Electronic Diversity and Charge-Transport Properties of DPP Semiconductors: A Comparative DFT/TD-DFT Study

Diketopyrrolopyrrole (DPP)-based semiconductors represent a versatile class of π-conjugated materials whose optoelectronic behavior can be effectively tuned through terminal-skeleton engineering. In this work, we present a comparative DFT/TD-DFT investigation of ten DPP derivatives in order to clarify how structural variation governs their electronic structure, optical response, excited-state character, and charge-transport tendencies. Benchmark calculations performed against the experimental frontier orbital energies of C10 identified B3PW91/6-31+G(d,p) as the most suitable computational level for the studied series. The results show that most compounds retain largely planar backbones, whereas localized torsional variations act as important modulators of conjugation. The calculated HOMO and LUMO energies span from −4.99 to −5.64 eV and from −2.74 to −3.95 eV, respectively, revealing substantial electronic diversity across the molecular set. TD-DFT analysis indicates that C8 is a promising candidate for near-infrared photodetection due to its narrow bandgap and pronounced charge-transfer character. Within the donor-relevant subset, C9 emerges as the most balanced photovoltaic candidate, combining favorable donor-side energetic alignment with a strong optical response, whereas C10 exhibits a more pronounced electron-transport tendency due to its relatively low electron reorganization energy. By combining intrinsic CT/LE contributions with the Δr and Λ descriptors, the present study distinguishes formal donor–acceptor polarization from genuinely spatially separated charge-transfer excitation. Overall, this work provides a consistent structure–property framework for the evaluation and design of DPP-based organic semiconductors.