Synthesis, characterization and computational evaluation of bicyclooctadienes towards molecular solar thermal energy storage

• Published in: Chemical science (Cambridge) Vol. 13; no. 3; pp. 834 - 841
• Main Authors: Quant, Maria, Hillers-Bendtsen, Andreas Erbs, Ghasemi, Shima, Erdelyi, Mate, Wang, Zhihang, Muhammad, Lidiya M., Kann, Nina, Mikkelsen, Kurt, Moth-Poulsen, Kasper
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 19.01.2022; Royal Society of Chemistry; The Royal Society of Chemistry
• Subjects: Absorption spectra; Chemical energy; Chemical reactions; Chemical synthesis; Chemistry; Chemistry, Multidisciplinary; Coupling (molecular); Cross coupling; Density functional theory; Diels-Alder reactions; Energy storage; Evaluation; Half-life; Molecular structure; Physical Sciences; Science & Technology; Solar energy conversion; Solar heating; Thermal energy; PHOTOISOMERIZATION; BOND-BREAKING; ELECTRONIC-STRUCTURE; EXCITED-STATES
• ISSN: 2041-6520; 2041-6539; 2041-6539
• DOI: 10.1039/d1sc05791j

Molecular solar-thermal energy storage (MOST) systems are based on photoswitches that reversibly convert solar energy into chemical energy. In this context, bicyclooctadienes (BODs) undergo a photoinduced transformation to the corresponding higher energy tetracyclooctanes (TCOs), but the photoswitch system has not until now been evaluated for MOST application, due to the short half-life of the TCO form and limited available synthetic methods. The BOD system degrades at higher temperature via a retro-Diels-Alder reaction, which complicates the synthesis of the compounds. We here report a cross-coupling reaction strategy that enables an efficient synthesis of a series of 4 new BOD compounds. We show that the BODs were able to switch to the corresponding tetracyclooctanes (TCOs) in a reversible way and can be cycled 645 times with only 0.01% degradation. Half-lives of the TCOs were measured, and we illustrate how the half-life could be engineered from seconds to minutes by molecular structure design. A density functional theory (DFT) based modelling framework was developed to access absorption spectra, thermal half-lives, and storage energies which were calculated to be 143-153 kJ mol(-1) (0.47-0.51 MJ kg(-1)), up to 76% higher than for the corresponding norbornadiene. The combined computational and experimental findings provide a reliable way of designing future BOD/TCO systems with tailored properties.