Light-Induced Self-Healing Behavior in Photosalient Coordination Polymer

Achieving self-healing in the photosalient (PS) crystals without compromising structural integrity is a challenge. So far, self-healing and photomechanical behaviors have predominantly been reported as independent phenomena. Systems that concurrently exhibit both properties under a single stimulus remain uncommon. Here, we report the integration of the photomechanical property with a self-healing behavior by embedding dynamic covalent disulfide (S–S) linkages into a photoreactive coordination polymer (CP). Using 2-mercaptobenzoic acid, which undergoes in situ oxidation to form S–S bonds during crystallization, we obtained two-dimensional (2D) CP. The crystal undergoes cracking followed by a pronounced PS motion under UV irradiation. Continued irradiation induces up to 95% volumetric self-healing, as confirmed by atomic force microscopy, and acts as a self-healing optical window by restoring optical transparency and single-crystal integrity, as verified by multimodal microscopic techniques and single-crystal X-ray diffraction (SXRD). Comprehensive analysis using SXRD and spectroscopy collectively disentangles both mechanisms, viz solid-state [2 + 2] cycloaddition, which is responsible for cracking, PS behavior, and dynamic covalent chemistry (DCC) (S–S) that enables subsequent self-healing. This work demonstrates a distinctive combination of cracking, PS, and self-healing behavior in a CP enabled by the synergistic interplay of light-induced irreversible [2 + 2] photocycloaddition and dynamic disulfide bond linkage within a single crystal, in addition to a 2D CP to 3D CP transformation mediated by an “SC-crack-heal-SC” (Single Crystal → Cracked Crystal → Crystal Healing → Healed Single Crystal) mechanism. This approach paves the way for advancements in soft robotics, adaptive optics, and resilient next-generation functional materials.