Conjugated donor-acceptor copolymer semiconductors with large intramolecular charge transfer: Synthesis, optical properties, electrochemistry, and field effect carrier mobility of thienopyrazine-based copolymers

Several conjugated thieno[3,4-b]pyrazine-based donor-acceptor copolymers were synthesized by Stille and Suzuki copolymerizations, and their optical, electrochemical, and field-effect charge transport properties were characterized. The new copolymers, poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine) (BTTP), poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine-alt-2,5-thiophene) (BTTP-T), poly(5,7-bis(3-dodecylthiophen-2- yl)thieno[3,4-b]pyrazine-alt-9,9-dioctyl-2,7-fluorene) (BTTP-F), and poly(5,7-bis(3-dodecylthiophen-2- yl)thieno[3,4-b]pyrazine-alt-1,4-bis(decyloxy)phenylene) (BTTP-P), had moderate to high molecular weights, broad optical absorption bands that extend into the near-infrared region with absorption maxima at 667-810 nm, and small optical band gaps (1.1-1.6 eV). They showed ambipolar redox properties with low ionization potentials (HOMO levels) of 4.6-5.04 eV. The field-effect mobility of holes varied from 4.2 x 10(-4) cm(2)/(V s) in BTTP-T to 1.6 x 10(-3) cm(2)/(V s) in BTTP-F. These results show that thieno[3,4-b]pyrazine-based donor-acceptor copolymers combine small optical band gaps with fairly high carrier mobilities and thus are promising for organic electronic devices.