THEORETICAL-STUDY OF THE 3RD-ORDER NONLINEAR-OPTICAL PROPERTIES OF SPIRO-LINKED POLYENE

The molecular second hyperpolarizability, gamma, and the third-order e lectric susceptibility, chi((3)), of spiro-linked polyenes, where the 1,4-cyclohexadiene rings were linked through the tetrahedral carbon at oms, 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 de duced from the AM1 time-dependent Hartree-Fock method, for the infinit e-length polymer form. Judging from the relationship between the numbe r of 1,4-cyclohexadiene rings and the transition energies, lambda(max) of spiro-linked polyene composed of an infinite number of 1,4-cyclohe xadiene rings was estimated to be shorter than 300 nm. Thus, it was sh own 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.