Exploring the Properties of an sp-Hybridized All-Carbonatomic Ring, Odd-Number Cyclo[13]Carbon

The recent breakthrough in synthesizing cyclo[13]carbon (C₁₃), an odd-membered all-carbon ring system, represents a significant advancement in developing nontraditional carbon allotropes with reduced structural symmetry. In this study, we systematically investigated the thermal stability, geometric structure, and electronic properties of C₁₃ using first-principles calculations. Our results show that the C₁₃ exhibits lower thermal stability due to its low symmetry. Notably, the π-electron delocalization is significantly enhanced over its shorter C─C bonds. Electrostatic potential (ESP) and average local ionization energy (ALIE) mapped on the van der Waals (vdW) surface of C₁₃ reveal considerable spatial heterogeneity, arising from intrinsic variations in bond lengths and bond angles within the ring. Magnetic response analysis further identified a counterclockwise ring current in C₁₃, consistent with its doubly antiaromatic electronic configuration. Additionally, the excitation process of C₁₃ displayed mixed excitation characters, which should be regarded as a highly localized π-π* type of excitation. These comprehensive theoretical insights advance the mechanistic understanding of experimental observations in C₁₃ and provide a foundational framework for investigating electron-deficient antiaromatic systems in carbon-rich molecular architectures.