Regulating the release temperature of guest molecules in porous materials is just as important as controlling adsorption capacity, but in traditional materials, desorption behavior is mostly determined by adsorption site energy and heating protocols, making it hard to program the release temperature. This work compares two isomorphic MOFs, C₄‑IRMOF and C₅‑IRMOF, and uses the long alkyl-oxygen side chains at the C₅‑IRMOF pore openings to build thermally responsive local flexible gates. Instead of relying on strong adsorption sites, the side chains’ thermal motion controls the opening and closing of the channels, allowing the release temperature to be determined by the adsorption loading temperature.

Low-temperature thermal desorption spectroscopy shows that the material’s desorption peak temperature shifts in sync with the adsorption temperature, forming a completely new adsorption‑temperature programmed desorption mechanism. This locally constrained pore environment can even perform hydrogen isotope kinetic quantum sieving at 100 K. The study demonstrates that just by modifying flexible side chains at the pore openings, the release behavior of guest molecules can be controlled, offering a simple and feasible new idea for designing porous adsorption materials.

Reference: DOI:10.1002/anie.2943024

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