Hydration Activates Dual‐Confined Shape‐Memory Effects of Cold‐Reprogrammable Photonic Crystals

Abstract Shape‐memory photonic crystals (SMPCs) transform the nanoscale deformation of copolymers into structural color through an undifferentiated response to stimuli; however, activatable selective responses are extremely rare. Herein, activatable dual confined shape‐memory effects (CSMEs) derived from the remodeling of the interchain hydrogen bonds (H‐bonds) in cold‐programmable SMPCs are revealed. The first level is the water‐triggered reconstruction of interchain H‐bonds, which can activate/lock the collapsed skeleton, showing shape recovery/retention in response to ethanol vapor. The second level is the pressure‐induced reorganization of interchain H‐bonds that results in the recovered skeleton being locked even when exposed to ethanol vapor or water, while the background porous structure can switch between collapse and recovery. Dual CSMEs result from the Laplace pressure difference and the binding effect of interchain H‐bonds in the skeleton according to insights of swelling, in situ deformation tracking, multidimensional infrared spectra, and water wetting/evaporation simulations. The signal interference, source code extraction, and color enhancement of structurally colored patterns can be implemented using CSMEs. This work opens up a new method for fabricating activatable responsive structural color and contributes to the expansion of nanophotonic technology in water printing, erasable watermarks, signal amplifiers, and information coding.