Permanent Encapsulation of Mobile Molecules in Ionic Solids: Unraveling the Local Microstructure Using Molecular Probes

Encapsulation of guest molecules into the voids of microporous media is a potent physicochemical strategy to obtain new functional materials. However, achieving durable confinement and mobility/flexibility of the guests simultaneously is often a challenging task. We report a straightforward approach to obtain such materials based on ionic liquids/solids and to study them using molecular probes. In these ionic solids, guest molecules are found encapsulated in closed micropores, allowing both free rotational motion and flexibility. This was approved by using stable nitroxide radicals as guest molecules and electron-paramagnetic resonance (EPR) spectroscopy and further exemplified by showcasing the photoisomerization reaction of azobenzene encapsulated in the materials. Since such ionic solids with entrapped mobile guests are crystalline, transparent for light, and easy to prepare, they represent promising platforms for the design of functional coatings, materials, and other media.