Development of polythiophenes

Organic semiconductors are currently scrutinized to identify, understand and apply the useful optoelectronic properties inherent in the electron-rich n-systems. Interest spans nearly 50 years of research 

Handbook of Thiophene-based Materials Applications in Organic Electronics and Photonics Edited by Igor F. Perepichka and Dmitrii F. Perepichka (c) 2009 John Wiley Sons, Ltd 

Solubility was improved by adding ring substituents. Jen and co-workers polymerized 3-alkylthiophenes to obtain soluble, processable conducting polymers (A/n = 5000, polydispersity index (PDI) = 2) 

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The development of polythiophenes since the early 1980s has been extensive. Processible conducting polymers are available and monomer derivathation has extended the range of electronic and electrochemical properties associated with such materials. Problem areas include the need for improved conductivity by monomer manipulation, involving more extensive research using stmcture—activity relationships, and improved synthetic methods for monomers and polymers alike, which are needed to bring the attractive properties of polythiophenes to fmition on the commercial scale. 

Since the discovery of insoluble polythiophene and the determination of its electroconductivity in 1980 [241], many studies have been completed to improve the synthetic feasibility and chemical and physical properties of this conjugated polymer. A milestone step in the development of polythiophene occurred in 1985 when the poly(3-alkylthiophene), which was a soluble, processable, and stable polymer, was achieved by introducing an alkyl group... 

First, the above-mentioned sensors have major drawbacks, as the detection and recognition event is a function of the nature and characteristics of the side chains, and the side chain functionalization of the CP requires advanced synthesis and extensive purification of numerous monomeric and polymeric derivatives. Second, this generation of sensors primarily employed optical absorption as the source for detection, resulting in lower sensitivity when compared with other sensing systems for biological processes. However, the use of fluorescence detection within these sensing systems could justify continued development. More recent examples include a fluorescent polythiophene derivative with carbohydrate functionalized side chains for the detection of different bacteria [15] and novel synthesis schemes for ligand-functionalization of polythiophenes [16]. 

Paid K, Leclerc M. Functionalized regioregular polythiophenes towards the development of biochromic sensors. Chem Commun 1996 2761-2762. 

Against this background of infusible conducting polymers, the development of the soluble polythiophenes is most interesting. Glass transition temperatures have been reported as 48 °C for poly(3-butylthiophene) and 145 °C for poly(3-methyl-thiophene) 261). These polymers also show crystallinity in films and can be crystallized from solution. Solution studies indicate that there are two chain conformations 262) and the availability of a non-conjugated conformation may be a key to the low transition temperatures and solubility, when compared to the stiff-chain conjugated polymers. 

The intractability of the conducting polymers makes characterization difficult and this in turn slows the development of better polymers. The precursor routes are very attractive because they provide intermediate polymers which can be properly characterized. A precursor for polypyrrole or polythiophene would greatly enhance our ability to understand the structure of the polymers produced electrochemically. 

After the development of catalyst-transfer condensation polymerization of polythiophene, the block copolymer of polythiophene and PMA could be prepared more easily. As mentioned above, the vinyl-terminated polythiophene was first prepared. The vinyl group was converted to the 2-hydroxyethyl group by hydroboration, followed by esterification with 2-bromopropionyl bromide to give a macroinitiator for ATRP (Scheme 101)... 

A major goal of the research on conducting polymers has been the development of a rechargeable plastic battery. Cells based on polypyrrole and lithium electrodes have been developed in which the energy per unit mass and discharge characteristics are comparable to nickel-cadmium cells. Current interest appears to center around stable, processable polymers, such as polythiophene and its derivatives, and polyaniline. 

This is particularly important because the development of systems utilizing thiophene have been thwarted by the polythiophene paradox. 2 It has been clearly shown that at potentials required to oxidize the thiophene monomer, the polymer itself becomes overoxidized. This overoxidation process proceeds according to Equation 6.2,3 and results in deterioration in the chemical and physical properties of the polymer. 

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