By excitation of molecules with inelastic tunneling electrons, we study molecular dynamics such as hopping, rotation and dissociation. Currently, we use molecular machines based on overcrowded alkenes, synthesized in the Feringa group at the University of Groningen.

In his famous experiment in 1848 Pasteur separated left- and right-handed ammonium sodium tartrate crystals manually and observed opposite optical activity for their aqueous solutions. His insight that the origin of chirality is based on molecular structure laid the foundation of modern structural organic chemistry. Two important details of his experiment actually allowed the manual separation: i) Handedness was transferred from the molecular structure to the macroscopic shape of the crystal (hemihedrism), and ii) the racemate precipitated into a conglomerate of enantiopure crystals. The underlying mechanisms of both processes are still poorly understood. We are neither able to predict the shape of a crystal from molecular structure nor do we know why less than ten percent of all racemates crystallize into conglomerates. One reason for the difficulty to understand and investigate these processes is their cooperative nature. Extremely small structural influences gov- ern the macroscopic result when they be- come amplified by many cooperating units. Cooperativity among different homochiral biomolecules is also of fundamental importance in life. Furthermore, the transfer of chirality into mesoscopic structures – a very important issue in liquid crystal science – is difficult to predict in three dimensions. More tractable and easier understood are two-dimensional (2D) crystals formed at surfaces, in particular because of the possibility to study these processes at the molecular level by exploitation of scanning tunneling microscopy (STM).