Intramolecular Torque, an Indicator of the Internal Rotation Direction of Rotor Molecules and Similar Systems

TL;DR

This paper introduces a simple quantum mechanics-based method to predict the preferred rotation direction of molecules and sub-units, aiding in the design and analysis of molecular rotors and related systems.

Contribution

The authors develop a quick, qualitative computational approach to determine molecular rotation tendencies and axes, enhancing the ability to screen and modify molecules before experiments.

Findings

Successfully applied to a light-driven molecular rotary motor

Effectively predicts rotation direction and responsible atoms

Provides insights to guide molecular design and analysis

Abstract

Torque is ubiquitous in many molecular systems, including collisions, chemical reactions, vibrations, electronic excitations and especially rotor molecules. We present a straightforward theoretical method based on forces acting on atoms and obtained from atomistic quantum mechanics calculations, to quickly and qualitatively determine whether a molecule or sub-unit thereof has a tendency to rotation and, if so, around which axis and in which sense: clockwise or counterclockwise. The method also indicates which atoms, if any, are predominant in causing the rotation. Our computational approach can in general efficiently provide insights into the rotational ability of many molecules and help to theoretically screen or modify them in advance of experiments or before analyzing their rotational behavior in more detail with more extensive computations guided by the results from the torque approach. As an example, we demonstrate the effectiveness of the approach using a specific light-driven molecular rotary motor which was successfully synthesized and analyzed in prior experiments and simulations.