Polythiophene redox properties

As synthetic chemists desired to tune the optoelectronic and redox properties of conjugated polymers in a fine manner, more complicated conjugated systems were required. The two fused heterocycles-substituted polythiophenes 16 and 17 (Chapter 18) illustrate this as electron-poor imine functionality in 16 brings donor-acceptor character to the material, while the more electron-rich thio-based system 17 provides for especially easy oxidation. Polymerization of these complicated bis-2-thienyl monomers by electrochemical methods paves the way for fundamental structure-property relationships to be understood, ultimately directing the synthetic chemist towards soluble polymers (Chart 1.6). 

Related Polymer Systems and Synthetic Methods. Figure 12A shows a hypothetical synthesis of poly (p-phenylene methide) (PPM) from polybenzyl by redox-induced elimination. In principle, it should be possible to accomplish this experimentally under similar chemical and electrochemical redox conditions as those used here for the related polythiophenes. The electronic properties of PPM have recently been theoretically calculated by Boudreaux et al (16), including bandgap (1.17 eV) bandwidth (0.44 eV) ionization potential (4.2 eV) electron affinity (3.03 eV) oxidation potential (-0.20 vs SCE) reduction potential (-1.37 eV vs SCE). PPM has recently been synthesized and doped to a semiconductor (24). 

Electrochemical oxidation of X produces a polymer film with polythiophene as the backbone and viologen centers as pendant redox groups. The electrochemical properties of the polymer are the combination of polythiophene and viologen. Using viologen subunits as the internal standard (one per repeat unit of the polymer), the "doping level" of the oxidized polythiophene backbone at its maximum conductivity can be measured and is about 25%. The charge transport via the pendant V2+/+ of poly(l) has been studied by... 

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 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. 

Polythiophenes are normally produced from nonaqueous media because the monomer is more soluble in these. Also, a wider electrochemical potential window is available, and this is required as polythiophene is more difficult to oxidize than pyrrole. The influence of water on the polymerization process for thiophene and on the redox switching properties has been studied.1314 The presence of water as low as... 

J. L. Reddinger and J. R. Reynolds, Tunable redox and optical properties using transition metal-complexed polythiophenes, Macromolecules, 30, 673-675 (1997). 

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