Many types of molecular motors have been proposed and synthesized in recent years, displaying different kinds of motion, and fueled by different driving forces such as light, heat, or chemical reactions. We propose a new type of molecular motor based on electric field actuation and electric current detection of the rotational motion of a molecular dipole embedded in a three-terminal single-molecule device. The key aspect of this all-electronic design is the conjugated backbone of the molecule, which simultaneously provides the potential landscape of the rotor orientation and a real-time measure of that orientation through the modulation of the conductivity. Using quantum chemistry calculations, we show that this approach provides full control over the speed and continuity of motion, thereby combining electrical and mechanical control at the molecular level over a wide range of temperatures. Moreover, chemistry can be used to change all key parameters of the device, enabling a variety of new experiments on molecular motors.
The motor’s rotor is a long, coal-derived molecule called anthracene, which spins around an axle composed of two ethynyl units. Each end of this axle is connected to an electrode, and a third electrode – called the gate – is located slightly below the axle.
Applying an alternating current to this gate electrode sets up an oscillating electric field that surrounds the molecular motor and, according to the researchers’ calculations, should cause the anthracene rotor to turn.
That’s because anthracene possesses what is known as a dipole moment – its negatively charged electrons tend to congregate at one end of the molecule, making the other end positively charged.