Bridge‐Length‐Dependent Diradical and Mixed‐Valence Radical in Benzene Triimide Cages

Supramolecular radical cages are captivating architectures in supramolecular chemistry and materials science; however, their construction and precise regulation of electronic states and magnetic properties remain substantially challenging. Herein, we report the synthesis, structures, and magnetic properties of a series of covalent organic radical cages, generated by reducing the benzene triimide (BTI) radical precursors within the corresponding neutral cages. The m ‐xylene‐bridged cage with two parallel BTI units separated by 5.4 Å undergoes stepwise reduction to afford both mixed‐valence monoradical and diradical cages. In contrast, the cavity‐expanded cage with naphthalene bridges (7.6 Å) preferentially gives a mixed‐valence monoradical even under excess reductant. This discrepancy originates from cavity‐mediated host–guest interactions of the radical cages, which selectively stabilize the mixed‐valence monoradical of the naphthalene‐bridged cage. All the radical cages exhibit good stability and are characterized by single‐crystal x‐ray diffraction, EPR, and UV–vis–NIR spectroscopy. For the m ‐xylene‐bridged diradical cage, the two BTI radical units are weakly coupled, exhibiting a singlet ground state with a narrow singlet–triplet energy gap (Δ E ST = –1.63 kcal/mol). The naphthalene‐bridged mixed‐valence monoradical cage features an unpaired electron delocalized over the two BTI units and exhibits antiferromagnetic interactions arising from its one‐dimensional linear assembly in the solid state.