Asymmetric B←N Functionalized Benzothiadiazoles for High‐Performance n‐Type Semiconducting Polymers

Abstract B←N containing polymers have emerged in organic electronics due to their fascinating optical and electronic properties. Despite these advantages, the development of B←N‐based n‐type polymers for high‐performance organic transistors remains a significant challenge, primarily due to the scarcity of effective B←N containing acceptor units. In this work, we address this challenge through the rational design and synthesis of two asymmetric half‐fused B←N functionalized benzothiadiazole derivatives, BTBN and FBTBN. These compounds leverage the unique electronic properties of the B←N motif, enabling the development of two new n‐type polymers, PBTBN and PFBTBN. Notably, the lowest unoccupied molecular orbital (LUMO) levels of PBTBN and PFBTBN are significantly lowered by 0.2–0.3 eV compared to their counterparts without B←N functionalization, with PFBTBN achieving a LUMO of ∼ −4.0 eV. Importantly, PFBTBN exhibits exceptional unipolar n‐type transistor performance with a high electron mobility ( µ e ) of 3.85 cm 2 V −1 s −1 . The asymmetric half‐fused B←N molecular backbone not only stabilizes the electronic structure but also induces a near‐amorphous morphology, thereby enabling PFBTBN‐based flexible transistors to retain a high µ e of 3.16 cm 2 V −1 s −1 even after 1000 bending cycles. This work demonstrates the transformative potential of incorporating asymmetric B←N functionalized acceptors for high‐performance n‐type semiconducting polymers.