Certain foldamers can form multiple helices, which is of interest in materials science, among other fields. By grafting tetrathiafulvalene units onto the ends of a helical oligomer, we report the synthesis and study of a foldamer that shows remarkably high stability in the single-helical state. Most importantly, we demonstrate that double-helix formation can be triggered by simple oxidation, enabled by radical ion pairing.

Abstract

Preparing new smart receptors and materials through controlling foldamer assemblies constitutes an appealing strategy. In this context, the use of a redox input appears as a relevant tool to monitor the self-assembly process, provided a careful design of well-chosen electroactive units. Our research group previously showed how the single-to-double helix equilibrium of foldamers can be shifted thanks to redox processes. Aiming at generalizing this strategy and rationalizing our findings, we designed a long oligopyridine dicarboxamide strand bearing tetrathiafulvalene (TTF) units, which are connected on the periphery through short amide linkers. This design proved to have a dramatic impact on the supramolecular behavior of the foldamer, preventing the formation of double helices in the neutral state. Using a combination of electrochemical and spectroscopic measurements, we show that duplex formation can be triggered by oxidizing a foldamer that does not form double helices in the neutral state.