Thienoisoindigo‐Based Conjugated Polymers Synthesized by Direct Arylation Polycondensation

Abstract 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 cm 2 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 cm 2 V −1 s −1 and p ‐channel OTFTs with hole mobility up to 0.62 cm 2 V −1 s −1 are fabricated by modifying source/drain electrodes with polyethylenimine ethoxylated (PEIE) and MoO 3 , respectively, to selectively inject electrons and holes.