High energy two-photon states in finite versus infinite polyenes

Mazumdar, S.; Guo, Dandan; Dixit, S.

doi:10.1063/1.462576

Cited by 27 publications

(9 citation statements)

References 25 publications

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“…In all cases our abcissa is the energy scaled with respect to E(1B u ). As pointed out before, 57 convergence in the scaled energies of high-energy states with increasing chain length is not expected in this region of relatively short chain lengths. This is because the lowest energy excitations ͑for example, the 1B u and the 2A g ) converge with increasing chain length much faster than the higher energy states.…”

Section: B Pa Spectra With Screened Coulomb Parametersmentioning

confidence: 85%

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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Section: B Pa Spectra With Screened Coulomb Parametersmentioning

confidence: 85%

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

2003

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“…In all cases our abcissa is the energy scaled with respect to E(1B u ). As pointed out before [39], convergence in the scaled energies of high energy states with increasing chain length is not expected in this region of relatively short chain lengths. This is because the lowest energy excitations (for example, the 1B u and the 2A g ) converge with increasing chain length much faster than the higher energy states.…”

Section: Correlated Electron Calculations Of Pa Spectramentioning

confidence: 87%

Ultrafast excited state absorption and charge separation in phenylene-based conjugated polymers

2004

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Ultrafast pump-probe spectroscopy of phenylene-based -conjugated polymers give low and high energy photoinduced absorptions (PAs) to final states with very different relaxation behavior. While the low energy two-photon state that is reached in PA relaxes to the optical exciton in ultrafast times, the higher energy two-photon state violates the Vavilov-Kasha rule and instead of relaxing to the optical exciton undergoes interchain dissociation to a polaron pair state. We have calculated the excited state absorptions of long oligomers of poly-paraphenylene and poly-paraphenylenevinylene within a rigid band correlated electron Hamiltonian, using the complete -electron basis and the powerful multi-reference singles and double configuration interaction technique. Our calculated PA spectra well reproduce the experimental PA. We further show that there exists a fundamental difference in the natures of the wavefunctions of the final states that are reached in low and high energy PA, and the difference originates from the existence of multiple kinds of bands in phenylene-based systems within one-electron theory. We speculate that the violation of the Vavilov-Kasha rule and charge separation into polaron pairs upon excitation to the high energy two-photon state is a consequence of its specific electronic structure, and discuss an earlier work on wavelength dependent photoconductivity of poly-paraphenylenevinylene to support this conjecture.

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“…The theoretical work of Mazumdar et al [63] and also experimental studies on carotenes [64,651 suggest that the 2A, state may only be weakly coupled to the 1Bu state and that a higher A, state is responsible for two-photon absorption. The higher A, state is considered to be above the B, state, although the energy separation these states decreases with increasing conjugation length.…”

Section: Internal Conversionmentioning

confidence: 97%

“…It has been argued [63] that extrapolations from oligomers of finite length to infinite polyenes based solely on a l/n dependence on the conjugation length, i.e. a 1-dimensional particle-in-a-box model, are unreliable and that for the higher energy excited states, the energy may depend nonlinearly on the reciprocal conjugation length, l / n ,…”

Section: Internal Conversionmentioning

confidence: 99%