A Chiral Saddle-shaped Nanographene with Two Heptagon-Embedded [4]Helicenes for Supramolecular Complexation

Chiral non-benzenoid nanographenes remain highly appealing but underexplored synthetic targets due to the lack of feasible synthetic strategies to simultaneously construct non-hexagonal rings and stable chirality. Herein, we present the synthesis and characterization of a novel chiral saddle-shaped nanographene (cSNG) incorporating two heptagon-embedded [4]helicenes. The structure of cSNG is unambiguously confirmed by single-crystal X-ray diffraction analysis, demonstrating its flexible π-skeleton. Due to the heptagon-embedded [4]helicene subunits, cSNG exists as configurationally stable enantiomers, which enable chiral resolution and lead to pronounced chiroptical responses. Remarkably, the chiral saddle-shaped framework presents strong host–guest interactions with fullerenes C60 and C70, which were investigated via several titration methods. The association constants for a 1:1 complex, determined by circular dichroism spectroscopy titration (Ka(C60) = 2.3 × 104 M-1; Ka(C70) = 8.7 × 104 M-1), are among the highest values reported for negatively curved nanographenes. Moreover, crystallographic analysis of cocrystals of cSNG with C60 revealed a 1:3 binding mode for supramolecular complexation, featuring two fullerenes accommodated inside the saddle cavity as well as two shared fullerenes located on each concave outward facing side.