Ionochromic and thermochromic phenomena in a regioregular polythiophene derivative bearing oligo(oxyethylene) side chains

Structural, thermal, and optical studies on regioregular poly[3-oligo(oxyethylene)-4-methylthiophene] have revealed interesting thermochromic and ionochromic effects related to a planar/nonplanar transition of the conjugated backbone. This first-order-like conformational transition (formation of twistons) seems driven by side-chain disordering induced by an increase of temperature or through noncovalent interactions with specific cations. The twisting of one repeat unit of this regioregular polythiophene derivative provokes the twisting of a large number of adjacent thiophene units (a domino effect) which leads to an amplification of the resulting optical (i.e., absorption or emission band) signal. These features are particularly promising for the development of novel affinitychromic and photochromic sensors based on new regioregular poly(3-alkoxy-4-methylthiophene)s.