<p>We report on the
synthesis of diketopyrrolopyrrole (DPP) derivatives functionalized with
N-annulated and Se-annulated perylene diimide (NPDI and SePDI, respectively) <i>via
</i>direct (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 p-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 p-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. Different is that the SePDI‒DPP‒NPDI
compound has a distinct melt observed at 343 °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. </p>