Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Functional Metallofullerene Materials and Their Applications in Nanomedicine, Magnetics, and Electronics

Endohedral metallofullerenes exhibit combined properties from carbon cages as well as internal metal moieties and have great potential in a wide range of applications as molecule materials. Along with the breakthrough of mass production of metallofullerenes, their applied research has been greatly developed with more and more new functions and practical applications. For gadolinium metallofullerenes, their water-soluble derivatives have been demonstrated with antitumor activity and unprecedented tumor vascular-targeting therapy. Metallofullerene water-soluble derivatives also can be applied to treat reactive oxygen species (ROS)-induced diseases due to their high antioxidative activity. For magnetic metallofullerenes, the internal electron spin and metal species bring about spin sensitivity, molecular magnets, and spin quantum qubits, which have many promising applications. Metallofullerenes are significant candidates for fabricating useful electronic devices because of their various electronic structures. This Review provides a summary of the metallofullerene studies reported recently, in the fields of tumor inhibition, tumor vascular-targeting therapies, antioxidative activity, spin probes, single-molecule magnets, spin qubits, and electronic devices. This is not an exhaustive summary and there are many other important study results regarding metallofullerenes. All of this research has revealed the irreplaceable role of metallofullerene materials.

Triptycene molecular rotors mounted on metallofullerene Sc3C2@C80 and their spin-rotation couplings

Molecular machines have received considerable attention due to their various applications. Except for mechanical motion, it is essential to design advanced molecular machines with integrated functions. In this study, the triptycene rotor has been covalently linked to paramagnetic metallofullerene Sc3C2@C80 with an unpaired electron spin, resulting in a coupled system between spin flip and rotor speed. Two types of triptycene rotors were employed, one is pristine triptycene and another one has a sterically hindered methyl group. Temperature-dependent electron paramagnetic resonance (EPR) spectroscopy revealed that spin-rotor coupling can be modulated by the rotation speed of triptycene rotors, which was further illustrated by variable-temperature 1H NMR. EPR simulation revealed that the rotations of the attached triptycene rotors can greatly influence the spin relaxation and spin-metal hyperfine couplings of Sc3C2@C80, realizing remote control on neighboring electron spin states. These findings of the coupled system between the molecular rotor and spin flip would provide an approach to design advanced molecular machines with magnetic function.

An implanted paramagnetic metallofullerene probe within a metal-organic framework

Paramagnetic endohedral metallofullerene can be used as a molecular probe because of its sensitive electron spin characters, one of which is to sense its surroundings. Metal-organic framework (MOF) materials have significant applications in selective adsorption owing to their porous structures. Herein, we report a Sc₃C₂@C₈₀ spin probe implanted in MOF-177 to detect the unusual host-guest interaction between the guest molecules of metallofullerene and the host pores of the MOF. Paramagnetic Sc₃C₂@C₈₀ molecules were incorporated into the pores of MOF-177 via absorption method, and there was strong π-π interaction between oleophilic metallofullerene and aromatic framework. The electron paramagnetic resonance (EPR) signals of Sc₃C₂@C₈₀ in MOF-177 exhibit anisotropic properties caused by the restricted motion of implanted Sc₃C₂@C₈₀. This unusual host-guest interaction between Sc₃C₂@C₈₀ and MOF-177 is gradually strengthened with decreasing temperature as revealed by the EPR signals. In addition, the gas desorption from the MOF-177 pores under subatmospheric pressure can weaken the host-guest interaction and lead to slightly enhanced Sc₃C₂@C₈₀ EPR signals. Furthermore, the changes in the host-guest interaction between Sc₃C₂@C₈₀ and MOF-177 at different temperatures and pressures exhibit reversibility, as shown by cycling EPR measurements. These results will inspire material design and applications of fullerene and MOF complexes.