Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 4: Organic Thin Films
DS 4.4: Vortrag
Montag, 25. Februar 2008, 17:00–17:15, H 2013
Direct spectroscopic evidence for the π–π–interaction between heteroaromatic molecules — •F. Holch1, D. Hübner1, R. Fink2, A. Schöll1, F. Reinert1, and E. Umbach1 — 1Universität Würzburg, Experimentelle Physik II — 2Universität Erlangen/ICMM, Physikalische Chemie II
High-resolution near-edge x-ray absorption fine structure (NEXAFS) spectroscopy is a very sensitive tool to analyse the electronic structure of condensed, liquid, and gaseous samples. Moreover, it provides local information due to the localized core hole excitation. We have utilized the potentials of this technique to probe the localisation of the π–interaction within aggregates of organic molecules.
An analysis of the intermolecular interaction requires a comparison of high–quality spectroscopic data of gaseous and condensed organic molecules. On the example of the heteroaromatic molecules 1,4,5,8-naphthalene-tetracarboxylic acid dianhydride (NTCDA) and 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) we present spectroscopic evidence which allows us to confine the intermolecular interaction to the π–system of the aromatic core. The NEXAFS spectra show a consistent shift of all resonances of the naphthalene ring system towards lower energy upon condensation, while such a shift can not be observed for the functional group. These experimental findings can be interpreted in terms of a π–π–interaction induced delocalisation of the naphthalene π–system leading to a lowering of the respective orbital energy.
This project is financed by the BMBF under contract 05KS4WWC/2