Conjugated copolymers of 2-methoxy-5-2′-ethyl-hexyloxy-1,4-phenylenevinylene and 2,5-dicyano-1,4-phenylenevinylene as materials for polymer light-emitting diodes

A new series of electroluminescent polymers has been synthesized by incorporating the segments of 2,5-dicyano-1,4-phenylenevinylene (DCN-PV) into the backbone of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV). The copolymers have similar optical properties with MEH-PPV. The oxidation potentials of the copolymers are slightly larger than that of MEH-PPV. The copolymers exhibit 'pre-reduction' processes, beginning at about -0.9 V (vs. SCE), before the main reduction processes. The 'pre-reduction' feature is thought to be helpful in improving electron injection, and thus to be helpful in improving EL performance. The improved EL performance of the copolymers in comparison with MEH-PPV is demonstrated by a single-layer polymer light-emitting diode (PLED) device employing one of the copolymers as the emissive material.