Berlin 2012 – scientific programme
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O: Fachverband Oberflächenphysik
O 24: [DS] Organic electronics and photovoltaics: simulations and optics I (jointly with CPP, HL, O)
O 24.4: Talk
Tuesday, March 27, 2012, 10:15–10:30, H 2032
Vibrational Davydov-splittings in oriented organic semiconductor crystals: polarization-dependent measurements versus theoretical calculations — •Tobias Breuer1, Mali Celik2, Peter Jakob3, Ralf Tonner2, and Gregor Witte1 — 1AG Molekulare Festkörperphysik — 2AG Theoretische Oberflächenchemie — 3AG Oberflächenphysik, Philipps-Universität Marburg, D-35032 Marburg
Vibrational properties of highly ordered crystalline perfluoropentacene (PFP) films epitaxially grown on KCl(100) and NaF(100) substrates have been studied by means of transmission infrared spectroscopy and density functional theory. The different molecular orientations adopted by PFP on both substrates (standing vs. lying) and their epitaxial ordering [1] enable precise polarization-resolved measurements along individual crystallographic directions and thus allow an unambiguous experimental determination of the polarizations of the IR modes. Computations of the vibrational spectra beyond the single-molecule approximation were employed at the periodic dispersion-corrected density functional level (PBE-D2PBC) and compared to non-periodic calculations (PBE/def2-TZVPP). Thereby, a comparison between experiment and different theoretical models was enabled. A microscopic explanation for the experimentally observed Davydov splitting of some modes and the IR-inactivity of others was derived, based on the mutual coupling of the dynamical dipole moments of the two molecules within the unit cell.
[1] T. Breuer et al., Phys. Rev. B 83, 155428 (2011).