Polythiophenes, properties solvatochromism

Regioregular poly(3-alkylthiophene)s have received a lot of attention, especially because of their high electrical conductivities in the doped state, and because of their unusual solvatochromic and thermochromic behavior . Hence, a lot of research has been focused on clarifying the structure of these materials, both in the solid state and in solution. Today, it is agreed that supramolecular aggregation of polythiophene chains plays an important role in their physical properties. 

The rationale for preparing this hybrid copolymer was to combine the desirable properties of polyaniline with those of polythiophene. For example, polythiophene has demonstrated thermo- and electrochromism, solvatochromism, luminescence, and photoconductivity while polyaniline has demonstrated reversible protonic dupability, excellent redox re-cyclability, and chemical stability. 

Poly thiophene [78] is a promising material for certain future electronic applications, due to its relatively high stability and processability in the substituted form [79-81]. Upon substitution, with e.g. alkyl side-chains [79, 80], polythiophene exhibit properties such as solvatochromism [82] and thermochromism [83]. Presently, a large variety of substituted polythiophenes with various band gaps exists (for example see Ref. [81]). 

Another interesting water-soluble polythiophene is 23 (L-POWT), bearing a chiral amino acid side chain, which was prepared by Inganas and coworkers69 by oxidative polymerization with FeCl3 (Figure 6.6). The chiroptical and solvatochromic properties of this optically active polymer are described later. 

M. Toba, Y. Takeoka and M. Rikukawa. Thermochromic and solvatochromic properties of polythiophene derivatives with liquid crystal moiety. Synth. Met. 135-136, 339-340 (2003). 

Because of the ease of chemical modification of the thiophene rings, especially at the a- and fl-positions, these materials acquire good solution-processability and mechanical drawability [10]. This versatility allowed the wide investigation of their structure-property relationships. For example, spectroscopic studies related to thermochromism and solvatochromism [11] revealed that the electronic properties of the polythiophenes are strongly coupled to the backbone conformation. Moreover, polarized IR studies of drawn polythiophene films showed that the charged carrier motion is highly confined along the backbone [12]. 

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. 

One breakthrough in applications of conjugated polymers was the development of soluble polymers, as in the case of polythiophene [75], by substitution with, for example, alkyl side chains [76,77], The polyalkylthio-phenes exhibit properties such as solvatochromism and thermochromism [78]. A large variety of substituted polythiophenes with various band gaps exist [79]. 

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