Photo-Controlled Dynamics of Cholesteric Polymer Coatings via Hydrazone Crosslinking.

Developing responsive coatings and materials requires discovering a breadth of mechanisms by which external stimuli can be converted into useful signals. Here, we demonstrate an approach driven by supramolecular mechanochemistry, where mechanical input-molecular shape change-is translated into structural color variation. By embedding bistable, negatively photochromic hydrazone photoswitches into cholesteric polymer networks, we achieve a reversible, stable color shift through molecular-scale pulling and pushing of the photonic scaffold. Unlike azobenzene-based systems, which typically disrupt liquid crystal order, this approach modifies the pitch of a cross-linked cholesteric helix without disrupting the organisation of the material. The long-lived stability of both hydrazone isomers ensures durable optical switching. This effect provides a new strategy for designing mechanoresponsive photonic coatings and tunable optical materials.