Diagrammatic exciton-basis valence-bond theory of linear polyenes

Chandross, Michael; Shimoi, Yukihiro; Mazumdar, S.

doi:10.1103/physrevb.59.4822

Cited by 52 publications

(116 citation statements)

References 52 publications

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“…The scaling law [12] is inapplicable to Mott-insulators, in which the origin of the optical nonlinearity is the very large dipole coupling between nearly degenerate excited states of opposite parities. The mechanism of optical nonlinearity here is related to that in the π-conjugated polymers, which are described within the one-band extended Hubbard model and in which also there occurs very large dipole coupling between the optical state and a two-photon state slightly higher in energy [13]. Not surprisingly, the magnitude of χ (3) in Sr 2 CuO 3 is therefore comparable to some of the best organic materials [14,15].…”

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confidence: 75%

Ultrafast Optical Nonlinearity in the Quasi-One-Dimensional Mott InsulatorSr2CuO3

et al. 2000

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We report strong instantaneous photoinduced absorption in the quasi-onedimensional Mott insulator Sr 2 CuO 3 in the IR spectral region. The observed photoinduced absorption is to an even-parity two-photon state that occurs immediately above the absorption edge. Theoretical calculation based on a two-band extended Hubbard model explains the experimental features and indicates that the strong two-photon absorption is due to a very large dipolecoupling between nearly degenerate one-and two-photon states. Room temperature picosecond recovery of the optical transparency suggests the strong potential of Sr 2 CuO 3 for all-optical switching.Typeset using REVT E X 1

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confidence: 75%

Ultrafast Optical Nonlinearity in the Quasi-One-Dimensional Mott InsulatorSr2CuO3

et al. 2000

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“…First, A g states that give rise to spectral feature III occur also in linear chain polyenes. 21 Their contribution to EA and TPA are vanishingly weak in long chains. In contrast, the contributions of the experimental kA g to EA and TPA in PPV derivatives are clearly visible.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…Frolov et al ascribe PA1 to the excited-state absorption from the optical 1B u state to the so-called mA g state ͑where m is a chain length dependent unknown quantum number͒, whose nature has been discussed extensively by theorists in the context of nonlinear spectroscopy of both luminescent polymers like PPV as well as nonluminescent linear chain polyacetylenes and polydiacetylenes. [20][21][22][23][24][25][26][27] PA2 has been ascribed by Frolov et al to the excited-state absorption to a higher energy kA g state ͑where k is again an unknown quantum number͒, whose counterpart does not exist in the linear chain polymers, according to these authors. Interestingly, the relaxation dynamics of PA1 and PA2 are very different: while the mA g decays back to the optical 1B u exciton by internal conversion, the kA g undergoes a different relaxation pathway that leads to dissociation into long-lived polaron pairs that are probably interchain.…”

Section: Introductionmentioning

confidence: 99%

Theory of excited-state absorption in phenylene-basedπ-conjugated polymers

2003

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Within a rigid-band correlated electron model for oligomers of poly-͑paraphenylene͒ ͑PPP͒ and poly͑paraphenylenevinylene͒ ͑PPV͒, we show that there exist two fundamentally different classes of two-photon A g states in these systems to which photoinduced absorption ͑PA͒ can occur. At relatively lower energies there occur A g states which are superpositions of one electron-one hole (1e -1h) and two electron-two hole (2e -2h) excitations, that are both comprised of the highest delocalized valence-band and the lowest delocalized conduction-band states only. The dominant PA is to one specific member of this class of states ͑the mA g ). In addition to the above class of A g states, PA can also occur to a higher energy kA g state whose 2e -2h component is different and has significant contributions from excitations involving both delocalized and localized bands. Our calculated scaled energies of the mA g and the kA g agree reasonably well to the experimentally observed low-and high-energy PA's in PPV. The calculated relative intensities of the two PA's are also in qualitative agreement with experiment. In the case of ladder-type PPP and its oligomers, we predict from our theoretical work an intense PA at an energy considerably lower than the region where PA's have been observed currently. Based on earlier work that showed that efficient charge-carrier generation occurs upon excitation to odd-parity states that involve both delocalized and localized bands, we speculate that it is the characteristic electronic nature of the kA g that leads to charge generation subsequent to excitation to this state, as found experimentally.

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“…Note that with the Ohno Coulomb parameters, which are intermediate in strength, relatively small increase in the confinement can lead to 2A g -1B u crossover. In the case of linear chain polyenes within the rigid bond approximation (i.e., hopping integrals t 0 (1±δ)) the difference in the electron-hole correlation length in the 1B u state 31 . between δ = 0.07 (E(2A g ) < E(1B u )) and δ = 0.3 (E(2A g ) > E(1B u )) is only 7 %.…”

Section: A Lowest Energy Absorptionmentioning

confidence: 99%

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

2000

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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 co-operative 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 mono-phenyl substituted polyacetylenes, but above the optical state in di-phenyl 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 trans-polyacetylene. The present work show that conceptually at least, it is possible to have light emission from systems with smaller optical gaps. 42.70.Jk,71.20.Rv,78.30.Jw

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Diagrammatic exciton-basis valence-bond theory of linear polyenes

Cited by 52 publications

References 52 publications

Ultrafast Optical Nonlinearity in the Quasi-One-Dimensional Mott InsulatorSr2CuO3

Ultrafast Optical Nonlinearity in the Quasi-One-Dimensional Mott InsulatorSr2CuO3

Theory of excited-state absorption in phenylene-basedπ-conjugated polymers

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

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