Directed Rotations of Single Porphyrin Molecules Controlled by Localized Force Spectroscopy

Directed molecular repositioning is a key step toward the build up of molecular machines. To
artificially generate and control the motion of molecules on a surface, excitations by light,
chemical, or electrical energy have been demonstrated. Here, the application of local
mechanical forces is implemented to achieve directed rotations of molecules. Threedimensional force spectroscopy with sub-Ångström precision is used to characterize porphyrin
derivatives with peripheral carbonitrile groups. Extremely small areas on these molecules
(≈100 100 pm2
) are revealed which can be used to control rotations. In response to the
local mechanical forces, the molecular structure elastically deforms and then changes its
conformation, which leads to its rotation. Depending on the selection of one of four
submolecular areas, the molecule is either rotated clockwise or counterclockwise.