Regensburg 2007 – scientific programme
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O: Fachverband Oberflächenphysik
O 41: Metal Substrates: Adsorption II
O 41.6: Talk
Wednesday, March 28, 2007, 17:00–17:15, H39
Racemic mixing in 2D molecular self-assembly — •Thorsten Kampen1, Rocio Cortes2, Philipp Martin Schmidt1, Hugo Dil1, Arantzazu Mascaraque2, and Karsten Horn1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany — 2Depto. Física de Materiales, Universidad Complutense de Madrid, Madrid, Spain
Inherently achiral molecules may become chiral when adsorbed on surfaces, through the loss of symmetry elements in a 2D structure. Here we show how this effect leads to chiral supramolecular assemblies in 4,4'-stilbene dicarboxylic acid (DCSB) on Cu(110) using scanning tunnelling microscopy. DCSB molecules are found to adsorb on Cu(110) surface via bonding of all four oxygen atoms of the deprotonated carboxylic end-groups to next- neighbour Cu atoms. In the 2D environment of a surface the molecule assumes to enantiomorphous orientation, that is, the molecules become chiral. Due to the chiral character of the adsorbed molecule and intermolecular interactions two chiral adsorption phases are found, namely a cubic and a herringbone phase. While in the metastable "rectangular" phase consists only of right- or left-handed molecules, i.e each domain is enantiomorphously pure, the "herringbone" phase is a "racemic mixture" built up of left- and right-handed molecules. The formation of the herringbone phase is thermodynamically preferred since it decreases the free enthalpy of the self-assembled DCSB islands.