Photoswitching of the association of a permethylated α-cyclodextrin-azobenzene dyad forming a Janus [2]pseudorotaxane

For achieving the on–off operation of the superstructure formation of hermaphrodite cyclodextrin derivatives, we synthesized azobenzene-modified permethylated α-cyclodextrins, 1 and 2. These compounds formed Janus [2]pseudorotaxanes in CD3OD–D2O mixtures. The E-Z photoisomerization of 1 by UV light irradiation resulted in the dissociation of the superstructure, but, by boiling the solution, the superstructure was recovered through the thermal isomerization of (Z)-1 to (E)-1. These processes could be repeated many times without any side reactions. This is the first example of the dynamic control of the [2]pseudorotaxane formation of modified cyclodextrins by external stimuli.