Quinoidal-Diketopyrrolopyrrole-Based Low-Bandgap n-Type Conjugated Polymers via Direct Arylation Polycondensation: Chalcogen Effects on Structures and Properties

Abstract

Low-bandgap conjugated polymers (CPs) with strong absorption in the short-wave infrared region usually show ambipolar characteristics. Herein, three low-bandgap CPs, that is, PQF, PQT, and PQS, with unipolar n-type transport behavior were synthesized via direct arylation polycondensation (DArP) with quinoids based on terchalcogenophene-flanked diketopyrrolopyrrole (DPP) derivatives as C−Br monomers and less electron-rich (E)-1,2-bis (3,4-difluorothien-2-yl) ethene (4FTVT) as a C−H monomer, and the chalcogen effects on the isomerism of the quinoids and the properties of the resultant CPs were investigated. Thiophene-flanked DPP-containing quinoids are the mixtures of (E, E), (E, Z), and (Z, Z) isomers, while the sole (E, E) isomer is found in furan-flanked DPP-based quinoids and (Z, Z) isomer is dominant in the quinoids based on selenophene-flanked DPP. The quinoidal monomers are stable to undergo DArP. All three CPs show lower bandgaps of ∼1.1 eV and unipolar n-type transport behavior with field-effect electron mobility (μe) above 0.1 cm2 V−1 s−1. Among them, the polymer PQF, comprising furan-flanked DPP, exhibits the highest μe of 0.21 cm2 V−1 s−1, possibly attributed to the simple chain conformation. This study provides a strategy to design low-bandgap unipolar n-type polymer semiconductors.