Non-planar nanographenes have potential electronic and optical applications because of their unique physical properties. However, the synthesis of such distorted molecules can be challenging.

Takayuki Tanaka, Kyoto University, Japan, and colleagues have synthesized the new hetero-nanographene molecule pentabenzopentaaza[10]circulene (pictured on the right). The team constructed the ten-membered ring inside a polycondensed aromatic structure via a so-called “fold-in” oxidative fusion reaction of an orthophenylene-bridged cyclic pyrrole pentamer (pictured on the left). The product is the largest fully conjugated hetero[n]circulene reported so far and has a saddle-like distorted structure.

Pentabenzopentaaza[10]circulene shows broad absorption and fluorescence spectra because of its flexible structure. The energy barrier for saddle-to-saddle interconversion in solution is small (approximately 3 kcal/mol). The researchers suggest that the synthesis method could be used to prepare even larger macrocycles.

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• Fold‐in Synthesis of a Pentabenzopentaaza[10]circulene,
  Yusuke Matsuo, Koki Kise, Yuki Morimoto, Atsuhiro Osuka, Takayuki Tanaka,
  Angew. Chem. Int. Ed. 2022.
  https://doi.org/10.1002/anie.202116789