Electrochemical and Optical Properties of Novel Poly(3-substituted-2,2′-bithiophene)s

Abstract

The electrochemical and optical properties of poly(3-substituted-2,2′-bithiophene)s with bromo, alkyl, alkoxy and alkylthio pendants obtained by electrochemical polymerisation were investigated. As 3-alkylthiothiophenes, 3-alkylthio-2,2′-bithiophenes cannot be electropolymerised although the polymer can be successfully generated via a chemical oxidative approach. Other monomers were successfully electropolymerised to afford uniform polymer films on the anodic electrodes by adopting either Bu4NBF4—CH3CN or boron trifluoride diethyl etherate (BF3—OEt2) as the electrolytic media. These two media exhibit contrasting effects on the film formation behaviour and optoelectronic properties in some of these polybithiophenes with different pendants. The oxidation potentials of monomers in Bu4NBF4—CH3CN follow the trend: 3-methoxy-2,2′-bithiophenes < 3-octylthio-2,2′-bithiophenes < 2,2′-bithiophenes < 3-octyl-2,2′-bithiophenes < 3-bromo-2,2′-bithiophenes while those of the polymers are poly(3-methoxy-2,2′-bithiophene)s < poly(3-octyl-2,2′-bithiophene)s < poly(2,2′-bithiophene)s < poly(3-bromo-2,2′-bithiophene)s. However, in BF3—OEt2 the trend of oxidation potentials for monomers is 3-octylthio-2,2′-bithiophenes < 2,2′-bithiophenes < 3-bromo-2,2′-bithiophenes < 3-octyl-2,2′-bithiophenes < 3-methoxy-2,2′-bithiophenes while that for polymers is poly(3-octyl-2,2′-bithiophenes) < poly(3-methoxy-2,2′-bithiophenes) < poly(2,2′-bithiophenes) < poly (3-bromo-2,2′-bithiophenes). The facile and stable p- and n-dopability of poly(3-alkyl-2,2′-bithiophene) was also investigated.