To achieve rationalization criteria for target-oriented molecular design of Th-X-Th (Th = thiophene) semiconductor building blocks, we have carried out an extensive investigation on the effects of the X core (X = fluorene, carbazole or phenothiazine) on the electronic properties and polymerization ability of Th-X-Th monomers and on the electronic and structural properties of the corresponding periodic conducting polymers -(Th-X-Th)(n)-, obtained by electropolymerization and, for comparison's sake, by FeCl3-catalyzed polymerization and/or Suzuki coupling. The effects of molecule bending and of solubilising bulky alkyl substituents have also been considered. The systematic, exhaustive template sequence combined with a rigorous, multitechnique investigation protocol affords a unique data library and a complete set of reliable interpretative/predictive guidelines. (C) 2011 Elsevier Ltd. All rights reserved.