Enhancing Chiroptical Responses in Helical Nanographenes via Geometric Engineering of Double [7]Helicenes

Helical nanographenes with high quantum yields and strong chiroptical responses are pivotal for developing circularly polarized luminescence (CPL) materials. Here, we present the successful synthesis of novel π‐extended double [7]helicenes (ED7Hs) where two helicene units are fused at the meta‐ or p...

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Published inAngewandte Chemie International Edition Vol. 63; no. 19; pp. e202319874 - n/a
Main Authors Niu, Wenhui, Fu, Yubin, Deng, Qingsong, Qiu, Zhen‐Lin, Liu, Fupin, Popov, Alexey A., Komber, Hartmut, Ma, Ji, Feng, Xinliang
Format Journal Article
LanguageEnglish
Published Germany Wiley Subscription Services, Inc 06.05.2024
EditionInternational ed. in English
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Summary:Helical nanographenes with high quantum yields and strong chiroptical responses are pivotal for developing circularly polarized luminescence (CPL) materials. Here, we present the successful synthesis of novel π‐extended double [7]helicenes (ED7Hs) where two helicene units are fused at the meta‐ or para‐position of the middle benzene ring, respectively, as the structural isomers of the reported ortho‐fused ED7H. The structural geometry of these ED7Hs is clearly characterized by single‐crystal X‐ray analysis. Notably, this class of ED7Hs exhibits bright luminescence with high quantum yields exceeding 40 %. Through geometric regulation of two embedded [7]helicene units from ortho‐, meta‐ to para‐position, these ED7Hs display exceptional amplification in chiroptical responses. This enhancement is evident in a remarkable approximate fivefold increase in the absorbance and luminescence dissymmetry factors (gabs and glum), respectively, along with a boosted CPL brightness up to 176 M−1 cm−1, surpassing the performance of most helicene‐based chiral NGs. Furthermore, DFT calculations elucidate that the geometric adjustment of two [7]helicene units allows the precise alignment of electric and magnetic transition dipole moments, leading to the observed enhancement of their chiroptical responses. This study offers an effective strategy for magnifying the CPL performance in chiral NGs, promoting their expanded application as CPL emitters. π‐Extended helical nanographenes (ED7Hs) have been synthesized where the two embedded [7]helicene units are fused at the ortho‐, meta‐ or para‐position of the middle benzene ring, respectively. The obtained ED7Hs display exceptional fivefold amplification in chiroptical responses with enhanced circularly polarized luminescence (CPL) brightness up to 176 M−1 cm−1.
Bibliography:These authors contributed equally to this work.
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ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202319874