Quinoxalineimide-Based Conjugated Polymers: Synthesis, Characterization and Field-Effect Transistor Performance

Quinoxalineimide (QI) building units are versatile electron-accepting components that can create n-channel and/or ambipolar polymer semiconductors in organic field-effect transistors. Herein, we report five QI-based copolymers with thienyldiketopyrrolopyrrole (TDPP) counterparts and systematically examine polymer structure-function correlations in terms of charge carrier transport properties. The introduction of two fluorine atoms into the QI moieties of a polymer backbone lowered both the HOMO and LUMO levels, resulting in n-channel dominant ambipolar FET performance with the highest maximum mobilities of 1.45 cm²V^-1s^-1for electrons and 0.71 cm²V^-1s^-1 for holes, which was attributed to improved crystalline ordering. The electronegative triazole- and thiadiazole-fused QI moieties resulted in drastically decreased LUMO levels in the copolymers, with values close to or below -4.0 eV, as required for stable n-channel operation, whereas the HOMO levels remained unchanged because of the quinoidal resonance contribution. As a result, triazole- and thiadiazole-fused QI-based polymers showed near-infrared (NIR) light absorption across the whole NIR-II window (1000-1700 nm) with an optical energy gap of less than 0.8 eV. Investigation of the charge carrier transport properties indicated that both polymers displayed n-channel-dominant and non-off ambipolar behavior. These results suggest that a series of QI electron-accepting units are excellent building blocks for the development of novel n-channel and/or ambipolar polymer semiconductors with a high NIR light response.