Electron-correlation-induced transverse delocalization and longitudinal confinement in excited states of phenyl-substituted polyacetylenes

Haranath Ghosh, Alok Shukla, Sumitendra Mazumdar

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51 Citations (Scopus)

Abstract

Electron-electron interactions in general lead to both ground-state and excited-state confinement. We show, however, that in phenyl-substituted polyacetylenes electron-electron interactions cause enhanced delocalization of quasiparticles in the optically excited state from the backbone polyene chain into the phenyl groups, which in turn leads to enhanced confinement in the chain direction. This cooperative delocalization confinement lowers the energy of the one-photon state and raises the relative energy of the lowest two-photon state. The two-photon state is slightly below the optical state in monophenyl-substituted polyacetylenes, but above the optical state in diphenyl-substituted polyacetylenes, thereby explaining the strong photoluminescence of the latter class of materials. We present a detailed mechanism of the crossover in the energies of the one- and two-photon states in these systems. In addition, we calculate the optical-absorption spectra over a wide wavelength region, and make specific predictions for the polarizations of low- and high-energy transitions that can be tested on oriented samples. Within existing theories of light emission from π-conjugated polymers, strong photoluminescence should be restricted to materials whose optical gaps are larger than that of transpolyacetylene. The present work shows that, conceptually at least, it is possible to have light emission from systems with smaller optical gaps.

Original languageEnglish (US)
Pages (from-to)12763-12774
Number of pages12
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume62
Issue number19
DOIs
StatePublished - Nov 15 2000

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Polyacetylenes
Electron correlations
polyacetylene
Excited states
Photons
photons
Electron-electron interactions
excitation
Light emission
electrons
light emission
Photoluminescence
electron scattering
energy
photoluminescence
Polyenes
Optical materials
Conjugated polymers
optical materials
Light absorption

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

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abstract = "Electron-electron interactions in general lead to both ground-state and excited-state confinement. We show, however, that in phenyl-substituted polyacetylenes electron-electron interactions cause enhanced delocalization of quasiparticles in the optically excited state from the backbone polyene chain into the phenyl groups, which in turn leads to enhanced confinement in the chain direction. This cooperative delocalization confinement lowers the energy of the one-photon state and raises the relative energy of the lowest two-photon state. The two-photon state is slightly below the optical state in monophenyl-substituted polyacetylenes, but above the optical state in diphenyl-substituted polyacetylenes, thereby explaining the strong photoluminescence of the latter class of materials. We present a detailed mechanism of the crossover in the energies of the one- and two-photon states in these systems. In addition, we calculate the optical-absorption spectra over a wide wavelength region, and make specific predictions for the polarizations of low- and high-energy transitions that can be tested on oriented samples. Within existing theories of light emission from π-conjugated polymers, strong photoluminescence should be restricted to materials whose optical gaps are larger than that of transpolyacetylene. The present work shows that, conceptually at least, it is possible to have light emission from systems with smaller optical gaps.",
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T1 - Electron-correlation-induced transverse delocalization and longitudinal confinement in excited states of phenyl-substituted polyacetylenes

AU - Ghosh, Haranath

AU - Shukla, Alok

AU - Mazumdar, Sumitendra

PY - 2000/11/15

Y1 - 2000/11/15

N2 - Electron-electron interactions in general lead to both ground-state and excited-state confinement. We show, however, that in phenyl-substituted polyacetylenes electron-electron interactions cause enhanced delocalization of quasiparticles in the optically excited state from the backbone polyene chain into the phenyl groups, which in turn leads to enhanced confinement in the chain direction. This cooperative delocalization confinement lowers the energy of the one-photon state and raises the relative energy of the lowest two-photon state. The two-photon state is slightly below the optical state in monophenyl-substituted polyacetylenes, but above the optical state in diphenyl-substituted polyacetylenes, thereby explaining the strong photoluminescence of the latter class of materials. We present a detailed mechanism of the crossover in the energies of the one- and two-photon states in these systems. In addition, we calculate the optical-absorption spectra over a wide wavelength region, and make specific predictions for the polarizations of low- and high-energy transitions that can be tested on oriented samples. Within existing theories of light emission from π-conjugated polymers, strong photoluminescence should be restricted to materials whose optical gaps are larger than that of transpolyacetylene. The present work shows that, conceptually at least, it is possible to have light emission from systems with smaller optical gaps.

AB - Electron-electron interactions in general lead to both ground-state and excited-state confinement. We show, however, that in phenyl-substituted polyacetylenes electron-electron interactions cause enhanced delocalization of quasiparticles in the optically excited state from the backbone polyene chain into the phenyl groups, which in turn leads to enhanced confinement in the chain direction. This cooperative delocalization confinement lowers the energy of the one-photon state and raises the relative energy of the lowest two-photon state. The two-photon state is slightly below the optical state in monophenyl-substituted polyacetylenes, but above the optical state in diphenyl-substituted polyacetylenes, thereby explaining the strong photoluminescence of the latter class of materials. We present a detailed mechanism of the crossover in the energies of the one- and two-photon states in these systems. In addition, we calculate the optical-absorption spectra over a wide wavelength region, and make specific predictions for the polarizations of low- and high-energy transitions that can be tested on oriented samples. Within existing theories of light emission from π-conjugated polymers, strong photoluminescence should be restricted to materials whose optical gaps are larger than that of transpolyacetylene. The present work shows that, conceptually at least, it is possible to have light emission from systems with smaller optical gaps.

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