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 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.

Keywords: ambipolar polymer semiconductors; conjugated polymers; direct arylation polycondensation; organic thin-film transistors; thienoisoindigo.