Self-assembly, spectroscopic, and electrochemical properties of [n]rotaxanes

Synthetic approaches to self-assembling [n]rotaxanes incorporating pi-eleclron deficient bipyridinium-based dumbbell-shaped components and pi-electron rich hydroquinone-based macrocycles have been developed. In particular, the so-called slippage methodology relies upon the size complementarity of preformed macrocyclic and dumbbell-shaped components. The spontaneous self-assembly of these complementary components into a rotaxane in solution can be achieved under the influence of an appropriate amount of thermal energy. The absorption spectra, luminescence properties, and electrochemical behavior of the rotaxanes and their dumbbell-shaped components have been investigated and discussed on the basis of the behavior of their chromophoric and electroactive units. Charge-transfer and energy-transfer processes between specific chromophoric subunits and unusual correlations between the redox patterns of the various compounds have been evidenced and interpreted.