Fullerenes and Buckyballs

Fullerenes are hollow molecules made entirely of carbon atoms arranged in closed, cage-like structures. The best-known fullerene is C60, also called a buckyball or buckminsterfullerene, whose 60 carbon atoms form a soccer-ball-like shape.

Also known as: buckminsterfullerene, C60, buckyball, carbon cage molecule, fullerene molecule.

Key term	A fullerene is a closed-cage molecule made only of carbon.
Buckyball	The common name for C60 buckminsterfullerene.
Formula	C60 for the classic buckyball.
Size	About 0.7 nm in diameter.
Shape	A truncated icosahedron with 12 pentagons and 20 hexagons.
Main uses	Organic electronics, photovoltaics, photodynamic therapy, nanomedicine, catalysis, and quantum-information research.

On this page: Definition Fullerene vs. buckyball C60 structure Discovery Types How they are made Properties Uses Comparison Safety FAQ

What Are Fullerenes?

A fullerene can be thought of as a nanoscale carbon cage. Unlike graphene, which is a flat sheet, or carbon nanotubes, which are cylinders, a fullerene is a closed molecule. The C60 buckyball is the most famous example because its atoms form the same pattern of pentagons and hexagons seen on a soccer ball.

Fullerenes are a family of pure carbon molecules in which the atoms are arranged at the vertices of closed, hollow structures built from pentagons and hexagons. Larger fullerenes such as C70, C76, C84, and C96 retain the rule of 12 pentagons but add hexagons, producing more elongated cages.

Together with diamond, graphite, graphene, and carbon nanotubes, fullerenes form one of the principal carbon allotropes studied in nanotechnology. They sit alongside other carbon nanomaterials as zero-dimensional, molecular building blocks with unusual electronic, optical, and chemical behavior.

Fullerene vs. Buckyball: What Is the Difference?

A fullerene is any closed-cage carbon molecule. A buckyball usually refers specifically to C60, the spherical fullerene also known as buckminsterfullerene. In other words, C60 is a fullerene, but not every fullerene is a buckyball.

Infographic showing the C60 buckyball fullerene structure, its carbon cage geometry, comparison with graphene and carbon nanotubes, and applications in organic electronics, nanomedicine, and catalysis.

Structure of C60 Buckminsterfullerene

A C60 molecule has a diameter of roughly 0.7 nm, placing it firmly at the lower end of the nanoscale. Its 60 atoms occupy 60 vertices and form 90 bonds across 12 pentagonal and 20 hexagonal faces. This geometry is a truncated icosahedron, the same shape used to describe the panels of a soccer ball.

Each carbon atom in C60 is bonded to three neighbors using sp2 hybridization, with one electron contributing to a delocalized π system spread across the cage. Two distinct bond lengths occur: shorter bonds shared between two hexagons and longer bonds shared between a hexagon and a pentagon. The pentagons enforce curvature, since a flat sp2 lattice such as graphene uses only hexagons.

Although C60 is highly symmetric and its π electrons are extensively delocalized, the curvature forces sp2 carbons to deviate from planarity. This pyramidalization helps make fullerenes strong electron acceptors: C60 can accept up to six electrons reversibly in solution. The molecule's high symmetry also gives it a sharp set of vibrational modes that can be fingerprinted by Raman spectroscopy and infrared absorption, and its structure has been imaged directly by high-resolution transmission electron microscopy.

How Were Fullerenes Discovered?

The discovery of fullerenes is rooted in astrophysics rather than nanotechnology. In 1985, Harold Kroto, Robert Curl, and Richard Smalley vaporized graphite with a pulsed laser at Rice University to study how long carbon chains might form in the atmospheres of red giant stars. Mass spectrometry of the resulting carbon clusters repeatedly showed a dominant peak at 720 atomic mass units, corresponding to a remarkably stable cluster of 60 carbon atoms. Proposing that the cluster had the shape of a truncated icosahedron, they named it buckminsterfullerene. Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for the discovery.

For five years, C60 remained accessible only as a tiny mass-spectrometer signal. The breakthrough came in 1990, when Wolfgang Krätschmer, Donald Huffman, and colleagues showed that an electric arc between graphite rods in a low-pressure helium atmosphere produces fullerene-rich soot from which milligram and gram quantities of C60 can be extracted with organic solvents. This synthesis turned fullerenes from a theoretical curiosity into a real material that could be studied, characterized, and modified.

Types and Examples of Fullerenes

The fullerene family includes many cages, encapsulates, and functionalized molecules. Common examples include:

C60: the classic spherical buckyball.
C70: an elongated fullerene molecule.
Higher fullerenes: larger cages such as C76, C78, C82, and C84, often with multiple structural isomers.
Endohedral fullerenes: cages containing atoms or small molecules inside, such as metallofullerenes M@C82 or N@C60.
Functionalized fullerenes: chemically modified cages used in electronics, medicine, and materials research.
Heterofullerenes: fullerene cages in which one or more carbon atoms are replaced by another element such as boron or nitrogen.

