“A new series of highly water soluble norbornadienes has been synthesized and characterized as molecular solar thermal (MOST) systems in gram scale. Particularly, concentrated solutions (1 M) and solid-state heat release showed a thermal heat release of 7.5 and 39.6 K, respectively, with full reversibility in both cases. These systems represent a new avenue for transferring the MOST technology to real and sustainable applications.”

Abstract

Solar energy storage is key to overcome the intermittent character of sunlight. We present a sustainable solution based on norbornadiene–quadricyclane pairs for molecular solar thermal (MOST) energy storage working in highly concentrated neutral water solutions and solid state. Photochemical preparation of high-energy, metastable isomers in previously unattainable 1.64 M solutions was achieved. The best compound can be stored for 1.9 years and is stable in solid state, allowing for the preparation of up to 3 M water solutions. Catalyzed back-conversion ensures efficient heat release and starting material recovery with remarkable fatigue resistance in water solution and solid state, exhibiting macroscopic heat release in both states, providing a ΔT of 39.6 K and fully recyclable use. These results highlight a promising avenue for the practical application of MOST technology.