Polythiophenes stability

Polythiophene [78] is a promising material for certain future electronic applications, due to its relatively high stability and processability in the substituted form [79-81]. Upon substitution, with e.g. alkyl side-chains [79, 80], polythiophene exhibit properties such as solvalochromism [82] and thermochromism [83]. Presently, a large variety of substituted polythiophenes with various band gaps exists (for example see Ref. [81 ]). 

The stoichiometry of the redox reactions of conducting polymers (n and m in reactions 1 and 2) is quite variable. Under the most widely used conditions, polypyrroles and polythiophenes can be reversibly oxidized to a level of one hole per ca. 3 monomer units (i.e., a degree of oxidation, n, of ca. 0.3).7 However, this limit is dictated by the stability of the oxidized film under the conditions employed (Section V). With particularly dry and unreactive solvents, degrees of oxidation of 0.5 can be reversibly attained,37 and for poly-(4,4 -dimethoxybithiophene), a value of n = 1 has been reported.38 Although much fewer data are available for n-doping, it appears to involve similar stoichiometries [i.e., m in Eq. (2) is typically ca. 0.3].34,39"41 Polyanilines can in principle be reversibly p-doped to one... 

ETEROAROMATics FURAN AND THIOPHENE. The chemical transformation of thiophene at high pressure has not been studied in detail. However, an infrared [441,445] study has placed the onset of the reaction at 16 GPa when the sample becomes yellow-orange and the C—H stretching modes involving sp carbon atoms are observed. This reaction threshold is lower than in benzene, as expected for the lower stability of thiophene. The infrared spectrum of the recovered sample differs from that of polythiophene, and the spectral characteristics indicate that it is probably amorphous. Also, the thiophene reaction is extremely sensitive to photochemical effects as reported by Shimizu and Matsunami [446]. Thiophene was observed to transform into a dark red material above 8 GPa when irradiated with 50 mW of the 514.5-nm Ar+ laser line. The reaction was not observed without irradiation. This material was hypothesized to be polythiophene because the same coloration is reported for polymeric films prepared by electrochemical methods, but no further characterization was carried out. 

Gringue, D., Horowitz, G., Garnier, E. 1987. Stabilization of CdS and CdSe photoelectrodes modified by a catalyst-containing polythiophene coating. Ber Buns Phys Chem 91 402 05. 

Polyacetylene has good inert atmospheric thermal stability but oxidizes easily in the presence of air. The doped samples are even more susceptible to air. Polyacetylene films have a lustrous, silvery appearance and some flexibility. Other polymers have been found to be conductive. These include poly(p-phenylene) prepared by the Freidel-Crafts polymerization of benzene, polythiophene and derivatives, PPV, polypyrrole, and polyaniline. The first polymers commercialized as conductive polymers were polypyrrole and polythiophene because of their greater stability to air and the ability to directly produce these polymers in a doped form. While their conductivities (often on the order of 10" S/m) are lower than that of polyacetylene, this is sufficient for many applications. 

Polythiophene is a highly crystalline polymer with the chain analog to cis-polyacetylene. The sulfur atoms stabilize the structure and interacts poorly with... 

Polythiophenes (PTs) have received a great deal of attention due to their electrical properties, environmental stability in doped and undoped states, non-linear optical properties, and highly reversible redox switching [1]. Thiophene possesses a rich synthetic flexibility, allowing for the use of several polymerization methods and the incorporation of various side chain functionalities. Thus, it is of no great surprise that PTs have become the most widely studied of all conjugated polyheterocycles [184]. 

The presence of a carboxylate function increased air stability of the polythiophene film (/.max 489 nm) (03S2255 05CM4892). 

Stable polythiophene semiconductors 237 incorporating the thieno[2,3-fc]thiophene ring system were synthesized by Stille coupling of 5,5 -dibromo-4,4 -dialkyl-2,2 -bithiophene 235 with thieno[2,3-fc]thiophene-2,5-diylbis(trimethystannane) 236 (Scheme 48). The polymers 237 described showed both good charge carrier mobility and stability to ambient air and light [62],... 

Cyclic voltammetric measurements of 5c and 5f in 0.1 m BU4CIO4/CH2CI2 solution reveal reversible oxidation peaks at 0.88 V and 0.74 V, respectively, relative to the Ag/AgCl electrode, corresponding to estimated HOMO levels of, respectively, 5.26 eV and 5.12 eV from vacuum. These values are lower than those of most re-gioregular polythiophenes (4.9-5.0 eV) [34-36], and higher oxidative stabilities are therefore expected of these compounds. 

Thiophene polymers, in particular, alkyl-substituted polythiophenes (PTH), are some of the conducting polymers being most actively investigated at present. This fact is attributable to their high degree of processability, environmental stability [49, 50] and, in some cases, ability to exhibit reversible electrochrom-ism [51] and thermochromism [52]. Another important family of sulfur-... 

In considering the potential applications of electroactive polymers, the question always arises as to their stability. The deterioration of a physical property such as conductivity can be easily measured, but the chemical processes underlying it are not as easy to be revealed. In order to understand them, XPS has been used to follow the structural changes which occur in the polymer chain and the counter-ions of the doped polymer. The following sections present some XPS findings on the degradation of electroactive polymers, such as polyacetylene, polypyrrole, polythiophene and polyaniline, in the undoped and doped states. 

Phosphirene 93 <20060M5176> has been proposed as a useful and novel conjugating spacer within polythiophenes. Model studies on the monomeric unit 90 show that all the important criteria for that purpose (conjugation, stability) are fulfdled. 

The rationale for preparing this hybrid copolymer was to combine the desirable properties of polyaniline with those of polythiophene. For example, polythiophene has demonstrated thermo- and electrochromism, solvatochromism, luminescence, and photoconductivity while polyaniline has demonstrated reversible protonic dupability, excellent redox re-cyclability, and chemical stability. 

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