Synthesis and spectroscopic studies of poly(1,4-phenylenevinylene) and its derivatives

Abstract

Asymmetrically disubstituted poly(2-methoxy-5-methyl-1,4-phenylenevinylene) PMMPV) and a series of poly(1,4-phenylenevinylene-co-2-methoxy-5-methyl-1, 4-phenylenevinylene)s (poly(PV-co-MMPV)) were synthesized through water- soluble precursor route. These polymers were characterized using UV- visible, FT-IR spectroscopy and DSC, TGA thermal analysis. The electrical conductivities of the polymers were investigated by four-in-line method at room temperature. PMMPV film could be stretched up to 5 times and doped with $FeCl_3$ and $I_2$ to give electrical conductivities of 27 S/cm and 7.4 S/cm, respectively along the draw direction. In copolymers, as the content of MMPV unit increases, the electrical conductivity steadily increases. The $χ^(3)$(-3ω; ω, ω, ω) value of PMMPV was determined by Third Harmonic Generation (THG) technique at 1907 nm, fundamental wavelength. The measured $χ^(3)$ value was 7.5×$10^{-12}$ esu. The comparative investigation was carried out for the photoluminescence (PL) properties of poly(1,4-phenylenevinylene) (PPV) and poly(2-halo-1,4- phenylenevinylene)s (PXPVs) (X=F, Cl, Br, I) by using steady-state and time-resolved photoluminescence and transient absorption spectroscopies. PFPV, PClPV and PBrPV exhibited a red-shifted structureless emission as compared to PPV. The time-resolved PL experiments revealed that the shorter wavelength emission is attributable to the free excitons and the longer wavelength emission to the self-trapped excitons associated with the charge separation between PPV and highly electronegative halogen atom resulting in the red-shifted emission of PXPVs in comparison with PPV. On the other hand, PIPV showed the emission at the similar range to that of PPV because of low electronegativity. The PL quantum efficiency and decay time of PXPV polymers increased with increasing the electronegativity of the substituted halogen atom on the phenylene ring in PPV. In addition to above investigation, the energy transfer in the bl...