Benzotriazole-containing planar conjugated polymers with noncovalent conformational locks for thermally stable and efficient polymer field-effect transistors

We report a series of benzotriazole-based semicrystalline π-conjugated polymers with noncovalent conformational locks for applications in polymer field-effect transistors. The benzotriazole moiety is a versatile electron-deficient building block that offers two chemically functionalizable sites, 2(N) and 5, 6(C) positions, allowing easy modulation of the solution processability and electronic structures of the resulting polymers. Fluorine or alkoxy substituents were introduced to the benzotriazole unit to enhance the molecular ordering through intra- and intermolecular F···S, F···H-C, C-F···π_F, or S···O attractive interactions. The fluorinated polymer (PTBTz-F) showed remarkably enhanced hole mobility (μ_h = 1.9 cm²/(V·s), on/off ratio = 8 × 10⁷) upon thermal annealing at 305 °C, compared to the unsubstituted one (PTBTz) (μ_h = 7.0 × 10^-3 cm²/(V·s), on/off ratio = 3 × 10⁶). Alkoxy unit substitution (PTBTz-OR) also improved the carrier mobility up to 0.019 cm²/(V·s) with an on/off ratio of 4 × 10⁵. Fluorine or alkoxy substitution induced tight interchain ordering with edge-on orientation, as confirmed by X-ray diffraction measurements. In particular, fluorinated PTBTz-F showed high thermal stability (T_d 453 °C) and the remarkable device characteristics with deep frontier orbital levels.