Simulation framework for screening of molecular solar thermal systems in the context of a hybrid device

Searching the Chemical Space of Bicyclic Dienes for Molecular Solar Thermal Energy Storage Candidates

Photoswitches are molecular systems that are chemically transformed subsequent to interaction with light and they find potential application in many new technologies. The design and discovery of photoswitch candidates require intricate molecular engineering of a range of properties to optimize a candidate to a specific applications, a task which can be tackled efficiently using quantum chemical screening procedures. In this paper, we perform a large scale screening of approximately half a million bicyclic diene photoswitches in the context of molecular solar thermal energy storage using ab initio quantum chemical methods. We further device an efficient strategy for scoring the systems based on their predicted solar energy conversion efficiency and elucidate potential pitfalls of this approach. Our search through the chemical space of bicyclic dienes reveals systems with unprecedented solar energy conversion efficiencies and storage densities that show promising design guidelines for next generation molecular solar thermal energy storage systems.

Status and challenges for molecular solar thermal energy storage system based devices

Molecular solar thermal energy storage systems (MOST) offer emission-free energy storage where solar power is stored via valence isomerization in molecular photoswitches. These photoswitchable molecules can later release the stored energy as heat on-demand. Such systems are emerging in recent years as a vibrant research field that is rapidly transitioning from basic research to applications. Since a major part of the attention is focused on molecular design and engineering, MOST-based device development has not been systematically summarized and introduced to a broad audience. This tutorial review will discuss the most commonly used and developed devices from a chemical engineering point of view. It is expected that future developers of MOST technology could be inspired by the existing devices, keeping in mind the summarized essential practical challenges towards large-scale implementations and more innovative applications.

Liquid-Based Multijunction Molecular Solar Thermal Energy Collection Device

Photoswitchable molecules-based solar thermal energy storage system (MOST) can potentially be a route to store solar energy for future use. Herein, the use of a multijunction MOST device that combines various photoswitches with different onsets of absorption to push the efficiency limit on solar energy collection and storage is explored. With a parametric model calculation, it is shown that the efficiency limit of MOST concept can be improved from 13.0% to 18.2% with a double-junction system and to 20.5% with a triple-junction system containing ideal, red-shifted MOST candidates. As a proof-of-concept, the use of a three-layered MOST device is experimentally demonstrated. The device uses different photoswitches including a norbornadiene derivative, a dihydroazulene derivative, and an azobenzene derivative in liquid state with different MOSTproperties, to increase the energy capture and storage behavior. This conceptional device introduces a new way of thinking and designing optimal molecular candidates for MOST, as much improvement can be made by tailoring molecules to efficiently store solar energy at specific wavelengths.

A QM/MM study of the conformation stability and electronic structure of the photochromic switches derivatives of DHA/VHF in acetonitrile solution

We present a detailed theoretical study of the electronic absorption spectra and thermochemistry of molecular photoswitches composed of one and two photochromic units of dihydroazulene (DHA)/vinylheptafulvene (VHF) molecules. Six different isomers are considered depending on the ring opening/closure forms of the DHA units. The solvent effect of acetonitrile is investigated using a sequential Molecular Mechanics/Quantum Mechanics approach. The thermochemical investigations of these photochromic molecules were performed using the Free Energy Perturbation method, and the simulations were performed using Configurational Bias Monte Carlo. We show that to open the 5-member ring of the DHA, there is no significant gain in thermal release of energy for the back reaction when a unit or two DHA units are considered. Overall, we found agreement between the solvation free energy based on Monte Carlo simulations and the continuum solvent model. However, the cavitation term in the continuum model is shown to be a source of disagreement when the non-electrostatic terms are compared. The electronic absorption spectra are calculated using TDDFT CAM-B3LYP/cc-pVDZ. Agreement with experiment is obtained within 0.1 eV, considering statistically uncorrelated configurations from the simulations. Inhomogeneous broadening is also considered and found to be well described in all cases.