Aromatic vapor responsive molecular packing rearrangement in supramolecular gels

Abstract

Developing robust hydrogel materials with stimulus responsiveness to apolar organic vapors or gases is significantly challenging due to the deficient interaction between solvents and gelators, the intrinsic colloidal stability of gels toward low content solvent molecules in the gas phase and their immiscibility. We herein report unprecedented aromatic vapor responsive hydrogels taking advantage of the convenient crystal transformation phenomenon of commercially available β-cyclodextrin (β-CD). One-dimensional crystallization-induced self-assembly in a dimethyl formamide (DMF)/water mixture with specific proportions allows for the formation of stable gels. The hydrogel could selectively transform into crystalline precipitates upon exposure to aromatic solvent vapors. The phase transition is initiated through a cage-type to a channel-type single crystal transformation with a gradual solvent etching process, in which the CH–π interaction between DMF and the benzene ring confined within β-CD dimers is regarded as the primary driving force. We demonstrated that this unique gel system could act as an efficient sensor and adsorbent for hazardous aromatic vapors indoors. In addition, binary organic–inorganic hydrogel composites coassembled by clay with β-CD showed haze evolution toward aromatic vapor and heating–cooling treatment, accompanied by mechanical strength enhancement dependent on the building unit proportion. The present research opens an avenue to apply hydrogels in selectively sensing/adsorbing organic vapors, and would pave an alternative route for further development of responsive soft materials.