Photocyclization of\nFluorinated Acetophenones Unlocks\nan Efficient Way to Solar Energy Storage

The ability to store and release energy efficiently is\ncrucial\nfor advancing sustainable energy technologies, and light-driven molecular\nisomerization presents a promising solution. However, a persistent\nchallenge in this field is achieving both high stability of the energy-storing\nphotoisomer and establishing efficient catalysis for back-isomerization,\na critical process for releasing the stored energy as heat. In this\nwork, we introduce a conceptually new molecular system designed for\nlong-term energy storage, which is based on the reversible isomerization\nof <i>ortho</i>-methylacetophenone ⇄ benzocyclobutenol.\nKey to the success of this system is the strategic placement of a\ntrifluoromethyl group, which enhances the overall performance by preventing\nunwanted side reactions during photochemical cyclization and by increasing\nthe stability of the benzocyclobutenol moiety. Back isomerization\nis established using simple organic bases as catalysts, taking advantage\nof significant rate differences between normal and anionic electrocyclic\nring-openings. This approach allows for controlled and predictable\nheat release under ambient conditions, positioning this molecular\npair as a promising candidate for practical energy storage solutions.