Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 34: Metal Substrates: Adsorption of Organic/Bio Molecules II
O 34.10: Vortrag
Dienstag, 26. Februar 2008, 16:00–16:15, MA 043
Reversible switching of tetra-tert-butylazobenzene on Au(111): A vibrational analysis — •László Óvári1,2, Martin Wolf1, and Petra Tegeder1 — 1Fachbereich Physik, Freie Universität Berlin — 2Reaction Kinetics Research Laboratory, Chemical Research Center of HAS, Szeged, Hungary
High resolution electron energy loss spectroscopy (HREELS) is employed to analyze reversible changes in the geometrical structure of the molecular switch 3,3’,5,5’-tetra-tert-butylazobenzene (TBA) adsorbed on Au(111), which are induced by UV-light and thermal activation. TBA was chosen because the four lateral tert-butyl-groups act as "spacer-legs" to increase the separation between the surface and the azobenzene π-system, and therefore leading to a reduced electronic coupling. From angular dependent measurements, viz. specular and off-specular scattering geometry, it could be proved that TBA adsorbs in the planar trans configuration in the submonolayer regime. UV-light exposure at 355 nm (3.5 eV) leads to pronounced changes in the vibrational structure of the TBA molecules in direct contact with the Au(111) surface, which we assign to a trans to cis isomerization. The reverse process, that is, the cis to trans isomerization, can be stimulated by thermal activation. An intensity decrease of vibrational modes as a function of photon dose allows calculation of an effective cross section of σ≈2*10−21 cm2 for the trans to cis isomerization.