkl, function exactly as αij in a centrosymmetric system and are dominated by the size and shape of the electron cloud. However, in a noncentrosymmetric environment, γijkl has a more complex behavior than either αij or βijk, and charge-transfer excitations can make an important contribution.",
author = "DeQuan Li and Marks, {Tobin J} and Ratner, {Mark A}",
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N2 - This contribution explores the use of perturbation theory and the chemically oriented, computationally efficient PPP π-electron model Hamiltonian to describe the first three molecular hyperpolarizabilities and their interrelationships. Relationships between various nonlinear phenomena are treated as degeneracy factors, and a more general definition emerges from this analysis. Derivations of formulas describing second- to fourth-order susceptibilities are given for the monoexcited CI (MECI) and doubly excited CI (DECI) perturbation approaches, and numerical results are in good to excellent agreement with experimental values where available for a variety of second- and third-order nonlinear phenomena (second harmonic generation, frequency mixing, linear electrooptic effect, optical rectification, third harmonic generation, dc-induced second harmonic generation, degenerate four-wave mixing, Kerr effect). Additional analysis of chromophore architecture-nonlinear optical relationships reveals that the observable second-order susceptibility, βvec, is quite sensitive to intramolecular charge transfer and molecular distortions. This becomes even more pronounced in fourth-order phenomena since δiiiii is related to charge transfer in a cubic manner rather than linearly as in the case of βiii. Third-order susceptibilities, γijkl, function exactly as αij in a centrosymmetric system and are dominated by the size and shape of the electron cloud. However, in a noncentrosymmetric environment, γijkl has a more complex behavior than either αij or βijk, and charge-transfer excitations can make an important contribution.

AB - This contribution explores the use of perturbation theory and the chemically oriented, computationally efficient PPP π-electron model Hamiltonian to describe the first three molecular hyperpolarizabilities and their interrelationships. Relationships between various nonlinear phenomena are treated as degeneracy factors, and a more general definition emerges from this analysis. Derivations of formulas describing second- to fourth-order susceptibilities are given for the monoexcited CI (MECI) and doubly excited CI (DECI) perturbation approaches, and numerical results are in good to excellent agreement with experimental values where available for a variety of second- and third-order nonlinear phenomena (second harmonic generation, frequency mixing, linear electrooptic effect, optical rectification, third harmonic generation, dc-induced second harmonic generation, degenerate four-wave mixing, Kerr effect). Additional analysis of chromophore architecture-nonlinear optical relationships reveals that the observable second-order susceptibility, βvec, is quite sensitive to intramolecular charge transfer and molecular distortions. This becomes even more pronounced in fourth-order phenomena since δiiiii is related to charge transfer in a cubic manner rather than linearly as in the case of βiii. Third-order susceptibilities, γijkl, function exactly as αij in a centrosymmetric system and are dominated by the size and shape of the electron cloud. However, in a noncentrosymmetric environment, γijkl has a more complex behavior than either αij or βijk, and charge-transfer excitations can make an important contribution.

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