Ultradynamic Isoreticularly Expanded Porous Organic Crystals

Porous organic materials showcasing large framework dynamics present new paths for adsorption and separation with enhanced capacity and selectivity beyond the size-sieving limits, which is attributed to their guest-responsive sorption behaviors. Porous hydrogen-bonded crosslinked organic frameworks (HOFs) are attractive for their remarkable ability to undergo guest-triggered expansion and contraction facilitated by their flexible covalent crosslinkages. However, the voids of HOFs remain limited, which restrains the extent of the framework dynamics. In this work, we synthesized a series of HOFs characterized by unprecedented size expansion capabilities induced by solvents. These HOFs were constructed by isoreticularly co-crystallizing two complementary sets of hydrogen bonding building blocks to generate porous molecular crystals, which were crosslinked through thiol-ene/yne single-crystal-to-single-crystal transformations. The generated HOFs exhibit enhanced chemical durability, high crystallinity, and extraordinary framework dynamics. For instance, HOF-104 crystals featuring a pore diameter of 13.6 Å expanded in DMF to 300 ± 10% of their original lengths within just 1 min. This expansion allows the HOFs to adsorb guest molecules that are significantly larger than the pore sizes of their crystalline states. Through methanol-induced contraction, these large guests were encapsulated in the fast-contracted HOFs. These advancements in porous framework dynamics pave the way for new methods of encapsulating guests for targeted delivery.