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HL: Fachverband Halbleiterphysik

HL 9: Poster 1

HL 9.94: Poster

Montag, 23. März 2009, 14:30–17:00, P2

Packing of Planar Organic Molecules: Interplay of van der Waals and Electrostatic Interaction — •Mira El Helou^1,2, Daniel Käfer², Christian Gemel³, and Gregor Witte^1,2 — ¹Molekulare Festkörperphysik, Philipps-Universität Marburg, D-35037 Marburg, Germany — ²Physikalische Chemie I, Ruhr-Universität Bochum, D-44780 Bochum, Germany — ³Anorganische Chemie II, Ruhr-Universität Bochum, D-44780 Bochum, Germany

The molecular packing and thermal stability of pentacene and its two oxo-derivatives (6,13-pentacenedione and 5,7,12,14-pentacenetetrone) in their crystalline phase have been analyzed and compared with quantum chemical calculations of the electronic structure of the molecular entities. While pentacene reveals a face-on-edge herringbone packing, both oxygen containing species adopt an almost coplanar stacking. Quantum chemical calculations reveal discernible charge localization at the oxygen atoms which in turn causes an electrostatic O-π-interaction and hence favours a planar stacking. On the other hand, the polarizability of the conjugated systems of both oxo-species is reduced and their intermolecular distance is enlarged, due to the bulky oxygen atoms, both leading to a lower van-der Waals interaction and thus explains the decreased thermal stability of the studied oxidized entities. The present study emphasizes the importance of the balance of electrostatic and van-der Waals interactions [1].

[1] D. Käfer, M. El Helou, Ch. Gemel, Gregor Witte Crystals Growth and Design 8, No.8, 3053 (2008).