High Mobility Ambipolar Diketopyrrolopyrrole-Based Conjugated Polymers Synthesized via Direct Arylation Polycondensation: Influence of Thiophene Moieties and Side Chains

Abstract

Seven diketopyrrolopyrrole (DPP)-based donor–acceptor (D–A) conjugated polymers, i.e., poly[2,5-bis(4-octadecyldocosyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-3,3′,4,4′-tetrafluoro-2,2′-bithiophene] (P4F2T-C40), poly[2,5-bis(4-octadecyldocosyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-1,2-bis(3,4-difluorothiophen-2-yl)ethyne] (P4FTAT-C40), poly[2,5-bis(4-octadecyldocosyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C40), poly[2,5-bis(4-tetradecyloctadecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C32), poly[2,5-bis(4-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C24), poly[2,5-bis(2-decyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C22), and poly[2,5-bis(2-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C10C12), were synthesized by direct arylation polycondensation (DArP) with multi-fluorinated thiophene derivatives 3,3′,4,4′-tetrafluoro-2,2′-bithiophene (4F2T), (E)-1,2-bis(3,4-difluorothien-2-yl)ethene (4FTVT), or 1,2-bis(3,4-difluorothiophen-2-yl) acetylene (4FTAT) as the comonomer. The structures of the multi-fluorinated thiophene derivatives have a noticeable influence on the optical properties and self-assembly properties of the polymers. Compared to P4F2T-C40, P4FTVT-C40 showed an ∼30 nm red-shift while P4FTAT-C40 exhibited an ∼60 nm blue-shift of the absorption spectrum. Top-gate and bottom-contact (TGBC) organic field-effect transistors (OFETs) of all the polymers exhibited ambipolar transport behavior. The devices based on P4FTAT-C40 displayed poor device performance since its film was almost amorphous. In contrast, the polymer based on 4FTVT with the same alkyl side chains delivered much better device performance due to its crystalline nature, favorable molecular orientations, and appropriate film morphology. With optimized side chains, P4FTVT-C32 exhibited the highest hole (μh) and electron mobilities (μe) of ca. 2.6 and ca. 8.0 cm2 V–1 s–1 in air, respectively.