Copolymers with substituted thiophene

Copolymers of Substituted Thiophenes. Random copolymers of substituted thiophenes have been prepared [71,93,396,433, 434, 512, 710-728]. Several designed bithiophenes and terthiophenes have also been polymerized to produce random but mostty alternating copolymers [503, 652, 729-736]. A copotymer consisting of thiophene and alkorythiophene luiits has been obtained by cyclization with Na2S of an intermediate polymer [737] (Fig. 48). 

While retaining much of the substituted PT character (e.g., good hole-transport properties and stability), these materials exhibit significantly improved fluorescence efficiency in the solid state (cl>Pi up to 29%) that leads to (hllof UP to 0.1% for ITO/453/Ca PLED (Table 2.6). Other widely studied thiophene copolymers with aromatic 9,9-disubstituted fluorene units were already described above in Section 2.3. 

Another acceptor unit that has achieved high-performance D A copolymers with a number of donors is thieno[3,4-c]pyrrole-4,6-dione, called TPD. The synthesis of TPD can start with un-substituted thiophene, which can be converted into 3,4-dibromothiophene via selective debromination of the tetrabrominated thiophene. After the cyano substitution and hydrolysis, as-formed thiophene-3,4-dicarboxylie acid is brominated to provide the halogens... 

Fig. 48. Substituted thiophene copolymer obtained by cyclization with... 

Irreversible undoping that led to the loss of electrical properties in doped poly(alkylthiophene)s on thermal treatment was reported by Inganas and co-workers. The rate of thermal undoping was observed to be faster in the case of longer chains substituted on the polythiophene when compared with nonsubsti-tuted polythiophene [128-131]. Random copolymers of methyl-and octyl-substituted polythiophene [132] and regular copolymers of dimer thiophene-co-octylphenylthiophene [133] demonstrated much better stability. 

Several vinyl, propenyl, and isopropenyl substituted thiophenes, with halogen substituents, have also been mixed with MA and copolymerized, using peroxides at 65-70°C. The structures of the various copolymers were not reported. However, use of equimolar feeds would suggest that some of the copolymers could be of the alternating type. Copolymerization of 4-methyl-5-vinylthiazole-MA mixtures was also studied.Alternating copolymers were also probably formed from this comonomer pair. 

In another study, pyrrole was chemically polymerized with a 3-substituted thiophene [3-(methoxyethoxy-ethoxymethyl)thiophene], XLVIll [76]. This copolymer had a pyrrole/thiophene ratio of 7 1 and a conductivity of 1 S/cm. Pyrrole acted as a initiator of the polymerization and produced a material that would be less expensive while still maintaining the solubility properties of the substituted thiophene. 

Copolymers with alternating benzene-thiophene units have been synthesized via the Stille reaction of both substituted aryl halide and triflate (equation 108) (255,254). The molecular weight was 14,000 by GPC when n was equal to 16. This corresponds to a DP of approximately 22. 

A series of four fluorene-phenylene vinylene copolymers 320-323 clearly demonstrates the effect of the exact position of CN groups in the vinylene fragment on the emission of the materials (Scheme 2.48) [408], Substitution of benzene rings in copolymers 320 and 321 by thiophene results in red-shifted PL and EL, where copolymers 322 and 323 exhibit pure red emission with chromaticity values very close to the standard red (CIE x = 0.66, y = 0.34), although no PLQY values were reported. The ITO/PEDOT/322/Ca/Al device showed a very... 

Copolymer 459, prepared by Stille coupling of dibromophenylene with 2,5-Mv(tributyl-stannyl)thiophene, represents another example of a phenylene-u/t-thiophene backbone, where the substituted phenylene unit forms an oligophenylene vinylene fragment that is not in the main conjugation chain [561]. A PLED fabricated with this polymer (ITO/459/A1) emitted green light (520 nm) with a turn-on voltage of ca. 9.5 V, but no other data on luminance or efficiency of the device were reported (Chart 2.111). 

Because their oxidation potentials are similar, substituted pyrroles can be copolymerized with pyrrole, allowing the limiting conductivity of the fully-doped polymer to be varied 194,19S). The oxidation potentials of the monomers, and hence their reactivity ratios, are sensitive to the substituent196). Inganas et al.197) reported the synthesis of pyrrole-thiophene copolymers starting from terthiophene, whose oxidation potential is similar to that of pyrrole. Sundaresan et al.198) copolymerized pyrrole with 3-(pyrrol-l-yl)propanesulphonate to give a polymer in which the sulphonate counter-ion is a part of the polymer structure. 

Cho et al. prepared 36 by incorporating low-band-gap thiophene together with CN-substituted vinylene, which gives pure red EL emission [CIE coordinates (0.66, 0.33)] that is almost identical to the standard red (0.66, 0.34) demanded by the NTSC [62], Another similar copolymer 37 also exhibited a pure red emission [CIE coordinates (0.63, 0.38)], and its maximum... 

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