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 (ΔE_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.