This article summarises the industrial applications of poly-(3,4-ethylenedioxythiophene) (PEDT, PEDOT). The basic chemical and physical properties of PEDT are discussed to outline the fundamentals which lead to PEDT as a highly valuable electric and electronic material. PEDT applications are reviewed depending on the two different ways of preparation: in situ polymerisation of the monomer, usually carried out by the user, and applying the prefabricated polymer in the form of its water-based complex with poly(styrene sulfonic acid). Several applications like antistatic coatings, cathodes in capacitors, through-hole plating, OLED's, OFET's, photovoltaics, and electrochromic applications are discussed in detail.

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A short survey of technological aspects of electrochromism with various electroactive species is given. Different approaches with inorganic and organic materials have been pursued in the past. So far widespread usage of this technology for large area applications has not been achieved. Nevertheless one major technical product, self‐darkening rear‐view mirrors for cars, is already well established. This article reviews some research results on electroactive polythiophenes, especially poly(3,4‐alkylenedioxythiophenes). Some promising results with the commercially available electrically conducting polymer Baytron P (PEDT/PSS) are presented. It is demonstrated that an all solid‐state electrochromic multilayer assembly based on a polymeric electrochromic material might be close to technical realization. The coating of large area substrates with aqueous poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) dispersion can be a way to an economically viable product.

Organic thin film transistors (TFTs) are of interest for lowcost, large-area electronic applications, such as active-matrix displays, electronic paper, flexible microelectronics, and chemical sensors.[1±8] The performance of organic TFTs is determined primarily by the field effect mobility of the charge carriers in the organic semiconductor layer and by the efficiency of injecting and extracting carriers at the source and drain contacts. For virtually all classes of organic semiconductors, the intrinsic carrier mobility depends critically on the degree of molecular ordering and on the extent of the p±p stacking in the material.[9±11] Consequently, optimizing the chemical structure of the organic semiconductor with regard to optimum molecular ordering and maximum orbital overlap continues to be of great importance for the further advancement of organic TFT technology. Despite the extraordinary number of organic semiconductors that have been synthesized and evaluated for use in organic TFTs, [12] the relationships between molecular structure and electrical TFT performance remain sketchy at best. The fused hydrocarbon pentaceneÐby all accounts a rather unspectacular moleculeÐcontinues to deliver the highest electrical performance, regardless of the method of film deposition (thermal evaporation, vapor phase epitaxy, conversion of a solution-processed precursor) and regardless of the contact configuration (top or bottom contacts).[13±15]A useful and practical strategy for investigating the relationships between molecular structure and electrical performance is the systematic variation of the number of repeat units in a particular type of molecular semiconductor. This can be done either by varying the number of units in the conjugated backbone of the molecule, or by varying the length of alkyl substituents. One particularly useful class of model compounds for this type of investigation are the oligothiophenes, due to their relatively straightforward synthesis and because of the wide range of possible modifications in their chemical structure. Organic TFTs based on oligothiophenes were first reported by Horowitz and Garnier [16±18] and later by Dodabalapur, Katz, and others. [19±21] Carrier mobilities reported for a-sexithiophene (a-6T) TFTs have improved from 10 ±4 cm 2 / V s to greater than 0.01 cm 2 /V s.[18±21] Substituting alkyl chains at the a-and a¢-positions of the a-6T molecule led to an increase in carrier mobility to 0.13 cm 2 /V s. [22,23] Carrier mobilities near 0.2 cm 2 /V s have been reported for a-octithiophene (a-8T) TFTs with active layers deposited at 150 C and higher.[24] For many years, oligothiophenes and their alkyl-substituted derivatives have been among the most intensely investigated organic semiconductors and have even led to the demonstration of fast integrated circuits.[3]We have synthesized and evaluated a series of alkyl-substituted oligothiophenes with chromophore length ranging from four to six thiophene units (a,a¢-didecylquaterthiophene, a,a¢-didecylquinquethiophene, and a,a¢-didecy...

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We have designed and successfully synthesized star‐shaped oligothiophenes, which could be used as semiconducting materials for solution‐processible organic field‐effect transistors (FETs). By systematically changing the chemical structure of the star‐shaped oligothiophenes we obtained the structural requirements needed for making working FETs from them. UV‐vis fluorescence measurements showed that a molecule of the star‐shaped compounds under consideration is not a fully conjugated molecule, but it has three independently conjugated oligothienyl‐phenylene blocks. A possible scheme of molecular packing of the star‐shaped oligothiophenes in a lamellar structure was proposed and confirmed by atomic force microscopy (AFM) and X‐ray diffraction (XRD) measurements. Although the star‐shaped semiconductors show a somewhat lower mobility than their linear analogs, they possess better solubility and film‐forming properties, leading to improved spin‐coating processing. The best FETs were made by spin‐coating 1,3,5‐tris(5″‐decyl‐2,2′:5′,2″‐terthien‐5‐yl)benzene from a chloroform solution, which resulted in a mobility of 2 × 10–4 cm2 V –1s–1, a 102 on/off ratio at gate voltages of 0 V and –20 V, and a threshold voltage close to 0 V.

a,a'-Didecylquater-, -quinque-and -sexi-thiophenes were synthesized by Kumada cross-coupling and oxidative coupling reactions. For the former reaction Pd(dppf)Cl 2 was found to be a more efficient catalyst than the usually applied Ni(dppp)Cl 2 . Thermal behaviour of all new oligothiophenes was investigated by differential scanning calorimetry and polarizing optical microscopy. It was shown that all these compounds possess not only crystal phases but also high temperature ordered smectic mesophases and that the clearing point increases linearly with the number of conjugated thiophene rings. A degree of order in the crystal phase was estimated on the basis of thermodynamic data. The highest degree of order was proposed for a,a'-didecylquaterthiophene, which explains why the mobility of end-a,a'-capped quaterthiophenes in FET (field effect transistor) devices is comparable or sometimes better than those of corresponding quinque-and sexi-thiophene derivatives.