“Two-in-One” DPP Building Blocks for Ambipolar Conjugated Polymers in Flexible Transistors

Advancements in conjugated donor-acceptor (D-A) polymers with superior semiconducting performance and reliability are pivotal to the evolution of flexible electronics. However, the development of electron-accepting building blocks has lagged far behind that of electron-donating ones, hindering the progression of ambipolar and n-type semiconductor polymers-especially ambipolar types-and thereby limiting the construction of logic circuits and p-n heterojunctions. In this study, we introduce a new electron-accepting building block, <b>2Ar'Ar2DPP</b>, meticulously engineered for semiconducting polymers tailored to flexible electronics applications. Synthesized through the modification of conventional diketopyrrolopyrrole (DPP), <b>2Ar'Ar2DPP</b>─including <b>2TPh2DPP</b> and <b>3T2DPP</b>─incorporates structural innovations, merging a single DPP unit with two aromatic groups into a configuration featuring two DPP units and three aromatic groups. This modification enhances the electron-accepting ability and modulates intra- and intermolecular D-A interactions. <b>2TPh2DPP</b> and <b>3T2DPP</b> were investigated to explore their structure-property relationships. Specifically, <b>3T2DPP</b> demonstrates improved backbone planarity, extended π-conjugation, and more efficient intramolecular D-A interactions. These features result in significantly lower LUMO levels and narrower band gaps compared to those of conventionally utilized thiophene-flanked DPP and even its dimer. Moreover, the change in the molecular structural symmetry of <b>3T2DPP</b> induces a relatively large dipole moment, thereby enhancing intermolecular interactions. Consequently, polymers derived from <b>2Ar'Ar2DPP</b> exhibit ambipolar semiconducting performance in flexible organic field-effect transistors, achieving hole and electron mobilities of up to 6.0 and 2.1 cm² V^-1 s^-1, respectively, with good bending resistance. These preliminary results indicate that <b>2Ar'Ar2DPP</b> holds significant promise for the future design of conjugated materials for flexible electronics.