pi-electron density dependence of third-order optical nonlinearities in poly(1,4-phenylene vinylene) derivatives

The third-order nonlinear optical properties of poly(1,4-phenylene vinylene ) (PPV), poly(2-bromo-1,4-phenylene vinylene) (BrPPV) and poly(2-chloro-1,4 -phenylene vinylene) (ClPPV) were studied by forward degenerate four-wave m ixing (DFWM). They have large and ultrafast third-order optical nonlinear r esponses, which mainly arise from the distortion of the large pi-conjugated electronic charge distribution in the backbone. It was found that there wa s a significant contribution to pi-electron density and thus chi((3)) value s from the substituents at the phenylene ring. (C) 1999 Published by Elsevi er Science B.V. All rights reserved.