Semiconducting polymers based on electron-donating bithiophene and electron-accepting 5,5′-bithiazole units for organic thin-film transistors

New type of π-conjugated polymers composed of electron-donating bithiophene and electron-accepting 5,5′-bithiazole were prepared by organometallic polycondensation using a zerovalent nickel complex, which have charge-transfer (CT) structures in the polymer backbone. The number average molecular weights (Mn) of the obtained polymers, PT2Z2-C8 and PT2Z2-H, were 45000 and 20000, respectively, estimated from GPC measurements. Head-to-head (HH) arrangements of 5,5′-bithiazole units leads to good solubility of the polymers in common organic solvents. Ionization potentials (IPs) of PT2Z2-C8 and PT2Z2-H were measured to be 5.15 and 5.20 eV, respectively. UV–vis peaks of the polymer films corresponding to the π–π* transition were shifted to longer wavelengths over 70 nm relative to those obtained for the corresponding chloroform solutions. PT2Z2-C8 is considered to have a coplanar π-conjugated backbone conformation, as judged from UV–vis data and XRD data. OTFTs fabricated using the polymer PT2Z2-C8 as a channel material show a typical p-type behavior and provide a mobility of 0.001 cm2/Vs with a low off-state current (of about 1 pA).