Third-order nonlinear optical properties of poly(-p-phenylenevinylene) derivatives substituted at vinylene position.

The techniques of closed and open aperture Z-scan as well as that of phase-matched and non-phase-matched degenerate four-wave mixing (DFWM) were used to investigate nonlinear optical properties of two poly(p-phenylenevinylenes) substituted with the phenoxyphenyl and fluorophenyl groups at the vinylene position. The polymers studied were poly[1,4-phenylene-1,2-di(4-phenoxyphenyl)vinylene] (DPOP-PPV) and poly[4,4'-biphenyl-diyl-1,2-di(4-fluorophenyl)vinylene] (DFP-PDPV). Spectroscopic studies showed a blue shift of absorption spectra of both polymers in comparison to that of poly(p-phenylenevinylene) (PPV). Z-scan experiments for solutions of the polymers in 1,4-dioxane and DFWM experiments for thin films of the polymers were carried out at 800 nm with amplified 100 femtosecond pulses. The results of both techniques are in good agreement, indicating that the nonlinear refractive index n(2) is on the order of 10(-14) cm(2)/W for the substituted polymers. The sign of the real and imaginary parts of n(2) is positive. The polymers possess relatively low values of two-photon absorption merit factors at 800 nm. The nonlinear properties of the substituted polymers were compared to the results obtained on unsubstituted PPV films.