Electrochemical behaviour of polythiophene films containing anthraquinone groups

Abstract

Electrochemical syntheses of conducting polythiophenes and polypyrroles received considerable attention. Unlike pyrrole based polymers, some 3-substituted polythiophene derivatives dissolve in common organic solvents. There are reports on preparation of 3-substituted polythiophene films and their applications such as field-effect transistors, chemical and biochemical sensors. 3-Substituted polythiophenes with long pendent redox groups in the polymer backbone act as electron transfer mediators. Electrodes modified with poly (pyrrole-anthraquinone) films catalyze the reduction of dioxygen. Therefore, it is of interest to examine the behaviour of its polythiophene analogue. In this communication, we report the synthesis of the monomer (5) and electrochemical behaviour of (5) and the resulting polymer, poly(5).

Perkin reaction of thiophene-3-carboxaldehyde with malonic acid gave 3- (3-thienyl) acrylic acid (1). Reduction of (1) with Na/Hg yielded 3-(3- thienyl) propionic acid (2). Further reduction of (2) with LiAlH4 afforded the alcohol (3) as colourless oil. The acid chloride (4) was prepared by reacting 9,10-anthraquinone-2-carboxylic acid with thionyl chloride. The monomer (5) was obtained in good yield by reacting (3) with (4). Cyclic voltammetry of (5) showed two reversible peaks at Eo = –0.80 and –1.36 V. The electrochemical behaviour of poly(5) has been examined. These films were quite stable to repetitive scanning between 0 and –1.35 V. The neutral, hydrophobic poly(5) films show some resistance to swelling in acetonitrile media.