Functionalized fullerenes, sometimes called exohedral fullerenes, carry chemical groups covalently attached to the outer surface. This surface chemistry is the entry point for most biomedical and electronic applications because it controls solubility, energy levels, biocompatibility, and self-assembly.

How Are Fullerenes Made?

The Krätschmer–Huffman arc-discharge method remains the most widely used route to C60 and C70: graphite electrodes are vaporized in a partial pressure of helium, and the resulting soot is extracted with toluene or carbon disulfide and chromatographically separated. Combustion synthesis, in which a benzene–oxygen flame is operated under fuel-rich conditions, can produce fullerenes continuously and has been operated at production scale, although arc-based methods remain the dominant industrial route. Laser ablation of graphite generates fullerenes in smaller amounts but with cleaner control of cluster size.

Yields and selectivity remain limiting. Crude fullerene soot is dominated by C60 followed by C70, with smaller amounts of higher fullerenes, and isolating pure individual species can require multi-stage chromatography. Endohedral fullerenes are made by including the encapsulated species in the carbon source, for example by doping graphite rods with a metal salt, but yields are typically very low. A route called molecular surgery chemically opens a fullerene cage, loads a guest such as H2, H2O, or HF, and reseals it, giving controlled access to small-molecule endohedral fullerenes.

Properties of Fullerenes

C60 is a soft brown solid in pure form and crystallizes into a face-centered cubic lattice held together by van der Waals forces. The molecule is soluble in nonpolar aromatic solvents such as toluene, giving a magenta solution, and carbon disulfide, but it is insoluble in water. This limited water solubility historically restricted biomedical applications until water-soluble derivatives such as fullerenols and carboxyfullerenes were developed through surface functionalization.

Electron acceptor behavior: Fullerenes are exceptional electron acceptors. C60 can be reduced reversibly to C606− in solution, which helps explain its use in organic photovoltaics, electron-transport layers, and photochemistry.

Optical and photochemical behavior: Pristine C60 has a HOMO–LUMO gap of about 1.7 eV and absorbs strongly in the ultraviolet and weakly across the visible. Photoexcited fullerenes generate triplet states efficiently and can produce singlet oxygen, a property exploited in photodynamic therapy and photocatalysis.

Mechanical and solid-state behavior: Individual fullerene molecules are stiff, while solid C60 is held together by weaker intermolecular forces. Alkali-doped fullerides such as K3C60 are superconducting below about 19 K, and high-pressure treatment can polymerize C60 into ultrahard carbon phases.

What Are Fullerenes Used For?

Functionalization is the gateway to most fullerene applications, since pristine C60 is hydrophobic and difficult to disperse in polar media. Substituents such as carboxylic acids, malonates, hydroxyls, or polyethylene-glycol chains can be installed on the cage to control solubility, biocompatibility, electronic energy levels, and self-assembly behavior. The most familiar derivative is PCBM ([6,6]-phenyl-C61-butyric acid methyl ester), which dominated organic photovoltaic research for two decades and remains a benchmark electron acceptor.

Organic photovoltaics and electronics

Fullerenes were the original electron acceptors in bulk-heterojunction organic photovoltaics. Blended with a conjugated polymer donor, PCBM and similar derivatives form interpenetrating networks that separate photogenerated electron–hole pairs efficiently. Although non-fullerene acceptors have surpassed fullerenes in record power-conversion efficiencies since the late 2010s, fullerene derivatives are still used in commercial perovskite solar cells as electron-transport layers and remain a benchmark material for understanding charge transport in organic semiconductors.

Biomedical applications

In nanomedicine, fullerenes are studied as antioxidants, photodynamic-therapy agents, MRI contrast carriers, and components of targeted drug delivery platforms. The cage of C60 can scavenge multiple radicals before saturation, the basis for the antioxidant behavior of fullerene derivatives. Endohedral metallofullerenes such as Gd@C82(OH)x have shown promise as MRI contrast agents because the gadolinium ion remains shielded inside the cage, reducing toxicity concerns associated with free Gd3+. Photoexcited fullerene derivatives generate reactive oxygen species that can selectively damage bacteria or tumor cells, supporting research on antimicrobial coatings and tumor-targeted therapies.

Materials and catalysis

In materials science, fullerenes are incorporated into polymer nanocomposites to modify mechanical strength, optical limiting, and electrical conductivity. Buckypaper is a freestanding sheet originally based on fullerene and now more often on carbon-nanotube networks, used for thermal management and lightweight composites. As nanocatalysts, fullerenes and their derivatives serve as supports or co-catalysts in hydrogenation, oxygen reduction, and photocatalytic water splitting, where their electron-acceptor character helps stabilize charge-separated states.

