Regensburg 2022 – scientific programme

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O: Fachverband Oberflächenphysik

O 52: Poster Wednesday: Adsorption and Catalysis 2

O 52.6: Poster

Wednesday, September 7, 2022, 18:00–20:00, P4

On-Surface Synthesis of Kekulene and Isokekulene — •Tim Naumann, Qitang Fan, Lukas Heuplick, Lukas Ruppenthal, Simon Werner, Tobias Vollgraff, Jörg Sundermeier, and J. Michael Gottfried — Fachbereich Chemie, Philipps-Universität Marburg, Marburg (Germany)

The concept of aromaticity explains the exceptional stability of monocyclic, planar, conjugated molecules. When extending this concept on cycloarenes, however, the question arises whether the π-electron system is best described by the Clar model or rather by annulenoid aromaticity, i.e. delocalization in the inner and outer annulene ring. This question has been discussed especially in the context of kekulene, an alternant benzenoid cycloarene. On-Surface techniques offer the possibility to synthesize kekulene and to investivate its resonance stabilisation. To create complete monolayers of kekulene for further spectroscopic studies, we developed a high-yield on-surface synthesis of kekulene on Cu(111) from vapor-deposited 1,4,7(2,7)-triphenanthrenacyclononaphane-2,5,8-triene, which undergoes cyclodehydrogenation upon annealing, resulting in extended (up to 100 nm) well-ordered domains of kekulene. While the reaction is highly selective towards kekulene on Cu(111), reaction on Cu(110) leads to an isomer of kekulene with a lower symmetry, named isokekulene. The precursor and the products were analyzed with scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and other methods. Further annealing leads to peripheral C-H bond activation and linking towards chains and islands.