Synthesis and characterization of α,ω-disubstituted quaterthiophenes functionalized with polar groups for solution processed OTFTs

A series of soluble quaterthiophenes (4Ta–g) bearing ester groups in the α,ω-terminal positions separated from the quaterthiophene core by ethylene (4Ta–c), vinylene (4Td–f) or ethynylene (4Tg) spacers was synthesized by means of a Pd-catalyzed homocoupling of bithiophenes proceeding via C–H bond activation. The synthetic approach gave satisfying yields of 4Ta–f but resulted in only 3% yield of 4Tg due to the competitive hydrofluorination of the triple bond. The quaterthiophenes 4Ta–g were characterized by NMR, FTIR, UV–vis, PL spectroscopies, HRMS, TGA and CV. Thin-films of 4Ta–g were deposited either by spin-coating or by thermal evaporation on Si/SiO2 for the fabrication of top-contact OTFTs. The devices prepared using 4Ta–c bearing the ester functional group separated from the quaterthiophene core by an ethylene spacer showed average hole field-effect mobility up to 2.7×10−3 cm2 V−1 s−1 and up to 6×10−3 cm2 V−1 s−1 for solution processed and for thermally evaporated OTFTs, respectively. The remarkably high solubility of 4Ta–c, along with their respectable performances in OTFTs render these molecules promising for practical applications as active layers in chemically-sensitive devices.