Synthesis and properties of a redox-switchable calixarene-based molecular lasso†
The synthesis and characterisation of calixarene-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 calixarene-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 ω-hydroxy ending with a bulky diphenylacetyl group converts the self-threaded structure in a blocked interwoven molecular compound belonging to the class of rotaxanes. The ability to form dimeric structures in the shape of a [c2]daisy chain was also demonstrated, an unprecedented result for calixarene macrocycles.