In this work we study a co-oligomer based on fluorenone and thiophene moieties, whose chemical design aimed at a molecule suitable for application as active material in organic field effect transistors. The molecule has been fully characterized in terms of its electrochemical, structural, morphological and electrical properties. Combining these measurements, it has been possible to address the role of the film morphology and of the crystal structure, due to the polymorphic behaviour of the molecule, in determining the mobility of films obtained by vacuum deposition on substrates held at different temperatures. (c) 2005 Elsevier B.V. All rights reserved.