Physical properties of regioregular polythiophene derivatives containing mesogenic or ionic group in the side chain

Abstract

We synthesized polythiophene (PTh) derivatives having a methyl group at 4-position and a mesogenic group, or an ionic group at 3-position in the thiophene ring via a flexible spacer by oxidative polymerization with FeCl₃ and investigated regioregularity, thermal, electrical and optical properties of the PTh derivatives. The regioregularity of the PTh derivatives with a mesogenic group was over 90%. A smectic phase was observed for two PTh derivatives with mesogenic group. The electrical conductivity was about 10^-3~10^-4 Scm^-1for the PTh derivatives doped with I₂ vapor in the film state. PTh derivatives containing methylimidazolium salt derivative at the 3-position of thiophene ring were soluble in water. To investigate ionochromism of the aqueous solution of PTh derivatives containing methylimidazolium salt derivative, some salts were added to the aqueous solution. The absorption peak based upon the π conjugation of the polymer backbone was shifted to the longer wavelength region, when NaI, KI or LiI salts were added to the aqueous solution of the PTh derivatives. This ionochromism behavior of the aqueous solution of PTh derivatives containing methylimidazolium salt derivative would be applied to the chemosensor.