Fullerenes

　Addition reactions and other chemical modifications of fullerenes easily produce fullerene derivatives. Precise structure analyses of these derivatives are possible because they are molecular species. Non-derivatized fullerenes are poorly soluble in similarity to the other nanocarbon materials. However, we can introduce soluble functional groups to form solution-processible electronic materials. Phenyl-C₆₁-butyric acid methyl ester ([60]PCBM) and indene-C₆₀ bisadduct (ICBA) are useful organic semiconductors for fabricating a solution-processible electronic device.^5,6) These fullerene derivatives are n-type organic semiconductors for organic photovoltaics (OPV) by mixing with a p-type conjugated polymer.⁷⁾ An application of a fullerene derivative for organic transistors was also reported.⁸⁾ A complexation of C₆₀ with tetrakis(dimethylamino)ethylene (TDAE) gives a charge transfer complex (TDAE-C₆₀), which is an organic magnet at low temperature.⁹⁾　
　Although a chemical modification of the outer surface of fullerene provides PCBM or ICBA, we can introduce a small component to the inner side of fullerene. For instance, fullerenes can encapsulate a metal atom on the inner side, when the fullerenes are produced in the presence of the metal. This is the so-called metal-encapsulated fullerene described as MC₆₀. The encapsulation modifies the electronic state¹⁰⁾ and chemical reactivity of fullerene.¹¹⁾ On the other hand, water-encapsulated fullerene (H₂OC₆₀) was also reported. A publication described that an organic synthetic procedure gave open-caged C₆₀ which could then encapsulate one water molecule. A following chemical modification could close the cage to from water-encapsulated fullerene H₂OC₆₀.¹²⁾