Theoretical Research of Substituted Bay Region with Helical Chirality: Structures and Enantiomerization

We systematically investigated the chirality of substituted bay regions in polycyclic aromatic hydrocarbons (PAHs) via density functional theory (DFT) calculations, focusing on effects of substituents, π -conjugation extension, heterocycles, and π -skeleton curvature. Most bay-substituted PAHs form non-planar helical structures. As the steric hindrance of the substituents increases, the enantiomerization barriers of the phenanthrene derivatives increase. Similarly, π -conjugation extension can also increase the enantiomerization barriers. Heterocycles could also modulate the enantiomerization barriers of the PAHs by tuning the identity of the central heteroatom, and specifically, heterocyclic PAH derivatives incorporating heteroatoms with larger atomic radii exhibit higher enantiomerization barriers. Hexa[7]circulene ( PAH8 ), which contains a central heptagonal ring, is already non-planar, with an enantiomerization barrier of 15.9 kcal mol ⁻¹ . When the bay region of PAH8 is substituted, the enantiomerization barrier increases (up to 80.1 kcal mol ⁻¹ ). This work elucidates bay-region enantiomerization rules, providing theoretical guidance for designing functional chiral π -conjugated molecules.