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Compressing a Non‐Planar Aromatic Heterocyclic [7]Helicene to a Planar Hetero[8]Circulene
Author(s) -
Lousen Bodil,
Pedersen Stephan K.,
Bols Pernille,
Hansen Kasper H.,
Pedersen Michelle R.,
Hammerich Ole,
Bondarchuk Sergey,
Minaev Boris,
Baryshnikov Glib V.,
Ågren Hans,
Pittelkow Michael
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201905339
Subject(s) - helicene , cyclooctatetraene , antiaromaticity , aromaticity , heteroatom , chemistry , molecule , thiophene , crystallography , stereochemistry , ring (chemistry) , organic chemistry
This work describes a synthetic approach where a non‐planar aromatic heterocyclic [7]helicene is compressed to yield a hetero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic [8]circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro‐hetero[7]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 [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically π‐conjugated [7]helicene to a fully planar heterocyclic [8]circulene significantly alters the spectroscopic properties of the molecules. Post‐functionalization of the [7]helicenes and the [8]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).