SYMMETRICALLY DISUBSTITUTED POLY(BITHIOPHENE)S - INFLUENCE OF HALOGEN SUBSTITUENTS

Poly(3,3'-dibromo-2,2'-bithiophene) (PBr2BT) and poly(3,3'-dichloro-2,2'-bithiophene) (PCl2BT) can be readily deposited on electrodes via electrochemical polymerization of the respective monomers. Visible cracks observed on the resulting PCl2BT and PBr2BT films were related to the steric influence of the substituents. The redox potentials of polymers were found to decrease in the order PBr2BT much greater than PCl2BT > poly(bithiophene) (PBT), suggesting that the steric hindrance and electronegative nature of the halogen groups impart a negative effect on the insulator-to-Conductor transition in PBr2BT and PCl2BT. In addition, the less extended pi-conjugation, together with the electrochemically unfavourable doped state and discontinuous macroscopic structure, prevent the solid-state PBr2BT and PCl2BT from achieving conductivity comparable to the parent PBT. However, the enhanced solubility with consequent improved processibility, coupled with the presence of reactive pendant halogens would make these systems useful as functional polymers for further modifications in the post-polymerization stage.