Electrochemical and optical properties of novel poly(3-substituted-2,2 '-bithiophene)s

The electrochemical and optical properties of poly(3-substituted-2.2'-bithi ophene)s with bromo, alkyl, alkoxy and alkylthio pendants obtained by elect rochemical polymerisation were investigated. As 3-alkylthiothiophenes, 3-al kylthio-2,2'-bithiophenes cannot be electropolymerised although the polymer can be successfully generated via a chemical oxidative approach. Other mon omers were successfully electropolymerised to afford uniform polymer films on the anodic electrodes by adopting either Bu4NBF4-CH3CN or boron trifluor ide diethyl etherate (BF3-OEt2) as the electrolytic media. These two media exhibit contrasting effects on the film formation behaviour and optoelectro nic properties in some of these polybithiophenes with different pendants. T he oxidation Potentials of monomers in Bu4NBF4-CH3CN follow the trend: 3-me thoxy-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'-bithiophe ne)s < poly(2,2'-bithiophene)s < poly(3-bromo-2,2'-bithiophene)s. However, in BF3OEt2 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 stabl e p- and n-dopability of poly(3-alkyl-2,2'-bithiophene) was also investigat ed.