ABSTRACT
Since the discovery1 and the bulk production2,3 of fullerenes an integrated research field involving organic transformations of these all-carbon hollow-cluster materials has emerged. C60 has been the most thoroughly studied member of fullerenes because it (1) is produced abundantly in the carbon soot by the arc discharge of graphite electrodes, (2) has high symmetry (icosahedral Ih with all 60 carbons chemically equivalent), (3) is less expensive, (4) is relatively inert under mild conditions, and (5) shows negligible toxicity. Electronically, C60 is described as having a closed-shell configuration consisting of 30 bonding molecular orbitals with 60 p electrons,4 which give rise to a completely full fivefold degenerate hu highest occupied molecular orbital that is energetically located approximately 1.5 to 2.0 eV lower than the corresponding antibonding lowest unoccupied molecular orbital (LUMO) one.5,6 The first electron in the reduction of C60 is added to a triply degenerate
t1u unoccupied molecular orbital and is highly delocalized.7 This threefold-degeneracy, together with the low-energy possession of the LUMO, make C60 a fairly good electron acceptor with the ability of reversibly gaining up to six electrons upon reduction.8,9 The facile reduction contrasts with its difficult oxidation. Only the first three reversible oxidation waves have been observed.10 This high degree of symmetry in the arrangement of the molecular orbitals of C60 provides the foundation for a plethora of intriguing physicochemical, electronic, and magnetic properties. Semiconducting,11 magnetic,12-16 and superconducting17-19 properties of unmodified C60 have been intensively investigated; however, these properties remain to be explored for functionalized fullerenes. On the other hand, nonlinear optical and photophysical properties of functionalized fullerene materials have been already under investigation.
