Unveiling Sophisticated Intermolecular van der Waals Interactions at the Single-Molecule Level

Weak yet ubiquitous van der Waals (vdW) interactions play an essential role in shaping the structure, stability, and functionality of materials. Particularly, intermolecular vdW interactions profoundly impact molecular stacking orders and electronic properties. However, comprehending and precisely controlling intermolecular vdW interactions has posed a longstanding challenge. Here, we employ a combination of single-molecule electrical measurements and theoretical calculations to dissect and further regulate sophisticated vdW interactions in a single-dimer junction. Specifically, by introducing an aminomethyl group, the electrostatic force resulting from the dipole–dipole interaction predominantly dictates the bistable conformation and conductance of benzylamine dimers. As molecular π-conjugation increases, the influence of exchange and dispersion interactions is significantly amplified in (9H-fluoren-2-yl)methylamine dimers. Furthermore, the application of electric fields effectively modulates the vdW interactions in dimers, impacting their structures and conductance. Investigating these vdW interactions yields profound insights into the fundamental principles governing the behavior of chemical and biological systems.