Exploring the Nanomechanical Properties of a Coordination-bond Based Supramolecular Polymer

Due to their dynamic nature and strength tunability, metallo-supramolecular polymers have been introduced into various materials. The mechanical strength of the metallo-supramolecular polymers in the system directly influences the mechanical properties (e.g., the toughness) of the materials. Therefore, it is necessary to explore the mechanical behavior of the metallo-supramolecular polymers. Herein, we present a single-molecule method to systematically explore the chain structure and mechanical properties of metallo-supramolecular polymer by using a loop protected architecture. Notably, we found that the mechanical stability of the individual chain, which is determined by the strength of terpyridine-Fe2+-terpyridine (tpy-Fe2+-tpy) bonds, was about 0.6–1.0 nN, depending on the pulling speed. This value is around three times higher than those measured using old methods. In addition, the unique loop protected structure further reduces the interference of non-specific polymer-AFM tip (or polymer-substrate) interactions on the quantification of the actual strength and kinetic parameter of noncovalent interactions in supramolecular polymers. Furthermore, the single chain flexibility of the metallo-supramolecular polymer was investigated and found to be comparable to the corresponding covalent analogues. Our findings provide a new way to explore the force response of supramolecular polymers composed of metal-ligand interactions and will be useful for the design of metallo-supramolecular polymer-based functional materials with tailored mechanical properties.