Quinoidal Diketopyrrolopyrrole-Based Conjugated Polymers for n-Type Organic Electronics

Abstract

Incorporation of quinoidal units into conjugated polymers provides an effective strategy for the development of n-type materials; however, the synthesis of polymerizable quinoidal building blocks remains challenging. Herein, we report a molecular design strategy that enables the construction of polymerizable quinoidal diketopyrrolopyrrole (DPP) units by introducing aromatic rings adjacent to the electron-withdrawing termini. Based on this approach, three conjugated polymers, PQT, PQTz, and PQCN, were synthesized with varied flanking units and terminal groups. While all polymers exhibit deep LUMO energy levels down to –4.45 eV, their charge transport properties differ markedly. PQT and PQTz display delocalized frontier molecular orbitals and nearly planar backbones, leading to unipolar n-type transport with maximum electron mobilities of 0.52 and 0.0048 cm2 V–1 s–1 respectively. In contrast, PQCN exhibits localized orbitals and a distorted backbone, resulting in suppressed charge transport. Benefiting from its broad absorption and efficient electron transport, PQT further enables photodetection and imaging applications, demonstrating clear photoresponse across the visible to NIR region. Furthermore, doped PQT achieves an electrical conductivity of 1.85 S cm–1 and a power factor of 14.5 μW m–1 K–2 in thermoelectrics.