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.