Revealing the “AABB/ABAB Sequential Isomeric Effect” on Diketopyrrolopyrrole-Based All-acceptor Semiconducting Polymers

To achieve high-performance organic semiconducting materials is very important for next-generation electronic devices. Currently, the development of n-type organic semiconducting materials is far behind that of p-type ones. Constructing all-acceptor (A) semiconducting polymers (SPs) has emerged as an effective strategy to achieve high-performance n-type organic semiconducting materials. In this work, we design and synthesize two AABB/ABAB isomeric SPs, P(ThDPP-PyDPP) and PThPyDPP, based on thiophene/pyridine-flanked diketopyrrolopyrrole (DPP) derivatives. Both polymers exhibit low-lying lowest unoccupied molecular orbitals due to their all-acceptor backbones, making them good candidates for n-type semiconducting materials. Interestingly, although the two polymers have the same chemical composition and a similar backbone, they display strikingly different organic field-effect transistor (OFET) performances. The AABB isomer P(ThDPP-PyDPP) exhibits a higher OFET electron mobility (μe) of 2.52 × 10–2 cm2 V–1 s–1, which is 10 times higher than that of the ABAB isomer PThPyDPP (μe = 2.33 × 10–3 cm2 V–1 s–1). This is attributed to the fact that P(ThDPP-PyDPP) has a more planar backbone compared with that of PThPyDPP, which originated from the symmetric nature of the monomer in AABB-type polymers. Our investigation indicates that the “sequential AABB/ABAB isomerization” of the backbone has great effects on SPs and will provide an alternative strategy to design n-type SPs.