title: Mechanochemical Cycloreversion of Cyclobutane Observed at the Single Molecule Level.
abstract: Mechanochemical cycloreversion of cyclobutane is known from ultrasound experiments. It is, however, not clear which forces are required to induce the cycloreversion. In atomic force microscopy (AFM) experiments, on the other hand, it is notoriously difficult to assign the ruptured bond. We have solved this problem through the synthesis of tailored macrocycles, in which the cyclobutane mechanophore is bypassed by an ethylene glycol chain of specific length. This macrocycle is covalently anchored between a glass substrate and an AFM cantilever by polyethylene glycol linkers. Upon mechanical stretching of the macrocycle, cycloreversion occurs, which is identified by a defined length increase of the stretched polymer. The measured length change agrees with the value calculated with the external force explicitly included (EFEI) method. By using two different lengths for the ethylene glycol safety line, the assignment becomes unambiguous. Mechanochemical cycloreversion of cyclobutane is observed at forces above 1.7 nN.
authors.affiliation: Department of Applied Natural Sciences and Mechatronics, Munich University of Applied Sciences, Lothstraße 34, 80335, Munich, Germany.|Center for Nanoscience (CeNS), Geschwister-Scholl-Platz 1, Munich, Germany.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Pill
authors.affiliation: Otto-Diels-Institut für Organische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstraße 40, 24098, Kiel, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Holz
authors.affiliation: Otto-Diels-Institut für Organische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstraße 40, 24098, Kiel, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Preußke
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Leopold-Franzens-Universität Innsbruck, Technikerstraße 25, 6020, Innsbruck, Austria.
authors.forename: Florian
authors.initials: F
authors.lastname: Berger
authors.affiliation: Department of Applied Natural Sciences and Mechatronics, Munich University of Applied Sciences, Lothstraße 34, 80335, Munich, Germany.|Center for Nanoscience (CeNS), Geschwister-Scholl-Platz 1, Munich, Germany.
authors.forename: Hauke
authors.initials: H
authors.lastname: Clausen-Schaumann
authors.affiliation: Otto-Diels-Institut für Organische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstraße 40, 24098, Kiel, Germany. luening@oc.uni-kiel.de.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Lüning
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Leopold-Franzens-Universität Innsbruck, Technikerstraße 25, 6020, Innsbruck, Austria. martin.beyer@uibk.ac.at.
authors.forename: Martin K
authors.initials: MK
authors.lastname: Beyer
keywords: cycloreversion; density functional calculations; macrocycles; mechanophores; single-molecule force spectroscopy