American Chemical Society
ja0c05504_si_002.cif (2.62 MB)

Negatively Curved Nanographene with Heptagonal and [5]Helicene Units

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posted on 2020-08-24, 21:29 authored by Zijie Qiu, Sobi Asako, Yunbin Hu, Cheng-Wei Ju, Thomas Liu, Loïc Rondin, Dieter Schollmeyer, Jean-Sébastien Lauret, Klaus Müllen, Akimitsu Narita
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).