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The [6,6]-ring bridged methanofullerenes 61,61-bis[4-tert-butylbenzoate]-1,2-dihydro-1,2-methanofullerene [60] (1), 61,61-bis[4-(tert-butyldiphenylsilyloxymethyl)phenyl]-1,2-dihydro-1,2-methanofullerene[60] (2), and 61-[(ethoxycarbonyl)methylcarboxylate]-1,2-dihydro-1,2-methanofullerene[60] (3) were synthesized by the Diederich method (3) or the Wudl method via tosylhydrazone salts (1 and 2). Groundstate absorption spectra of the methanofullerenes in toluene and cyclohexane solutions are presented and possible assignments discussed. The sharp, 430 nm transition is associated with the existence of less than 60 p electrons, whereas a broad band peaking at 495 nm as well as weak features in the 700 nm region could be related to forbidden transitions of C 60 . The allowed transitions of C 60 in the UV region are modified relatively little in the methanofullerenes. Laser flash photolysis and pulse radiolysis techniques were used to obtain triplet ± triplet absorption spectra between 400 and 1100 nm and determine photophysical properties. The three methanofullerenes have very similar T ± T spectra, with a strong peak at 720 nm whose molar absorption coefficient is of the order of 14 000 m ) production by energy transfer from the triplet state of the three methanofullerenes, implying that the quantum yield of triplet production of each is % 1. The results indicate that it is possible for the spectroscopic and photophysical properties of methanofullerenes to vary little with the nature of the methano adduct and to undergo only slight modifications with respect to the corresponding properties of C 60 . Up to now, this has been found valid only when the functionalization does not involve an electron donor. The biological photosensitization efficiencies of these methanofullerenes are therefore expected to be similar to those of C 60 but with their hydrophobicity and intracellular site delivery modulated by the nature of the methano-adduct.

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Aggregation of C 60 and of three C 60 derivatives in phosphatidylcholine liposome model membranes was studied via photophysical investigations. The triplet properties of these fullerenes, including the absorption spectrum between 400 and 900 nm, molar absorption coefficient, quantum yield of formation and/or quantum yield for the photosensitised production of 1 O 2 were determined in benzene solution and in liposomes. One of the derivatives was a cyclopropyl-fused hexa-addended C 60 containing as addend C(CO 2 C 18 H 37 ) 2 (1). The other two derivatives were cyclohexyl-fused C 60 with leucine (2) or hydrophilic acidic (3) mono-addend functionalisation. The synthesis of derivative 2, by thermal extrusion of sulfur dioxide from the corresponding sulfone in the presence of C 60 , is described. [60]Fullerene and derivative 1 show no T-T absorption in liposomes, although they do so in benzene solution (with a low triplet quantum yield for hexa-addended 1). The absence of triplet-triplet absorption in liposomes is indicative of fullerene aggregation. By contrast, the amphiphilic mono-addend derivatives 2 and 3 present appreciable T-T absorption in liposomes, although less marked than in benzene solution. Mono-addend functionalisation therefore appears to be an interesting way to prevent or diminish fullerene aggregation. Moreover, in this type of derivatisation most of the photophysical properties of pristine [60]fullerene are retained.

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A molecule with three stacked zinc-porphyrin cycles and two basket-handles has been synthesized and incorporated into a bilayer lipid membrane. Under light excitation and in the presence of redox compounds in the aqueous phases bathing the membrane, this molecule induces a net electron flux across the membrane. The experimental variations of the flux with some external physicochemical parameters are accounted for by a tentative mechanism which relies on the ability of the porphyrin to act as an electron wire.

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