Covalent Dimerization of an Aza-5–7–7 Saddle Unlocks Fullerene Recognition toward Both C₆₀ and C₇₀ with Preference for C₇₀

Herein, we report the synthesis and full characterization of a covalently linked aza-5–7–7 saddle dimer (<b>1</b>). Single-crystal X-ray diffraction verifies its S-shaped conformation with two independent concave cavities.

Notably, the monomeric saddle precursor (<b>2</b>) shows no detectable fullerene binding, whereas covalent dimerization unlocks efficient host–guest interactions. NMR and UV–vis titrations reveal that <b>1</b> binds C₇₀ preferentially over C₆₀, and cocrystallization further validates its ability to encapsulate these fullerenes.