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 [11¯0] direction (2α[11¯0]). When CO2 molecules are introduced, they assemble to occupy the interchain spaces, expanding the interchain width to 3α[11¯0], 4α[11¯0] and 5α[11¯0]. 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.