Negatively Curved Nanographene with Heptagonal and [5]Helicene Units
Zijie Qiu, Sobi Asako, Yunbin Hu, Cheng‐Wei Ju, Thomas Liu, Loïc Rondin, Dieter Schollmeyer, Jean‐Sébastien Lauret, Kläus Müllen, Akimitsu Narita
Abstract
High Resolution Image Download MS PowerPoint Slide 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 ).