Guest releasing from solution to solid-state triggered by cyclomaltohexaose (α-cyclodextrin) aggregation.

Supramolecuar aggregations 1 and 2 were prepared by complexing cyclomaltohexaose with two azodipyridine isomers: 4,4'-azodipyridine and 2,2'-azodipyridine, and their binding abilities and assembly behaviors were investigated comprehensively by X-ray crystallography, 2D NMR spectroscopy, and isothermal titration calorimetry. In solution, 1:1 host-guest complexation is generally assumed, whereas in the solid state, a 2:1 stoichiometry is observed. Crystal structures reveal that channel-type aggregation exists in complex 1, while a layer-type manner is the dominant packing mode in complex 2. The disparity of nitrogen atom position leads to the different binding modes and further affects the aggregation types in complexes 1 and 2.