München 2019 – wissenschaftliches Programm
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K: Fachverband Kurzzeit- und angewandte Laserphysik
K 7: Laser Applications II
K 7.3: Vortrag
Mittwoch, 20. März 2019, 14:40–15:00, HS 3
Generating Enantiomeric Excess in Thin Films of Chiral Molecules with Femtosecond Pulses — •Katrin Oberhofer1, Farinaz Mortaheb2, Johann Riemensberger1, Florian Ristow1, Reinhard Kienberger1, Ulrich Heiz2, Hristo Iglev1, and Aras Kartouzian2 — 1Physics Department, Technical University of Munich, James-Franck-Str., 85748 Garching, Germany — 2Chair of Physical Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748 Garching, Germany
Circularly polarized fs-pulses are used to desorb chiral molecules enantiospecifically from an achiral surface. We probe the optical activity of thin films of BINOL (1,1*-bi-2-naphtol), which are evaporated onto BK7 substrates, with the highly sensitive technique of second harmonic generation circular dichroism. The measured SHG-signal ILCP/RCP upon excitation with left/right circularly polarized (LCP/RCP) incoming fundamental light depends linearly on the thickness of the BINOL film. The anisotropy factor g = 2(ILCP−IRCP)/(ILCP + IRCP) is determined after distinct desorption time steps. We reproducibly observe symmetric desorption and antisymmetric anisotropy factors for irradiation with LCP (Δ g < -0.18) and RCP (Δ g > 0.18) light. Measurements on pure R- and S-BINOL samples allow the estimation of the generated enantiomeric excess, for which we can give a conservative lower limit of 21 %. Furthermore, these observations demonstrate that enantio-enrichment is possible by desorbing chiral molecules from an achiral surface with circularly polarized light, which opens up new opportunities in the field of absolute asymmetric analysis.