Oligomerization of an orthogonally arranged donor–acceptor segregated molecule gave π-conjugated oligomers. The combined results of NMR, absorption, cyclic voltammetry, and DFT calculations supported the π-conjugation with both through-bond and through-space interactions.

Abstract

This study reports the synthesis, structural characterization, and physical properties of D–A segregated π-conjugated oligomers. Traditional D–A segregated structures are often achieved in solid states as co-crystals or supramolecular assemblies, making precise structural control challenging. Here, we developed novel π-conjugated oligomers with naphthobipyrrole as the donor and stacked fluoroarenes as the acceptor. Single-crystal X-ray analysis and NMR measurements confirmed the orthogonal arrangement of D and A moieties. DFT calculations revealed that the HOMO is delocalized on the naphthobipyrrole unit, while the LUMO is localized on the stacked fluoroarene moiety. Variable-temperature NMR spectroscopy demonstrated rotational motion of the naphthobipyrrole units, with an estimated energy barrier of 9–10 kcal/mol. Absorption and electrochemical measurements showed that oligomerization leads to an increase in the HOMO energy level and a decrease in the LUMO energy level, narrowing the HOMO–LUMO gap. These results indicate that oligomerization effectively maintains the D–A segregated electronic structure while extending π-conjugation. This study provides valuable insights for designing single-molecule conductors and contributes to future advancements in molecular electronics.