Studies of Third-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 χ(3)(-3ω; ω, ω, ω) of 1.53×10-12 esu for a pentamer and 8.0×10-12 esu for propylmethylpolyazine at 1.5 µm. Dipole polarizability (α) and second hyperpolarizability (γ) of oligomer model compounds were also calculated by employing the ab initio coupled-perturbed Hartee-Fock (CPHF) theory. Both polarizabilities and χ(3)(-3ω; ω, ω, ω) increase significantly as the length of π-electron delocalization increases in the polyazine backbone.