Berlin 2018 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 11: Responsive and Adaptive Systems

CPP 11.4: Talk

Monday, March 12, 2018, 12:00–12:15, C 230

Spiropyran ring opening reactions to measure forces on the molecular scale — •Oliver Brügner and Michael Walter — FIT Freiburger Zentrum für interaktive Werkstoffe und bioinspirierte Technologien, Universität Freiburg

Spiropyrans are mechanochromatic molecules which change color under the influence of force. These molecules can be integrated into polymers. By stretching the polymer, mechanical forces are transferred to spiropyran and lead to a ring opening reaction. Thereby the colorless spiropyran transforms into the colored merocyanine form. This reaction is reversible and the back reaction is already induced by thermodynamic excitations at room temperature [Kem]. Therefore spiropyran can be used as a molecular switch and belongs to the group of interactive materials.

In order to understand the molecular insides needed for using spiropyran as the responsive material in polymeric force sensors in the future, we investigated the energetics of spiropyran based on density functional theory and added entropic effects of the polymer. The model used is a combination of a relatively simple description of the polymer combined with an accurate description of the spiropyran ring opening reaction. We determine the dependence of the force on the polymer stretching length and find a very good agreement with experimental results from single molecule AFM experiments.

[Kem] Fabian Kempe, Oliver Brügner, Hannah Buchheit, Sarah N. Momm, Felix Riehle, Sophie Hameury, Michael Walter, and Michael Sommer, Angew. Chem. Int. Ed. 56 (2017) 1-5