Rotaxanes with a calix[6]arene wheel and axles of different length. Synthesis, characterization, and photophysical and electrochemical properties

We have synthesized a series of three rotaxanes constituted of a calix[6]arene wheel and a 4,4′-bipyridinium unit on the axle, which differ in the length of the two aliphatic chains that connect the central bipyridinium unit with the two terminal stoppers. We have investigated the photophysical and electrochemical properties of these systems and of suitable model compounds in two prototypical solvents, namely, acetonitrile and methylene chloride. Our results show that these rotaxanes are characterized by a complex pattern of intercomponent interactions whose strength can be influenced by the length of the axle as well as the nature of the solvent.