Fullerenes

Fullerenes

1. Fullerenes: discovery, properties and applications

2. How did we get to know about fullerenes? Nuclear physics researchers Hahn & Strassman in Germany noticed that carbon cluster ions up to C 15 + were produced in a high frequency arc with a graphite electrode in the 1943. A Japanese physical organic chemist E. G. Osawa had perceived that carbon in the single layer closed cages structure would be aromatic and therefore stable, in early 1970. Gal’pern (Russian scientist) had completed the first of many Hückel calculations showing that it would be a closed shell molecule with a large HOMO-LUMO gap in 1973. Fullerenes were discovered experimentally for the first time by a group of scientists at Rice University, Houston, Texas, in September of 1985.

3. What are fullerenes? Fullerenes are closed hollow cages consisting of carbon atoms interconnected in pentagonal and hexagonal rings . Each carbon atom on the cage surface is bonded to three carbon neighbors therefore is sp2 hybridized. The most famous fullerene is C60, known also by “ buckyball ". Other relatively common clusters are C70, C72, C74, C76, C80, C82 and C84 (plenty of others, higher or lower than C60, exist too but less abundant in the experimentally produced mixture fullerene soot).

4. What are fullerenes ? (c ontinued…) C 60 C 70

5. How are fullerenes made? Fullerenes can be made by vaporizing carbon within a gas medium (they could form spontaneously in a condensing carbon vapor) Schematic cross-sectional drawing of the supersonic laser-vaporization nozzle used in the discovery of fullerenes

6. Properties of fullerenes No other element has such wonderful properties as carbon. Buckyballs are relatively cheap; carbon is everywhere ! Even though each carbon atom is only bonded with three other carbons (they are most comfortable with four bonds) in a fullerene molecule, dangling a single carbon atom next to the structure is not strong enough to break the structure of the fullerene molecule.

7. Properties of fullerenes (continued…) In fullerenes, 12 pentagonal rings are necessary and sufficient to effect the cage closure. Fullerenes contain carbon atoms arranged as a combination of 12 pentagonal rings and n hexagonal rings. The chemical formula is C20+2n. Fullerene cages are about 7-15 Å in diameter, and are one carbon atom thick.

8. Properties of fullerenes (continued…) Quite stable from chemical and physical points of view (breaking the balls requires temperatures of about 1000 °C). Highest tensile strength of any known 2D structure or element. Highest packing density of all known structures. Impenetrable to all elements under normal circumstances, even to a helium atom with an energy of 5 eV .

9. Photo-ionization of fullerenes Ion-photon merged-beams end station at ALS Photo-ionization process Photo-ionization of C60 Photo-ionization of C84 Comparison between the two spectra

10. Ion-photon merged-beams endstation at the Advanced Light Source

11. Photoionization of C60 ions e - photon C 60 + molecular ion C 60 2+ molecular ion

12. Photoionization of C84+ molecular ion

13. Applications of fullerenes Due to their extremely resilient and sturdy nature, fullerenes are being considered for use in combat armor. Researchers have found that water-soluble derivates of fullerenes inhibit the HIV-1 protease (enzyme responsible for the development of the virus) and are therefore useful in fighting the HIV virus that leads to AIDS. Elements can be bonded with C 60 or other fullerenes to create more diverse materials, including superconductors and insulators.