A-Azo: Tuning storage in MOST systems using intra- and intermol- ecular interactions with Azobenzenes

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The success of Molecular Solar Thermal Energy Storage (MOST) systems is indispensably connected to the light-switchable molecular entity (mostophore) utilized. There are multiple factors controlling the properties, which directly correlate to its MOST function. Critical parameters are inter alia the energy storage density, the half-life, or the match with the solar spectrum. In this proposal, general strategies to tackle the MOST-molecule inherent parameters for an optimized candidate will be explored with the example of azobenzenes: (1) Combination of multiple mostophores in one molecule; (2) Stabilization of the storage state by follow-up reaction; (3) Control of switching process by non-covalent interactions. In (1) not only multiple azobenzenes will be connected, but also other mostophores investigated within the Research Group FOR MOST. Here, the azaborines are especially interesting candidates, as they can replace one (or two) of the phenyl-units within the azobenzene, potentially leading to a drastic increase in storage energy while shifting the absorption of the azaborine favorably into the visible range. Depending on the application different storage times are desirable. Long-term storage poses a special challenge. If the energy loading process of the mostophore is connected to a follow-up reaction fixing the MOST-system in the storage state, the energy could be kept for an infinitive time. Ideally, the follow-up reaction is also promoted photochemically. This concept will be brought to life in the (2) part. The attachment of additional groups to alter the MOST properties leads mostly to a reduced storage density due to the increased molecular weight. Therefore, in part (2) non-covalent interactions are explored to optimize the MOST properties at different stages of the energy storage and release process. The main part of this project consists of the design, synthesis, and analysis of MOST components. Flow chemistry is playing an integral role, allowing large scale synthesis for testing, but also in high-throughput analysis. All parts will be well integrated with the other projects within the Research Group, e.g. exchange of compounds, knowledge in synthesis (A-BN, A-Nor, B-Cat), analysis (B-Spec, B-Surf), computational design, and elucidation of mechanisms (D-Ground, D-Photo), as well as testing in proof-of-concept devices (D-Dev). The insights gained will provide new fundamental insights into organic photochemistry, ranging from synthesis, analysis, and mechanistic understanding. This knowledge gained as an ensemble of this Research Group will allow us to push the MOST technology to a new level and pave the way to practical applications.