Aromatic Rules of C₂₂H₁₂^2+/2•/2-: Flexibility in Electronic Structures of 2D Superatomic Molecules

Triangulene (C₂₂H₁₂^2•), a nonclassic non-Kekulé polycyclic aromatic hydrocarbon, is identified to be aromatic by structural and magnetic criteria. However, its aromatic origin remains confusing. Herein, the aromatic rules of C₂₂H₁₂^2• and its two charged counterparts C₂₂H₁₂^2+/2- were investigated on the basis of a recently developed two-dimensional (2D) superatomic-molecule theory. [C₂₂H₁₂]^2+/2•/2- exhibit obvious local aromatic characters and can be regarded as [^◊N₃^◊O₃]⁺, [^◊N₃^◊O₃]^-, and ^◊N₃^◊F₃ superatomic molecules, respectively, where ^◊N, ^◊O, and ^◊F denote 2D superatoms bearing 3π, 4π, and 5π electrons. [C₂₂H₁₂]^2+/2- realize electronic shell closure via superatomic lone pairs and covalent bonds, mimicking simple molecules, whereas the α-π and β-π electrons in C₂₂H₁₂^2• follow the superatomic bonding patterns of C₂₂H₁₂^2- and C₂₂H₁₂²⁺, respectively. Furthermore, based on the local character in 2D superatomic molecules, a doped nanoporous graphene, namely, C₉N₁₂B monolayer, was predicted. The material possesses excellent dynamical and thermodynamical stability, as well as a wide band gap of 2.77 eV, positioning it as a promising 2D material for future electronic applications.