Syntheses and Self-Assembly Behaviors of the Azobenzenyl Modified β-Cyclodextrins Isomers

Abstract

A couple of analogues of azobenzenyl beta-cyclodextrins 1 and 2 with self-locked and self-unlocked conformations have been synthesized via the Huisgen cycloaddition from the same reactants, but in distinct reaction conditions (i.e., the hydrothermal synthesis and the "click" reaction, respectively), their conformations were sufficiently proved by X-ray crystal structural analysis, molecular modeling study, and 2D NMR spectroscopy, and their self-assembly behaviors in aqueous solution were also investigated by NMR spectroscopy. Interestingly, the self-locked conformer 1, which could be regarded as a new type of [1]rotaxane, self-assembled to a novel bimolecular capsule, where its azobenzene substituent was included in both its own cavity and the counterpart's cavity, in aqueous solution and in the solid state. In contrast, by adjusting the conformation of 1 to a self-unlocked one, the resulting conformer 2 was found to self-assemble to a linear supramolecule. These studies have shown the stronger impact of the reaction condition changing in cyclodextrin's modification products and will provide a new access to control the structure of supramolecular assemblies by tuning the conformation of building blocks.