SOLVATOCHROMISM ON REGIOCHEMICALLY SUBSTITUTED POLY(HEXYLTHIOPHENES)

Poly (3, 3 ''-dihexylterthiophene) and poly (3',4'-dihexylterthiophene ) have been synthesized and studied with respect to their solvatochrom ic properties. While both polymers in chloroform solution have maximum absorption at approximately the same wavelength, they behave differen tly with respect to changes observed on their UV-visible spectra when the quality of the solvent is changed. A microscopic model for the sol vation of both polymers has been developed based on semi-empirical qua ntum chemical calculations. The results are consistent with a high deg ree of conformational disorder in the 3', 4'-substituted polymer even in the solid state, leading to chains of short conjugation length, and thus less sensitive to solvation effects. In 3,3 ''-substituted polyt hiophene on the other hand, the substituents impose smaller torsional barriers, similar to the ones found in regioregular poly (3-hexylthiop hene). A rod-to-coil like transition is thus expected to occur as a fu nction of solvent quality.