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O: Fachverband Oberflächenphysik

O 65: Metal substrates: Adsorption of organic / bio molecules VII

O 65.1: Vortrag

Donnerstag, 17. März 2011, 11:15–11:30, PHY C213

Coverage dependent isomerisation behaviour of tetra-tert-butyl-imine on Au(111) — •Felix Leyssner, Matthias Koch, Stephan Meyer, and Petra Tegeder — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, D-14195 Berlin

High resolution electron energy loss spectroscopy (HREELS) is employed to analyze thermally activated changes in the geometrical structure of the photochromic molecular switch 3,3’,5,5’-tetra-tert-butyl-imine (TBI) adsorbed on Au(111). Measurements have been performed for two coverage regimes: The monolayer and the bilayer regime. For both coverages all molecules are found in the trans state after deposition at sample temperatures of T=210K, but conformational changes upon heating are observed, which are assigned to a trans to cis-isomerization. When heating the sample to T=440K two different conformations are observed depending on the initial coverage. Annealing of a monolayer leads to an increasing number of cis isomers, pointing towards an inverted thermal isomerisation behaviour of TBI, since the trans-isomer is the more stable compound in solution. Whereas for a bilayer the temperature induced isomerization of the TBI can be monitored as well, but desorption of the second layer at T=440K leads to the formation of a trans-monolayer. The fact that different molecular configurations are found for equal coverages annealed at the same temperature is highly surprising and shows that collective effects may govern the switching properties of molecular switches on surfaces.