Precision Switching and Coupled Motion in a [3]Rotaxane Molecular Machine

We report the synthesis and the characterization of a multicomponent molecular machine based on a [3]rotaxane architecture. The system is composed by two crown ether macrocycles and an axle with three recognition sites for the rings: ammonium (AmH⁺), bipyridinium (Bpy²⁺), and triazolium (Trz⁺). The position of the two rings can be precisely controlled via a sequence of chemical and electrochemical inputs: the two rings can be located on neighboring stations, forced on the same station or separated at the opposite extremities of the axle. This complex mechanism is elucidated by a combination of NMR spectroscopy and voltammetric techniques, allowing to characterize the thermodynamics of the reaction network. The investigation shows that each ring is influenced by the presence and position of the other, resulting in a coupled motion, a critical feature for the development of next-generation molecular machines.