Quantum mechanics

Chemical physics

Materials science

Molecule

Intermolecular force

Van der Waals radius

Physics

Nanotechnology

Organic chemistry

van der Waals force

Crystallography

Chemistry

Atomic units

Van der Waals surface

Nature

Single-molecule imaging is challenging but highly beneficial for investigating intermolecular interactions at the molecular level1-6. Van der Waals interactions at the sub-nanometre scale strongly influence various molecular behaviours under confinement conditions7-11. Inspired by the traditional compass12, 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 microscopy13-15 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.

A single-molecule van der Waals compass