Title:	Elucidating the effect of mechanical friction on the excited-state reaction dynamics of molecular motors and switches
DNr:	SNIC 2020/14-83
Project Type:	SNIC Small Storage
Principal Investigator:	Bo Durbeej <bo.durbeej@liu.se>
Affiliation:	Linköpings universitet
Duration:	2020-12-01 – 2021-12-01
Classification:	10407
Homepage:	https://liu.se/en/employee/bodu88
Keywords:

Abstract

Molecular motors are molecules that can perform work by absorbing energy and converting the energy into directed mechanical motion such as rotation around a chemical bond. Because of this ability, it has long been recognized that these systems have enormous potential for applications in nanotechnology and medicine. In the last few years, we have initiated a line of research unique to Swedish academia in which more powerful and useful light-driven molecular motors are designed through computational studies in theoretical chemistry. Thereby, we have found a number of ways to increase the speed, improve the efficiency, and tailor the light-absorption characteristics of such motors. For example, regarding efficiency, we have discovered that the ability of molecular motors to become aromatic in their photoactive excited states can improve their quantum yields by up to 50% (Org Lett 2017, ChemPlusChem 2018 and ChemPhotoChem 2019). In general, by analogy with the macroscopic motors in our everyday lives (e.g., in cars), it is clear that one would like to construct nanodevices that are able to exploit the rotary motion of molecular motors for various useful purposes. However, a prerequisite for realizing such devices is to clarify how mechanical friction affects the dynamics of the photochemical reactions producing the rotary motion. Despite its fundamental importance, this issue remains poorly understood. From a modeling perspective, this is due to the steep methodological challenge to accurately simulate the reaction dynamics of the motors, occurring in excited states, while also accounting for the molecular collisions causing the friction. Nonetheless, it is the aim of this project to meet this challenge. To this end, our approach will be to couple non-adiabatic molecular dynamics (NAMD) simulations of the motors based on quantum chemical methods to MD simulations of the environments in which the motors are operated based on classical force fields. In this way, we will be able to model the photochemical reaction dynamics of the motors as they experience friction in a solvent, from a surface, and, ultimately, from other molecules with which they interact in different nanodevices. Thereby, by calculating the photochemical quantum yields of the motors in such situations, we will assess how friction affects their overall performance, which is a long-standing goal in this field of research. In a previous SNIC compute project (SNIC 2019/3-631), we have developed the required computer code to be used in this continuation project, and studied friction exerted by solvent molecules (please see the corresponding activity report). Now, in the continuation project, we will use this code to study the more complicated cases of friction exerted by different surfaces and nanodevice components. Furthermore, besides studying the role of friction for the function of molecular motors, we will will also investigate how friction influences the ability of molecular photoswitches to store solar energy, which we have recently embarked upon and which has led (in 2020) to a publication in The Journal of the American Chemical Society.