Fullerenes

Abstract Fullerenes are a class of three‐dimensional all‐carbon hollow molecules containing a conjugated n system and are sometimes referred to as the “third form of carbon”. Each fullerene Cn consists of an even number of carbon atoms and represents a closed‐cage structure with 12 pentagons and (n–20)/2 hexagons. The isolated pentagon rule is an important principle to determine the stability of fullerene cages. [60]Fullerene (C60) has a truncated icosahedral spherical structure with 20 hexagons and 12 pentagons. [70]Fullerene (C70) is a kiwi‐like ellipsoidal molecule and its structure contains an additional equatorial band of 10 carbons relative to that of C60. Fullerenes containing > 70 atoms are known as “higher fullerenes”. Unlike the other forms of carbon, fullerenes are soluble and thus can undergo a wide range of chemical reactions. The main chemical reactions of fullerenes are nucleophilic additions, cycloadditions, and radical additions. The hollow cavities of fullerenes can enclose a wide variety of atoms, molecules, or metal clusters, and the class of fullerenes are named as endohedral fullerenes. In addition, the replacement of one or more carbons of the fullerene cage by other non‐carbon atoms such as nitrogen can lead to heterofullerenes. Fullerene derivatives bearing electrondonor groups have been investigated because of the potential for conversion of light into electricity. Some alkali metal‐doped fullerenes show the interesting superconducting properties. Although fullerenes are insoluble in water, some derivatives are very soluble and this has led to investigations of biological properties.