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Helical Nanographenes Containing an Azulene Unit: Synthesis, Crystal Structures, and Properties
Author(s) -
Ma Ji,
Fu Yubin,
Dmitrieva Evgenia,
Liu Fupin,
Komber Hartmut,
Hennersdorf Felix,
Popov Alexey A.,
Weigand Jan J.,
Liu Junzhi,
Feng Xinliang
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201914716
Subject(s) - azulene , antiaromaticity , density functional theory , chemistry , steric effects , crystallography , crystal structure , electron paramagnetic resonance , cyclic voltammetry , molecule , materials science , photochemistry , computational chemistry , aromaticity , stereochemistry , nuclear magnetic resonance , electrochemistry , organic chemistry , physics , electrode
Three unprecedented helical nanographenes ( 1 , 2 , and 3 ) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X‐ray crystallographic analysis. The embedded azulene unit in 2 possesses a record‐high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis‐spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps ( 2 : 1.88 eV; 3 : 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in‐situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties.