Dynamic thiourea networks enable self-healing chromic films for visual detection of light and acidic vapors

Abstract

Smart chromic materials that respond to light and acidic environments are essential for real-time environmental sensing, wearable devices, and safety monitoring, yet their practical use remains limited by poor mechanical durability and the inability to recover functionality after damage. Most existing chromic systems suffer from mechanical failure, irreversible fatigue, and loss of sensing capability, highlighting the need for responsive materials that combine robustness with sustainability. Here, we report a multifunctional self-healing chromic film constructed from polythiourea (PTU), thermoplastic polyurethane (TPU), and a dual-responsive spiropyran-COOH (SPCOOH) chromophore. The dynamic thiourea network in PTU enables autonomous room-temperature healing, while TPU provides mechanical reinforcement to overcome the intrinsic softness of PTU. Incorporation of SPCOOH imparts rapid and reversible photochromic and acidochromic responses. Through compositional optimization, the resulting film exhibits excellent homogeneity, stable optical switching, and superior mechanical and healing performance. The optimal composite exhibits autonomous room-temperature healing with a healing efficiency of 72% within 12 h, sufficient to restore mechanical integrity and chromic functionality without external stimuli, while mild heating (50 °C) further enhances the healing efficiency to 86.85 ± 1.79% by increasing chain mobility. This synergistic design provides a sustainable platform that unifies mechanical self-repair, light and acid sensing, and reliable chromic reversibility, offering broad potential for next-generation soft electronics, environmental sensors, and smart protective coatings.