Polypyrrole, polythiophene and related systems

High intrinsic conductivities have been observed for all these polymers. Because they are more stable to oxygen than polyacetylene, they have proven to be more useful in various technologies. 

Polypyrrole has the interesting property of having a conductivity which depends on the pH of the medium. In an acid, the N-H group can be quater-nised into the -N H2 form. The proto nation can change the conductivity of the polymer by four orders of magnitude, so allowing it to be used as a pH sensor. 

The related polymer, polyanihne, can exist in several forms depending on its state of oxidation or reduction. The oxidation and reduction of the polymer 

Polythiophene has a narrow band gap and electrons can readily be excited by photons, so allowing the polymer to exhibit photoconductivity. Because of this, it is finding appHcations in solar cells and organic transistors. 

Electrons are injected into the polymer via an indium tin oxide transparent conducting electrode. The other electrode is usually formed from a thin 

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