Mixed selenium-sulfur fused ring systems as building blocks for novel polymers used in field effect transistors

Eight novel polymer materials for transistor applications were prepared based on the fused ring building block selenolo[3,2-b]thiophene. The molecular structure of selenolo[3,2-b]thiophene was determined by single-crystal X-ray diffraction and was further modified for use as a monomer during the Stille synthesis of various copolymers containing substituted and unsubstituted thiophenes, thiazoles, dithienopyrroles (DTP) and benzothiadiazole subunits. The resultant polymers were analyzed for UV-Vis absorption and show a significant red shift when compared to regioregular poly(3-hexylthiophenes) (P3HT), attributed to the increased planarity and conjugation of the polymer backbone. Cyclic voltammetry experiments on the new polymers show that almost all of the new structures have a higher oxidation potential compared to P3HT, making them more stable toward oxidative doping under ambient atmospheres. The polymers were also evaluated for their electrical properties through their performance as the active layer in field effect transistors. The polymers showed relatively high mobility values, of which the highest observed value is 0.11 cm2 V−1s−1, with on/off ratios of about 105.