Controlling the Molecular Shuttling of pH‐Responsive [2]Rotaxanes with Two Different Stations

A novel synthesis of degenerate [2]rotaxanes with two different amine stations is presented. Variable‐temperature 1H NMR and rotating‐frame nuclear Overhauser effect correlation spectroscopy experiments revealed that the addition of trifluoroacetic acid initiates molecular shuttling. The activation barrier for the motion remained constant even when the amine in the outer station was changed. Conversely, the addition of camphorsulfonic acid caused a rotational motion, which was demonstrated by synthesizing a new [2]rotaxane without an outer station and examining its molecular behavior in the presence of acid. A newly synthesized degenerate [2]rotaxane engages in a molecular‐shuttling motion when trifluoroacetic acid (TFA) is added, but a rotational motion when camphorsulfonic acid (CSA) is added. A similar rotaxane without an outer station exhibited rotational motion regardless of the type of acid (TFA or CSA), which was used as evidence to validate the molecular‐motion behavior of these rotaxanes.