Stretchable Semiconducting Polymers with Hydrogen-Bonding-Capable Conjugation Breakers: Synthesis and Application in Organic Thin-Film Transistors

Diketopyrrolopyrrole (DPP)-based conjugated copolymers are important organic semiconductors for applications in high-efficiency organic thin-film transistors (OTFTs). However, the direct application of these polymers with rigid backbones in stretchable devices has limitations. In this study, we designed and synthesized three kinds of DPPBT-based copolymers, DPPBT-A1, DPPBT-A3, and DPPBT-A5, which have amide-coupled alkylene conjugation breakers capable of hydrogen bonding. Linkers with different segment lengths were copolymerized with DPP and bithiophene (BT) backbone units. A DPP-based copolymer with alternating BT moieties, DPPBT, was synthesized as a reference fully conjugated copolymer. The synthesized polymers with freely rotational backbone linkers have sufficient flexibility to develop ordered phase domains, even in thin films, in comparison to the reference copolymer. However, the introduction of the conjugation breakers, which disconnect the intramolecular π–π overlapping, tends to decrease the hole mobility (μ) from 0.76 to 0.20 cm2 V–1 s–1 in the corresponding OTFT devices. The TFT fabricated using DPPBT-A3 showed a mobility of 0.50 cm2 V–1 s–1, and the mobility value did not show a significant change even when elongated by more than 50%. Therefore, the molecular design strategy of introducing amide-coupled alkylene conjugation breakers into conjugated polymer chains can contribute significantly to the development of high-mobility stretchable conjugated polymers in future.