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Author: Büchner, Bernd × Author: Knupfer, Martin × DDC: 530 × Has files: Yes ×

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Now showing 1 - 3 of 3
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    Exciton dispersion in para-quaterphenyl: Significant molecular interactions beyond Coulomb coupling
    (New York, NY : American Inst. of Physics, 2021) Graf, Lukas; Krupskaya, Yulia; Büchner, Bernd; Knupfer, Martin
    We have experimentally determined the momentum dependence of the electronic excitation spectra of para-quaterphenyl single crystals. The parallel arrangement of para-quaterphenyl molecules results in a strong Coulomb coupling of the molecular excitons. Such crystals have been considered to be a very good realization of the Frenkel exciton model, including the formation of H-type aggregates. Our data reveal an unexpected exciton dispersion of the upper Davydov component, which cannot be rationalized in terms of inter-molecular Coulomb coupling of the excitons. A significant reduction of the nearest neighbor coupling due to additional charge-transfer processes is able to provide an explanation of the data. Furthermore, the spectral onset of the excitation spectrum, which represents a heavy exciton resulting from exciton-phonon coupling, also shows a clear dispersion, which had been unknown so far. Finally, an optically forbidden excitation about 1 eV above the excitation onset is observed. © 2021 Author(s).
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    Charge transfer characteristics of F6TCNNQ–gold interface
    (Chichester [u.a.] : Wiley, 2020) Kuhrt, Robert; Hantusch, Martin; Knupfer, Martin; Büchner, Bernd
    The metal–organic interface between polycrystalline gold and hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ) was investigated by photoelectron spectroscopy with the focus on the charge transfer characteristics from the metal to the molecule. The valence levels, as well as the core levels of the heterojunction, indicate a full electron transfer and a change in the chemical environment. The changes are observed in the first F6TCNNQ layers, whereas for further film growth, only neutral F6TCNNQ molecules could be detected. New occupied states below the Fermi level were observed in the valence levels, indicating a lowest unoccupied molecular orbital (LUMO) occupation due to the charge transfer. A fitting of the spectra reveals the presence of a neutral and a charged F6TCNNQ molecules, but no further species were present.
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    Electronic properties of molecular solids: The peculiar case of solid picene
    (Milton Park : Taylor & Francis, 2010) Roth, Friedrich; Gatti, Matteo; Cudazzo, Pierluigi; Grobosch, Mandy; Mahns, Benjamin; Büchner, Bernd; Rubio, Angel; Knupfer, Martin
    Recently, a new organic superconductor, K-intercalated picene, with high transition temperatures Tc (up to 18 K) has been discovered. We have investigated the electronic properties of an undoped relative of this superconductor, solid picene, using a combination of experimental and theoretical methods. Our results provide deep insights into the occupied and unoccupied electronic states.