Dynamic Intermolecular Space for Reversible CO₂ Capture and Release

Molecular constructs define the elementary units in porous materials for efficient CO₂ capture. The design of appropriate interpore and intermolecular space is crucial to stabilize CO₂ molecules and maximize the capacity. While the molecular construct usually has a fixed dimension, whether its intermolecular space could be self-adjustable during CO₂ capture and release, behaving as a balloon, has captured imagination. Here we report a flexible intermolecular space of the double chain structure of self-assembled 1,4-phenylene diisocyanide (PDI) molecules on Ag(110) surface, which dynamically broadens and recovers during the CO₂ capture and release. The incipient PDI double chains organize along the 001 direction of Ag(110), in which individual PDI molecules stand up in a zigzag order with the interchain width defined by twice the Ag lattice distance along \left1\bar10\right direction (2 \alpha _\left1\bar10\right ). When CO₂ molecules are introduced, they assemble to occupy the interchain spaces, expanding the interchain width to 3 \alpha _\left1\bar10\right , 4 \alpha _\left1\bar10\right and 5 \alpha _\left1\bar10\right . Warming up the sample leads to the thermally-driven CO₂ desorption that recovers the original interchain space. High-resolution scanning tunneling microscopy (STM) jointly with density functional theory (DFT) calculations determine the structural and electronic interactions of CO₂ molecules with the dynamical PDI structures, providing a molecular-level perspective for the design of a self-adjustable metal-organic construct for reversible gas capture and release.