Stabilizing the 8π-Conjugated Bicyclic Species via Two-Dimensional Superatomic-Molecule Theory

The electronic structure of various 8π-conjugated bicyclic species has been extensively studied for decades. Herein, we proposed an intrinsic regulatory mechanism for stabilizing 8π bicyclic species via heteroatom doping in a D_2h C₈H₆ molecule. Based on the recently developed two-dimensional (2D) superatomic-molecule theory, D_2h C₈H₆ can be treated as a 2D superatomic ^◊O₂ molecule with superatomic double bonds. Nevertheless, the ^◊O₂ is unstable due to its large superatomic radius, which hinders the formation of side-by-side superatomic π-bonds. Subsequently, a series of 8π bicyclic species are constructed by atom doping to stabilize the superatomic π-bond. It is found that the electronegativity of the doping atom effectively shifts the positions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), thereby increasing the energy gap and stabilizing the superatomic π-bond. Particularly, the aromaticity of 8π-B₄N₄H₆ and 8π-B₄N₂O₂H₄ molecules is comparable to that of benzene and naphthalene, surpassing their inorganic analogues. This regulatory mechanism is further validated in the tricyclic 12π-C₁₃H₉⁺ (^◊O₃) and 14π-C₁₃H₉^- (^◊O₃^2-) conjugated species. This work expands 2D superatomic bonding and provides several promising structural units for graphene-based 2D materials to achieve band gap regulation.