Donor–Acceptor Conjugated Copolymers Containing Difluorothienylethylene-Bridged Methyleneoxindole or Methyleneazaoxindole Acceptor Units: Synthesis, Properties, and Their Application in Field-Effect Transistors

We report the synthesis and characterization of two novel difluorothienylethylene-bridged methyleneoxindole (FVTI) and methyleneazaoxindole (FVTAI) acceptor units and six FVTI- or FVTAI-based donor–acceptor (D–A) copolymers P1–P3F. On the basis of the optimized conjugated backbone conformations, we put forward the intramolecular noncovalent interactions existing in these copolymers and suggested that the fluorine and pyridine-nitrogen atoms could improve the polymeric backbone planarity by forming multiple conformation locks such as N···H, F···H, and F···S interactions, etc. Thin film microstructure investigations indicate the copolymers with more fluorine or pyridine-nitrogen atoms in their respective single D–A pair generally formed more orderly thin films. All the six copolymers exhibited p-type charge transport characteristics with increasing mobilities from P1 to P1F and P2 to P2F. On the contrary, P3F showed relatively lower mobility than that of P3, which was attributed to the higher hole injection barrier for the P3F-based field-effect transistor device.