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Negatively Curved Nanographene with Heptagonal and [5]Helicene Units.

Zijie QiuSobi AsakoYingping ZouCheng-Wei JuThomas LiuLoïc RondinDieter SchollmeyerJean-Sebastien LauretKlaus MüllenAkimitsu Narita
Published in: Journal of the American Chemical Society (2020)
Negatively curved nanographene (NG) 4, having two heptagons and a [5]helicene, was unexpectedly obtained by aryl rearrangement and stepwise cyclodehydrogenations. X-ray crystallography confirmed the saddle-shaped structures of intermediate 3 and NG 4. The favorability of rearrangement over helicene formation following radical cation or arenium cation mechanisms is supported by theoretical calculations. NG 4 demonstrates a reversible mechanochromic color change and solid-state emission, presumably benefiting from its loose crystal packing. After resolution by chiral high-performance liquid chromatography, the circular dichroism spectra of enantiomers 4-(P) and 4-(M) were measured and showed moderate Cotton effects at 350 nm (|Δε| = 148 M-1 cm-1).
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