Rostock 2019 – scientific programme

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MO: Fachverband Molekülphysik

MO 11: Photochemistry

MO 11.3: Talk

Wednesday, March 13, 2019, 11:15–11:30, S HS 001 Biologie

Time-dependent mass spectra studies of gas-phase trans-stilbene oxide as probed by ultrafast UV pump-probe laser techniques — •Matthew S. Robinson, Mario Niebuhr, and Markus Gühr — Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany.

The photo-chemical ring-opening mechanisms of oxirane-based molecules are heavily dependent on the substituent groups attached to the molecule. Photo-excited unsubstituted and alkyl-substituted oxiranes favor cleavage of the C-O bond, whilst cyano- and aryl-substituted oxiranes cleave at the C-C bond and open in disrotary fashion, in agreement with Woodward-Hoffman rules. [1]

However, in direct contrast to these rules, theory predicts that there is no favored route between the conrotary and disrotary opening paths of photo-excited aryl-substituted oxiranes, despite the conrotary motion rarely being observed. [2] In order to better understand these systems we have performed time-resolved UV pump-probe mass spectra studies on gas-phase trans-stilbene oxide (trans-2,3-diphenyloxirane). Here we present the results from these experiments, detailing information on the lifetimes of the observed fragments, as well as what this informs us about the photo-excited state of stilbene oxide.

1. Woodward, R. B. & Hoffmann, R., Angew. Chemie 81, 797-870 (1969).

2. Friedrichs, J. & Frank, I. Chem. - A Eur. J. 15, 10825-10829 (2009).