Neutral polythiophenes

Polymers, large molecules made up of smaller molecules in a repeating pattern, are used for many electrochromic materials. Conjugating polymers, which have alternating single and double bonds, are particularly suitable. Figure B shows the electrochemical oxidation of the conjugated polymer, polythiophene. Oxidation (in which electrons are removed) produces a semiconductive polymer. The neutral (unoxidized) polythiophene is red in color, whereas the semiconductive polythiophene (oxidized) is blue. In their neutral... 

Different color transitions are obtained by simply changing the molecular structure of the polythiophene and then oxidizing or reducing it. Figure C. p. 93. shows the different colors obtained by taking the neutral form... 

Neutral polythiophene (left) is red in color and becomes blue and semiconductive when electrons are removed. The process can be reversed by adding electrons to the blue polymer to make it transition back to red. 

Conducting Polymers Electronically conducting polymers (such as polypyrrole, polythiophene, and polyaniline) have attracted considerable attention due to their ability to switch reversibly between the positively charged conductive state and a neutral, essentially insulating, form and to incorporate and expel anionic species (from and to the surrounding solution), upon oxidation or reduction ... 

As might be expected, the properties of polythiophene show many similarities with those of polypyrrole. As with polypyrrole, polythiophene can be prepared via other routes than electrochemical oxidation both as the neutral material [390-392] or in the p-doped form [393]. This material is produced as an infusible black powder which is insoluble in common solvents (and stable in air up to 360°C), with conductivities ranging from approximately 10 11 Scm-1 in the neutral form [390] to 102 Scm-1 when doped [19, 393, 394]. Early work on thiophene polymers showed that the p-doped material is air-sensitive in that the conductivity decreases on exposure to the atmosphere [20, 395] although no evidence of oxygen-containing species was seen in XPS measurements [19],... 

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

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

The direct oxidative polymerization of a thiophene monomer has also been successfully employed to prepare polythiophene, for example, using FeCl3 in chloroform solvent.32 MoC15 may be similarly employed as both the oxidant and dopant.33 Subsequent reduction with ammonia of the doped polythiophene products from these FeCl3 and MoC15 oxidations provides the neutral polymer. 

Leclerc, M. et ah. Chromic phenomena in neutral polythiophene derivatives, Macro-molec. Chem. Phys. 197, 2077-2087, 1996. 

Twenty years ago, a new class of organic polymer materials was discovered with the new property of electronic conductivity comparable to metallic conductors [55]. The first representative was the polyacetylene followed in the subsequent years by several other polymers, such as polyaniline, polypyrrole, and polythiophene (see Fig. 7). The neutral structure is shown in Fig. 7. This structure has properties comparable to a semiconductor. The metal like conductance is obtained by chemical or electrochemical oxidation (shown for polypyrrole in Fig. 8). In this example, up to 30% of the pyrrole rings can be oxidized. The positive charge of the heterocyclic ring... 

IBM introduced a family of polyanilines, referred to as PanAquas , which are highly soluble in neutral water in the conducting form. The PanAqua provides a simple and effective discharge layer for e-beam lithography and can be cleanly removed during the alkaline development of the resist. A water-soluble polythiophene derivative referred to as ESPACER (a trade mark and product of Showa Denko K. K.) is also very effective at eliminating resist charging and can be removed by water wash. 

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