We have investigated the photoexcitation dynamics of poly(1,4-phenylene vinylene) (PPV) and poly(2-fluoro-1,4-phenylene vinylene) (PFPV) by using the femtosecond transient absorption spectroscopic technique. It was demonstrated that photoinduced absorption originates from nonemissive indirect polaron pairs which are more efficiently produced in PFPV than in PPV. The decay processes of polaron pairs are mainly contributed by collisional annihilation and internal conversion by phonon emission in PFPV and PPV, respectively. The differences in photoexcitation dynamics between PPV and PFPV are believed to be caused by the strong electronegativity of substituted fluorine atom. ©1997 American Institute of Physics.