Design of New Isoindigo-Based Copolymer for Ambipolar Organic Field-Effect Transistors.

We report the synthesis of a new conjugated polymer composed of isoindigo (IID) and 2,3-bis[thiophenyl-2-yl]thiophene acrylonitrile (CNTVT) subunits for high-performance n-type organic field-effect transistors (OFETs). To realize high electron mobility for the IID-based conjugated polymer, an electron-withdrawing nitrile group is incorporated into the vinylene unit, thereby shifting the energy of the lowest unoccupied molecular orbital for efficient electron injection from Au electrodes without disrupting the backbone planarity. Uniaxially aligned IID-CNTVT-conjugated polymer films for efficient intramolecular charge transport are achieved by off-center spin-coating from preaggregated solutions. To obtain its stable preaggregation in solution, a binary solvent system (a mixture of good and bad solvents) chosen with the assistance of Hansen solubility parameter simulation is used. Through this process, highly aligned IID-CNTVT films are obtained by off-center spin coating from a solvent mixture of 9:1 dichlorobenzene/2-methoxyethanol as the good and bad solvents, respectively. The properties of the aligned IID-CNTVT films are characterized with various analytical techniques, including UV-visible absorption spectroscopy, angle-resolved near-edge X-ray absorption fine structure spectroscopy, and grazing-incidence wide-angle X-ray scattering. Top-gate/bottom-contact OFETs with IID-CNTVT films aligned in the direction of charge transport exhibit a high-electron field-effect mobility of 0.83 ± 0.13 cm/V·s.