Surface-Mounted Dipolar Molecular Rotors Driven by External Electric Field, As Revealed by Torque Analyses

Abstract

Driven by a high-speed rotating electric field ( E -field), molecular motors with polar groups may perform a unidirectional, repetitive, and GHz frequency rotation and thus offer potential applications as nanostirrers. To drive the unidirectional rotation of molecular motors, it is crucial to consider factors of internal charge flow, thermal noise, molecular flexibility, and so forth before selecting an appropriate frequency of a rotating E -field. Herein, we studied two surface-mounted dipolar rotors of a “caltrop-like” molecule and a “sandwich” molecule by using quantum–mechanical computations in combination with torque analyses. We find that the rotational trend as indicated by the magnitude and the direction of torque vectors can sensitively change with the lag angle (α) between the dipolar arm and the E -field. The atomic charges timely flow within the molecule as the E -field rotates, so the lag angle α must be kept in particular intervals to maintain the rotor’s unidirectional rotation. The thermal effect can substantially slow down the rotation of the dipolar rotor in the E -field. The flexible dipolar arm shows a more rigid geometry in the E -field with higher rotation speed. Our work would be useful for designing E -driven molecular rotors and for guiding their practical applications in future.

Confined Space Nanoarchitectonics for Dynamic Functions and Molecular Machines

“…In particular, considerations of factors such as internal charge flow, thermal noise, and molecular flexibility are critical to selecting and predicting the appropriate frequency of the rotating electric field to drive the unidirectional rotation of the molecular motor. Theoretical analysis of two surface-mounted dipole rotors was performed using a combination of quantum mechanical calculations and torque analysis as reported by Zhao, Zhang, Hove, and co-workers [313]. The driving force for the unidirectional rotation of the rotor can be quantified and considered in terms of a torque vector acting on the rotor projected onto the axis of rotation.…”

Droplet Rolling Transport on Hydrophobic Surfaces Under Rotating Electric Fields: A Molecular Dynamics Study

“…Rotating electric fields have been widely used in many fields as an effective means of manipulating micro- and nanoscale fluids. The actuation of dipole molecules by rotating electric fields can power nanomotors or molecular motors. − In the biomedical field, rotating electric fields can be used to rotate cells, capsules, and micro- and nanobiological machines. − In other aspects, the rotating electric fields can also be used for electropumping of water in nanochannels, − curling of graphene nanoribbons, and colloidal particle self-assembly, − etc.…”