Endohedral Fullerene Complexes and Molecular Encapsulation

Endohedral fullerenes are hollow carbon cages, typically C₆₀ or C₇₀, within which atoms, ions or small molecules are permanently enclosed. This encapsulation alters both the electronic and mechanical properties of the host cage and the confined guest, giving rise to unique quantum phenomena, spin dynamics and enhanced stability. Synthetic approaches range from high-pressure filling and photochemical orifice contraction to precise “molecular surgery,” in which a temporary opening is created in the carbon framework to admit the guest and is subsequently repaired. These techniques have enabled the study of free-rotor behaviour of enclosed molecules, superatom molecular orbitals, spin-isomer conversion and record-breaking chiroptical responses. The interplay of host–guest interactions under confinement has implications for molecular electronics, quantum information science, magnetic resonance imaging contrast agents and targeted drug delivery. Rapid advances in synthesis and characterisation are driving the field towards scalable production and real-world applications in nanotechnology and materials science.

Research from Nature Portfolio

Recent synthetic breakthroughs have produced inherently chiral inter-[60]fullerene conjugates comprising two covalently linked C₆₀ cages. Crystallographic analyses reveal double-caged architectures that assemble into tetrahedral tetra-cage clusters via heterochiral recognition. These conjugates exhibit intense absorptions, strong electronic communication in reduced states and unprecedented dissymmetry factors in chiroptical measurements, opening avenues for chiral photonics and enantioselective catalysis under nanoscale confinement.

Advances in the “molecular surgery” methodology have refined the sequence of cage opening, guest insertion and cage closure. By optimising key steps for both C₆₀ and C₇₀ hosts, recent work has expanded the scope of encapsulated species to include noble gases, small metal clusters and diatomic molecules. Comprehensive reviews of cage-opening chemistries and closure strategies now guide reproducible preparations of high-purity endohedral fullerenes on scales compatible with spectroscopic and device-level investigations.

Endohedral Fullerene Complexes and Molecular Encapsulation publication trend

The graph below shows the total number of articles in endohedral fullerene complexes and molecular encapsulation across all publications each year (not limited to Nature Index journals).

Technical terms

Endohedral fullerene: A molecular complex in which one or more atoms, ions or molecules are trapped inside a hollow carbon cage.

Molecular surgery: A synthetic approach involving the controlled opening of a fullerene cage, insertion of a guest species and reclosure of the cage to form an endohedral complex.

Orifice contraction: The photochemical or chemical process that seals an open-cage fullerene after guest encapsulation.

Superatom molecular orbitals (SAMOs): Delocalised electronic states in fullerenes that extend beyond the conventional πsystem, resembling atomic-like orbitals in energy and symmetry.

Ortho-para conversion: The interconversion between nuclear-spin isomers of a homonuclear molecule, such as H₂O or H₂, confined within a host cage.

References

1. Synthesis of inter-[60]fullerene conjugates with inherent chirality. Nature Communications (2024).
2. Synthesis of endohedral fullerenes by molecular surgery. Communications Chemistry (2022).
3. First Synthesis and Characterization of CH4@C60. Angewandte Chemie International Edition (2019).
4. Infrared spectroscopy of an endohedral water in fullerene. The Journal of Chemical Physics (2021).
5. Encapsulation of a Water Molecule inside C60 Fullerene: The Impact of Confinement on Quantum Features. Journal of Chemical Theory and Computation (2021).