Dithienonaphthobisthiadiazole synthesized by thienannulation of electron-deficient rings: an acceptor building unit for high-performance π-conjugated polymers†

The development of building units for π-conjugated polymers is a driving force in advancing the field of organic electronics. In this study, we designed and synthesized dithienonaphthobisthiadiazole (TNT) as a thiophene-fused acceptor (A) building unit and two TNT-based π-conjugated polymers named PTNT2T and PTNT1-F. We found that the microwave-assisted thiophene annulation reaction (thienannulation) of arylethynylated naphthobisthiadiazole (NTz) via C–H functionalization effectively produced TNT moieties. With the π-extended structure of TNT, the polymers had rigid backbones that benefited in-plane and out-of-plane charge carrier transport. Organic field-effect transistors (OFETs) based on PTNT2T exhibited hole mobilities as high as 1.10 cm² V⁻¹ s⁻¹. Furthermore, organic photovoltaic cells (OPVs) based on PTNT1-F showed high power conversion efficiencies of up to 17.4% when combined with a nonfullerene acceptor. This work provides an efficient method for the thienannulation of electron-deficient rings to access thiophene-fused A building units and shows the great promise of TNT as a building unit for high-performance π-conjugated polymers for organic electronic devices.