Photodynamic therapy (PDT) employs the combination of nontoxic photosensitizers and visible light that is absorbed by the chromophore to produce long-lived triplet states that can carry out photochemistry in the presence of oxygen to kill cells. The closed carbon-cage structure found in fullerenes can act as a photosensitizer, especially when functionalized to impart water solubility. Although there are reports of the use of fullerenes to carry out light-mediated destruction of viruses, microorganisms and cancer cells in vitro, the use of fullerenes to mediate PDT of diseases such as cancer and infections in animal models is less well developed. It has recently been shown that fullerene PDT can be used to save the life of mice with wounds infected with pathogenic Gram-negative bacteria. Fullerene PDT has also been used to treat mouse models of various cancers including disseminated metastatic cancer in the peritoneal cavity. In vivo PDT with fullerenes represents a new application in nanomedicine.

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Novel cyclosulfation chemistry for the functionalization of Ceo and its analogs is described. The cyclosulfation of Ceo is accomplished in neat fuming sulfuric acid at 55-60 °C under N3 to afford polycyclosulfated fullerene derivatives. Hydrolysis of these derivatives, either in the presence of water at 85-90 °C or in aqueous NaOH solution at ambient temperature, gives the corresponding polyhydroxylated fullerenes (fullerenols) in high yield. The functional characteristics and number of sulfate moieties per Ceo molecule in the polycyclosulfated fullerene precursors, and the structure of fullerenols, were determined primarily by the analysis of the TGA-mass spectrum and the sulfur (S2P) and carbon (Cu) absorption bands in the XPS spectrum. We resolved an average of 10 to 12 hydroxyl addends in the chemical structure of fullerenols that can be correlated to the structure of polycyclosulfated fullerene precursors containing 5 to 6 cyclosulfate units. The cyclosulfation chemistry is, presumably, initiated by a one-electron oxidation of Ceo, followed by the attack of anionic sulfate species on the resulting cationic Ceo radical intermediates, to form the corresponding hydrogen sulfated Ceo radicals. Further oxidation and intramolecular cyclization of this hydrogensulfated C6o yields the polycyclosulfated Ceo products.

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Sterically hindered fullerenyl chromophore dyad and triads, C 60 (>DPAF-C 9 ) x (x ) 1 and 2, respectively), in an acceptor-donor (A-D) molecular linkage of C 60 -(keto-fluorene) x were synthesized and fully characterized. Attachment of two 3,5,5-trimethylhexyl groups on C 9 of the fluorene ring moiety greatly improves their solubility and makes direct intermolecular aromatic stacking contacts more difficult. They are the first series of fullerene derivatives showing high three-photon absorptivity (3PA). Accordingly, C 60 (>DPAF-C 9 ) 2 exhibits 2PA and 3PA cross sections in the values of 0.824 × 10 -48 cm 4 s (or 82.4 GM) and 6.30 × 10 -25 cm 6 /GW 2 , respectively, in femtosecond region among the highest ones reported for many diphenylaminofluorene-derived AFX chromophores. Utilization of a keto linker located immediately between C 60 cage and fluorene chromophore moieties facilitates molecular polarization of the DPAF ring toward the C 60 cage. That may serve as the fundamental cause for correlation of enhanced A-D electron interactions to, ultimately, observed multiphoton absorption cross sections. By using nanosecond laser flash photolysis results taken at 355 nm as the reference, transient absorption data obtained from femtosecond pump-probe experiments at 800 nm unambiguously verified the occurrence of two-photon excitation processes of C 60 (>DPAF-C 9 ) in air-saturated benzene and subsequent efficient energy transfer from the two-photon pumped DPAF-C 9 moiety to the C 60 cage moiety.