Toward Zigzag-edged Helical Nanographene Based on [7]Helicene.

Due to their unique chemical and physical properties, zigzag-edged nanographenes have attracted increasing interest in recent years. Herein, a novel zigzag-edged nanographene (6) containing a [7]helicene subunit was designed and synthesized. However, because of the high reactivities of zigzag edges, compound 1 with a diketone structure was obtained owing to the oxidation of 6. The helical carbon skeleton of 1 is unambiguously revealed by single-crystal X-ray crystallography analysis. The photophysical properties of the precursor and helical diketone 1 are studied by UV-vis absorption spectroscopy. The electrochemical property of 1 is investigated by cyclic voltammetry, which was further studied by density functional theory (DFT) calculations (ΔE =2.94 eV). The work reported here not only represents the synthesis of an unprecedented [7]helicene-embedded nanographene, but also provides the possibility for the synthesis of helical nanographenes with rich zigzag edges.