Femtosecond energy relaxation in π-conjugated polymers

Kersting, R.; Lemmer, Uli; Mahrt, Rainer F.; Leo, Karl; Kurz, H.; Bäßler, H.; Göbel, E. O.

doi:10.1103/physrevlett.70.3820

Cited by 428 publications

(274 citation statements)

References 17 publications

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“…[10][11][12][13][14][15][16][17][18][19][20][21] For example, in polydiacetylene, the primary excitation is a neutral exciton with strong exciton binding energy. 10,11 In contrast, the primary excitation in poly(p-phenylenevinylene) (PPV) and its derivatives is debated to be a neutral exciton [12][13][14][15][16][17] or a charged polaron. [18][19][20][21] By contrast, chemically doped conjugated polymers, which show high electrical conductivity at room temperature, have clearly charged defect (polaron) states that are extrinsically introduced in the bandgap by chemical treatment.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Dynamics of Polarons in Conductive Polyaniline: Comparison of Primary and Secondary Doped Forms

2008

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Time-and wavelength-resolved pump-probe measurements are performed on the conductive, primary and secondary doped, forms of polyaniline in solution to investigate the relaxation dynamics of photoexcited polarons. Contrasting dynamics observed in the two forms allow investigation of electronic (and structural) relaxation of this material. Pump pulse at 800 nm photoexcites an electron from the valence to polaron band, and subsequent relaxation dynamics are probed by a white light continuum pulse. Three distinct features are observed in the primary doped sample: (1) absorption near time zero in the 900-1025 nm probe wavelength region; (2) delayed absorption from 850 to 1025 nm; (3) pronounced oscillations with frequencies of 165 and 210 cm -1 . The first two features are associated with intraband absorptions to higher-lying states in the polaron band from the initial excited and conformationally changed intermediate states. The oscillations reflect torsional motions associated with photoexcitation and relaxation. In the secondary doped material, only bleaching and stimulated emission are observed throughout the whole spectral region; neither transient absorption signals nor oscillatory dynamics are observed. Kinetic modeling is performed to establish the mechanism of relaxation. We propose that the excited polaron relaxes nonradiatively to the ground state through an intermediate state(s) with a twisted geometry. Our measurements and analysis allow us to describe the structure of the polaron bands for primary and secondary doped polyaniline; they are in the small and large polaron limits, respectively, and are consistent with a bandgap for the primary doped form and without a bandgap (i.e., metallic) for the secondary doped material.

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Section: Introductionmentioning

confidence: 99%

Ultrafast Dynamics of Polarons in Conductive Polyaniline: Comparison of Primary and Secondary Doped Forms

2008

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“…This is because, prior to recombination, excitons diffuse to those parts of the sample where they have the lowest energy. 37 The second reason is that after photoexcitation, the rings, which may be twisted around their common C-C bond, tend to co-planarize in the excited state, due to the fact that the excited state is slightly more quinoid than the aromatic ground state. 2 As we are performing our calculations for a perfect, co-planar chain of PT, we should therefore compare our optical gap to the luminescence gap.…”

Section: Crystalline Polythiophenementioning

confidence: 99%

Ab initioprediction of the electronic and optical excitations in polythiophene: Isolated chains versus bulk polymer

et al. 2000

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initio prediction of the electronic and optical excitations in polythiophene : isolated chains versus bulk polymer. Physical Review B, 61(23), 15817-15826. DOI: 10.1103/PhysRevB.61.15817 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. We calculate the electronic and optical excitations of polythiophene using the GW ͑G stands for one-electron Green function, W for the screened Coulomb interaction͒ approximation for the electronic self-energy, and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. Two different situations are studied: excitations on isolated chains and excitations on chains in crystalline polythiophene. The dielectric tensor for the crystalline situation is obtained by modeling the polymer chains as polarizable line objects, with a long-wavelength polarizability tensor obtained from the ab initio polarizability function of the isolated chain. With this model dielectric tensor we construct a screened interaction for the crystalline case, including both intra-and interchain screening. In the crystalline situation both the quasiparticle band gap and the exciton binding energies are drastically reduced in comparison with the isolated chain. However, the optical gap is hardly affected. We expect this result to be relevant for conjugated polymers in general.

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“…For -conjugated polymers the time-dependent shift of the luminescence spectrum ͑dynamic Stokes shift͒ has been modeled by assuming excitons localized on a few repeat units, which migrate spatially as well as energetically through Förster transfer. [21][22][23] It was concluded that the Stokes shift in these systems cannot be explained from nuclear displacements, as would be the case for single molecules, and that the migration process plays a crucial role. 21 Also for J aggregates, with strongly delocalized exciton states, the belief is that the Stokes shift induced by nuclear displacements is small, in fact much smaller than the Stokes shift of their single-molecule constituents.…”

Section: Introductionmentioning

confidence: 99%

Low-temperature dynamics of weakly localized Frenkel excitons in disordered linear chains

Bednarz

Малышев

Knoester

2004

The Journal of Chemical Physics

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Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We calculate the temperature dependence of the fluorescence Stokes shift and the fluorescence decay time in linear Frenkel exciton systems resulting from the thermal redistribution of exciton population over the band states. The following factors, relevant to common experimental conditions, are accounted for in our kinetic model: ͑weak͒ localization of the exciton states by static disorder, coupling of the localized excitons to vibrations in the host medium, a possible nonequilibrium of the subsystem of localized Frenkel excitons on the time scale of the emission process, and different excitation conditions ͑resonant or nonresonant͒. A Pauli master equation, with microscopically calculated transition rates, is used to describe the redistribution of the exciton population over the manifold of localized exciton states. We find a counterintuitive nonmonotonic temperature dependence of the Stokes shift. In addition, we show that depending on experimental conditions, the observed fluorescence decay time may be determined by vibration-induced intraband relaxation, rather than radiative relaxation to the ground state. The model considered has relevance to a wide variety of materials, such as linear molecular aggregates, conjugated polymers, and polysilanes.

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Femtosecond energy relaxation in π-conjugated polymers

Cited by 428 publications

References 17 publications

Ultrafast Dynamics of Polarons in Conductive Polyaniline: Comparison of Primary and Secondary Doped Forms

Ultrafast Dynamics of Polarons in Conductive Polyaniline: Comparison of Primary and Secondary Doped Forms

Ab initioprediction of the electronic and optical excitations in polythiophene: Isolated chains versus bulk polymer

Low-temperature dynamics of weakly localized Frenkel excitons in disordered linear chains

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