Photoresponsive Single-Ion Nanocomposite Hydrogels: Competition of Host-Guest Interactions

Exploring stimuli-responsive ionic-conductive materials is a challenging task and has gained considerable attention owing to their noninvasive manipulation and applications. Here, we demonstrate versatile and on-demand photocontrollable ionic conductive nanocomposite hydrogels via host-guest chemistry. Supramolecular hydrogels containing β-cyclodextrin (β-CD) and ionic liquid monomers are synthesized in the nanopores of anodic aluminum oxide (AAO) templates, on which light-responsive azobenzene polymers are tethered. Under visible light irradiation, the β-CD molecules preferentially form inclusion complexes with the trans-Azo moieties, resulting in higher concentrations of the mobile anions and lower resistances of the hydrogels; under UV irradiation, rather than the cis-Azo moieties, the β-CD molecules favor assembly with the anions, which leads to lower concentrations of the mobile anions and higher resistances of the hydrogels. By tuning the surface-area-to-volume ratio of the AAO nanopores and the alkyl chain length of the anions, the response amplitudes can be further manipulated.