Polyheterocycles, electronic structure

TABLE 1. Electronic structures of a series of polyheterocycles 1 based on DFT calculations"... 

Polyheterocycles. Heterocychc monomers constitute a third class of monomers that can he polymerized to form fully conjugated polymers the most common of these monomers, shown in equation 7, are p5urole (X = NH), thiophene (X = S), and furan (X = O). They can he doped to give electrical conductivity when pol5unerization occurs in the 2,5-positions. These monomers can be polymerized both by electrochemical and chemical methods. The polyheterocycles have received considerable attention for their electron-rich nature, which leads to materials that are easily oxidized and therefore more stable in the oxidized state. Additionally, the increased structural complexity of polyheterocycles relative to polyacetylenes makes structural modifications possible for improved processability. 

The first mention of polythiophenes as potential conducting polymers can be found in the literature in 1967. A. G. Davies and coauthors investigated the acid catalyzed polymerization of furan, pyrrole, and thiophene hetero-cycles. Although this polymerization reaction was known before, several new and interesting facts could be elucidated. Besides the confirmation of the cyclic structure of the polymer units (instead of ring opened), the electric conductivity was investigated. In contrast to the already known types of electronically conducting polymers (polyaniline and polypyrrole, see Chapter 1), the conductivity of all polyheterocycles in Armour s paper, isolated as trichloro- or trifluoroacetates (triflate), is ionic. In the case of the polythiophene, ion pairs formed by the reaction of polythiophene with trifluoro acetic acid dissociated in methylene chloride solution to the protonated polymer and triflate anions. The polythiophene triflate decomposed at relatively low temperatures (60°C-80°C). ... 

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