Photocyclization of Fluorinated Acetophenones Unlocks an Efficient Way to Solar Energy Storage

The development of light-driven isomerization offers a promising avenue for energy storage applications. However, a persistent challenge lies in controlling the stability of the photoisomeric state and in catalyzing the thermal reversal effec-tively. In this work, we introduce the molecular pair ortho-methylacetophenone ⇄ benzocyclobutenol as a promising platform for long-term energy storage. To obtain an overall good performance, a trifluoromethyl group is strategically introduced. This group prevents unproductive reaction pathways during the photochemical cyclization (yield >99%), ensures stable photoisomers, and facilitates back-isomerization by critically lowering the pKa of the benzocyclobutenol scaffold. Thus, efficient reversal using simple organic bases is achieved, capitalizing on substantial rate differences for normal vs. anionic electrocyclic ring-openings. Ultimately, this discovery enables controlled heat release under ambient conditions.