Conjugated Polymers from Direct Arylation Polycondensation of 3,4‐Difluorothiophene‐Substituted Aryls: Synthesis and Properties

Abstract

Abstract3,4‐Difluorothiophene‐substituted aryls, i.e., 1,4‐bis(3,4‐difluorothiophen‐2‐yl)‐benzene (Ph‐2FTh), 1,4‐bis(3,4‐difluorothiophen‐2‐yl)‐2,5‐difluorobenzene (2FPh‐2FTh), and 4,7‐bis(3,4‐difluorothiophen‐2‐yl)‐2,1,3‐benzothiadiazole (BTz‐2FTh), are synthesized as C─H monomers for the synthesis of conjugated polymers (CPs) via direct arylation polycondensation (DArP) with diketopyrrolopyrrole (DPP) and isoindigo (IID) derivatives as C─Br monomers. The Gibbs free energies of activation for direct arylation (ΔG298 K, kcal mol−1) for α─C─H bonds of thiophene moieties as calculated by density functional theory (DFT) are 14.3, 16.5, and 16.4 kcal mol−1 for Ph‐2FTh, 2FPh‐2FTh and BTz‐2FTh, respectively, meaning that inserting an electron‐deficient unit in 3,3′,4,4′‐tetrafluoro‐2,2′‐bithiophene (4FBT, ΔG298K: 14.6 kcal mol−1) may cause a reactivity decrease of the C─H monomers. Photophysical and semiconducting properties of the resulting six CPs (i.e., DPP‐Ph, DPP‐2FPh, DPP‐BTz, 2FIID‐Ph, 2FIID‐2FPh, and 2FIID‐BTz) are characterized in detail. DPP‐based CPs show ambipolar transport properties while IID‐based ones exhibited n‐type behavior owing to the deeper frontier molecular orbital energy levels of IID‐based CPs. With source/drain electrodes modified with polyethylenimine ethoxylated, n‐channel organic thin‐film transistors with maximum electron mobility of 0.40, 0.54, 0.29, 0.05, 0.16, and 0.01 cm2 V−1 s−1 for DPP‐Ph, DPP‐2FPh, DPP‐BTz, 2FIID‐Ph, 2FIID‐2FPh, and 2FIID‐BTz, respectively, are fabricated. DPP‐2FPh exhibits the best device performance due to the good film morphology and the highest intermolecular packing order.