Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 11: Metal substrates: Adsorption of organic / bio molecules II

O 11.1: Talk

Monday, March 23, 2009, 15:00–15:15, SCH A118

Molecular chemistry at surfaces: Ring opening reaction of Spiropyrane molecules on a metal surface — •Gunnar Schulze, Marten Piantek, Cristina Navío, Jorge Miguel, Matthias Koch, Felix Leyssner, Katharina J. Franke, Petra Tegeder, Wolfgang Kuch, and Jose Ignacio Pascual — Inst. für Experimentalphysik, Freie Universität Berlin, Arnimalle 14, 14195 Berlin

The ring-opening reaction of spiropyran (SP)to the merocyanine (MC) form is a reversible photochromic process in solution. The interest in this basic reaction stems from the different properties of each isomer, regarding to structure (SP is chiral), electrical dipole moment (MC has a large dipole) and electronic structure (MC is coloured). In solution SP is the thermally stable isomer. Here, we report that on a metal surface, MC turns out to be more stable. We investigate the thermally induced ring-opening transition from the organic photo switch 6-nitro-spriropyran to its merocyanine isomer on a Au(111) surface by means of low temperature scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS) and force-field simulations. In submonolayer coverages, each isomer presents a very distinct behaviour in terms of electronic properties and structure of the self-assembled molecular domains. Once that the merocyanine domains are created by thermal activation, they remain stable, suggesting that the interaction of the conjugated planar backbone with the metal surface helps to stabilize this isomer. The ring opening reaction can be also induced by local electric currents conducted through the molecule by the STM tip.