Chromism in polythiophene derivatives

Thermochromism has been observed in some polythiophene derivatives both in the solid state and in solution. These optical effects are related to a planar/non-planar transition of the conjugated backbone. Various measurements have revealed a strong dependence of these chromic properties upon the nature, the position and the conformation of the substituents. These results seem to indicate that the twisting of the main chain could be driven by order-disorder “transitions” of the side chains. Order-disorder side-chain transition can be induced from different stimuli and this concept has led to the development of novel ionochromic polymers. Similar phenomena could also be induced through side chain cis-trans photoisomerisation (photochromism), or by side chains that would possess some affinity to chemical or biochemical molecules (affinity chromism).