Recently, polymeric light-emitting materials have attracted much attention for their potential applications in large-area displays. 1 Following the discovery of poly-(p-phenylene vinylene) (PPV), 2 a wide range of polymers, for example, polythiophene, 3,4 poly(p-phenylene), 5 poly(vinylcarbazole), 6,7 and polyfluorene, 8 have been reported in the literature as potential candidates for polymeric light-emitting diodes (LEDs). One of the greatest advantages of these devices over molecular LEDs is the ease of processing of the polymers into high-quality thin films. In particular, organic-soluble conjugated polymers, such as poly[2-(2′-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV), have received considerable attention. 9-12 Although MEH-PPV can be fabricated into a LED possessing a high quantum efficiency (η ext ) 1%), there are several deficiencies, such as the polymer's synthesis. The polymer uses the 2-(2′-ethylhexyloxy)-5-methoxy-1,4-bis(chloromethyl)benzene monomer, which often results in a significant amount of insoluble polymer gel due to the cross-linking of the polymer chains. In addition, an inherent thermal property, its low glass-transition temperature (T g ) 65°C ), may prohibit the long-term use of the device. In this paper, we report the synthesis and characterization of a novel copolymer (TPD-MEH-PPV) consisting of tetraphenyldiaminobiphenyl (TPD) and MEH-PPV moieties. The design of the polymer was based on the motivation (1) to improve both the hole-transporting property and oxidative stability of the MEH-PPV by inserting into the polymer chain an easily p-dopable and electrochemically reversible TPD moiety; (2) to raise the T g of the MEH-PPV by inserting the TPD moiety which has more rigid biphenyl structure; and (3) to improve simultaneously both the synthetic procedure and the solublity of the polymer 13 by using the Wittig-Horner condensation reaction to avoid potential cross-linking problems and to enhance the solubility of the polymer in common organic solvents by attaching two n-butyl groups onto the benzene rings of the TPD.The method for preparing the copolymer is outlined in Scheme 1. Monomer 2 was synthesized from 4,4-dibromobiphenyl by a three-step reaction 14-16 (overall yield, 33%). Alkylation of 4-methoxyphenol, followed by chloromethylation of 3, gave 2-(2′-ethylhexyloxy)-5-methoxy-1,4-bis(chloromethyl)benzene 4 in 60% yield. The condensation reaction between 4 and triethyl phosphite afforded the diphosphonate 5 in quantitative yield. 17 The TPD-MEH-PPV was prepared by the Wittig-Horner condensation reaction 18 between the dialdehyde 2 and 2-(2′-ethylhexyloxy)-5-methoxy-1,4-xylene tetraethyl diphosphonate 5 in tetrahydrofuran (THF). 19 The chemical structure of the resulting polymer was confirmed by 1 H NMR and elemental analysis. It is worth pointing out that polymer gels were not formed during this polymerization process.TPD-MEH-PPV was a yellow powder which dissolved easily in common organic solvents such as chloroform, tetrahydrofuran, and xylene. The molecular weigh...

New luminescent polymers that contain both electron-withdrawing cyano groups and electron-rich moieties, triphenylamine (TPA) or tetraphenyldiaminobiphenyl (TPD), were synthesized by Knoevenagel condensation of 1,4-bis(cyanomethyl)-2-[(2-ethylhexyl)oxy]-5-methoxybenzene with the dialdehyde of TPA or TPD, respectively. The polymers were characterized by NMR, FT-IR, microanalysis, GPC, DSC, and TGA. Efficient orange photoluminescence was observed with an absolute quantum efficiency of 48% for the TPA incorporated polymer (TPA-CNPPV). Cyclic voltammetry investigation showed that the polymers presented reversible oxidation and reduction with relatively low potentials, which suggested that the polymers have both good electron and hole injection abilities. We demonstrated an effective approach to synthesize polymers with the triad properties of efficient photoluminescence, good hole injection and high electron-affinity properties, which are highly desirable for application in light-emitting devices. This point was supported by the demonstration of a single layer light-emitting device with a configuration of ITO/TPA-CNPPV/Al, in which good external quantum efficiency (0.1%) and bright luminance of 2100 cd/m2 was achieved. Multilayer LEDs using the polymers as the active layers and different charge injection/transporting layers were also investigated.