A molecular switch based on acid and base promoted, cation governed binding in a crown ether threaded rotaxane

A rotaxane, containing both oligo ethylene glycol and secondary ammonium cation binding sites for a threaded crown ether, has been prepared. 1H NMR spectroscopy has been used to show that the crown ether moiety in the rotaxane undergoes acid–base and alkali metal cation dependent switch from binding at the ammonium cation position to cooperative binding to the metal cation at the oligo ethylene glycol site.