We report the synthesis, characterization, and field-effect transistor properties of novel semiconducting polymers, PQA2T and PQA3T, incorporating a quinacridone unit, and discuss the structure−property relationships. Comparison of the optical and electrochemical properties between the monomer, repeat unit, and polymer suggests that the effective π-conjugation and the delocalization of HOMO along the backbone are relatively limited. X-ray diffraction studies revealed that the polymers form a π−π stacking with a short distance of 3.6 Å and that the orientational order was enhanced by an increase of molecular weight. The hole mobilities are found to be around 0.2 cm 2 V −1 s −1 and are, interestingly, insensitive to the molecular weight and to the orientational order; the randomly oriented low molecular weight polymer showed similar mobilities to the edge-on oriented high molecular weight polymer. We speculate that the relatively localized HOMO might hinder the charge transport along the backbone, and thus the longer polymer chain is not necessary to facilitate the charge transport. The locally but strongly π−π interacted polymer crystallites seem to be sufficient for the effective charge transport in the QA-based polymer system. These features in the present polymers offer great interest of using QA moieties as the building block for semiconducting polymers and give new insight into the design of a new class of semiconducting polymers.

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Incorporation of pigment or dye molecules as building units is of great interest in the development of semiconducting polymers, due to their strong intermolecular interactions arising from the strong local dipoles in the unit structure, which would facilitate the charge transport property. In this paper, semiconducting polymers based on well-known pigments, namely, quinacridone and diketopyrrolopyrrole, are synthesized and characterized. The π-stacking distances are found to be 3.5–3.8 Å, which is fairly narrow for semiconducting polymers, indicating that they possess strong intermolecular interactions. Interestingly, polymer orientation is influenced by the composition of alkyl side chains. While the edge-on orientation is observed when the linear alkyl groups are introduced for all the side chains, the face-on orientation is observed when the branched alkyl groups are introduced either in the quinacridone or diketopyrrolopyrrole unit. It is found that the electronic structure of the present polymers is mostly affected by that of the diketopyrrolopyrrole unit, as evidenced by the absorption spectra and computation. Although the field-effect mobility of the polymers is modest, i.e., in the order of 10−4–10−3 cm2/Vs, these findings could be important information for the development of semiconducting polymers.

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Semiconducting polymers with new “electron-neutral” amide-bridged building units were designed, synthesized, and studied as materials for organic devices.