Chiral Molecular Carbon Nanostructures

Abstract

CONSPECTUS:Chirality is a fascinating property present in naturally occurring and artificial molecules and materials, observable as chiroptical behavior. The emerging area of carbon nanostructures has undergone tremendous development, with a wide variety of carbon nanoforms reported over the last two decades. However, despite interest in merging chirality and nanocarbons, this has been successfully achieved only in empty fullerenes, whereas in other kinds of fullerenes or carbon nanostructures such as carbon nanotubes, graphene, and graphene quantum dots (GQDs), to name the most popular systems, it is almost unknown. Therefore, controlling chirality in carbon nanostructures currently represents a major challenge for the chemical community. In this Account, we show our progress in the synthesis of chiral molecular carbon nanostructures, namely, metallofullerenes, endohedral fullerenes, GQDs, and curved molecular nanographenes, by using asymmetric catalysis and both topdown and bottom-up chemical approaches. Furthermore, we bring in a new family of lesser-known molecular chiral bilayer nanographenes, where chirality is introduced from the starting helicene moiety and a single enantiomer of the nanographene is synthesized. Some important landmarks in the development of chiral molecular carbon nanostructures shown in this Account are the application of synthesis-tailored, enantiomerically pure metallofullerenes as catalysts for hydrogen transfer reactions and the use of endohedral fullerenes to determine the effect of the incarcerated molecule in the carbon cage on the cis−trans stereoisomerization of optically active pendent moieties. Furthermore, the first top-down synthesis of chiral GQDs by functionalization with chiral alcohols is also presented. An emerging alternative to GQDs, when the desire for purity and atomistic control outweighs the cost of multistep synthesis, is the bottom-up approach, in which molecular nanographenes are formed in precise sizes and shapes and enantiomeric control is feasible. In this regard, a singular and amazing example is given by our synthesis of a single enantiomer of the first chiral bilayer nanographene, which formally represents a new family of molecular nanographenes with chirality controlled and maintained throughout their syntheses. The aforementioned synthetic chiral nanostructures represent groundbreaking nanocarbon systems where chirality is a further dimension of structural control, paving the way to a new scenario for carbon nanoforms in which chirality selection determines the properties of these novel carbon-based materials. Fine-tuning of such properties is envisioned to impact biomedical and materials science applications.

Vinyl‐/Furoindoles and Gold Catalysis: New Achievements and Future Perspectives for the Synthesis of Complex Indole Derivatives

“…Besides, metallo‐peptides find applications in the same field with the advantage that peptides can be conveniently prepared via automated methodologies . Moreover, application of different type of nanostructures underwent incredible expansion over the last years including in catalysis . The most developed materials include chiral nanostructures mainly organized in nanotube, nanocage and micelles and based on the assembly of small and medium sized molecules.…”

Fullerene Desymmetrization as a Means to Achieve Single‐Enantiomer Electron Acceptors with Maximized Chiroptical Responsiveness

“…To date, chiral fullerene derivatives have mostly been explored as an academic curiosity and in limited applications, with a notable exception perhaps being enantioselective catalysis. [ 23 ] Given the importance of this material class to organic electronic devices, it is curious that single‐enantiomer fullerene devices are yet to be explored in this context. This may be because the opportunities provided by chiral organic semiconducting materials are, in general, underexploited in technological applications.…”

Chiral Transition Metal Oxides: Synthesis, Chiral Origins, and Perspectives

“…The introduction of chirality to TMOs has revolutionized the motif of TMOs with respect to their applications in area of chiroptical sensing and detection, enantioselective catalysis, biological‐tissue‐based therapy, and chirality‐based devices. Since a body of related reviews has well summarized the details about the possible applications of chiral inorganic NCs, [ 6,47–55 ] we would prefer only to highlight some representative examples of chiral TMOs here: 1)Chiroptical sensing and detection: Xu and co‐workers [ 56 ] reported recently that chiral CuxOS@ZIF‐8 nanostructures can be used as ultrasensitive probe for detection of H 2 S in vivo with the limit of detection of 0.3 × 10 −9 and 2.2 × 10 −9 m for CD and fluorescence methods because H 2 S can reduce the chiroptical intensity and increase the fluorescent signal of the nanostructures ( Figure A). Jiang's group [ 57 ] also demonstrated that cysteine‐capped Au/Fe 3 O 4 NPs can enantioselectively detect the percentage of d ‐tyrosine in a mixture of enantiomers via cysteine as the chiral selector. 2)Enantioselective catalysis: Qu and co‐workers [ 58 ] developed phenylalanine‐modified cerium oxide nanoparticles (CeNPs) as chiral nanozyme for stereoselective oxidation of 3,4‐dihydroxyphenylalanine (DOPA) enantiomers where l ‐CeNP showed higher catalytic ability for oxidation of d ‐DOPA while d ‐CeNP were more effective to l ‐DOPA (Figure 4B).…”