Cooperative light-induced breathing of soft porous crystals via azobenzene buckling.

Krause, Simon; Evans, Jack D; Bon, Volodymyr; Crespi, Stefano; Danowski, Wojciech; Browne, Wesley R; Ehrling, Sebastian; Walenszus, Francesco et al. · Nat Commun · 2022

basic_science · Level V

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Abstract

Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.