Experimental and theoretical studies of electrochemical switching processes in crown ether/ammonium rotaxanes

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Mechanically interlocked molecules like rotaxanes are an important class of molecular switches and machines. For example, motion and transport can be controlled on the molecular scale when using switchable rotaxanes that change their co-conformations when external stimuli are applied. Influences of the environment, e.g. solvent and counterion effects, may strongly affect the co-conformational equilibria and thus the function of these switchable interlocked molecules. As these effects, however, operate in a complex interplay with intramolecular non-covalent interactions as well as the mechanical bond, it is challenging to single out and quantify these environmental effects. The project aims at a more profound understanding of these effects in a combination of experiment and theory. Also, a model will be developed that allows a better prediction of co-conformational changes in interlocked molecules. At first, a library of electrochemically switchable crown ether/ammonium pseudorotaxanes is synthesized which allows to quantify the dependence of intramolecular interactions on environment effects by a network analysis. Based on this data set, DFT-based theoretical models in combination with molecular dynamics simulations allow to predict the energy profiles of co-conformational changes. This enables us to fine-tune conformations and thus functions of switchable rotaxanes with the help of environment effect. In the last part of the project, these models will be used to design, prepare and study novel molecular machines, which allow for directional transport phenomena.