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

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.