Photoresponsive Slide-Ring Gels Enable Modulation of Sliding Dynamics.

Cyclodextrin-based slide-ring gels (SRGs) have emerged as a promising class of materials owing to their unique topology. Upon mechanical loading, the slidable cross-links of the polymer network freely translocate along the polymer backbone enabling pronounced energy dissipation in the material, which is associated with exceptional ductility and toughness. Despite the critical role of sliding dynamics in defining SRG mechanical properties, attempts to control them have primarily been limited to tuning the overall loading of macrocycles. Further, SRGs that can be triggered via an external stimulus have yet to be reported. In this work, we present light-responsive SRGs based on azobenzene-containing polymers. Reversible photoswitching of the azobenzenes modulates the sliding dynamics of the threaded α-cyclodextrin (α-CD) macrocycles. By using UV-Vis and circular dichroism spectroscopy, we show that α-CDs readily bind to the azobenzenes along the polymer backbone in the E configuration. Upon light irradiation, and thus isomerization to the Z isomer, the macrocycles no longer interact with the azobenzenes, allowing them to freely translocate along the polymer backbone. As a result of this E to Z isomerization and difference in sliding dynamics, the mechanical properties of the SRGs reversibly alternate between a stiff and a soft state.