Amino-nitro-azobenzene dimers as a prototype for a molecular-level machine

Low-temperature scanning tunnelling microscope measurements of an X-shaped dimer, consisting of two amino-nitro-azobenzene molecules, on a Au(111)-surface are presented. Electron-induced manipulation switches either the upper- or the lower-lying molecule. These reversible switching processes are based on the cis-trans isomerization of the azobenzene molecules. The switching of the upper molecule moves the lower-lying molecule in a controlled way. Thus mechanical work is performed. This proof-of-principle shows the ability of azobenzene molecules to act as a molecular-level machine.