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A series of thienoisoindigo (TIG)‐based conjugated polymers (CPs) with high molecular weights are synthesized by direct arylation polycondensation (DArP) by using TIG derivatives as CBr monomer and multi‐halogenated thiophene derivatives, i.e., (E)–1,2‐bis(3,4‐difluorothien‐2‐yl)ethene (4FTVT), (E)–1,2‐bis(3,4‐dichlorothien‐2‐yl)ethene (4ClTVT), 3,3',4,4'‐tetrafluoro‐2,2'‐bithiophene (4FBT), and 3,3',4,4'‐tetrachloro‐2,2'‐bithiophene (4ClBT), as CH monomers. Density functional theory (DFT) calculations reveal the high selectivity between α‐CH bonds in 4FTVT, 4ClTVT, 4FBT, and 4ClBT and β‐CH bonds in TIG CBr monomer. All four resulting CPs exhibit low optical bandgaps of ca. 1.20 eV and ambipolar transport characteristics with both electron and hole mobility above 0.1 cm2 V−1 s−1 as elaborated with organic thin‐film transistors (OTFTs). The polymer TIG‐4FTVT delivers the best device performance. With this polymer, n‐channel OTFTs with electron mobility up to 1.67 cm2 V−1 s−1 and p‐channel OTFTs with hole mobility up to 0.62 cm2 V−1 s−1 are fabricated by modifying source/drain electrodes with polyethylenimine ethoxylated (PEIE) and MoO3, respectively, to selectively inject electrons and holes. [ABSTRACT FROM AUTHOR]

3,4‐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. [ABSTRACT FROM AUTHOR]

n‐Type conjugated polymers (CPs) are crucial in the applications of organic electronics. Direct coupling of electron‐deficient C−H monomer via selective C−H activation, namely C−H/C−H oxidative direct arylation polycondensation (Oxi‐DArP), is an ideal approach toward such CPs. Herein, Oxi‐DArP is firstly adopted to synthesize a high‐performance n‐type CP using a newly developed monomer, i.e. 3,6‐di(thiazol‐5‐yl)‐diketopyrrolopyrrole (Tz‐5‐DPP). Tz‐5‐DPP based homopolymer PTz‐5‐DPP with a molecular weight of 22 kDa has been synthesized via Oxi‐DArP. After n‐doping, PTz‐5‐DPP films exhibited electric conductivity values up to 8 S cm−1 and power factors (PFs) up to 106 μW m−1 K−2. Notably, this PF value is the highest for n‐type polymer thermoelectric materials to date. The Oxi‐DArP synthesis and the excellent n‐type performance of the polymer make this work an important step toward the straightforward and sustainable preparation of high‐performance n‐type polymer semiconductors. [ABSTRACT FROM AUTHOR]

Abstract: High‐performance unipolar n‐type conjugated polymers (CPs) are critical for the development of organic electronics. In the current paper, four “weak donor–strong acceptor” n‐type CPs based on pyridine flanked diketopyrrolopyrrole (PyDPP), namely PPyDPP1‐4FBT, PPyDPP2‐4FBT, PPyDPP1‐4FTVT, and PPyDPP2‐4FTVT, are synthesized via direct arylation polycondensation by using 3,3′,4,4′‐tetrafluoro‐2,2′‐bithiophene (4FBT) or (E)‐1,2‐bis(3,4‐difluorothien‐2‐yl)ethene (4FTVT) as weak donor unit. All four polymers exhibit low‐lying highest occupied molecular orbital (≈ −5.90 eV) and lowest unoccupied molecular orbital energy levels (≈ −3.70 eV). Top‐gate/bottom‐contact organic field‐effect transistors based on all four polymers display unipolar n‐channel characteristics with electron mobility (µe) above 1 cm2 V−1 s−1 in air, and presented linear |ISD|1/2 −VGS plots and weak dependence of the extracted moblity on gate voltage (VGS), indicative of the reliability of the extracted mobility values. Importantly, the devices based on PPyDPP1‐4FBT and PPyDPP2‐4FBT show a pure unipolar n‐channel transistor behavior as revealed by the typical unipolar n‐channel output characteristics and clear off‐regimes in transfer characteristics. Attributed to its high crystallinity and favorable thin film morphology, PPyDPP2‐4FBT shows the highest µe of 2.45 cm2 V−1 s−1, which is among the highest for unipolar n‐type CPs reported to date. This is also the first report for DPP based pure n‐type CPs with µe greater than 1 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]