A Fused [5]Helicene Dimer with a Figure‐Eight Topology: Synthesis, Chiral Resolution, and Electronic Properties

Abstract

Chiral shape‐persistent molecular nanocarbons are promising chiroptical materials; their synthesis, however, remains a big challenge. Herein, we report the facile synthesis and chiral resolution of a double‐stranded figure‐eight carbon nanobelt 1 in which two [5]helicene units are fused together. Two synthetic routes were developed, and, in particular, a strategy involving Suzuki coupling‐mediated macrocyclization followed by Bi(OTf)3‐catalyzed cyclization of vinyl ether turned out to be the most efficient. The structure of 1 was confirmed by X‐ray crystallographic analysis. The isolated (P,P)‐ and (M,M)‐ enantiomers show persistent chiroptical properties with relatively large dissymmetric factors (|gabs|=5.4×10−3 and |glum|=1.0×10−2), which can be explained by the effective electron delocalization along the fully conjugated belt and the unique D2 symmetry. 1 exhibits local aromatic character with a dominant structure containing eight Clar's aromatic sextet rings.

Infinitenes as the Most Stable Form of Cycloarenes: The Interplay among π Delocalization, Strain, and π–π Stacking

“…As an added note, during the review of this article, the facile synthesis of an n-butoxy-substituted [16]K-infinitene was reported. 112 We found that the molecular structure identified by X-ray crystallography corresponds exactly to the lowest-energy isomer of [16]infinitenes, [1,2,1,1,2,1|1,1,2,1,1,2](−1), as predicted in this work. Furthermore, we might find certain infinitene structures, among a multitude of proposed candidates, that possess enhanced or desirable properties.…”

“…With recent advances in the synthesis of looped polyarenes and in expanding kekulene and helicenes, we are confident to anticipate the expansion from the known [12] or [20]­infinitene to larger infinitenes in the foreseeable future. As an added note, during the review of this article, the facile synthesis of an n -butoxy-substituted [16]­K-infinitene was reported . We found that the molecular structure identified by X-ray crystallography corresponds exactly to the lowest-energy isomer of [16]­infinitenes, [1,2,1,1,2,1|1,1,2,1,1,2](−1), as predicted in this work.…”

CPL calculations of [7]helicenes with alleged exceptional emission dissymmetry values

“…The situation is common among [6]helicenes or smaller analogues 14,37,38,44,45,48,50,51,77 and may be tackled by different structural designs, such as double-helicenes, S-shaped or 8-shaped helical conjugated systems, elongated or extended helicenes. 46,77–84 Interestingly enough, in several of the just mentioned reports, the molecular design was steered by a preliminary computational screening, which confirms the demand for accurate computational approaches for property predictions.…”

Carbon Nanobelts: Brief History and Perspective

“…Since this report, fascinating properties of infinitene have been predicted. 70−78 Wu and Isobe et al synthesized a twisted CNB in 2021 and a fused [5]helicene dimer in 2023 79,80 as a related molecule of infinitene. In addition to aromatic hydrocarbon-based CNBs, heteroatom-embedded CNBs have also been reported.…”