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

Abstract Nonplanar curved π-conjugated molecules are promising building blocks for supramolecular fullerene hosts, yet negatively curved saddle-based dimeric receptors remain largely underexplored. Herein, we report the synthesis and full characterization of a covalently linked aza-5–7–7 saddle dimer (1). Single-crystal X-ray diffraction verifies its S-shaped conformation with two independent concave cavities. Notably, the monomeric saddle precursor (2) shows no detectable fullerene binding, whereas covalent dimerization unlocks efficient host–guest interactions. NMR and UV–vis titrations reveal that 1 binds C70 preferentially over C60, and cocrystallization further validates its ability to encapsulate these fullerenes.