The experimental investigation of molecular interactions bears a great challenge despite its importance in all areas of molecular science. Especially small interactions, such as London dispersion, the attractive part of the van der Waals forces, are difficult to quantify as they are usually low in energy. Nevertheless, these forces are omnipresent in any interaction of two molecular entities and can be decisive for structure and properties especially in large molecules. In the past years we have established the azobenzene switch as a powerful tool to characterize London dispersion interactions of different molecular entities. Recently, we could show, that there is a subtle interplay between intramolecular interactions, the flexibility of the attached groups as well as the interaction with solvent molecules. The insights will serve as a basis to reliably utilize London dispersion as design element for functional materials, catalysis or other chemical processes.