45Communications Scheme 3. Monomers and polymers under discussion. Synthetic route to the new monomer M5 and to the polymers P1 to P9: a) Pd(PPh 3 ) 4 , toluene, water, Na 2 CO 3 , reflux, 95 %. b) LiAlH 4 , THF, reflux, 99 %. c) SOCl 2 , room temperature, distillation, 46 %. d) KO t Bu, dioxane, reflux, reprecipitation. C 10 = 3,7-dimethyloctyl.

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The blue emission of ladder-type polybara-phenylene) films is unstable under heat treatment due to the formation of aggregates that emit yellow light. Novel statistical copolymers possessing ladder-type oligobara-phenylene) segments connected via twisted phenylene spacers are used to suppress the formation of these aggregates and to obtain blue emission stable under annealing.

Even though their discovery dates back less than a decade, [1] polymer light-emitting diodes (PLEDs) have made an unexpectedly dramatic progress in comparison with classical semiconductor LEDs. Through a simple coating procedure, PLEDs have the potential to provide an innovative low-cost technology for illumination and display applications. [2] In this communication we introduce a new class of soluble electroluminescent poly(p-phenylenevinylene)s (PPVs) that show unprecedented performance.Phenyl-substituted PPVs are known from the literature [3] but very low solubility is limiting their applicability. Even for recently reported 2,3-bisphenyl-substituted PPV derivatives [4] the molecular weight has to be artificially decreased in order to render them soluble. We have now found that alkoxy-substituted 2-phenyl PPVs of type 1 (see Scheme 1) exhibit very good solubility in the conjugated state, good film-forming properties, high molecular weights, which improves mechanical stability, and, ultimately, excellent electroluminescence performance.PPVs of type 1 were prepared by copolymerization of the monomers 2, 3, and 4 following a modified Gilch procedure (dehydrohalogenation polymerization). [5] Yields of polymerization are typically 50 ± 10 %. Analytical data are in agreement with the assumption of an ideal copolymerization, i.e., the copolymer ratio equals the comonomer feed. Monomer 2 was synthesized via the standard alkylation/chloromethylation sequence leading to the 1,4-bisalkoxy-2,5-bischloromethylbenzene. [6] The newly developed monomers 3 and 4 were prepared in a three-step synthesis strategy starting with the Suzuki coupling of the corresponding boronic acids 7a and 7b with the bromoterephthalic acid diethylester 8, resulting in the biphenyls 9a and 9b, respectively. Reduction with LiAlH 4 and subsequent reaction with thionyl chloride yield the key monomers 3 and 4.We found that especially copolymers of monomers 3 and 4 exhibit very good properties as concerns solubility and electroluminscence (EL), respectively. Furthermore it turned out that addition of smaller quantities of monomer 2 allows a tuning of the emission color without significant changes in the other properties. This paper describes the properties of copolymers 1a±1e in comparison to polymer 1f and poly[2-methoxy-5(3¢,7¢dimethyloctyloxy)-1,4-phenylenvinylen] (OC 1 C 10 ), [7] which show basically identical electrical behavior to that of the well-established poly(2methoxy-5-(2¢-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) [8] (see Table 1). However, the processibility and film-forming properties are found to be superior for OC 1 C 10 and polymer 1f.Despite the high molecular weight of the polymers under discussion (M w > 10 6 , M n » 3´10 5 ) complete solubility in standard organic solvents (e.g., toluene, xylene, tetrahydrofuran, chloroform, chlorobenzene, cyclohexanone) is achieved and no gelation at room temperature occurs (see Fig. 1). Therefore these polymers are well suited to solution-based coating processes, e.g., spin-coating....