Compressing a Non-Planar Aromatic Heterocyclic Helicene to a Planar Hetero Circulene

Pittelkow, M., Lousen, B., Pedersen, S. K., Bols, P. S., Pedersen, M. R., Hansen, K. H., Hammerich, O., Bondarchuk, S. V., Minaev, B. F., Baryshnikov, G. V., Agren, H. (2020) Compressing a Non-Planar Aromatic Heterocyclic Helicene to a Planar Hetero Circulene. Chem.-Eur. J, Vol.26 (N 22). с. 4935-4940.

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Резюме

This work describes a synthetic approach where a non-planar aromatic heterocyclic helicene is compressed to yield a hetero irculene containing an inner antiaromatic cyclooctatetraene (COT) core. This circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro-hetero helicene, which is partially a helicene and partially a circulene: it is non-planar and helically chiral as helicenes, and contains a COT motif like circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically p-conjugated helicene to a fully planar heterocyclic circulene significantly alters the spectroscopic properties of the molecules. Post-functionalization of the helicenes and the circulenes by oxygenation of the thiophene rings to the corresponding thiophene-sulfones allows an almost complete fluorescence emission coverage of the visible region of the optical spectrum (400–700 nm).

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