Defect Analysis of High Electron Mobility Diketopyrrolopyrrole Copolymers Made by Direct Arylation Polycondensation

Defect structures in high-performance conjugated polymers are generally known but still challenging to characterize on a quantitative basis. Here, we present a detailed analysis of backbone topology of a series of copolymers PDPPTh2F4 having alternating dithienyldiketopyrrolopyrrole (DPPTh2) and tetrafluorobenzene (F-4) units made by direct arylation polycondensation (DAP). In contrast to early expectations of unselective C-H activation during the DAP of monomers with multiple C-H bonds, detailed structure analysis by high-temperature H-1 NMR spectroscopy reveals well-defined and alternating backbones with a quantifiable amount of 0-12% DPPTh2 homocouplings as the only defect structure in the main chain. Homocoupled -DPPTh2-DPPTh2- structural units are additionally characterized by UV-vis spectroscopy. While -DPPTh2-H end groups are inert to other side reactions, -F-4-Br end groups are weakly susceptible to both dehalogenation and reaction with toluene. However, despite the presence of DPPTh2 homocouplings, high field-effect transistor electron mobilities up to similar to 0.6 cm(2)/(V s) are achieved. This study highlights both that DPPTh2 homocouplings pose a prevalent structural defect in DPPTh2-based conjugated polymers made by DAP and that a very simple four-step DAP protocol can yield materials with varying molar mass and excellent n-type transistor performance.