Synthesis and properties of a redox-switchable calix[6]arene-based molecular lasso

The synthesis and characterisation of calix[6]arene-based lasso-like molecular structures is described. These interwoven structures consist of an electrochemical responsive N,N '-dialkylviologen arm covalently anchored at the upper rim of a triphenylureido calix[6]arene-based wheel. Upon reduction of the viologen core, a hollow tridimensional macrocyclic structure can be generated. This process is reversible, and the original lasso-like structure can be regenerated by oxidizing the viologen arm to its original dicationic form. Electrochemical and EPR techniques investigated the ability of the system to perform threading/dethreading movements upon redox switching. The functionalisation of the arm omega-hydroxy ending with a bulky diphenylacetyl group converts the self-threaded structure in a blocked interwoven molecular compound belonging to the class of [1]rotaxanes. The ability to form dimeric structures in the shape of a [c2]daisy chain was also demonstrated, an unprecedented result for calixarene macrocycles.