1,2,5,6-Naphthalenediimide Based Donor–Acceptor Copolymers Designed from Isomer Chemistry for Organic Semiconducting Materials

Abstract

Two new donor–acceptor (D–A) copolymers based on 1,2,5,6-naphthalenediimides (iso-NDI) and thiophene units, iso-P(NDI2OD-T2) and iso-P(NDI2OD-TT), were designed from isomer chemistry and compared with the reported isomeric copolymers P(NDI2OD-T2) and P(NDI2DT-TT) to investigate the influence of isomeric structure on their optoelectronic properties. DFT calculations reveal that iso-P(NDI2OD-T2) and iso-P(NDI2OD-TT) have higher HOMO and LUMO energies and better backbone planarity relative to their isomeric polymers. Iso-P(NDI2OD-T2) and iso-P(NDI2OD-TT) were synthesized by the Stille coupling polymerization and characterized by elemental analysis, 1H NMR, GPC, UV–vis absorption, cyclic voltammetry, TGA, DSC, and organic thin film transistors (OTFTs). It was found that iso-P(NDI2OD-T2) and iso-P(NDI2OD-TT) had higher LUMO energies and broader band gaps than their isomeric ones and showed hole-dominated charge transport behavior, which is quite different from the electron-dominated charge transport feature of P(NDI2OD-T2) and P(NDI2DT-TT). In spite of the amorphous-like thin-film features, iso-P(NDI2OD-T2) exhibited high hole mobility of up to 0.3 cm2 V–1 s–1, and iso-P(NDI2OD-TT) showed ambipolar property with hole and electron mobility of up to 0.02 and 4 × 10–3 cm2 V–1 s–1, respectively.