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PGI-1 Seminar: Dr. Florian Klappenberger

Bottom-up constructing of 2D nanoarchitectures: from supramolecular assemblies via covalent coupling to novel hydrocarbon materials

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08 Oct 2014 11:30
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PGI Lecture Hall

Technische Universität München

Abstract:

The bottom-up construction of two-dimensional (2D) functional molecular nanoarchitectures under ultra-high vacuum conditions is reported in various examples including hydrogen-bonded layers, metal-organic coordination networks (MOCN), and covalent architectures. A comprehensive understanding is obtained by the STM+XS approach combining LT-scanning tunneling microscopy (STM) and X-ray spectroscopy with density functional theory investigations and all-atom molecular dynamic simulations allowing to precisely characterize the obtained nanostructures and unraveling the underlying formation mechanisms.

In a first example, a MOCN serves as template for confining supramolecular dynamers. The complex dynamics of the system, including the homeomorphic, asynchronous rotation pathways and the heteromorphic stereoisomerization, is unraveled with unprecedented detail on the single molecule level.

Next, upstanding chiral architectures (UCAs) are assembled from allene derivatives which are famous for their outstanding chiroptical responses. The complex structure of the monolayers thin domains results from morphological assembly principles relevant due to the enormous conformational phase space of the tectons.

Then the versatile potential of terminal alkynes for the construction of a range of nanoarchitectures is discussed. Homo-coupling allows for the synthesis of novel molecular species and conjugated 2D polymers at relatively low reaction temperatures (300 – 400 K) with volatile H2 as the only by-product. A profound analysis of the reaction mechanism demonstrates that on the noble metal surface the reaction is initiated via a covalentlycoupled tautomer and continues via step-wise dehydrogenation in contrast to the established solution pathways for Glaser-type coupling.

Employing a linear ditopic monomer on the stepped Ag(877) surface, a novel hydrocarbon semiconducting molecular wire was fabricated which represents an extended version of the thinnest possible graphdiyne nanoribbon.

On Cu(111) deprotonation of the terminal alkyne groups sets in at 300 K and leads to a novel binding motif namely a three-fold ionic C-H...π hydrogen bond strong enough to stabilize dense packed islands at room temperature. The difference of the covalent coupling mechanisms on the Ag and the Cu surfaces are discussed.

Contact

Prof. Dr. Stefan Blügel
Phone: +49 2461 61-4249
Fax: +49 2461 61-2850
email: s.bluegel@fz-juelich.de

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