Modifying the molecular skeleton with different numbers and/or varieties of substituents has been proved to be a very effective way to change the electronic structure of a system . For a series of cyclocarbon oxides C 18 -(CO) n (n = 2, 4, and 6), it is just equivalent to introducing several electron-accepting -CO groups with strong electron-withdrawing ability into the carbon ring, so their multiple properties are expected to be fundamentally distinct from those of the C 18 . Although the theoretical studies on various physicochemical properties and behaviors of C 18 ring and its analogues have been quite extensive , the research on the precursors C 18 -(CO) n (n = 2, 4, and 6) for manufacturing C 18 has not been fully carried out. As far as we know, only our latest work has systematically studied and comparatively analyzed bonding character, electron delocalization, and aromaticity of relevant systems up to now . The results show that C 18 -(CO) n (n = 2, 4, and 6) possess two perpendicular π-conjugated electron systems, in-plane and out-of-plane π molecular orbitals (MOs), similar to the C 18 ring. Importantly, the number of -CO groups is closely related to π conjugation in the molecule, and therefore affects their overall aromaticity. Our another theoretical research has revealed that C 18 ring shows strong absorption spectrum and significant optical nonlinearity, indicating its potential as an advanced optical material . Given these facts, a question naturally arises as to how do the sequential grafting of -CO groups change the optical properties of C 18 ? This is the very focus of the current paper.