Dynamic switching between single- and double-axial rotaxanes manipulated by charge and bulkiness of axle termini.

Twin-axial [3]pseudorotaxanes, in which two multicharged axles simultaneously thread through the gamma-CD cavity, were formed for the first time in solution. The twin-axial [3]pseudorotaxane was converted exclusively to a CB [6]-stoppered [4]pseudorotaxane by the addition of CB[6] but regenerated from the [4]pseudorotaxane by the addition of spermine, implementing an unprecedented switching of single/twin-axial rotaxanation.