Construction of Multi-Stimuli Responsive Highly Porous Switchable Frameworks by In-Situ Solid-State Generation of Spiropyran Switches.

Stimuli-responsive molecular systems supported within permanently porous materials offer the opportunity to host dynamic functions operating multifunctional smart materials. However, the construction of highly porous frameworks featuring external-stimuli responsiveness, for example by light excitation, is still in its infancy. Here we present a general strategy to construct spiropyran-functionalized highly porous switchable aromatic frameworks (PSFs) by modular and high-precision anchoring of molecular hooks and an innovative in-situ solid-state grafting approach. Three spiropyran-grafted frameworks bearing distinct functional groups exhibiting various stimuli-responsiveness were generated by two-step post-solid-state synthesis of a parent indole-based material. The quantitative transformation and preservation of high porosity were demonstrated by spectroscopic and gas adsorption techniques. For the first time, we provide a highly efficient strategy to construct multi-stimuli-responsive, yet structurally robust, spiropyran materials with high pore capacity which was proved essential for the reversible and quantitative isomerization in the bulk as demonstrated by solid-state NMR spectroscopy. The overall strategy allowed to construct dynamic materials which undergo reversible transformation of spiropyran to zwitterionic merocyanine, by chemical and physical stimulation, showing potential for pH active control, responsive gas uptake and release, contaminant removal, and water harvesting. This article is protected by copyright. All rights reserved.