Theoretical study of the third-order nonlinear optical properties of spiro-linked polyene

The molecular second hyperpolarizability, gamma, and the third-order electric susceptibility, chi((3)), of spiro-linked polyenes, where the 1,4-cyclohexadiene rings were linked through the tetrahedral carbon atoms, were investigated through the ab initio and the semiempirical AM1 molecular orbital methods. The static chi((3)) value was estimated to be 3.2 x 10(-14) esu from the extrapolated gamma values, which was deduced from the AM1 time-dependent Hartree-Fock method, for the infinite-length polymer form. Judging from the relationship between the number of 1,4-cyclohexadiene rings and the transition energies, lambda(max) of spiro-linked polyene composed of an infinite number of 1,4-cyclohexadiene rings was estimated to be shorter than 300 nm. Thus, it was shown that spiro-linked polyene will be an unique third-order nonlinear optical material from the standpoint of the high transparency and the relatively large chi((3)) value.