Poly(diketopyrrolopyrrole- alt -bichalcogenophene)s from Direct Arylation Polycondensation: Effects of F, Cl, and CN Substitution

Efficient direct arylation polymerization (DArP) largely relies on the rational design of C–H monomers. In the current paper, three thiophene-flanked diketopyrrolopyrrole (ThDPP) derivatives, i.e., FDPP, ClDPP, and CNDPP, in which the β-positions of thiophene rings are substituted with electron-withdrawing groups (EWG) fluorine (F), chlorine (Cl), and cyano (CN) groups, respectively, were synthesized as C–H monomers. The DArP of the C–H monomers with ThDPP and selenophene-flanked DPP (SeDPP) C–Br monomers underwent efficiently, affording six low bandgap conjugated polymers, i.e., PFTh, PClTh, PCNTh, PFSe, PClSe, and PCNSe, with high molecular weights. The polymers based on FDPP and ClDPP (PFTh, PClTh, PFSe, and PClSe) show n-type-dominant ambipolar transport behavior. Of the four polymers, PFSe delivered the best device performance with maximum hole and electron mobilities of 0.76 and 1.86 cm 2 V –1 s –1, respectively. CN substitution substantially lowers the LUMO energy level of the polymers. Consequently, the CNDPP-based polymers PCNTh and PCNSe exhibited unipolar n-type transport characteristics with electron mobilities up to 0.42 cm 2 V –1 s –1 . The β-EWG substitution provides an effective strategy to concurrently enhance DArP reactivity and tune polymer properties without increasing backbone complexity. This work suggests poly(diketopyrrolopyrrole- alt -bichalcogenophene) as a versatile platform for the rational design of high-performance polymer semiconductors.