First Structural Determination of an Isolable and Planar Tropyl Radical

Planar hydrocarbon‐based tropyl radicals remain elusive because seven‐membered open‐shell systems readily undergo structural deformation and intermolecular reactions. Herein, we report the design, isolation, and structural characterization of dibenzotropyl radicals bearing anthryl‐based π ‐systems. Density functional theory (DFT) calculations predicted that bianthryl and teranthryl substituents stabilize orthogonally twisted conformations containing a planar dibenzotropyl radical unit while suppressing the formation of reactive folded structures. One‐electron reduction of the corresponding dibenzotropyliums afforded persistent neutral radicals for both the bianthryl and teranthryl derivatives, which are stable under ambient conditions. Single‐crystal X‐ray diffraction analysis of the bianthryl‐substituted radical revealed a sterically unperturbed planar dibenzotropyl structure, providing the first crystallographic evidence for a planar hydrocarbon‐based tropyl radical. Spectroscopic, electrochemical, and theoretical studies revealed reversible redox interconversion between the cationic and radical states while retaining the planar seven‐membered framework. These findings provide insight into redox‐active seven‐membered π ‐systems and establish a design strategy for stable open‐shell hydrocarbons.