Cyclopenta-fused polyaromatic hydrocarbons: synthesis and characterisation of a stable, carbon-centred helical radical

• Published in: Organic & biomolecular chemistry 2022-04, Vol.2 (14), p.2873-288
• Main Authors: Herzog, Stefan, Hinz, Alexander, Breher, Frank, Podlech, Joachim
• Format: Article
• Language: English
• Subjects: Benzene; Carbon; Conjugation; Crystallography; Crystallography, X-Ray; Cyclization; Hydrocarbons; Hydrocarbons, Aromatic; Moisture effects; Polyaromatic hydrocarbons; Polycyclic aromatic hydrocarbons; Polycyclic Aromatic Hydrocarbons - chemistry; Quantum chemistry; Spectroscopy; Spectrum analysis
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/d2ob00172a

An air- and moisture-stable helical radical with seven six- and five-membered rings arranged alternately was synthesized by cyclizations in a suitably ortho , ortho ′-substituted terphenyl and re-establishment of its conjugation. Mesityl groups at the five-membered rings prevent radical reactions. This cyclopenta-fused polyaromatic hydrocarbon (CP-PAH) was characterized by X-ray crystallographic analysis, EPR and UV/Vis spectroscopy, and by cyclic voltammetry. Further properties and spectra were determined by quantum chemical calculation (spin densities, orbital energies, UV/Vis/NIR and ECD spectra). It turned out that this radical is best described with its radical centre being in the outer five-membered rings, which allows for the largest number of fully intact benzene rings. Its triradical character is rather small and can be neglected. The five-membered rings show significant antiaromatic character, which is highest in the central ring. An air- and moisture-stable helical radical with seven six- and five-membered rings arranged alternately was synthesized by cyclizations in a suitably ortho , ortho ′-substituted terphenyl and re-establishment of its conjugation.