Polythiophenes substitution effects

FET applications of thiophene-based materials have a two-decade history. Pioneering work was conducted by Koezuka and co-workers [33], The device utilized electrochemically synthesized polythiophene as the channel layer, its mobility being 10 cm V s . This work was followed by Garnier and co-workers [13], who used sexithiophene as the channel layer and recorded an enhanced mobility of 10 cm s . Akimichi et al. [14] made FET devices using alkyl-capped oligothiophenes and mentioned that the alkyl substitution not only improves the chemical stability of the oligothiophenes but also enhances the mobility. A similar substitution effect was also observed with other oligomers [34, 35]. 

Many other polymeric systems are of interest in polymer LEDs. Polythiophenes have been known for some time but it was not until improved synthetic methods were developed that their potential was realised. The process involves the reaction of the substituted monomer with FeClj in chloroform solution. After polymerisation has occurred the product precipitates and is isolated and washed. Further special purification methods are required to obtain satisfactorily pure materials. One product, of commercial interest, developed by Bayer is poly(ethylenedioxy)thiophene, known as PEDOT (3.110). This product when doped with polystyrene sulfonate, sold as Baytron P, has been found to be effective as a conducting, hole-injecting layer on the ITO electrode. ... 

We mentioned above that in real materials, disorder of any kind localizes the excitations over a limited length on the chain, generating effective conjugation lengths so that, for instance, the optical properties are those of a finite, often quite small, molecule. It may well be that excitons are very important in such cases. This has been proposed, for instance, for substituted PPV and polythiophene [83]. This is not by itself a proof that were it possible to prepare the corresponding perfect chain, the excitons would still be important there, although this is precisely what is found in PDAs, because electron correlations have different intensities on different CPs. 

The colour of ICPs can also be sensitive to temperature. Substituted polythiophenes, in particular, show a marked blue shift of the highest wavelength absorption band when films or solutions are heated [7-9]. These reversible colour changes have been attributed to a twisting of the polymer backbone to a less ordered non-planar conformation. Less dramatic thermochromic effects have also been reported for polyanilines [3,10,11] where circular dichroism studies of... 

Substituted-polythiophenes showed a remarkable effect on degradation and stability in electrochemical systems where poly(3-methylthiophene) was observed to be the most stable and poly(3,4-bis(ethylmercapto) thiophene) to be the least stable in the experiments conducted by Tsai et al. [272] on poly(3-ethyl-mercapto-thiophene), poly(3-hexylthiopliene), poly(3-methyl-thiophene) and poly(3,4-bis(ethylmercapto)thiophene). 

M.Leclerc and G.Daoust, Structural effect in alkyl and alkoxy-substituted polythiophenes,... 

In most cases, stability and oxidation potential issues mean that polythiophenes are prepared, studied, and used in non-aqueous media, and the influence of the solvent can be significant. The extent of solvent swelling is determined by polymer-solvent interactions, which can be manipulated both by choice of solvent and introduction of substituents, here in the 3- and 4-positions. Electropolymerization of alkyl-substituted thiophenes provides good examples of the effects one can observe. EQCM (with PBD) measurements of potentiodynamic deposition from acetonitrile benzonitrile (4 1) of poly(didodecylterthiophene) (with the substituents in the 3, 4 - or 3,3"-positions) showed that film deposition occurred primarily during the reductive half-cycle, in the form of short chain oligomers of the... 

Levesque, I., and M. Leclerc. 1995. lonochromic effects in regioregular ether-substituted polythiophenes. 7 Chem Soc Chem Commun 22 2293-2294. 

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