Ullmann coupling mediated assembly of an electrically driven altitudinal molecular rotor

Area of Science:

• Surface Science
• Organic Chemistry
• Nanotechnology

Background:

• Molecular rotors are crucial for nanoscale devices, with most studies focusing on azimuthal rotation.
• Altitudinal molecular rotors, rotating parallel to the surface, are less explored.
• Surface-mediated reactions offer unique control over molecular configurations and dynamics.

Purpose of the Study:

• To synthesize and characterize novel altitudinal molecular rotors on a surface.
• To investigate the dynamics and control mechanisms of surface-bound molecular rotation.
• To establish a chemically tunable platform for studying molecular rotor and motor behavior.

Main Methods:

• Surface-mediated Ullmann coupling of aryl halides on a Cu(111) surface.
• Low-temperature scanning tunneling microscopy (STM) for real-time visualization of reaction steps.
• Inelastic electron tunneling spectroscopy (IETS) to induce and quantify molecular rotation.

Main Results:

• Altitudinal molecular rotors were successfully formed via a surface-mediated Ullmann coupling reaction.
• The intermediate metal-organic complex exhibited significant rotational motion of para-ethyl groups.
• Electron tunneling current measurements confirmed reaction state-dependent rotational activity.
• Inelastic electron tunneling stimulated ethyl group rotation via a one-electron process with a 45 meV threshold.

Conclusions:

• The study demonstrates the successful creation of reaction state-dependent altitudinal molecular rotors.
• The intermediate complex of the Ullmann coupling is key to observing molecular rotation.
• This system provides a versatile platform for fundamental research into molecular rotor and motor dynamics.