ULTRAFAST OPTICAL PROBES OF EXCITED-STATES IN POLY(1,4-PHENYLENE VINYLENE) AND POLY(2-FLUORO-1,4-PHENYLENE VINYLENE)

We have investigated the photoexcitation dynamics of poly(1,4-phenylen e 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 nonemis sive indirect polaron pairs which are more efficiently produced in PFP V than in PPV. The decay processes of polaron pairs are mainly contrib uted by collisional annihilation and internal conversion by phonon emi ssion in PFPV and PPV, respectively. The differences in photoexcitatio n dynamics between PPV and PFPV are believed to be caused by the stron g electronegativity of substituted fluorine atom. (C) 1997 American In stitute of Physics.