Two angular-shaped 4,9-didodecyl α-aNDT and 4,9-didodecyl β-aNDT isomeric structures have been regiospecifically designed and synthesized. The distannylated α-aNDT and β-aNDT monomers are copolymerized with the Br-DTNT monomer by the Stille coupling to furnish two isomeric copolymers, PαNDTDTNT and PβNDTDTNT, respectively. The geometric shape and coplanarity of the isomeric α-aNDT and β-aNDT segments in the polymers play a decisive role in determining their macroscopic device performance. Theoretical calculations show that PαNDTDTNT possesses more linear polymeric backbone and higher coplanarity than PβNDTDTNT. The less curved conjugated main chain facilitates stronger intermolecular π–π interactions, resulting in more redshifted absorption spectra of PαNDTDTNT in both solution and thin film compared to the PβNDTDTNT counterpart. 2D wide-angle X-ray diffraction analysis reveals that PαNDTDTNT has more ordered π-stacking and lamellar stacking than PβNDTDTNT as a result of the lesser curvature of the PαNDTDTNT backbone. Consistently, PαNDTDTNT exhibits a greater field effect transistor hole mobility of 0.214 cm² V⁻¹ s⁻¹ than PβNDTDTNT with a mobility of 0.038 cm² V⁻¹ s⁻¹. More significantly, the solar cell device incorporating the PαNDTDTNT:PC₇₁BM blend delivers a superior power conversion efficiency (PCE) of 8.01% that outperforms the PβNDTDTNT:PC₇₁BM-based device with a moderate PCE of 3.6%.

A series of donor–acceptor polymers incorporating the thieno[3,2-b]thiophene-2,5-dione (TTD) acceptor unit and different donor units are synthesized. The synthesis of a TTD-based key monomer, 3,6-bis(5-bromo-4-alkylthiophen-2-yl)thieno[3,2-b]thiophene-2,5-dione, is successfully improved to afford higher total yield with less reaction steps (42%/4 steps) than those previously reported (14%/7 steps). The polymers exhibit low-lying lowest unoccupied molecular orbital (LUMO) energy levels of around −3.8 eV and highest occupied molecular orbital (HOMO) energy levels ranging from −5.49 to −5.14 eV. Organic field-effect transistors based on the polymers exhibit ambipolar characteristics with high hole and electron mobilities in the order of 10⁻¹ cm² V⁻¹ s⁻¹ in air. These high mobilities can be attributed to the formation of highly crystalline lamellar structure with preferential edge-on orientation of the polymer thin films. Interestingly, the ratio of the electron to hole mobilities decreases with the extension of the donor units. This can be explained by the distribution of HOMOs and LUMOs along the backbones. Additionally, complementary inverters using the polymers with well-balanced ambipolar characteristics exhibit sharp switching characteristics with high gain of ≈140 at the supply voltage of 40 V.

Linear-fused naphthodithiophenes (NDTs) are emerging building blocks in the development of new semiconducting small molecules, oligomers, and polymers. The promising nature of NDT-based materials as organic semiconductors has been demonstrated by superior device characteristics in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs) in the last few years. In particular, it is quite impressive that a power conversion efficiency as high as 8.2% has been achieved for a single-junction OPV cell consisting of NDT-based semiconducting polymers and a fullerene derivative in such a short period of time. Here, we provide an overview of recent synthetic evolutions in NDT chemistry and progress in NDT-based materials, especially conjugated oligomers and polymers and their applications to OFETs and OPVs.