Elucidating the Anion-Induced Switching Behavior of Rotaxane Dendrimers with Small-Angle Neutron Scattering^†

Although rotaxane dendrimers have shown extensive applications in stimuli-responsive materials, photocatalysis, and chiral luminescent materials, the detailed elucidation of their stimuli-induced motion behaviors remains a major challenge primarily attributed to the dynamic and complicated three-dimensional architectures. Herein, we present the first successful preparation of a new family of selectively-deuterated rotaxane dendrimers, in which deuterated pillar[5]arene wheels were precisely distributed on different generations of the dendrimer skeleton. In particular, the third-generation fully-deuterated rotaxane dendrimer with 28 deuterated [2]rotaxane units was successfully synthesized, enabling the deuteration of 1,400 hydrogen atoms. More importantly, the introduction of acetate anions at varying ratios induced differential contraction motions across different generations of the rotaxane dendrimer, as systematically investigated using a combination of ¹H NMR and small-angle neutron scattering (SANS) techniques, providing fundamental insights into the operational mechanism of molecular machines and the cooperative behavior of dynamic systems for further development of novel smart nanodevices and materials.