Modification of the thiophene rings

When one of the two aryl rings is completely removed and replaced by a C=C double bond (structure 58 (Chart 21.13), for example) [122, 123], the photochromic property is retained, although there is a 

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Improvements of the electropolymerization process can be achieved by substitution at the -position of the thiophene ring with various electron-donating substituents. Some examples of modifications of the thiophene ring are presented below. 

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]. 

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