Polymer light-emitting diodes based on PPDFV copolymers with fluoro groups in vinylene units

Organic light emitting diodes (OLEDs) have attracted much interest because of their particular low driving voltage, convenient design of the device structures, possible control of emission band, and low fabrication cost compared with any other devices. Since the discovery of electroluminescence (EL) from a conjugated polymer, main-chain conducting polymers such as poly(plenylene vinylene) (PPV), poly(p-phenylene) (PPP), their copolymers and soluble derivatives, has been studied intensively for the possible application as large-area light emitting diodes (LEDs). However, PPV has the disadvantage that electron injection is much more difficult than hole injection. Using additional organic charge-transporting layers, and adjusting the energy band of the polymer by introduction of electronwithdrawing groups attached to the polymer backbone were reported to overcome the imbalance of charge carrier injection or mobility. The introduction of electron-withdrawing groups onto the arylene rings or the vinyl groups of PPV lowers the HOMO and LUMO energy levels of the polymer, thereby permitting the use of a higher work function metal in the LED device. Numerous derivatives of PPV have been reported with electron-withdrawing substituents such as halide, cyano, trifluoromethyl, or methylsulfonylphenyl on the arylene rings. In our previous work, we reported poly(p-phenylenedifluorovinylene) (PPDFV) and poly(2-dimethyloctylsilyl-p-phenylenedifluorovinylene) (DMOS-PPDFV) with fluoro groups as electron withdrawing substituents on vinylene units of conjugated polymers, which showed the high performance of OLEDs. In the present paper, we report the synthesis and electroluminescent properties of the copolymers with p-phenylenedifluorovinylene and 2-dimethyloctylsilyl-p-phenylenevinylene units. The resulting EL polymers were synthesized by the Gilch polymerization method.