Fullerene approach

An alternative approach envisages the stimulating idea to produce an all-carbon fullerene polymer in which adjacent fullerenes are linked by covalent bonds and align in well characterized one-, two- and tliree-dimensional arrays. Polymerization of [60]fullerene, with the selective fonnation of covalent bonds, occurs upon treatment under pressure and relatively high temperatures, or upon photopolymerization in the absence of a triplet quencher,... 

An approach for improving the response of conjugated polymcr/fullerene bilayer devices, which is based on an additional excitonic middle layer inserted into the D-A interface, was suggested by Yoshino el al. [94. In the middle layer light absorption produces electron-hole pairs, which migrate towards the interlace and... 

FuUerodendrimers also allow an evaluation of the accessibility of the Cgo core unit by studying bimolecular deactivation of its excited states by external quenchers. Recently Ito, Komatsu, and co-workers have used this approach to investigate a series of fuUerodendrimers (9-11) in which Frechet-type dendrons have been connected to a fullerene moiety via an acetylene linker (Fig. 5) [35]. 

Molecules of the size of the fullerenes require such approaches to help rationalise the results. Even though the number of classical structures can be very large the same qualitative reasoning can be used as with the smaller molecules, typically benzene. The enumeration of classical structures is easily accomplished using computers. It is simply a problem of determining how many ways a set of points (in our case carbon atoms) can be coimected given rules governing their connectivity. 

Foote, C.S. Photophysical and Photochemical Properties of Fullerenes. 169,347-364 (1994). Fossey, J., Sorba, J., and Lefort, D. Peracide and Free Radicals A Theoretical and Experimental Approach. 164, 99-113 (1993). 

Alternative strategies utilizing the initial introduction of suitable chemical functionality onto the fullerene have been adopted by several research groups, allowing conjugation of the saccharides with complementary functions in the final synthetic steps. This approach has led to improved flexibility with the chemical functions on the carbohydrate moieties, especially the anchoring ones, and a better control on the number of attached saccharide residues. 

An alternative synthetic approach, first developed by Bingel225 allowed the efficient nucleophilic cyclopropanation of fullerenes via their reaction with bromomalonate derivatives in the presence of base. This approach, the most reliable method for the synthesis of functionalized methanofullerenes, combined the advantages of mild... 

A. Yashiro, Y. Nishida, M. Ohno, S. Eguchi, and K. Kobayashi, Fullerene glycoconjugates A general synthetic approach via cycloaddition of per-O-acetyl glycosyl azides to [60]fullerene, Tetrahedron Lett., 39 (1998) 9031-9034. 

Langa et al. [26, 59, 60], while conducting the cycloaddition of N-methylazo-methine ylide with C70 fullerene, proposed a rather similar approach. Theoretical calculations predict an asynchronous mechanism, suggesting that this phenomenon can be explained by considering that, under kinetic control, microwave irradiation will favor the more polar path corresponding to the hardest transition state . 

Redox molecules are particularly interesting for an electrochemical approach, because they offer addressable (functional) energy states in an electrochemically accessible potential window, which can be tuned upon polarization between oxidized and reduced states. The difference in the junction conductance of the oxidized and the reduced forms of redox molecules may span several orders of magnitude. Examples of functional molecules used in these studies include porphyrins [31,153], viologens [33, 34,110,114,154,155], aniline and thiophene oligomers [113, 146, 156, 157], metal-organic terpyridine complexes [46, 158-163], carotenes [164], nitro derivatives of OPE (OPV) [165, 166], ferrocene [150, 167, 168], perylene tetracarboxylic bisimide [141, 169, 170], tetrathia-fulvalenes [155], fullerene derivatives [171], redox-active proteins [109, 172-174], and hydroxyquinones [175]. 

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