  The real-space imaging of small molecules is always challenging under the
electron microscopes, but highly demanded for investigating various nanoscale
interactions, such as hydrogen bond and van der Waals (vdW) force. Especially,
identifying the host-guest interactions in porous materials directly at the
molecular level will bring a deeper insight into the behaviors of guest
molecules during the sorption, catalysis, gas separation and energy storage. In
this work, we directly resolved the ordered configurations of p-xylenes (PXs)
adsorbed in ZSM-5 frameworks by the scanning transmission electron microscopy
(STEM) with the integrated differential phase contrast (iDPC) technique to
identify the host-guest vdW interactions. Based on these observations, we
revealed that the PXs in one straight channel modified the channel geometry
with a coherent orientation. And the adjacent straight channels were deformed
up to 8.8% along the different directions corresponding to three dominant PX
configurations, resulting a negligible overall expansion of ZSM-5 lattices.
Then, we could also image the disorder and desorption of PXs in ZSM-5 channels
during the in situ heating. This work not only helped us to study the
host-guest vdW interactions and the sorption behaviors of PXs in ZSM-5, but
also provided an efficient tool for further imaging and studying other
single-molecule behaviors under STEMs.
