We present new semiconducting polymers incorporating naphtho[1, 2-b:5, 6-b′] dithiophene (NDT3) and naphtho[2, 1-b:6, 5-b′] dithiophene (NDT4), which are linked at the naphthalene positions, in the polymer backbone. It is interesting that the trend in the ordering structure and thus charge transport properties are quite different from what were observed in the isomeric polymers where the NDT3 and NDT4 cores are linked at the thiophene α-positions. In the thiophene-linked NDT system, the NDT3-based polymer (PNDT3BT) gave the better ordering in thin films and thus the high charge carrier mobility compared to the NDT4-based polymer (PNDT4BT). In the meantime, in the naphthalene-linked NDT system, the NDT4-based polymer (PNDT4iBT) provided the superior properties. Considering that PNDT4iBT has relatively low highest occupied molecular orbital (HOMO) energy level (-5.2 eV) and moderately high mobilities in the order of 10-2 cm2 V-1 s -1, the NDT4 core, when linked at the naphthalene positions, can be a good building unit for the development of high-performance semiconducting polymers for both organic field-effect transistors and photovoltaic devices.
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