Conducting polymer doping" with electron donors

The unique properties of polymers such as polyacetylene, whose backbones consist of an alternating succession of single and double bonds, and most of which show extraordinary electrical, optical and magnetic properties including electrical conductivity when "doped" with electron donors or acceptors [35], are also outside the scope of this work. Sophisticated quantum mechanical treatments are required to predict these properties of such polymers. 

Many other air-stable conducting polymers followed (Fig. 12.10) polypyrrole, polythiophene, polyaniline (which had been known since the nineteenth century as "aniline black"), and so on (Table 12.4). These polymers are semiconducting, not metallic, when "doped" with electron donors or acceptors the individual conjugated chains have finite length, so the conductivity is limited by chain-to-chain hopping. Also, if the individual strands exceed four or so oligomers, the conjugation tends to decrease, as the strand tends to adopt a screw-type distortion. The transport within each strand is attributed to polarons and bipolarons. 

The electric conductivity of p-PODA at room temperature is 10 Scm This corresponds to common insulating polymers in the glassy state. However, above 440 K, ionic conduction is observed. " Electrically conductive PODAs can be obtained by doping with electron donors or electron acceptors. Some varieties of PODA are semiconductors and exhibit photoconductive properties. Therefore, they are used in electrical applications. PODA films exhibit exceptional gas separation properties. ... 

The values of bandgap of polymers A-D are smaller than that of rmn -polyacetylene, and lead to the expectation of semiconductive behavior in these polymers. The predicted order of bandgap is Celectron affinity increase in the order of B < D < A < C while ionization potentials are in the order of Chighly conducting materials on doping with electron donors. 

Polyquinolines form another class of heteroaromatic polymers exhibiting photoconductivity. The interest in the synthesis of polyquinolines has increased rapidly during the last decade because of their excellent oxidative and thermal stability. When doped with alkali metal donor compounds like sodium naphthalide or sodium anthracide, several polyquinolines show electrical conductivity as high as 10 S/cm [336,337], When doped with electron-donor compounds such as TNF or 2,3-dichloro-5,5-dicyano-l,4-benzoquinone some poly-quinolines show distinct photoconductivity. One such polyquinoline is poly(4-phenyl-2,6-(p-phenoxy)-quino-line) (54b) [338,339]. It is obtained by the acid catalysed self-condensation reaction of 4-amino-4 -acetyl-3-benzoyl diphenyl ether (54a). 

POLYACETYLENE. A linear polymer of acetylene having alternate single and double bonds, developed in 1978. It is electrically conductive, but this property can be varied in either direction by appropriate doping either with electron acceptors (arsenic pentaflnoride or a halogen) or with electron donors (lithium, sodium). Thus, it can be made to have a wide range of conductivity from insulators to n- or >-type semiconductors to strongly conductive forms, Polyacetylene can be made in both cis and trans modifications in the form of fibers and thin films, the conductivity... 

A number of organic polymers become electrically conducting on addition of electron donors or acceptors.(1-5) Despite the enormous interest in these conducting polymer systems, many theoretical aspects of the problem remain poorly understood, especially with regard to the electronic properties of the "doped" (partially ionized) polymers. Progress is being made, however, in understanding the undoped polymer precursors. In a series of recent papers, we have demonstrated the utility of the... 

The Cgg doped with neutral polymers such as emeraldine base of polyaniline show higher conductivities due to the charge transfer complex formation mechanism whereby the neutral polymer acts as electron donor and Cgg acts as acceptor [22]. Not only Cg, but also a combination of and can be doped with polyaniline, where the same effect of enhancement in conductivity is observed (of the order of 10 ). But, when doped polyaniline is prepared from N-methyl-2-pyrrolidinone (NMP)/toluene-solution, a slightly lower conductivity is observed. The free-standing nanocomposite films possess conductivities up to 6.2 x 10 S/cm [23]. 

Note 2 The electric conductivity of a conjugated polymer is markedly increased by doping it with an electron donor or acceptor, as in the case of polyacetylene doped with iodine. 

Polysilanes are cr-conjugated polymers composed of Si-Si skeletons and organic pendant groups. They are insulators with filled intramolecular valence bands and empty intramolecular conduction bands. However, because of strong cr conjugation, they have rather narrow band gaps of less than 4 eV [24,25] and are converted to conductors by photoexcitation or by doping electron donors or acceptors. Recently they have attracted much attention because of their potential utility as one-dimensional conductors, nonlinear optical materials, and electroluminescent materials [26-28]. 

The conductivity of polyacetylene is also increased by dopants that are electron donors. For example, the polymer can be doped with alkali metals to give, for example, [Li5 (CH) ln. The wide range of conductivities produced by these two forms of doping is illustrated in Figure 6.3. 

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