Berlin 2008 – scientific programme
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O: Fachverband Oberflächenphysik
O 34: Metal Substrates: Adsorption of Organic/Bio Molecules II
O 34.8: Talk
Tuesday, February 26, 2008, 15:30–15:45, MA 043
The role of surface-molecule interaction in the isomerisation of Azobenzene molecules — •Nils Henningsen1, Riccardo Rurali2, Katharina J. Franke1, Isabel Fernandez Torrente1, Gunnar Schulze1, Beate Priewisch3, Karola Rück-Braun3, and Nacho Pascual1 — 1Institut für Experimentalphysik, Freie Universität Berlin, Germany — 2Departament d'Enginyeria Electrònica, Universitat Autònoma de Barcelona, Spain — 3Institut für Chemie, Technische Universität Berlin, Germany
Azobenzene is a prototype molecular switch in the gas phase and in solution. Upon adsorption on a surface, the switching properties are largely influenced. By means of scanning tunnelling microscopy (STM) and density functional theory (DFT) we investigate the switching behaviour of an azobenzene derivative (DMC: di-meta-cyano-Azobenzene) on several noble metal surfaces, Au(111), Ag(100) and Cu(100). STM reveals that, after vacuum deposition, DMC adsorbs exclusively as trans-isomers. By applying voltage pulses with the STM tip, we are able to induce a conformational change into the cis-configuration on Ag(100) and on Cu(100). DFT calculations show that the stabilization of the cis isomers is mediated by a strong hybridization of the azo-group with the substrate. We argue that the larger the hybridization with the substrate the more stable is the cis configuration. This causes that the cis isomer is very stable on Cu(100), while the reversible switching into the trans state is possible on Ag. On Au(111) almost no hybridization is present thus we observe that only the trans molecules is a stable state on the surface.