Authors
Jeppe S Mogensen, Christoffer Bræstrup, Christoffer Warming, Georg I Junker, Yann Lie, Mathias Hermann, Kurt V Mikkelsen, Michael Pittelkow
Published in
Angewandte Chemie (International ed. in English). Pages e2703281. Aug 14, 2026. Epub Aug 14, 2026.
Abstract
Helicenes are attractive emitters of circularly polarized light, yet strategies to enhance their luminescence dissymmetry factor (glum) remain underdeveloped. Herein, we report a scalable, facile synthetic route to hetero[9]helicenes utilizing a benzofuran scaffolding strategy. This efficient one-pot protocol provides access to the hetero[9]helicenes at gram scale, enabling progressive axial elongation to hetero[12]- and hetero[15]helicenes. Structural characterization by NMR and single-crystal xX-ray diffraction confirms increasing helical distortion and reduced helical pitch upon elongation. Chiroptical investigations reveal a pronounced enhancement of both absorption (gabs) and emission (glum) dissymmetry factors with increasing ring count. Notably, annulation with a three-ring extension via a naphtofuran unit yields a twofold increase in glum, reaching 1.95 × 10-2 at 475 nm for the [15]helicene. TD-DFT calculations reproduce these trends, revealing that the enhancement originates from a systematic decrease in the electric transition dipole moment while the magnetic transition dipole moment remains constant, thereby increasing the relative magnetic contribution to the S1 →S0 transition as well as the angle between the dipole moments. These findings establish axial elongation as a robust design principle for amplifying chiroptical responses in helicenes.
PMID:
42599820
Bibliographic data and abstract were imported from PubMed on 15 Aug 2026.
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