Deformable inverse opal polyurethane photonic crystal film with high mechanical and liquid stability.

Photonic crystals regulate light propagation through their periodic structures and generate vivid structural color, making them highly attractive for sensing, anti-counterfeiting, and detection applications. However, self-assembled photonic crystals are inherently fragile, and their periodic structures are readily disrupted under liquid immersion or mechanical disturbance, leading to attenuation or even complete loss of structural color. This instability severely limits their practical application in complex environments. Herein, polyurethane was modified with a toughening resin and processed using a segmented thermal-curing strategy to fabricate an inverse opal polyurethane photonic crystal film with high tensile strength and high fracture strain. The resulting film maintained vivid structural color under liquid immersion and preserved distinct reflection peaks and stable optical properties under temperature variation, pH variation, salt-solution immersion, and mechanical disturbance. In addition, the film exhibited good optical reversibility and cycling stability during repeated exchange between anhydrous ethanol and deionized water. This work demonstrates a structurally stable and deformable inverse opal polyurethane photonic crystal film and provides a new design strategy for liquid-immersion optical identification, flexible photonic devices, and long-term reliable visual indicator materials.