Synthesis and electroluminescent properties of copolymers based on PPV with fluoro groups in vinylene units

New electroluminescent copolymers with fluoro groups in vinylene unit, poly(2-ethylhexyloxy-5-methoxy-p-phenylenevinylene-co-2-dimethyloctylsilyl-p-phenylenedifluorovinylene) (MEH-PPV-co-DMOS-PPDFV) and poly(2-dimethyloctylsilyl-p-phenylenevinylene-co-2-dimethyloctylsilyl-p-phenylenedifluorovinylene) (DMOS-PPV-co-DMOS-PPDFV), have been synthesized by the Gilch polymerization. The fluoro groups were introduced on vinylene units to increase the electron affinity of the copolymers. In both types of the copolymers, the band gaps were increasing with higher ratio of DMOS-PPDFV. As compared to the PL spectra in solution state, PL spectra in solid state and EL spectra of both types of copolymers showed red shifted and broad peaks caused by the aggregation. The polymer LEDs of MEH-PPV-co-DMOS-PPDFVs emit light with maximum peaks at around 538-577 nm. By adjusting the feed ratios of DMOS-PPDFV in the copolymers, we could tune the emission colors from orange yellow to green. DMOS-PPV-co-DMOS-PPDFVs showed the maximum EL peaks at about 514-543 nm. DMOS-PPV-co-DMOS-PPDFV with 1:9 feed ratio showed the highest luminescence efficiency of 1.31 lm/W.