Subject polythiophene

Order-disorder, or rod-to-coil , transitions in dilute solution have been reported for polydiacetylenes (2, 5-11), polysilylenes (12-15), and alkyl-substituted polythiophenes (16). The interpretation of the experimental observations has been the subject of considerable controversy with respect to whether the observations represent a single-polymer-molecule phenomenon or a many-chain aggregation or precipitation process (3-16). Our own experimental evidence (12, 13) and that of others (5-8, 10, 16) weigh heavily in favor of the single-chain interpretation. In our theoretical interpretation, we will assume that the order-disorder transitions observed in dilute pol-ysilylene solutions represent equilibrium, single-chain phenomena. 

Electrically conducting polymers are quite different systems to the above elec-troinitiated chain polymerizations since they are formed by an unusual step-growth mechanism involving stoichiometric transfer of electrons. The polymers are obtained directly in a conductive polycationic form in which charge-compensating counter anions from the electrolyte system are intercalated into the polymer matrix [173], Exact mechanistic details remain the subject of discussion, but Scheme 4, which shows polypyrrole formation is plausible. Polythiophene is similar where S replaces NH in the ring. 

Polythiophene has been the subject of many diffraction studies. Several soluble, film-forming derivatives have been synthesized, and several oligomers and substituted model compounds have been obtained as single crystals or deposited as ordered thin films. This broad field will be covered in a separate contribution to this Handbook, written by Samuelsen and MIrdalen (.see chapter 2). For this reason, the current chapter does not contain a section on polythiophenes. 

An electrochromic display (BCD) is a thin solid state device that changes color reversibly when subjected to a small electrical potential. Since the doping processes of certain conducting polymers are accompanied by changes in the color, this effect has been conveniently exploited in the realization of BCD devices. Thin films of a conducting polymer polythiophene, for example, are red in the doped state and deep blue in the undoped state. 

Conjugated polymers have been the subject of great interest, both theoretically and experimentally, since the discovery of conductivity in doped polyacetylene in the seventies [1]. Many works have been devoted to their synthesis, characterizations and properties [2]. They have found many apphcations, particularly in the field of optoelectronics, as light-emitting diodes (LEDs), field-effect transistors (FETs), solar cells, etc., due to the semi-conducting behavior of the conjugated backbone [3]. Among them, polythiophenes (PTh) and polypyrroles (PPy) have been extensively studied because of their synthesis versatility and environmental stability [4-6]. Their functionalization permits the combination of their... 

Self-organization of polythiophenes in liquid crystals with a multitude of morphologies and wide areas of application is the subject of the Chapter 12, presented by Kazuo Akagi. 

The property of polythiophenes to change color upon the reversible oxidation/reduction process and the resulting electrochromic applications (e.g. smart windows) are the subject of the review Chapter 20 by Greg Sotzing and co-workers. 

Conductive polymers such as polypyrrole (PPy), polyaniline (PAni), and polythiophen (PTh) have been the subject of much research owing to their wide applications in biosensors, electrochemistry, and electrocatalysis [191, 192]. Recently, conductive polymers have been also investigated as ORR electrocatalysis in three different ways (1) utilizing conductive polymers as ORR electrocatalysts on their own, (2) incorporating non-precious metal complexes into the conductive polymer matrix, and (3) employing conductive polymers as a nitrogen/carbon precursor material for pyrolyzed M-N c/C catalysts [105]. 

Another route to achieve melt and solution processability is to substitute long-chain alkyl groups at the 3-position of the heterocycle. This is the subject of an excellent review [2] with 68 references on polythiophene, but only five on polypyrrole. A state-of-the-art review of processable polythiophenes is included in Volume 3. The principal drawback of this approach is that there is a significant increase in the cost of the product. 

Soluble 3.4-disubstituted polythiophenes have found application as antistaticcomponents for film materials and are on the market electrochromic and electroluminescent devices are subject to intensive research and surely will be effective in the near future. Biosensor devices with functionalized polythiophene carrier systems for immobilizing enzymes are also applicable for the electro-analytical determination of analytes in micromolar concentrations. 

Reductive Electropolymerization. Besides the oxidative anodic electropolymerization of the monomer, which is the most convenient and the most widely used method, polythiophene can also be prepared by a cathodic route involving the electroreduction of the complex Ni(2-bromo-5-thienyl)(PPh3)4Br in acetonitrile. This method, initially proposed for the synthesis of poly(p-phenylene) [374-376], has been extended to polythiophene [520]. The major drawback is that the polymer is produced in its neutral insulating form, which leads rapidly to a passivation of the electrode and limits the attainable film thickness to approximately 100 nm. On the other hand, this technique presents the advantage of being applicable to electrode materials subject to anodic corrosion such as small-bandgap semiconductors [521]. 

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