Synthesis and characterization of highly luminescent asymmetric poly(p-phenylene vinylene) derivatives for light-emitting diodes

Asymmetric and color tunable polyp-phenylene vinylene) (PPV) derivatives with a dimethyldodecylsilylphenyl pendant group, poly [2-(3'-dimethyldodecylsilylphenyl)-1,4-phenylene vinylene] (m-SiPhPPV) and poly [2-(3'-dimethyldodecylsilylphenyl)-1,4-phenylene vinylene-co-2-methoxy-5-(2'-ethylhexyl oxy)-1,4-phenylene vinylene] (m-SiPhPPV-co-MEH-PPV), have been synthesized by a dehydrohalogenation method. Newly synthesized, these homo- and copolymers are highly soluble in common organic solvents. The defect-free uniformly thin films easily formed onto the indium tin oxide (ITO) coated glass substrate. The resulting polymers had high molecular weights with narrow polydispersities and high thermal stability up to 400 degreesC. The copolymers showed better optical and electroluminescent (EL) properties than those of the homopolymer. Single-layer light-emitting devices with an ITO/polymer/Al:Li alloy configuration were fabricated by using the resulting polymers. The maximum EL emissions of m-SiPhPPV and m-SiPhPPV-co-MEHPPV with various monomer feed ratios were observed at 528 and 588-595 run, respectively. The emission color of the resulting polymers changed from green to orange. The EL properties of the m-SiPhPPV-co-MEH-PPV dramatically improved compared to those of m-SiPhPPV and MEH-PPV. The maximum brightness and the external luminance efficiency of the m-SiPhPPV-co-MEHPPV were up to 19 180 cd/m(2) and 2.9 lm/W. The half lifetime of a single-layer device at 1000 cd/m(2) is about 120 h.