Reversible Interconversion between a Carbon-Carbon Double Bond and Diradical beyond External Stimulus

The reversible interconversion between a carbon-carbon double bond and a diradical species represents a fundamental challenge in organic chemistry, with implications for molecular design and electronic materials. While steric strain and external stimulus can induce partial twisting of a carbon-carbon double bond, achieving stable diradical states through controlled, reversible bond twisting remains a significant challenge. Here, we report a strategy in which Lewis acid coordination enables the controlled twisting of C═C bonds to form diradical species with torsional angles of over 70°. Through coordination of Al(OR_F)₃ (R_F = C(CF₃)₃) or SiEt₃⁺ to bianthrone derivatives, we isolate twisted adducts characterized by X-ray crystallography, EPR spectroscopy, and magnetic studies. The process is reversible─competitive displacement of Lewis acids by CH₃CN restores folded alkenes, as monitored by UV-vis and NMR spectroscopy. This work provides a strategy for manipulating carbon-carbon double-bond topology with potential applications in reversibly responsive molecular systems.