Diketopyrrolopyrrole Derivatives Functionalized with N-Annulated PDI and Se-Annulated PDI by Direct (Hetero)Arylation Methods

We report on the synthesis of diketopyrrolopyrrole (DPP) derivatives functionalized with N-annulated and Se-annulated perylene diimide (NPDI and SePDI, respectively)viadirect (hetero)arylation methods. DPP is symmetrically bifunctionalized with SePDI (SePDI-DPP-SePDI) and unsymmetrically functionalized with SePDI and NPDI (SePDI-DPP-NPDI). The effects of Se substitution compared to N substitution on physical, electrochemical, and optical properties are investigated along with performance as non-fullerene acceptors in photovoltaic devices. It is found that Se substitution increases the electron affinity of the pi-conjugated molecule and blue shifts the optical absorption spectra, observations that were supported by computational analysis. Steric strain between the PDI endcap and DPP core prevent complete electronic communication along the pi-conjugated backbone and results in the unsymmetrical compound, SePDI-DPP-NPDI, having electronic and optical properties that are a linear combination of both the symmetrical SePDI and NPDI based compounds. The SePDI-DPP-NPDI compound has a distinct melt observed at 343 degrees C and organic photovoltaic devices based on this compound had lower than expected open-circuit voltages, suggesting a unique solid-state packing arrangement. SePDI-based compounds performed worse than the NPDI-based compound in organic photovoltaic devices using the donor polymer PTB7-Th.