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

New type of pi-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 (M) of the obtained polymers, PT2Z2-CS and PT-2Z2-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 P72Z2-C8 and PT2Z2-H were measured to be 5.15 and 5.20eV, respectively. UV-vis peaks of the polymer films corresponding to the pi-pi* transition were shifted to longer wavelengths over 70 nm relative to those obtained for the corresponding chloroform solutions. P72Z2-C8 is considered to have a coplanar pi-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 cm(2)/Vs with a low off-state current (of about 1 pA). (C) 2008 Elsevier B.V. All rights reserved.