Mechanical robustness and healing ability are important properties of polymeric materials. However, the development of mechanically robust yet rapidly healable polymers is challenging. Herein, we demonstrate that long alkyl side chains simultaneously improve mechanical properties and the healing rate of a photoswitchable polymer. The photoswitchable polymer is a polyacrylate. Its side chain contains a hexamethylene spacer, a photoresponsive azobenzene group, and a long n-hexadecyl tail. The n-hexadecyl tail increases the decomposition temperature and glass transition temperature (T g ) of the polymer by 92 and 40 °C, respectively. Such an increase of T g is opposite to textbook knowledge, which makes the polymer robust even at elevated temperatures. The photoswitchable polymer, which has increased T g and improved mechanical properties, is a hard solid under normal usage conditions. It exhibits healing ability because it can be reversibly switched between a solid and a liquid via photoisomerization of the azobenzene groups. The polymer in the liquid state has significantly reduced viscosity for rapid healing. Importantly, the n-hexadecyl tail increases the healing rate of the polymer by 470 times. The introduction of long alkyl side chains is a new strategy for simultaneously improving mechanical properties and the healing rate of polymeric materials.

Photodynamic bonds are stable in the dark and can reversibly dissociate/form under light irradiation. Photodynamic bonds are promising building blocks for responsive or healable materials, photoactivated drugs, nanocarriers, extracellular matrices, etc. However, reactive intermediates from photodynamic bonds usually lead to side reactions, which limit the use of photodynamic bonds. Here, we report that the Ru–Se coordination bond is a new photodynamic bond that reversibly dissociates under mild visible-light-irradiation conditions. We observed that Ru–Se bonds form via the coordination of a selenoether ligand with [Ru­(tpy)­(biq)­(H2O)]­Cl2 (tpy = 2,2′:6′,2″-terpyridine, biq = 2,2′-biquinoline) in the dark, while the Ru–Se bond reversibly dissociates under visible-light irradiation. No side reaction is detected in the formation and dissociation of Ru–Se bonds. To demonstrate that the Ru–Se bond is applicable to different operating environments, we prepared photoresponsive amphiphiles, surfaces, and polymer gels using Ru–Se bonds. The amphiphiles with Ru–Se bonds showed reversible morphological transitions between spherical micelles and bowl-shaped assemblies for dark/light irradiation cycles. The surfaces modified with Ru–Se-bond-containing compounds showed photoswitchable wettability. Polymer gels with Ru–Se cross-links underwent photoinduced reversible sol–gel transitions, which can be used for reshaping and healing. Our work demonstrates that the Ru–Se bond is a new type of dynamic bond, which can be used for constructing responsive, reprocessable, switchable, and healable materials that work in a variety of environments.

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