Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 4: Metal substrates: Adsorption of organic / bio molecules I

O 4.6: Vortrag

Montag, 23. März 2009, 12:30–12:45, SCH A118

Ring opening reaction of spiropyran on a Au(111) surface — •Marten Piantek, Cristina Navio, Alex Krüger, Matthias Bernien, Jorge Miguel, and Wolfgang Kuch — Institut für Experimentalphysik, Freie Universität Berlin

Molecules that exhibit a photon-induced reversible transition between two isomeric states entail an enormous potential for applications in electronics, photonics, and computing. 1',3',3'-trimethyl-6-nitro-spiro[chromene-2,2'-indole](BIPS) undergoes such a photochromic process involving a heterolytic cleavage of the C--O bond in the pyran ring which goes along with a drastic change of the molecular electronic properties. In the gas phase, in solution, and in the crystalline form, this ring opening/closing mechanism is well understood.

Here we present a temperature-dependent adsorption study of one monolayer of BIPS on a Au(111) single crystal surface. By means of angle-dependent near edge X-ray absorption fine structure (NEXAFS) and X-ray photoemission spectroscopy (XPS) we obtained information about the adsorption geometry and the electronic properties. The simulation of NEXAFS by means of DFT calculations was used for the interpretation of the experimental data. We find that the BIPS molecules deposited at 150 K are in the closed-ring configuration. While the illumination with UV-light had no effect on the monolayer, during heating the sample up to 330 K the molecules transform to the ring opened configuration. Since we did not find a back transformation by cooling back to 150 K, the opened-ring geometry is the preferred conformation on the the surface, in contrast to gas phase and solution.