Quantum information

A more recent direction uses endohedral fullerenes as building blocks for molecule-based quantum technologies. The encapsulating cage isolates a paramagnetic spin, such as the electron spin of N@C60 or the magnetic moment of a lanthanide ion in M@C82, from environmental decoherence, producing relatively long spin-coherence times. Single-molecule magnets built around dimetallofullerenes have been proposed as components of molecular qubits, supported by density functional theory studies of cage–guest interactions, though large-scale device integration remains a research goal.

Fullerenes vs. Other Carbon Allotropes

Fullerenes differ from graphene, carbon nanotubes, diamond, and graphite in dimensionality, hybridization, and the properties they make accessible. The table below summarizes the practical distinctions that influence which allotrope is selected for a given application.

Allotrope	Dimensionality	Hybridization	Notable property	Typical use
Diamond	3D crystal	sp3	Hardest known natural material; high thermal conductivity	Abrasives, optical windows, quantum sensors based on nitrogen-vacancy centers
Graphite	3D layered	sp2	Soft, conductive in plane; cleaves into sheets	Electrodes, lubricants, neutron moderators, pencil leads
Fullerenes (C60)	0D molecular cage	sp2	Strong electron acceptor; rich excited-state and redox chemistry	Photovoltaics, electron-transport layers, photodynamic therapy, antioxidants
Carbon nanotubes	1D cylinder	sp2	Extreme tensile strength; metallic or semiconducting depending on chirality	Transistors, conductive films, composites, sensors
Graphene	2D sheet	sp2	Record carrier mobility; high mechanical and thermal conductivity	Electronics, sensors, energy storage, composites

Each allotrope occupies a distinct niche. Fullerenes stand out for their molecular discreteness: they can be handled chemically like an organic compound. They also combine three-dimensional curvature with extended π-conjugation, which produces the strong electron-accepting behavior that motivates much of their use in optoelectronics and biomedicine. Related molecular zero-dimensional carbons such as carbon dots, graphene quantum dots, and carbon nanohorns share some of these characteristics but differ in structure, photoluminescence, and surface chemistry.

Challenges and Safety Considerations

Despite four decades of progress since the 1985 discovery, fullerenes face several barriers to wider adoption. Production costs remain high because of low isolation yields and the multi-step chromatography needed for pure C60. Photochemical and oxidative degradation can limit long-term device performance, particularly in solar cells, and pristine C60 is sparingly soluble in biological media, requiring derivatization that can alter pharmacokinetics, biodistribution, and toxicity profiles.

Health and environmental considerations are an active area of study. Pristine C60 has shown low acute toxicity in many laboratory studies, but functionalized derivatives differ widely in cellular uptake, biodistribution, and potential generation of reactive oxygen species. Inhalation exposure during industrial production may pose risks similar to those of other engineered nanoparticles, and the long-term environmental fate of fullerenes released into water or soil is not yet fully characterized.

Frequently Asked Questions about Fullerenes

What is C60?

C60 is a spherical fullerene molecule made of 60 carbon atoms. It is also called buckminsterfullerene or a buckyball.

What is the difference between a fullerene and a buckyball?

Why are fullerenes important in nanotechnology?

Fullerenes are important because they are nanoscale carbon cages with useful electronic, optical, and chemical properties. Their ability to accept electrons makes them valuable in organic electronics, solar cells, photochemistry, and nanomedicine research.

Are fullerenes the same as carbon nanotubes?

No. Fullerenes are closed cage-like carbon molecules, while carbon nanotubes are cylindrical carbon structures. Both are carbon nanomaterials, but they differ in shape, dimensionality, and typical applications.

Are fullerenes safe?

There is no single answer because behavior varies by derivative. Pristine C60 has shown relatively low acute toxicity in laboratory studies, but each functionalized fullerene must be evaluated on its own, with inhalation of fullerene-containing dust during industrial handling as the main occupational concern.

Do fullerenes occur naturally?

Yes. Trace amounts have been detected in soot, fulgurites, shungite deposits, and meteorites. C60 has also been observed in interstellar and circumstellar environments by infrared space telescopes, confirming the original astrophysical motivation for its discovery.

Why is C60 such a strong electron acceptor?

The 60 sp2 carbons in C60 are forced out of planarity by the curvature of the cage, which lowers the energy of its lowest unoccupied molecular orbital. As a result, C60 can accept up to six electrons reversibly in solution, which underlies its use as an acceptor in organic photovoltaics and as a redox-active component in photochemistry.