Polythiophenes formation

Figure 61 Polythiophene formation via mechanism involving electrophilic attack of cation radical upon neutral thiophene monomer. (From Ref. 247.)...

Soon after the publication of the spontaneous polymerization reaction of 2,5-dibromo EDOT to PEDOT by Wudl and colleagues, - this kind of polythiophene formation was transferred to EDIT and similar compounds by Skabara and coworkers. Three dibromothiophenes—DBMDTT, DBEDTT and DBPTT— were prepared from thieno[3,4-d][l,3]dithiol-2-one (see Figure 13.19). 

In 1979, the formation of conductive polypyrrole films by the electrochemical oxidation of pyrrole was reported for the first time This work has stimulated intense and fruitful research in the field of organic conducting polymers. Further important conductive polymers are polythiophene, polyaniline and polyparaphenylene. The development and technological aspects of this expanding research area is covered... 

Ho et al. were able to verify the a-helical shape of the polymer by circular dichroism (CD) spectra. No structural elements were observed until the formation of the double helical DNA at which point they observed a right-handed a-helix in the polythiophene backbone. Their work demonstrates the power of fluorometric detection as they noted a seven order of magnitude increase in detection sensitivity (20 fM in 200 pi) simply through the use of fluorometric detection as opposed to UV-vis absorption. The polymer in solution has a high fluorescence yield with a maximum at 530 nm (Fig. 11a). Upon formation of the duplex the fluorescence is significantly quenched (Fig. lib), while with the addition of the complementary DNA and triplex formation, the fluorescence intensity is enhanced by a factor of 5 (Fig. 11c). The inherent sensitivity of the spectral shift even allowed distinction between DNA with only one and two mismatched bases (Fig. lOBd, e). 

The bipolarons are energetically described as spinless bipolaron levels (scheme (9.30a)) which are empty and which, at high doping levels, may overlap with the formation of bipolaronic bands (9.30b). Finally, for polymers with band gap, values smaller than that of polypyrrole - such as polythiophene - the bipolaronic bands may also overlap with the valence and conduction bands, thus approaching the metallic regime. 

The electropolymerisation of the electrically conducting polymers thiophene (mentioned briefly aready in Chapter 5) and polypyrolle are thought to be produced by a scheme to that given in Fig. 6.22. (The scheme shows polypyrrole formation. Polythiophene is similar in that NH is replaced by S.)... 

Figure 12.16 Photographs of solutions of (a) polymer 12, (b) 12 + single-stranded DNA, and (c) 12 + double-stranded DNA. (d) Schematic description of the formation of pol)dhio-phene/single-stranded nucleic acid duplex and polythiophene/hybridized nucleic acid triplex forms. Reprinted from Ho et al. (2002). Copyright 2002 Wiley-VCH Verlag GmbH and Co. KGaA.

Ohkita H, Cook S, Astuti Y, Duffy W, Tierney S, Zhang W, Heeney M, McCulloch I, Nelson J, Bradley DDC, Durrant JR (2008) Charge carrier formation in polythiophene/fullerene blend films studied by transient absorption spectroscopy. J Am Chem Soc 130 3030... 

Another method for the analysis of aptamer-protein complexes involved the use of a positively charged ferrocene-tethered polythiophene, (19), as redox label reporting unit (Fig. 12.19). The antithrombin aptamer was immobilized on an electrode surface, and the electrostatic binding of the redox polymer (19) to the aptamer monolayer resulted in a supramolecular complex that revealed electrical contact between the polymer and the electrode.74 The formation of the aptamer-thrombin complex removed the polymer from the surface and blocked the electrical contact between the polymer label and the electrode. As a result, higher concentrations of thrombin increased the surface coverage of the aptamer-thrombin complex on the electrode, and this decreased the amperometric responses of the sensing device. 

Thiophene, pyrrole and their derivatives, in contrast to benzene, are easily oxidized electrochemically in common solvents and this has been a favourite route for their polymerization, because it allows in situ formation of thin films on electrode surfaces. Structure control in electrochemical polymerization is limited and the method is not well suited for preparing substantial amounts of polymer, so that there has been interest in chemical routes as an alternative. Most of the methods described above for synthesis of poly(p-phenylene) have been applied to synthesise polypyrrole and polythiophene, with varying success. 

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