A Chiral Saddle-Shaped Nanographene With Two Heptagon-Embedded [4]Helicenes

Chiral non-benzenoid nanographenes (NGs) remain highly appealing, yet underexplored synthetic targets due to the lack of feasible synthetic strategies to simultaneously construct non-hexagonal rings and stable chirality. Herein, we demonstrate a novel synthetic strategy to construct a chiral saddle-shaped nanographene (cSNG) via stepwise oxidation of an anthracene-containing oligophenylene precursor. Scholl-type oxidation first yields a key intermediate featuring sp³-defect heptagons, and subsequent oxidative dehydrogenation furnishes target cSNG incorporating two heptagon-embedded [4]helicenes. The structure of cSNG is unambiguously confirmed by single-crystal analysis, demonstrating its saddle-shaped geometry with intrinsic chirality. Remarkably, due to the heptagon-embedded [4]helicene subunits, cSNG exists as configurationally stable enantiomers which enable chiral resolution, leading to pronounced chiroptical responses and enhanced dissymmetry factors, compared with its sp³-defect precursor. Moreover, profiting from chiral saddle geometry with shape-adaptive character, cSNG presents strong host-guest interactions with fullerenes, with association constants up to 2.3 × 10⁴ M^-1 for C₆₀ and 8.7 × 10⁴ M^-1 for C₇₀, which are among the highest values reported for negatively curved nanographenes. Crystallographic analysis of cocrystals of cSNG with C₆₀ further revealed a distinct 1:3 binding mode for supramolecular complexation, featuring two fullerenes accommodated within the saddle cavity and two additional fullerenes externally shared between neighboring saddle units.