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Helically chiral mixed-valence systems comprising N-heterotriangulenes: stabilization of the cationic species by π-Expansion

We report the efficient stabilization of nitrogen-centered radical cations in a dimeric N-heterotriangulene bridged by a rigid π-conjugated [5]helicene backbone (NTH). The rigid scaffold exhibits helical chirality, allowing the enantiomers to be separated and their chiroptical properties studied, in...

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Main Authors: Borstelmann, Jan (Author) , Zank, Simon (Author) , Krug, Marcel (Author) , Berger, Georg (Author) , Fröhlich, Nina (Author) , Glotz, Gabriel (Author) , Gnannt, Frederik (Author) , Schneider, Lars (Author) , Rominger, Frank (Author) , Deschler, Felix (Author) , Clark, Timothy (Author) , Gescheidt, Georg (Author) , Guldi, Dirk M. (Author) , Kivala, Milan (Author)
Format: Article (Journal)
Language:English
Published: April 11, 2025
In: Angewandte Chemie. International edition
Year: 2025, Volume: 64, Issue: 16, Pages: 1-11
ISSN:1521-3773
DOI:10.1002/anie.202423516
Online Access:Verlag, kostenfrei, Volltext: https://doi.org/10.1002/anie.202423516
Verlag, kostenfrei, Volltext: https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202423516
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Author Notes:Jan Borstelmann, Simon Zank, Marcel Krug, Georg Berger, Nina Fröhlich, Gabriel Glotz, Frederik Gnannt, Lars Schneider, Frank Rominger, Felix Deschler, Timothy Clark, Georg Gescheidt, Dirk M. Guldi, and Milan Kivala
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Summary:We report the efficient stabilization of nitrogen-centered radical cations in a dimeric N-heterotriangulene bridged by a rigid π-conjugated [5]helicene backbone (NTH). The rigid scaffold exhibits helical chirality, allowing the enantiomers to be separated and their chiroptical properties studied, including circular dichroism (CD) and circularly polarized luminescence (CPL). Successive oxidation towards the radical cation NTH⋅+ and dication NTH2+ reveals strong electronic communication between the two nitrogen-centers, as demonstrated by X-ray crystallography, electrochemistry, UV/Vis/nIR spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. CD measurements of the enantiomerically pure cations reveal strong Cotton effects in the nIR region extending up to 2000 nm. Density functional theory confirms the observed enhanced electronic communication, classifying NTH⋅+ as a Robin-Day Class III mixed-valence charge-transfer (MV-CT) system. NTH2+ exhibits a quinoidal structure with partial diradical character and open-shell singlet ground state, as shown by variable temperature EPR measurements. Time-resolved transient absorption spectroscopy shows the photo-induced generation of NTH⋅+ in the presence of a suitable electron acceptor.
Item Description:Online veröffentlicht am 10. Februar 2025
Gesehen am 18.08.2025
Physical Description:Online Resource
ISSN:1521-3773
DOI:10.1002/anie.202423516

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