Ionochromism. polythiophene

Levesque I, Leclerc M (1996) Ionochromic and thermochromic phenomena in a regioregular polythiophene derivative bearing oligo(oxyethylene) side chains. Chem Mater 8 2843-2849... 

Marsella MJ, Swager TM (1993) Designing conducting polymer-based sensors - selective ionochromic response in crown-ether containing polythiophenes. J Am Chem Soc 115 12214-12215... 

Boldea, A., I. Levesque, and M. Leclerc. 1999. Controlled ionochromism with polythiophenes bearing crown ether side chains. J Mater Chem 9 2133-2138. 

Marsella, M.J., R.J. Newland, and T.M. Swager. 1995. The ionochromic response of crown ether and calix[4]arene substituted polythiophenes Towards chemoresistive sensory materials. Polym Prep... 

Functionalised conjugated polymers such as polythiophenes were studied from the point of view of the detection and transduction of chemical and physical information into an optical or electrical signal. Their ionochromism (reversible change of colour in the presence of ions), photochromism (reversible change of colour on exposure to light), affinity chromism (tendency to colour change) and electroluminescence of polythiophene complexes with crown ethers and other solutions are discussed in detail [295]. 

Polythiophenes are not only interesting because of their electrical properties. On oxidation (p-doping), the electrical conductivity can be enhanced from about 10 S.cm (pristine material) up to several thousand S.cm in the oxidized form. This layers of polythiophenes are also of interest due to their large number of special electrophysical properties Thermochromism, electrochromism, solvatochromism, ionochromism, color changes under pressure and effected by electricity. 

Many experimental results have suggested that the conformational modification of the polythiophene backbone can be induced through order-disorder transitions of the side-chains [59]. It was then postulated that various external stimuli could pertuib the side-chain organization and consequently induce some chromic effects. These side-chain transitions can be induced by heating (thermochromism), varying the solvent quality (solvatochromism), ion complexation (ionochromism), photo-induced isomerization (photochromism) and affinity binding (affinity or biochromism) giving rise to a novel class of field responsive materials. 

More dramatic effects were observed with regioregular polyether-substituted polythiophenes. As reported by Levesque and Leclerc, chemically synthesized head-to-tail poly[3-oligo(oxyethy-lene)-4-methylthiophene] poly(5) led to ionochromic effects, with a clear isosbestic point on the UV-visible absorption spectrum, indicating the coexistence of long sequences of nonplanar and planar thiophene units [244, 245]. With the addition of a cation such as the main chain became twisted. However, in contrast to poly(4), this phenomenon was observed only with the polymer in solution. 

Fig. 9.38 Synthesis of water-soluble, highly ionochromic HT polythiophenes.

Levesque and M. Leclerc. Ionochromic effects in regioregular ether-substituted polythiophenes. J. Chem. Soc., Chem. Commun. 7995 2293. 

Irregular polythiophenes carrying carboxylic acids [170] have been prepared elec-trochemically and dramatic ionochromism or ionic self-assembly was not reported. However, other reports have looked at irregular PT carboxylic add derivatives in competitive immunoassays for antigens and haptens [171]. The carboxylate function attached directly to the thiophene ring has been reported to be prepared [172] from the 2,5-dichloro-3-methylthiophene carboxylate by the Yamamoto route [8]. 

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