Direct observation of porous coordination polymer surfaces by atomic force microscopy

Flexible porous coordination polymers (PCPs) and metal-organic frameworks (MOFs) have attracted significant attention as emerging nanoporous materials because their responsive functions have many promising applications in molecular recognition systems and gas storage/separation applications. Flexible PCP/MOFs undergo dynamic structural transformations in response to guest accommodation into the nanopores; here, the outermost surfaces of the PCP/MOFs play a key role in their porous functions. However, the surface structures and behavior in response to external environmental changes are largely unknown due to the limitations of observation techniques. This review provides a brief overview of the surface chemistry and progress of in situ imaging technology as a new tool for the direct visualization of dynamic PCP/MOF surfaces.