Electrochemical Polymerization of Oligothiophene Derivatives and Their Doping Properties

Preparation of high quality conducting poly( trans ‐TTTE) and poly( trans ‐BTTTE) by the electrochemical polymerization of oligothiophene derivatives such as trans ‐(thiophene‐2‐yl)‐2,2':5'2''‐terthiophene‐5‐yl)ethylene, trans ‐TTTE, and trans ‐(2,2'‐bithiophene‐5‐yl)‐2,2':5'2''‐terthiophene‐5‐yl)ethylene, trans ‐BTTTE have been carried out. Evidence for electrochemical p‐type doping of poly( trans ‐TTTE) and poly( trans ‐BTTTE) is obtained from in situ measurements of the cyclic voltammetry, optical absorption spectroscopy, and electron spin resonance and compared with the data of polythiophene. These results are tentatively explained in terms of a conformation change in the molecular structure, such as a difference in the torsion angle between neighboring thiophene rings due to the introduction of vinylene groups and are discussed in terms of polaron and/or bipolaron model. The bipolaron levels in the gap states appear upon p‐type doping and the electronic band scheme of poly( trans ‐TTTE) and poly( trans ‐BTTTE) is discussed.