THE SLIPPING APPROACH TO SELF-ASSEMBLING [N]ROTAXANES

A synthetic approach-namely slippage-to self-assembling [n]rotaxanes i ncorporating pi-electron deficient bipyridinium-based dumbbell-shaped components and pi-electron-rich hydroquinone- and/or dioxynaphthalene- based macrocyclic polyether components has been developed. The kinetic s of rotaxane formation by the slipping procedure were investigated by absorption UV-visible and H-1-NMR spectroscopies in a range of temper atures and solvents, varying systematically the size of both the stopp ers and the macrocyclic components. As expected, the rate constants fo r these processes are affected by the size complementarity between mac rocycles and stoppers. Furthermore, the enthalpic and entropic contrib utions to the free energies of activation associated with the slippage and the effect of solvent polarity upon the outcome of these processe s have been evaluated. In addition, the spectroscopic and electrochemi cal properties of some of the rotaxanes are presented and discussed wi th reference to the properties of their chromophoric and electroactive units.