Pendent No More: Direct Backbone Integration of Stenhouse Salt Enables Multi‐Responsive Commodity Polyurethanes

While donor-acceptor Stenhouse adducts (DASAs) have shown exceptional photochromic properties at the molecular level, their integration into polymeric materials has been limited to pendent group architectures that compromise both switching efficiency and materials performance. Here, we report a versatile strategy to overcome these limitations by leveraging the symmetric design of Stenhouse salts-structural analogues of DASAs-for direct backbone integration into polyurethane backbones. This approach overcomes the synthetic hurdles and performance compromises typical of pendent DASA systems, producing mechanically robust materials with strain-to-break exceeding 1100% and tensile strengths up to 44 MPa, while delivering fully reversible colorimetric responses (ΔE > 50) to trace amounts of acids, bases, amines, and nerve agent mimics. Integrating the chromophores into the polymer backbone eliminates leaching and ensures high reproducibility alongside excellent mechanical properties. Moreover, incorporating photoacid generators allows for micrometer-scale photolithographic patterning, enabling precise spatial and temporal control of chromophore switching under solar or UV light. These backbone-integrated Stenhouse salt polyurethanes mark a significant advancement over pendent chromophore systems, transforming conventional elastomers into versatile, responsive materials for applications ranging from food packaging and security to protective gear and medical devices.