Dendrimer fullerene core

The ability of a dendritic shell to encapsulate a functional core moiety and to create a specific site-isolated microenvironment capable of affecting the molecular properties has been intensively explored in recent years [19]. A variety of experimental techniques have been employed to evidence the shielding of the core moiety and to ascertain the effect of the dendritic shell [19, 20]. Dendrimers with a fullerene core appear to be appealing candidates to evidence such effects resulting from the presence of the surrounding dendritic branches. Effectively, the lifetime of the first triplet excited state of fullerene derivatives... 

Light-Harvesting Dendrimers with a Fullerene Core... 

Other examples for the use of this template activated method include the formation of hexakis-adducts [15,16] with, for example, dendrimers featuring a fully buried fullerene core [8,17,18],... 

Fullerenes have been used as cores for redox dendrimers, and a system of fullerenes functionalized with poly(arylacetylene) dendritic branches has been studied. However, electrochemical experiments indicated no significant interaction between the dendrimers and the fullerene core [57]. 

Dendrimer-(Fullerene) [S-l (H-5) ] Core-Shell-Type Nanocompounds... 

Nierengarten JF, Habicher T, Kessinger R, Cardullo F, Dieder-ich F, Gramlich V, Gisselbrecht JP, Boudon C, Gross M. Mac-rocyclization on the fullerene core direct regio and diastereoselective multi-functionalization of [60]fullerene, and synthesis of fullerene- dendrimer derivatives. Helv. Chim. Acta 1997 80 2238-2276. 

Fullerenes possess electronic and photophysical properties which make them natural candidates for the preparation of functional dendrimers. The attachment of a controlled number of dendrons on a core provides a compact insulating layer around the carbon sphere, and the... 

Both energy and electron transfer quenchers have been employed to show that the quenching rates of the fullerene triplet state are decreased as a function of the size of the dendrimer shell [36]. These results further demonstrate that fullerene is an excellent functional group to probe the accessibility of a dendrimer core by external molecules. 

All the fullerene-containing dendrimers reported to date have been prepared with a Cgo core but never with fullerene units at their surface or with Cgg spheres in the dendritic branches. We have recently started a research program on the synthesis of dendrons substituted with fullerene moieties. These fulleroden-drons are interesting building blocks for the preparation of monodisperse fullerene-rich macromolecules. In addition, they are also amphiphilic compounds capable of forming stable Langmuir films at the air-water interface. 

Reaction of 217 with Cjq leads to the amino-protected porphyrin-fulleropyrroli-dine, which can easily be deprotected to the corresponding amine [229, 277]. By further functionalization via amide coupling an easy access to extended donor-acceptor systems is possible. A carotene-porphyrin-fullerene triad was prepared by reaction of the amine with the appropriate carotene acid chloride. The motivation for the synthesis of all these donor-acceptor systems is the attempt to understand and imitate the photosynthetic process. On that score, a model for an artificial photosynthetic antenna-reaction center complex has been achieved by attaching five porphyrin cores in a dendrimer-like fashion to the fullerene [242]. 

Nierengarten et al. have reported many examples of fullerene-rich dendrimers, obtained by either covalent linking or self-assembly of proper units.72,73 A very interesting example is represented by a family of fullerodendrimers from the first to the third generation, containing a hexaphenylbenzene core and 6, 12, and 24 C60 units (compound 26 in Fig. 6.19) at the periphery, respectively.74... 

Another example of fullerene-rich dendrimers consist of a Cu(I) bis-phenanthro-line complex as core, linked to four dendrons, each one containing 1,2 (compound 28 in Fig. 6.22), or 4 fullerene moieties appended at the periphery.77... 

Owing to their spheroidal molecular shape, fullerenes represent attractive functional core units for light-harvesting dendritic systems. In fullerene dendrimers of... 

A range of amphiphilic dendrimers have been reported based on fullerene C60 or a calix[4]arene core with dendritic branches on one side and long aliphatic tails on the other, Figure 14.8. The amphiphiles self-assemble into micelles with the aliphatic chains buried in the micelle core and the more hydrophilic dendritic portion facing out.14... 

An important field where the cyclopropanation reaction finds growing application is the construction of dendrimers possessing fullerenes either as functional cores [26-33] or branches [34-38]. Dendrimers can serve as building blocks for the construction of organized materials with nanosize precision due to the well-defined three-dimensional structure they possess. An issue of great importance is to incorporate photoactive and/or redox-active units at the center of the dendrimer in order to establish these types of materials as molecular devices. An example of an organofullerene material that has the potential to serve as a core building block for the construction of dendrimeric compounds... 

Convergent dendrimers, with their versatile three-dimensional scaffold, may be tailored to mimic, perhaps crudely, some elements of enzymatic structures. Numerous catalytic moieties, including manganese porphyrins,253,254 bis(oxazoline) copper complexes,304 305 tertiary amines,306 binaphthol titanium complexes,285 307 titanium taddolates,292,308 thiazolio-cyclophanes,309 and fullerene-bound bisoxazoline copper complexes,310 have been incorporated at the core of dendritic molecules to determine the effect of dendritic encapsulation on their catalytic activity. 

As with chromophores, the steric encapsulation of a dendrimer core can be utilized to prevent intermolecular interactions between redox active sites. A number of different redox active core moieties have been investigated, including, iron—sulfide clusters,9394 bis(terpyridine)iron(II) complexes,92 tris-(bipyridine)ruthenium(II) complexes,330 zinc porphyrins,252 oligothienylenevinylenes,331 fullerenes,236,332 ferrocenes,333-336 oligothiophenes,322 oligonaphtha-lenes,337 and 4,4 -bipyridinium.338... 

Highly symmetric dendrimers with a core of Qo are obtained starting from sixfold cyclopropanated, Th-symmetric derivatives of the fullerene (Figure 2.69). This central unit features twelve connective sites in shape of the acid functions, which leads to a dendrimer structured evenly in all directions. Other derivatives of Qo bearing four cyclopropanes are just as well suitable to dendrimer synthesis. These... 

Other examples include the fullerene dendrimer 57 [61] with a molecular mass of 7344 Da, dendrimer 59 featuring a bis(l,10-phenanthroline)copper(II) core and 16 peripheral fullerene groups (molecular mass 31601 Da) [72,73], and porphyrin derivatives with two [74] and four (58) [75] appended fullerenes. 

Armaroli et al. have designed a series of dendrimers, mentioned briefly in the preceding text, built around a phenanthroline core and functionalized with fullerene-containing branches. The largest macromolecule synthesized was a dendrimer with 16 fullerenes around the central core. Electrochemical studies of the fullerene reductions indicated that the first was electrochemically reversible, whereas the second was followed by a chemical reaction. It was also noted that, when a copper ion was complexed with the phenanthroline, the larger dendrimers entirely shielded it and completely prevented its oxidation [43]. 

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