Near‐Infrared‐Absorbing Chiral Open [60]Fullerenes

• Published in: Angewandte Chemie International Edition 2023-01, Vol.62 (2), p.e202215380-n/a
• Main Authors: Hashikawa, Yoshifumi, Sadai, Shumpei, Okamoto, Shu, Murata, Yasujiro
• Format: Article
• Language: English
• Subjects: Benzonitrile; Carbenes; Chirality; Chromophores; Circular dichroism; Dichroism; Fullerenes; Infrared absorption; Isomers; Near infrared radiation; Near-Infrared; Open Fullerenes; Organic chemistry; Ring Expansion; Symmetry
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202215380

Though [60]fullerene is an achiral molecular nanocarbon with Ih symmetry, it could attain an inherent chirality depending upon a functionalization pattern. The conventional chiral induction of C60 relies mainly upon a multiple addition affording a mixture of achiral and chiral isomers while their chiral function would be largely offset by the existence of pseudo‐mirror plane(s). These are major obstacles to proceed further study on fullerene chirality and yet leave its understanding elusive. Herein, we showcase a carbene‐mediated synthesis of C1‐symmetric chiral open [60]fullerenes showing an intense far‐red to near‐infrared absorption. The large dissymmetry factor of |gabs|=0.12 was achieved at λ=820 nm for circular dichroism in benzonitrile. This is, in general, unachievable by other small chiral organic molecules, demonstrating the potential usage of open [60]fullerenes as novel types of chiral chromophores. A dimethylaminocarbene‐mediated orifice expansion gave the first near‐infrared‐absorbing chiral open [60]fullerenes. The introduced aminomethylidene moiety is well‐conjugated with the fullerene cage, thus considerably elevating the HOMO level as supported by the electrochemical analysis. The optical resolution revealed a large dissymmetry factor of gabs=±0.12 at 820 nm in o‐dichlorobenzene.