Dynamic extension-contraction motion in supramolecular springs.

One of the most significant recent highlights in the field of supramolecular polymer chemistry is the development of folded helical structures which are important modules in the engineering of functional nanoobjects such as nanotubes, nanowires, and nanomachines.1 In particular, helical architecture that undergoes conformational changes triggered by external stimuli has received attractive attention during recent years.2,3 Although DNA and proteins are well-known to exhibit molecular motions in response to external stimuli,4 synthetic helical systems to mimic the molecular motions of complicated biological systems remain challenging. With this in mind, we have become interested in the preparation of stimuli-responsive helical chains by using supramolecular coordination polymers with bent conformations.5 In this Communication, we present the formation of supramolecular springs with switchable pitch, from the aqueous selfassembly of supramolecular coordination polymers (Figure 1). We have synthesized the coordination polymers based on Ag(I) ion complexed with pyridine ligands with a bent conformation and investigated their dynamic self-assembling behavior in aqueous solution. The ditopic bridging ligands based on phenanthrene and pyridine units were selected as helical building blocks and were synthesized according to previously reported similar methods.5 The resulting pyridine ligands were complexed with AgOTf to afford the coordination chains, C1 and C2.