The influence of the halogen atom on the intrinsic properties of poly(3-halidethiophene)s has been investigated using experimental and theoretical methodologies. Specifically, the electrochemical, electrical, electronic and morphological properties of poly(3-bromothiophene) have been determined and compared with those recently reported for poly(3-chlorothiophene) [Aradilla et al., Polym. Chem., 2012, 3, 436.]. The electrochemical stability and porosity are smaller for poly(3-bromothiophene) than for poly(3-chlorothiophene) while the p–p* lowest transition energy is higher for the former than for the latter. Moreover, quantum mechanical calculations on model oligomers have evidenced that the conformational properties of poly(3-halidethiophene)s, where the halogen is fluorine, chloride or bromine, are dominated by steric interactions and, therefore, are significantly influenced by the size of the halogen atoms. Both the ionization potential and the p–p* lowest transition energy have been predicted to increase slightly when the p-p-donor character of the halogen atom decreases, in agreement with experimental observations.

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