Laser vaporization experiments with graphite in a supersonic cluster beam apparatus indicate that the smallest fullerene to form in substantial abundance is C(28). Although ab initio quantum chemical calculations predict that this cluster will favor a tetrahedral cage structure, it is electronically open shell. Further calculations reveal that C(28) in this structure should behave as a sort of hollow superatom with an effective valence of 4. This tetravalence should be exhibited toward chemical bonding both on the outside and on the inside of the cage. Thus, stable closed-shell derivatives of C(28) with large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps should be attainable either by reacting at the four tetrahedral vertices on the outside of the C(28) cage to make, for example, C(28)H(4), or by trapping a tetravalent atom inside the cage to make endothedral fullerenes such as Ti@C(28). An example of this second, inside route to C(28) stabilization is reported here: the laser and carbon-arc production of U@C(28).

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Intramolecular charge separation (CS) and charge recombination (CR) processes of the dyad molecule linking C 60 and N,N-di(6-tert-butylbiphenyl)benzenamine (BBA) were investigated by pico-and nanosecond laser flash photolysis methods. Furthermore, intermolecular electron transfer to a methanofullerene (C 61 H 2 ) was also investigated; the electron-transfer rate between triplet excited C 61 H 2 and BBA was somewhat slower than that of C 60 due to less negative reduction potential of C 61 H 2 . As for the BBA-C 60 dyad molecule, CS was successfully observed in polar solvents by excitation of C 60 moiety with picosecond laser pulse, while only the intersystem crossing was observed in nonpolar solvent. The CS process in the Marcus "normal region" was confirmed. In moderately polar solvent, radical ion pairs recombined within a few nanoseconds to generate the ground state and the triplet excited state of the C 60 -moiety. On the other hand, in polar solvents, the radical ion pairs decayed by two-steps: Most part decayed within 1 ns, while the radical ions were also observed in the submicrosecond region for a ca. 10% yield of generated BBA •+ -C 60 •-. An equilibrium between CS and triplet states was proposed for the mechanism of long-lived CS state.