Dual-stage shape memory polyurethanes with solar-driven actuation via catechol–Fe³⁺ coordination

Shape memory polyurethanes (SMPUs) enabling programmable actuation are critical for smart materials. We report a multifunctional system integrating cold crystallization–induced two-stage shape memory with solar-driven actuation via catechol–Fe³⁺ coordination. By systematically tuning the polyethylene glycol/catechol ratio and Fe³⁺ incorporation, we controlled chain mobility to realize both one- and two-stage shape memory effects. The catechol–Fe³⁺ bonds served as sacrificial crosslinks, enhancing mechanical toughness. Furthermore, ligand-to-metal charge transfer narrowed the effective absorption edge from 2.40 eV to 1.44 eV, extending absorption into visible and near-infrared regions for efficient photothermal conversion. Consequently, the polymer achieved reliable shape recovery under solar irradiation. This strategy combines programmable crystallization, mechanical robustness, and renewable energy actuation in a single platform for energy-efficient smart materials.