Driving a Third Generation Molecular Motor with Electrons Across a Surface

Excitation of single molecules with electrons tunneling between a sharp metallic tip of a scanning tunneling microscope and a metal surface is one way to study and control dynamics of molecules on surfaces. Electron tunneling induced dynamics may lead to hopping, rotation, molecular switching, or chemical reactions. Molecular motors that convert rotation of subgroups into lateral movement on a surface can in principle also be driven by tunneling electrons. For such surface-bound motor molecules the efficiency of motor action with respect to electron dose is still not known. Here, the response of a molecular motor containing two rotor units in the form of overcrowded alkene groups to inelastic electron tunneling has been examined on a Cu(111) surface in ultrahigh vacuum at 5 K. Upon vibrational excitation, switching between different molecular conformations is observed, including conversion of enantiomeric states of chiral conformations. Tunneling at energies in the range of electronic excitations causes activation of motor action and movement across the surface. The expected unidirectional rotation of the two rotor units causes forward movements but with a low degree of translational directionality.

Automated summary

Exciting single molecules through electron tunneling between a sharp metallic tip and a metal surface can be used to research and manipulate molecule dynamics on surfaces. Such dynamics can involve hopping, rotation, molecular switching, or chemical reactions. This study investigates the response of a molecular motor with two rotor units to inelastic electron tunneling, observing switching between different molecular conformations and movement across the surface. However, the degree of translational directionality is low due to the motor's unidirectional rotation.