Title:	Design of molecular photoswitches for storage of solar energy
DNr:	LiU-compute-2022-7
Project Type:	LiU Compute
Principal Investigator:	Bo Durbeej <bo.durbeej@liu.se>
Affiliation:	Linköpings universitet
Duration:	2022-04-01 – 2025-04-01
Classification:	10407
Homepage:	https://liu.se/en/employee/bodu88
Keywords:

Abstract

The goal of this proposal is to acquire HPC resources for our research in which quantum chemical modelling is performed to design new molecular photoswitches capable of storing solar energy. Such photoswitches are known as molecular solar thermal energy (MOST) systems, and function through the interconversion between one sunlight-absorbing form (isomer 1) and one energy-storing form (isomer 2) of the switch. Specifically, absorption of sunlight by isomer 1 triggers a photochemical reaction that produces isomer 2, which lies much higher in energy. Still, this isomer is stable and is prevented to return to the parent isomer by a large energy barrier. In this way, the absorbed solar energy is stored as chemical energy in the bonds of isomer 2. However, with a suitable catalyst, it is possible to reduce the barrier and trigger the back-reaction even at ambient temperatures. Thereby, whenever needed, the solar energy can be released as heat, which is the modus operandi of MOST systems. Our research in this field, which is supported by several sources (Vetenskapsrådet, Olle Engkvists Stiftelse, ÅForsk and Carl Tryggers Stiftelse) and is done in collaboration with a group at the Hungarian Academy of Sciences that both synthesize our computationally designed photoswitches and test their MOST performance experimentally, was started in 2020. In particular, at that time, we reported (in the Journal of the American Chemical Society) that a type of organic photoswitches (dithienylbenzenes) designed by my group and synthesized by the Hungarian group are promising candidates for MOST applications. Now, the aim of the quantum chemical modelling to be performed in this project is to identify the dithienylbenzenes that best enable such applications. In order for a molecular photoswitch to be useful for MOST applications, a number of intrinsic features are desirable. Naturally, isomer 1 needs to show a large spectral overlap with the most intense band around 500 nm in the solar spectrum and exhibit a high quantum yield for its photoconversion into isomer 2. Furthermore, the energy difference between the two isomers should be large and the molecular weight low, so as to afford a high energy-storage density. Additionally, the energy barrier for the thermal back-reaction from isomer 2 to isomer 1 needs to be large, which ensures that the solar energy can be stored in the chemical bonds of isomer 2 for as long as required by the intended MOST application - be it hours, days or even months. In this project, we will use basic concepts in organic chemistry to design new dithienylbenzene photoswitches that exhibit as many of these desirable features as possible, and evaluate the resulting designs based on state-of-the-art quantum chemical modelling, including both non-adiabatic molecular dynamics (NAMD) simulations (to predict photoisomerization quantum yields) and static calculations (to predict UV-Vis absorption spectra, energy-storage densities and thermal energy barriers). This is an ambitious undertaking, especially by requiring NAMD simulations at the very forefront of photochemical modelling that cannot be performed without adequate HPC resources.