A CHEMICALLY AND ELECTROCHEMICALLY SWITCHABLE MOLECULAR SHUTTLE

The developing field of nanotechnology has generated wide interest acr oss a broad range of scientific disciplines(1). In particular, the rea lization of nanoscale switching devices might have far-reaching implic ations for computing and biomimetic engineering(2-4). But miniaturizat ion 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 t echniques(5). The approach observed in the natural world, whereby nano structures are built up through the self-assembly(6-9) of smaller mole cular entities, holds substantial promise. Nature abounds with molecul ar switching devices which perform a variety of functions, such as the transport of metabolites across cell membranes or the signalling of n erve impulses. These processes are commonly controlled by stimuli such as changes in ion concentrations and electrical potentials. Here we r eport the synthesis of a supramolecular structure (compound 1.[PF6](4) , Fig. 1A) that can be reversibly switched between two states by proto n concentration changes or by electrochemical means. The supermolecule is a rotaxane comprising a molecular ring threaded on an axle contain ing two 'docking points'. We can effect controlled switching of the ri ng from one of these positions to the other. We use H-1 NMR and ultrav iolet/visible spectroscopy to characterize the dynamics of the bead's movement along the thread before and after switching.