Mechanochemical Cycloreversion of Cyclobutane Observed at the Single Molecule Level |
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Authors: | Dr. Michael F. Pill Dr. Katharina Holz Nils Preußke Florian Berger Prof. Dr. Hauke Clausen‐Schaumann Prof. Dr. Ulrich Lüning Prof. Dr. Martin K. Beyer |
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Affiliation: | 1. http://www.fb06.fh‐muenchen.de/fb/index.php/de/;2. Department of Applied Natural Sciences and Mechatronics, Munich University of Applied Sciences, Lothstra?e 34, Munich, Germany;3. Center for Nanoscience (CeNS), Geschwister-Scholl-Platz 1, Munich, Germany;4. http://www.luening.otto‐diels‐institut.de/de;5. Otto-Diels-Institut für Organische Chemie, Christian-Albrechts-Universit?t zu Kiel, Olshausenstra?e 40, Kiel, Germany;6. http://www.uibk.ac.at/ionen‐angewandte‐physik/;7. Institut für Ionenphysik und Angewandte Physik, Leopold-Franzens-Universit?t Innsbruck, Technikerstra?e 25, Innsbruck, Austria |
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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. |
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Keywords: | cycloreversion density functional calculations macrocycles mechanophores single-molecule force spectroscopy |
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