Bithiazole Dicarboxylate Ester: An Easily Accessible Electron-Deficient Building Unit for π-Conjugated Polymers Enabling Electron Transport

Abstract

Thiazole has been less focused, compared to thiophene, as the building unit for π-conjugated polymers that are used in organic electronic devices despite its electron deficiency and ability to coplanarize the polymer backbone, which are crucial for design of such π-conjugated polymers. Here, we show that bithiazole dicarboxylate ester (BETz), which is quite easily synthesized, is a promising building unit for π-conjugated polymers. Copolymers based on BETz, having unsubstituted bithiophene and bithiazole as counits, indeed form highly crystalline structures in thin films, which is beneficial for semiconducting properties. Of particular interest is that the BETz-based polymers are found to show electron-transport property even though the lowest unoccupied molecular orbital (LUMO) energy levels are not very low, as they show ambipolar and unipolar n-channel behaviors depending on the counit in organic transistor devices. We believe that BETz allows us to design a wide variety of π-conjugated polymers that provide fascinating functions in organic electronic devices.