Showing papers by "J. Fraser Stoddart published in 1994"

A chemically and electrochemically switchable molecular shuttle

Abstract: THE developing field of nanotechnology has generated wide interest across a broad range of scientific disciplines1. In particular, the realization of nanoscale switching devices might have far-reaching implications for computing and biomimetic engineering2–4. 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 techniques5. The approach observed in the natural world, whereby nanostructures are built up through the self-assembly6–9 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-[PF6]4, Fig. 1A) that can be reversibly switched between two states by proton concentration changes or by electrochemical means. The super-molecule 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 ultra violet/visible spectroscopy to characterize the dynamics of the bead's movement along the thread before and after switching.

The self assembly of controllable [2]catenanes

Abstract: The dynamic and electrochemical properties of two new [2]catenanes, in which bisparaphenylene-34-crown-10 is encircled by a cyclophane incorporating either (i) one bipyridinium and one bis(pyridinium)ethylene unit or (ii) two bis(pyridinium)ethylene units, are investigated in solution.

A self-organised layered superstructure of arrayed [2]pseudorotaxanes

Abstract: A [2]pseudorotaxane, built up from a macrocyclic cyclophane containing two atomatic π-acceptors and an acyclic molecular containing three aromatic π-donors, has the ability to undergo self-organisation on crystallisation to form a layered superstructure of arrayed [2]pseudorotaxanes.

Towards the self‐assembly of polyrotaxanes

Abstract: The self-assembly of a number of rotaxanes, pseudorotaxanes, and a pseudopolyrotaxane based on the π-electron deficient cyclobis(paraquat-p-phenylene)d and threads and dumbbell components composed of π-electron rich hydroquinone rings incorporated symmetrically within polyether chains terminated in the case of the rotaxanes by adamantoyl stoppers

The solid-state self-organisation of a self-assembled [2]catenane

Abstract: The reluctance of a [2]catanane, comprised cf macrocycles incorporating π-donors and π-acceptors, to be catenated further to form a [3]catenane may be explained by the molecular arrangement revealed in the solid-state structure of the [2]catenane, which shows all aromatic units to be involved in intramolecularπ–π stacking interactions; moreover, the molecules self-organise in the solid-state to form a quilt-like two-dimensional array by virtue of intermolecularπ–π stacking interactions.

Self-assembled [2]catenanes exhibiting highly selective translational isomerism

Abstract: Template-directed synthesis is used to construct two isomeric [2]catenanes incorporating the macrocyclic polyether, (paraphenylene-metaphenylene)-33-crown- 10, and either (i) cyclobis (paraquat-p-phenylene) or (ii) cyclo(paraquat-p-phenylene)(paraquat-m-phenylene) as their tetrakis(hexafluorophosphates); these isomeric [2]catenanes are found to have a remarkable preference to exist as one translational isomer, both in the solid (by X-ray crystallography) and solution (by variable-temperature 1H NMR spectroscopy) states–the one in which a hydrouinone, rather than a resorcinol, ring is located inside the cavities of the isomeric tetracationic cyclophanes.