Due to the sp-hybridized form of carbon molecule, C 16 also has a pair of mutually perpendicular π-conjugated systems, named π in and π out molecular orbitals (MOs), besides valence occupied σ MOs (Figures and), just like C 18 . According to the Hückel's rule and analogizing the double aromaticity of ground-state C 18 , it is highly likely that C 16 with two sets of 16 π-electron systems has double anti-aromaticity in the S 0 state. The Baird's rule, in turn, determines the anti-aromaticity of C 18 and aromaticity of C 16 in their lowest triplet excited states (T 1 states) at least in their ground-state geometries. Many studies have reported the special aromaticity characteristics of C 18 from multiple perspectives, but to our knowledge, only Dai et al. briefly discussed the aromaticity of C 16 in its S 0 and T 1 states through nuclear independent chemical shifts (NICS) calculations. Given that C 16 has been recently successfully generated and observed, we are now interested in accurately determining the aromatic specificity of its S 0 and T 1 states, as well as the characteristics of lowest quintet excited state (Q 1 state), which has been rarely explored in previous studies of any variety of cyclic molecules.