Redox Switchable Daisy Chain Rotaxanes Driven by Radical-Radical Interactions

We report the one-pot synthesis and electrochemical switching mechanism of a family of electrochemically bistable ‘daisy chain’ rotaxane switches based on a derivative of the so-called ‘blue box’ (BB4+) tetracationic cyclophane cyclobis(paraquat-p-phenylene). These mechanically interlocked molecules are prepared by stoppering kinetically the solution-state assemblies of a self-complementary monomer comprising a BB4+ ring appended with viologen (V2+) and 1,5-dioxynaphthalene (DNP) recognition units using click chemistry. Six daisy chains are isolated from a single reaction: two monomers (which are not formally ‘chains’), two dimers, and two trimers, each pair of which contains a cyclic and an acyclic isomer. The products have been characterized in detail by high-field 1H NMR spectroscopy in CD3CN—made possible in large part by the high symmetry of the novel BB4+ functionality—and the energies associated with certain aspects of their dynamics in solution are quantified. Cyclic voltammetry and spectroelectro...