Among the large number of molecular subunits used for dendrimer chemistry, fullerene has proven to be a versatile building block. Fullerene itself is a convenient core for dendrimer chemistry.We have shown that specific advantages are brought about by the encapsulation of a fullerene moiety in the middle of a dendritic structure. In particular, the shielding effect resulting from the presence of the surrounding shell has been found useful to optimize the optical limiting properties of fullerene derivatives andto obtain amphiphilic derivatives with good spreading characteristics. The use of the fullerene sphere as a photoactive core unit has also been exploited. In particular, the special photophysical properties of fullerene have been used to prepare dendrimer-based light-harvesting systems.
Whereas almost all the fullerene-containing dendrimers reported in the literature have been prepared with a fullerene core, dendritic structures with fullerene units at their surface or with fullerene spheres in the dendritic branches have been scarcely considered. This is mainly associated with the difficulties related to the synthesis of fullerene-rich molecules. Indeed, the two major problems for the preparation of such dendrimers are the low solubility of fullerene and its chemical reactivity limiting the range of reactions that can be used for the synthesis of branched structures bearing multiple fullerene units. Over the past years, we have developed efficient convergent methodologies allowing the preparation of dendrons substituted with multiple fullerene moieties. These fullerodendrons are interesting building blocks for the preparation of large fullerene-rich dendritic molecules by using either covalent chemistry or supramolecular interactions.
Substantial research efforts have also been carried out to organize such compounds onto surfacesor to study their electronic properties. Finally, we have shown that dendrimers bearing multiple fullerene units are good candidates for solar energy conversion. Importantly, significant changes in the photoelectrochemical properties have been evidenced by increasing the generation number. In particular, the incident photon-to-photocurrent efficiency (IPCE) of the devices is significantly increased by increasing the generation number and thus the number of fullerene subunits of the dendritic molecules used in the photoactive layer.
In order to further increase the number of peripheral subunits without increasing significantly the number of synthetic steps, we have recently developed macromonomers from our fullerene hexa-adduct building blocks. These macromonomers have been grafted onto a fullerene hexa-adduct core to assemble first generation dendrimers with 120 peripheral sugars. This represents the fastest dendritic growth ever reported. A very clean and robust infection assay has been employed to test the ability of these megamolecules to inhibit the infection of cells by an artificial Ebola virus. The results obtained in these experiments revealed that mannosylated superballs are potent inhibitors of cell infection by this artificial Ebola virus with IC50s in the sub-nanomolar range. This implies over three orders of magnitude increase of activity in comparison to the hexakis-adduct containing 12 mannose residues.