Photochromism, polythiophene

This photo-induced chromic effect is reversible and the irradiated polymers slowly recover their initial absorptions features. Moreover, the same effect has been observed in solid state upon irradiation of thin film of azobenzene-substituted polythiophenes, opening the way to the design of novel photochromic polythiophenes that can be useful in a variety of optical devices. 

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]. 

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. 

Azobenzene-subsdtuted polythiophenes has led to the development of novel dual-photochromic polymers, where the isomerization of the photo-active side-chains. 

Zhao X.Y, Wang M. and Liu H.J. (2008), Structure dependence of photochromism of azobenzene-functionalized polythiophene derivatives./owrna/ of Applied Polymer Science, 108 pp. 863-869. 

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