Conductive polymers conjugated type

Polymers. The Tt-conjugated polymers used in semiconducting appHcations are usually insulating, with semiconducting or metallic properties induced by doping (see Flectrically conductive polymers). Most of the polymers of this type can be prepared by standard methods. The increasing use of polymers in devices in the last decade has led to a great deal of study to improve the processabiUty of thin films of commonly used polymers. 

U. Scherf, in Handbook of Conducting Polymers, 2nd edn, (Eds. T. Skolhcim, J.R. Reynolds), Marcel Dekkcr, New York 1997, Chapter 14 (Conjugated Ladder-Type Structures), p. 363. 

The relatively high electronic conductivity of conducting polymers is connected with the presence in polymers of internal system of poly-7t-conjugated bonds. This is easy to understand on the example of a simplest type of conducting polymer (polyacetylene) in the main and activated states (Figure 6). 

The materials studied for 2PA properties involve a number of types of conjugated structures with donor and acceptor groups from stryl to cyanine dyes. Our group is particularly interested in conjugated fluorene derivatives. Fluorene derivatives have been used in conducting polymers, more recently in... 

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. 

Whether conjugated polymers are best described by a band model, such as the SSH model, or an exciton model, will depend crucially on the relative strengths of the electron-phonon and electron-electron interactions. After the discovery of highly conductive polymers, the band model was widely accepted and applied to the interpretation of experimental data. Gradually since that time, evidence that suggests that an exciton picture is more appropriate has been accumulating. Comparison of experimental results with the models described above has been used to estimate the relative importance of the two types of interaction. This will be discussed in the following sections. 

G. Leising, S. Tasch, W. Graupner, Fundamentals of Electroluminescence in Paraphenylene-Type Conjugated Polymers and Oligomers, in Handbook of Conducting Polymers (Ed. T. Skotheim), Marcel Dekker, New York 1997. 

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