A single-molecule van der Waals compass

Single-molecule imaging is challenging but highly beneficial for investigating intermolecular interactions at the molecular level(1-6). Van der Waals interactions at the sub-nanometre scale strongly influence various molecular behaviours under confinement conditions(7-11). Inspired by the traditional compass(12), here we use a para-xylene molecule as a rotating pointer to detect the host-guest van der Waals interactions in the straight channel of the MFI-type zeolite framework. We use integrated differential phase contrast scanning transmission electron microscopy(13-15) to achieve real-space imaging of a single para-xylene molecule in each channel. A good correlation between the orientation of the single-molecule pointer and the atomic structure of the channel is established by combining the results of calculations and imaging studies. The orientations of para-xylene help us to identify changes in the van der Waals interactions, which are related to the channel geometry in both spatial and temporal dimensions. This work not only provides a visible and sensitive means to investigate host-guest van der Waals interactions in porous materials at the molecular level, but also encourages the further study of other single-molecule behaviours using electron microscopy techniques.

Automated summary

Single-molecule imaging is a challenging yet beneficial technique for investigating intermolecular interactions at the molecular level, particularly van der Waals interactions at the sub-nanometre scale under confinement conditions. The use of a rotating para-xylene molecule as a pointer allows for real-space imaging and identification of changes in van der Waals interactions related to channel geometry. This study not only provides insight into host-guest interactions in porous materials, but also encourages further exploration of other single-molecule behaviors using electron microscopy techniques.