Negatively Curved Chiral Bilayer Nanographene.

Discrete π-π stacked nanocarbons, which serve as atomically precise models for layered graphitic materials, exhibit distinct optical and electronic properties. However, most reported examples are limited to planar building blocks. In this work, two negatively curved chiral nanographenes (1 and 2) containing a hexa[7]circulene core were synthesized. Both 1 and 2 form bilayer structures in the crystalline state, adopting eclipsed and displaced conformations, respectively. The bilayer stacking is driven by interlayer π-π and C-H···π interactions. NMR studies confirmed the well-defined bilayer structure of (1)2 in solution. Cyclic voltammetry measurements demonstrated interlayer coupling in (1)2. The inversion behavior of the chiral isomers was investigated using circular dichroism spectroscopy and theoretical calculations, revealing that the bilayer stacking stabilizes the chiral structure of (1)2. Enhanced chiroptical dissymmetry factors were observed in (1)2. This work not only establishes (1)2 as a molecular model for negatively curved bilayer graphene but also highlights the modulation of chiral behavior through stacking, offering a strategy for constructing well-defined chiral assemblies based on negatively curved nanocarbons.