Theoretical Study of the Third-Order Nonlinear Optical Properties of Spiro-Linked Polyene

The molecular second hyperpolarizability, γ, and the third-order electric susceptibility, χ (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 χ (3) value was estimated to be 3.2 × 10 -14 esu from the extrapolated γ 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, λ 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 χ (3) value.