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Superoctazethrene: An Open-Shell Graphene-like Molecule Possessing Large Diradical Character but Still with Reasonable Stability

Zeng, Wangdong, Gopalakrishna, Tullimilli Y., Phan, Hoa, Tanaka, Takayuki, Herng, Tun Seng, Ding, Jun, Osuka, Atsuhiro, Wu, Jishan
Journal of the American Chemical Society 2018 v.140 no.43 pp. 14054-14058
electrochemistry, energy, gel chromatography
Laterally extended zethrenes can be regarded as Z-shaped nanographenes with four zigzag edges, but their synthesis is very challenging. Herein, we report the successful synthesis of by far the largest zethrene molecule, a superoctazethrene (SOZ) derivative SOZ-Cl, in crystalline form. Although the parent SOZ is calculated to have a very large diradical character (y₀ = 81.0%), SOZ-Cl shows reasonable stability (t₁/₂ = 64 h under ambient conditions) and can be purified by silica gel column chromatography. It exhibits a small electrochemical energy gap (Eg = 1.01 eV) and characteristics for open-shell singlet diradicaloids. Compared with a previously reported octazethrene derivative (OZ-TIPS), SOZ-Cl shows much larger diradical character (y₀ = 76.3% vs 43.4%) and smaller singlet–triplet gap (ΔES₋T = −2.30 kcal/mol vs −3.87 kcal/mol). Calculations also demonstrate global aromatic character of SOZ, but the smaller size octazethrene shows local aromaticity.