Solid state properties of oligomers containing dithienothiophene or fluorene residues suitable for field effect transistor devices

A series of three thiophene based oligomers has been extensively characterized. The chemical design has been addressed to obtain ionization potential (IP) and electronic affinity (EA) values matching the work function of commonly used electrode materials. Such IP and EA values were tested by cyclovoltammetry. In order to tune electron-donation and drawing strength the sequence of the molecule subunits in the oligomer has been varied. The thermal properties with particular reference to their stability during preparation and operation were checked by using differential scanning calorimetry, polarised light microscopy and thermogravimetric analysis techniques. Prototypes of thin film field effect transistor, based on this series of oligomers have been electrically and structurally characterized. The long axes of the molecules are oriented nearly perpendicular to the gate insulator, in agreement with both highly sensitive X-ray diffraction and atomic force microscopy. From powder diffraction data the structure of oligomer I was solved. A general relation is envisaged between charge mobility and packing closeness in the series. For the most promising molecule a study of mobility/temperature behaviour was performed yielding interesting results.