Regensburg 2007 – wissenschaftliches Programm

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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices

SYOE 8: Poster Session SYOE

SYOE 8.29: Poster

Dienstag, 27. März 2007, 18:00–20:00, Poster B

Why a switch doesn't switch - a case study on stilbene on Si(100) — •Philipp Martin Schmidt, Karsten Horn, and Thorsten Kampen — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

Stilbene is the monomer building block of phenylenevinylene-type oligomers and polymers. In gas-phase and solutions the molecule undergoes an interconversion around its central C=C double bond upon irradiation with UV-light of 250-320nm wavelength [1].This cis-trans-isomerization of the free molecule follows an in-plane hula-twist mechanism [2] whose pathway can be assumed to work as well in constraint systems, that is on surfaces - thus assessing a "molecular switch". Stilbene-isomers on the Si(100)-surface have been investigated by UPS, XPS and NEXAFS thereby gaining information on the orientation of the molecules and their interaction with the surface. Especially NEXAFS-spectroscopy allows for an identification and differentiation of the two isomers in the adsorbed phase. Cis-Stilbene has been exposed to monochromatized UV-light of different wavelengths between 250 and 450nm. NEXAFS spectra reveal that the molecules are absolutely stable upon radiation and no conformational changes could be induced. A further analysis of NEXAFS spectra in combination with theoretical calculations gives an explanation of the inhibition of isomerization due to molecule-surface-interactions. 1. R.J. Sension et al., J. Chem. Phys. 98, 6291 (1993) 2. W.Fuß, et al., Angew. Chem. Int. Ed. 43, 4178 (2004)