It should be noted that the calculated polarizability [α iso (∞)] of the C 18 -(CO) n for n = 2, 4, and 6 are 1.1, 1.3, and 1.4 times, respectively, that of the free C 18 ring (293.9 au), and the values are observed to be 1.5, 1.9, and 2.5 times for the second hyperpolarizability [γ || (∞), 140909 au for C 18 ] [9,10], which show that these precursors are better candidates for high-performance optical materials than the C 18 molecule, and moreover, the number of -CO groups in them plays a crucial role in determining their (hyper)polarizability.