Self-Assembling Catenanes and Rotaxanes

Recently, self-assembly processes have been used for the construction of a wide diversity of molecular and supramolecular architectures. We have developed an approach to self-assembling mechanically-interlocked structures such as catenanes and rotaxanes. The methodology relies upon the stereoelectronic complementarity between pi-electron deficient bipyridinium-based components and pi-electron rich hydroquinone- or 1,5-dioxynaphthalene-based components. The driving forces responsible for the self-assembly are (i) pi-pi stacking interactions between the bipyridinium units and either the hydroquinone or 1,5-dioxynaphthalene rings, together with (ii) hydrogen bonding interactions between the CH-acidic protons of the bipyridinium units and the polyether oxygen atoms incorporated within the pi-electron rich components. By employing this approach, we have been able to self-assemble a large number of [2]catenanes, [3]catenanes, [4]catenanes and, very recently, two [5]catenanes, incorporating five interlocked macrocyclic subunits. We have also achieved the template-directed synthesis of several [2]rotaxanes, [3]rotaxanes, and a dendritic [4]rotaxane. Here, we report the syntheses of several mechanically-interlocked molecular compounds, along with a description of their dynamic properties in solution and their electrochemical behaviour. Furthermore, the possibility of controlling, by external stimuli - chemical or electrochemical - the dynamic processes occurring in solution, within these molecules, with the ultimate goal of generating molecular machines, is illustrated.