Quantum chemical design of rotary molecular motors

Abstract

This tutorial review describes how recent quantum chemical calculations and non-adiabatic molecular dynamics simulations have provided valuable guidelines and insights for the design of more powerful synthetic rotary molecular motors. Following a brief overview of the various types of rotary motors synthesized to date, we present computationally identified steric and electronic approaches to significantly reduce the free-energy barriers of the critical thermal isomerization steps of chiral overcrowded alkenes, a main class of motors whose potential for many different kinds of applications is well documented. Furthermore, we describe how computational research in this field has provided new motor designs that differ from overcrowded alkenes by either (1) completing a full 3608 rotation through fewer steps, (2) exhibiting more efficient photochemical steps, or (3) requiring fewer chiral features for their function, including a design that even in the absence of a stereocenter achieves unidirectional rotary motion from two Z/E photoisomerizations alone.chirality, molecular motors, non-adiabatic molecular dynamics, photoisomerization, steric interactions | I N TR ODU C TI ONIn this tutorial review, we give an account of how quantum chemical research has contributed to advance the field of artificial molecular machines.This field [1][2][3][4][5][6][7][8][9][10][11] is devoted to the fabrication of molecular systems capable of performing the same type of machine-like functions that Nature-made protein complexes carry out in order to, among other things, propel cells, store energy in cells, equip cells with transport systems, and generate biomechanical forces. [12][13][14] Although artificial molecular machines are yet to make an impact on our everyday lives, the field is currently undergoing a rapid expansion both in terms of what man-made molecules can accomplish and the areas of expertise of the scientists drawn to the field. In many ways, this development, envisioned already in 1959 by Richard Feynman in his prophetic "There's Plenty of Room at the Bottom" lecture, [15] is testament to the groundbreaking work on the design and synthesis of molecular machines [16][17][18][19][20][21][22][23][24][25] for which Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard (Ben) L. Feringa were awarded the Nobel Prize in Chemistry 2016.While a molecular machine can be defined as "an assembly of a discrete number of molecular components designed to perform mechanical-like movements (output) as a consequence of appropriate external stimuli (input)," [2] this tutorial review focuses on the subset of such systems known as molecular motors. Loosely speaking, molecular motors are molecules that can produce net work by absorbing external energy and converting the energy into directed (non-random) mechanical motion in a controllable fashion. The ability to produce net work is the distinguishing feature of molecular motors vis-a-vis molecular switches, the latter of which sustain back-and-forth motion but not the continuous m...

Nonadiabatic Molecular Dynamics on Graphics Processing Units: Performance and Application to Rotary Molecular Motors

“…The reason for this might be the slightly different coupling vectors between the ground state and the first excited state (Supporting Information). In contrast to refs (43) and (44), we do not observe an influence of the puckering of the ring on the rotation. The ratios of CW and CCW rotations ( r ) are close to 1 for all four rotors, and no general trend is visible in the γ plots (Supporting Information).…”

Molecular Photoswitching Aided by Excited‐State Aromaticity

“…In this minireview, we illustrate based on computational research how the performance of molecular photoswitches can be improved with respect to the first of the aforementioned criteria by invoking the evolving concept of excited‐state aromaticity (ESA) ,. First, developed as part of our own research on photoswitches more commonly known as light‐driven rotary molecular motors (because their switching produces 360° unidirectional rotary motion), we describe a novel approach using this concept for the design of E / Z photoswitches with high QYs and fast response times . The discussion of this approach is followed by a presentation of another ESA‐based strategy to achieve fast response times for photoswitches driven by H‐atom/proton transfer reactions, due to Rocha‐Rinza and co‐workers .…”

Light-induced shape morphing of thin films

“…However, empirical studies of large libraries of photoswitches is synthetically time-consuming and even thoughtful molecular design can often be little better than a shot in the dark. To circumvent these issues, computational tools can be used for the targeted design of photoactive compounds [68]. Thus, while synthesizing and characterizing multitudes of photoswitch derivatives is slow and cumbersome, quantum mechanical simulations of large libraries of chromophores can be used to inform targeted synthesis.…”