The developing field of nanotechnology has generated wide interest across a broad range of scientific disciplines. In particular, the realization of nanoscale switching devices might have far-reaching implications for computing and biomimetic engineering. But miniaturization of existing semiconductor technology may not be the best approach to the fabrication of structures whose dimensions are smaller than the wavelength of the radiation used in optical lithography and etching techniques. The approach observed in the natural world, whereby nanostructures are built up through the self-assembly of smaller molecular entities, holds substantial promise. Nature abounds with molecular switching devices which perform a variety of functions, such as the transport of metabolites across cell membranes or the signalling of nerve impulses. These processes are commonly controlled by stimuli such as changes in ion concentrations and electrical potentials. Here we report the synthesis of a supramolecular structure (compound 1·[PF 6] 4, Fig. 1A) that can be reversibly switched between two states by proton concentration changes or by electrochemical means. The supermolecule is a rotaxane comprising a molecular ring threaded on an axle containing two 'docking points'. We can effect controlled switching of the ring from one of these positions to the other. We use 1H NMR and ultraviolet/visible spectroscopy to characterize the dynamics of the bead's movement along the thread before and after switching.
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