ULTRAFAST OPTICAL PROBES OF EXCITED-STATES IN HALOGEN-SUBSTITUTED PPVDERIVATIVES

Photoexcitation dynamics of poly(1,4-phenylene vinylene) (PPV) and pol y(2-fluoro-1 P-phenylene vinylene) (PFPV) were investigated. The femto second transient absorption spectra were recorded by using a high powe r femtosecond Ti:sapphire laser system. The laser pulses with 150 fs a nd 300 mu J/pulse at 800 nm were used to generate white light continuu m for a probe beam, and the second harmonic generation at 400nm was em ployed as a pump beam. Transient absorption spectra and their decay pr ofiles were measured by a dualdiode array detector and two photodiodes , respectively. We assign that photoinduced absorption(PA), which has similar to 1 ps lifetime, arises from inter-chain polaron pairs. The d ecay of PA in PFPV was faster than that in PPV. This behavior is attri buted to the large electronegativity of fluorine substituted at phenyl ring of PPV.