Peri-pentacene and Peri-hexacene Diradicaloids

Peri-acenes are valuable models for zigzag-edged graphene nanoribbons, but their synthesis poses significant challenges. In this study, stable derivatives of peri-pentacene (Peri-P) and peri-hexacene (Peri-H) were synthesized. Through kinetic blocking and a synergistic captodative effect, both compounds displayed remarkable stability under ambient air and light conditions. They show significant diradical character (y₀), with y₀ = 75.4% for Peri-P and y₀ = 90.7% for Peri-H, alongside narrow singlet-triplet energy gaps of -1.68 ± 0.04 and -1.28 ± 0.02 kcal/mol, respectively. The structure of Peri-H was confirmed by X-ray crystallography, with bond-length analysis and theoretical calculations indicating a dominant structure featuring five aromatic sextet rings. Their optical and electrochemical properties were also studied and compared to those of smaller peri-acenes.