N-Benzyltriazolium as Both Molecular Station and Barrier in [2]Rotaxane Molecular Machines

A two-station [2]rotaxane, consisting of a dibenzo-24-crown-8 macrocycle (DB24C8) that surrounds a molecular axle containing an anilinium and a monosubstituted pyridinium amide molecular stations, has been synthesized via alkyne-azide click chemistry. The subsequent N-benzylation of the triazole moiety, which is located in the middle of the threaded axle, was then envisaged. In addition to affording a third molecular station (i.e., a triazolium station) for the DB24C8, it was found that the benzyl moiety behaves as a kinetic molecular barrier that prevents the DB24C8 from shuttling along the molecular encircled axle from one extremity to the other. Depending on where the DB24C8 is initially located, the N-benzylation of the triazole allows trapping of the DB24C8 on either the left or the right side of the thread with respect to the triazolium station. The presence of the benzyl barrier thus affords two different three-station [2]rotaxane molecular machines, in which some of co-conformational states remain unbalanced and not at the equilibrium.