A Photoresponsive Polymeric Actuator Topologically Cross-Linked by Movable Units Based on a [2]Rotaxane

A photoresponsive polymeric material, in which [2]rotaxane units with α-cyclodextrin threading onto an azobenzene derivative is used as a topological cross-link for the main chains of the polymeric material in aqueous media, was achieved. [2]Rotaxane structures were found to act as movable links in the polymer network, and the mechanical properties of the material were enhanced to show a rupture strain of 2800%. The materials were reversibly deformed by irradiation with UV or visible light in aqueous media, which caused photoisomerization of the azobenzene moiety and changed the structure of the [2]rotaxane linker, leading to deformation of the polymer network. Surprisingly, the dry materials, which had been uniaxially extended in air, showed a faster response than the hydrogel. The orientation of the polymeric network in the materials enables the efficient response. This dry material (5.6 mg) performed 5.6 μJ of mechanical work within 10 s, which is approximately 50 times higher than that achieved in our previous work.