Methyl-, chloro-and fluoro-substitution in the C6 ring has little effect on the oxidation of polybenzo [c] thiophene films to the p-doped conducting form, but has a marked effect on reduction to the n-doped form: poly (5, 6-dichlorobenzo [c] thiophene) is n-doped at E<–0.35 V (SCE).
[Aitken, R. Alan; Hodgson, Philip K.G.; Morrison, John J.; Oyewale, Adebayo O. Journal of the Chemical Society. Perkin Transactions 1, 2002 , # 3 p. 402 - 415]