Elucidating the effect of mechanical friction on the excited-state reaction dynamics of molecular motors and switches
Title: Elucidating the effect of mechanical friction on the excited-state reaction dynamics of molecular motors and switches
SNIC Project: SNIC 2021/5-553
Project Type: SNIC Medium Compute
Principal Investigator: Bo Durbeej <bo.durbeej@liu.se>
Affiliation: Linköpings universitet
Duration: 2021-12-01 – 2022-12-01
Classification: 10407 21001 10405
Homepage: https://liu.se/en/employee/bodu88


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. 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 that produce 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 the previous SNIC Medium Compute projects upon which the present proposal is based (SNIC 2019/3-631 and SNIC 2020/5-618), we have developed the required "wrapper" codes (i.e., interfaces between in-house codes for NAMD simulations and commercial electronic-structure codes) to be used in this continuation project, and studied how friction exerted by both solvent molecules and surfaces influences the motor performance. Now, we will use these codes to study the more complicated case of friction exerted by different nanodevice components. Furthermore, besides studying the role of friction for the function of molecular motors, we will also investigate how friction (especially solvent friction) influences the ability of molecular photoswitches to store solar energy. In the preceding project, we have carried out one such investigation for a well-known class of solar-energy-storing photoswitches. In this continuation project, we will carry on this work, but now instead with a focus on photoswitches that we have designed ourselves.