Polyoxometalate-Based Photochromic Supramolecular Hydrogels with Highly Ordered Spherical and Cylindrical Micellar Nanostructures

Graphical Gelling behavior : Polyoxometalate-based supramolecular hydrogels with highly ordered spherical and cylindrical micellar nanostructures exhibit excellent photochromic ability (see figure). By adjusting the molar ratio of the zwitterionic amphiphile component to the polyoxometalate, ordered spherical micelle-based hydrogels and aligned wormlike micelle-based hydrogels can be obtained. Polyoxometalates (POMs) have attracted much attention in the field of photochromic materials. However, POM-based photochromic supramolecular hydrogels with high transparency and good photochromic properties are seldom reported. In this work, a homogenous, optically transparent, injectable, and photochromic supramolecular hydrogel was fabricated through the coassembly of ammonium heptamolybdate (Mo 7 ) and an imidazolium-based zwitterionic amphiphile (3-(1-hexadecyl-3-imidazolio)propanesulfonate (C 16 IPS)). The balance between electrostatic attraction and repulsion of Mo 7 clusters and zwitterionic amphiphiles enables them to coassemble into a homogenous and transparent supramolecular hydrogel. By adjusting the molar ratio of C 16 IPS/Mo 7 , ordered spherical micelle-based hydrogels and aligned wormlike micelle-based hydrogels can be obtained. The incorporation of Mo 7 into hydrogels endows these hydrogels with excellent photochromic properties. Specifically, after coassembly with C 16 IPS, the photochromic ability of hydrogels is significantly enhanced compared with that of a pure aqueous solution of Mo 7 . These hydrogels exhibit great potential applications as photochromic materials for the recording of rewritable information.