Elements for the construction of molecular devices: template effects and self-assembly

Four elements which may prove useful for the construction of molecular shuttles and other devices at the molecular level are discussed. (i) A novel anion-mediated template effect allows functionality to be introduced into the axle center pieces of rotaxanes so that molecular motions of the axle and wheel can be controlled by external stimuli. (ii) The deslipping kinetics of rotaxanes provide valuable insight into large changes of the deslipping rate caused by minimal structural changes. These effects, once understood, could be exploited for an optimization of the functionality of molecular devices. (iii) A wheel with an exocyclic metal coordination site provides access to self-assembled species that combine more than one macrocycle or rotaxane. This is a step towards a controlled growth of more complex species and in future may help to reduce the synthetic efforts needed for the generation of large and complex systems through self-assembly rather than covalent synthesis. (iv) In particular, for self-assembled systems with their often high degree of symmetry, mass spectrometry provides a valuable tool for the determination of their sizes. Beyond characterization, mass spectrometry provides an insight into structural details and the intrinsic reactivity of supramolecular species and thus can be expected to play an increasingly important role in the examination of molecular devices. Copyright (C) 2004 John Wiley Sons, Ltd.