With the deep understanding and application of known carbon materials, the research on new carbon allotropes is still in progress. Among the carbon clusters that have been recognized, the sp -hybridized forms of fullerene, carbon nanotube (CNTs), graphene, and their partial substructures called molecular nanocarbons have gained widespread enthusiasm in materials science and physics. Carbon molecules hybridized in a double coordinated manner, however, have remained mysterious, despite evidence of their existence being obtained for a long time. The sp-hybridized carbon ring predicted by Hoffman as early as 1960 was not revealed until the condensed-phase experiment conducted by Kaiser et al. in 2019. The imaging of the first member of the cyclocarbon family, that is, the cyclo [18]carbon molecule commonly abbreviated as C 18 , quickly triggered a wave of theoretical research on various aspects of its properties. Meanwhile, the generation of its homologues, namely carbon rings of other sizes, is also being vigorously explored. Excitingly, Gao et al. succeeded in preparing cyclo [16]carbon (C 16 ) very recently by taking the similar approach to that of Kaiser et al. For strictly planar cyclic molecules like C 18 and C 16 , the aromaticity is undoubtedly one of their most concerning properties. It is generally believed that the singlet ground-state (S 0 state) molecules follow the Hückel's rule, that is, molecular rings with [4n+2] π electrons display aromaticity, while those with [4n] π electrons are anti-aromatic. The excited-state molecular aromaticity, however, is usually associated with Baird's rule, according to which the familiar Hückel's [4n+2]/[4n] rule for electronic S 0 state of cyclic conjugated systems is reversed for the lowest triplet state (T 1 state). The reversals in aromaticity feature usually result from alterations in the electronic structure of molecules and are accompanied by profound changes in chemical properties.