Electrochemically Switchable Hydrogen-Bonded Molecular Shuttles

A series of [2]rotaxanes containing succinamide and naphthalimide hydrogen-bonding stations
for a benzylic amide macrocycle is described. Electrochemical reduction and oxidation of the naphthalimide
group alters its ability to form hydrogen bonds to the macrocycle to such a degree that redox processes
can be used to switch the relative macrocycle-binding affinities of the two stations in a rotaxane by over 8
orders of magnitude. The structure of the neutral [2]rotaxane in solution is established by 1H NMR
spectroscopy and shows that the macrocycle exhibits remarkable positional integrity for the succinamide
station in a variety of solvents. Cyclic voltammetry experiments allow the simultaneous stimulation and
observation of a redox-induced dynamic process in the rotaxane which is both reversible and cyclable.
Model compounds in which various conformational and co-conformational changes are prohibited
demonstrate unequivocally that the redox response is the result of shuttling of the macrocycle between the
two stations. At room temperature in tetrahydrofuran the electrochemically induced movement of the
macrocycle between the two stations takes ∼50 μs.