Dresden 2014 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 14: Organic/bio Molecules on Metal Surfaces II
O 14.8: Vortrag
Montag, 31. März 2014, 17:45–18:00, TRE Phy
Chiral Conflict among Different Helicenes Suppresses Formation of One Enantiomorph in 2D Crystallization — •Johannes Seibel1, Oliver Allemann2, Jay S. Siegel2, and Karl-Heinz Ernst1,2 — 1Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland — 2Department of Chemistry, University of Zürich, 8057 Zürich, Switzerland
Intermolecular chiral recognition plays a key role in the spontaneous resolution of enantiomers in crystallization or diastereomeric salt crystallization, a common technique for enantiomer separation in industry. Diastereomeric interactions in 2D crystals formed at solid surfaces serve as excellent models to study the underlying molecular recognition processes, where scanning tunneling microscopy provides submolecular resolution. The adsorption of a [5,6,9,10]-dibenzopentahelicene (db[5]H) racemate on Au(111) leads to 2D conglomerate formation, i. e. homochiral mirror domains containing only one enantiomer are observed, which is in contrast to previous results obtained for [7]H on Cu(111). Upon mixing M-[7]H into the monolayer, the balance between the mirror domains shifts gradually, until only the P-db[5]H enantiomorph is left in a monolayer containing 26% M-[7]H. This is explained by a preferred diastereomeric interaction between different helicene species of opposite handedness, suppressing the formation of the pure P-db[5]H enantiomorph by capturing P-db[5]H in non-ordered areas. These results show that dispersive forces can act in a manner comparable to polar forces in chiral discrimination at surfaces.