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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical calculation of the electro-absorption spectrum of the α-sexithiophene single crystal (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 1328-1335 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An extended two-dimensional analogue of the Merrifield model of the mixing between Frenkel and charge-transfer excitons is used to calculate the electro-absorption spectrum of the α-sexithiophene single crystal. The model reflects the symmetry of the crystal and takes into account all the major interactions between the molecules. The input parameters are estimated from independent quantum-chemical and micro-electrostatic calculations. The simulated spectrum is in very good agreement with experiment, both in shape and in absolute amplitude. The results demonstrate that the eigenstates of the crystal between 2.55 and 2.85 eV are primarily of charge-transfer parentage, so that charge-transfer contributions dominate the electro-absorption spectrum in that region. This first successful reproduction of the electro-absorption spectrum of a single crystal is a stringent test of the theoretical description that confirms its validity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1484378
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  • 2
    Electronic Resource
    Electronic Resource
    Vibronic interpretation of the low-energy absorption spectrum of the sexithiophene single crystal (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 11306-11314 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The classic model of vibronic coupling in dimers and tetramers is used for calculating the vibronic fine structure of the lowest-energy electronic transition in the sexithiophene crystal. Good semiquantitative agreement with experiment is achieved, lending credence to the applied model. The observed intensity pattern is interpreted in terms of the deviations from the adiabatic approximation in closely spaced electronic states. The intramolecular Herzberg–Teller corrections are of lesser importance, but are the probable cause of the minor discrepancies in the simulated spectra. The results suggest a modified interpretation of the experimental fluorescence spectra. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290026
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  • 3
    Electronic Resource
    Electronic Resource
    Charge transfer induced local Frenkel exciton states in naphthalene crystals heavily doped with durene (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3099-3103 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absorption and luminescence spectra of durene-doped naphthalene crystals are reported for different dopant concentrations. New impurity-induced absorption bands are interpreted as charge transfer induced local Frenkel exciton states. The results of theoretical calculations, performed (without invoking any adjustable parameters) for a series of finite model clusters are in very good agreement with experiment and support this interpretation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468619
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  • 4
    Electronic Resource
    Electronic Resource
    Autoionization of excited Frenkel states in the anthracene crystal (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4607-4614 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Autoionization of Frenkel excitons is re-examined as a potential source of the anthracene photocurrent at photon energies higher than 4.4 eV. A crude estimate of the rate constant suggests autoionization as a feasible depletion channel, the resultant photocurrent quantum yield being in reasonable agreement with experiment. Bounds for the thermalization radius of charge carriers produced by autoionization are estimated. The estimates, based on a simple model of charge carrier transport and scattering, are found to agree, as to the order of magnitude, with experimental data. A fit of the experimental photocurrent spectrum indicates that while in the near-threshold region the photocurrent is dominated by charge pairs produced by direct optical excitation, at higher energies the autoionization mechanism generally prevails.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466293
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical interpretation of the electroabsorption spectra of polyacene crystals. II. Charge-transfer states (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7576-7582 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In recent articles, a two-dimensional analog of the Merrifield model of the coupling between the Frenkel and charge transfer (CT) excitations of a molecular crystal was successfully applied for the calculation of the electroabsorption (EA) spectra of polyacene crystals. Presently, the results of those calculations are rationalized in terms of a simplified two-state model, designed specifically for interpretational purposes. Particular attention is given to the CT manifold where symmetry considerations rule out the existence of eigenstates endowed with nonzero dipole moment, seemingly contradicting the existing experimental evidence of second-derivative EA signals. The apparent contradiction is resolved by analyzing EA contributions from pairs of zero-field eigenstates coupled by the modulating field. The new approach provides a bridge to the conventional interpretation rooted in the localized model of CT excitations, and allows to determine the limits of validity of the traditional analysis of EA spectra. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480084
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical calculation of the electroabsorption spectra of polyacene crystals (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4427-4440 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A two-dimensional analog of the Merrifield model of the coupling between the Frenkel and charge transfer (CT) excitations of a molecular crystal is applied for the calculation of the electroabsorption (EA) spectra of polyacene crystals. The approach is essentially nonempirical, with most of the necessary input data estimated either from theoretical calculations or from independent experiments. Good quantitative reproduction of the experimental EA spectra is achieved, both in their absolute amplitude and intensity pattern. The large amplitude of the Frenkel exciton part of the spectra is successfully accounted for without the necessity to invoke anomalously large molecular polarizabilities. Some basic assumptions of previous analyses are shown to be invalid and future prospects of the new approach are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472295
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  • 7
    Electronic Resource
    Electronic Resource
    Charge-transfer exciton band structure in the fullerene crystal-model calculations (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7923-7931 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A three-dimensional analog of the Merrifield model of the coupling between Frenkel and charge-transfer (CT) excitons of the C60 fullerene crystal is presented. The model is based on the nearest-neighbor approximation for the off-diagonal interactions and is essentially nonempirical. The parameters are estimated from free-molecule data and from the results of theoretical calculations published by other authors. The band structure of CT excitons in C60 is calculated and discussed in the context of available experimental evidence. Residual ambiguities in the parametrization are removed by calculation of the electroabsorption spectrum and comparison with experiment, as described in the accompanying paper. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477626
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical interpretation of the electroabsorption spectra of polyacene crystals. I. Role of Frenkel states (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7114-7119 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently proposed two-dimensional model of the coupling between the Frenkel and charge transfer (CT) excitations of a molecular crystal, successfully applied for the calculation of the electroabsorption (EA) spectra of polyacenes [Petelenz et al., J. Chem. Phys. 105, 4427 (1996)], is applied to probe the influence of different intramolecular excited states on the EA signal in the CT energy range. The study highlights the preeminent role of Frenkel excitons that are energetically close to the CT manifold, even if they are inactive in conventional absorption spectroscopy. The high-energy intense excitons are found to have a lesser effect. The study suggests EA spectroscopy as a potential tool to detect and locate some of the absorption-inactive intramolecular excitations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474952
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical interpretation of the electroabsorption spectrum of fullerene films (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7932-7939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A three-dimensional analogue of the Merrifield model of the coupling between the Frenkel and charge transfer (CT) excitations of a molecular crystal is used to calculate the electroabsorption (EA) spectrum of buckminsterfullerene films. The approach is essentially nonempirical, with most of the input parameters estimated from theoretical calculations or from independent experiments, but in doubtful cases a comparison of the calculated and experimental EA spectra guides the choice between alternative sets of parameters. Semiquantitative agreement between the calculated and experimental EA spectra lends credence to the model, which can therefore be used to draw conclusions concerning the underlying physical mechanisms. The EA signal of the CT states is shown to be substantially affected by the off-diagonal CT interactions, and by interactions with the optically inactive Frenkel excitons, whose intramolecular parentage is tentatively assigned. The results confirm the validity of previous calculations of the electrostatic CT state energies. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477440
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  • 10
    Electronic Resource
    Electronic Resource
    Multiple charge-transfer-induced local exciton levels in doped naphthalene crystals (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3737-3746 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements of the absorption spectra of naphthalene crystals doped with benzene derivatives are reported. For a typical dopant, a set of bands (some genuinely local, some due to resonances) is observed. The patterns of local levels are interpreted in terms of the recently proposed two-dimensional cluster model. It gives a good qualitative description of the general features of the observed spectra. Probable reasons of quantitative discrepancies are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464052
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