STUDIES OF 3RD-ORDER NONLINEAR OPTICAL-PROPERTIES OF POLYAZINE AND ITS OLIGOMERS

The third-order nonlinear optical properties of a polyazine and its oligomers are reported for the first time. Third-harmonic generation measurements revealed a nonresonant third-order nonlinear optical susceptibility chi(3) (-3omega; omega, omega, omega) of 1.53 X 10(-12) esu for a pentamer and 8.0 X 10(-12) esu for propylmethylpolyazine at 1.5 mum. Dipole polarizability (alpha) and second hyperpolarizability (gamma) of oligomer model compounds were also calculated by employing the ab initio coupled-perturbed Hartee-Fock (CPHF) theory. Both polarizabilities and chi(3)(-3omega; omega, omega, omega) increase significantly as the length of pi-electron delocalization increases in the polyazine backbone.