Title:	Computational design of molecular photogears
DNr:	NAISS 2024/5-628
Project Type:	NAISS Medium Compute
Principal Investigator:	Bo Durbeej <bo.durbeej@liu.se>
Affiliation:	Linköpings universitet
Duration:	2024-12-01 – 2025-12-01
Classification:	10407 21001 10405
Homepage:	https://liu.se/en/employee/bodu88
Keywords:

Abstract

Light-responsive molecular motors and switches are molecules that can perform many useful functions in nanotechnology by absorbing light energy and converting it to other forms of energy. In the last decade, we have initiated a line of research unique to Swedish academia in which more useful and potent light-responsive molecular motors and switches are designed through computational modeling in theoretical chemistry. Thereby, by studying the dynamics of the photochemical reactions by which the motors and switches are powered, we have discovered a number of ways to improve the functions of these systems. From a modeling perspective, this challenging task has required accurate simulation of reaction dynamics in electronically excited states, combined with a simultaneous description of the solvent or surface environments in which the motors and switches are operated. In our work, the strategy to meet this challenge has been to couple semi-classical, non-adiabatic molecular dynamics (NAMD) simulations of the motors and switches based on quantum chemical methods, to classical MD simulations of the solvent or surface environments based on empirical force fields. In this way, we have been able to model the reaction dynamics of the motors and switches in as realistic fashion as possible, and thereby gain very valuable insights into how their performance can be optimized. As part of this work, we have developed so-called "wrapper" codes that integrate our own in-house codes for NAMD simulations with commercial electronic-structure software packages. In this continuation project, we will now use these codes to address another outstanding challenge in the field of artificial molecular machines, which is to design so-called molecular photogears that can achieve through-space transmission of the double-bond rotary motion of light-driven molecular motors onto a remote single-bond axis. Indeed, molecular photogears with this capability are just as important for the future usefulness of artificial molecular machines as "real" gearboxes are for the functions of macroscopic machines in our everyday lifes (see discussion in Nat. Chem. 2022, 14, 670). In this context, it is noteworthy that, as part of the previous NAISS Medium Compute project upon which the present proposal is based (NAISS 2023/5-495), our group has recently developed and published the first ever functional design of a molecular photogear of this kind (see Chem. Eur. J. 2024, 30, e202303191). However, despite its functionality and despite immediately leading to an invitation from ChemPlusChem to describe our work in a concept article (currently in preparation), our design has ample room for improvement in terms of efficient usage of the absorbed light energy (quantum yield) and the ability to maintain a preferred direction of rotation (gearing fidelity). Furthermore, the design is not perfectly "clean", containing groups that are not critical for the photogearing and that make organic synthesis difficult. Against this background, the overall goal of the present continuation project is to improve our initial photogear design in these respects and test our corresponding predictions using the aforementioned NAMD codes as key evaluation tools.