Of fullerenes

The scope of tire following article is to survey the physical and chemical properties of tire tliird modification of carbon, namely [60]fullerene and its higher analogues. The entluisiasm tliat was triggered by tliese spherical carbon allotropes resulted in an epidemic-like number of publications in tire early to mid-1990s. In more recent years tire field of fullerene chemistry is, however, dominated by tire organic functionalization of tire highly reactive fullerene... 

One aspect that reflects the electronic configuration of fullerenes relates to the electrochemically induced reduction and oxidation processes in solution. In good agreement with the tlireefold degenerate LUMO, the redox chemistry of [60]fullerene, investigated primarily with cyclic voltammetry and Osteryoung square wave voltammetry, unravels six reversible, one-electron reduction steps with potentials that are equally separated from each other. The separation between any two successive reduction steps is -450 50 mV. The low reduction potential (only -0.44 V versus SCE) of the process, that corresponds to the generation of the rt-radical anion 131,109,110,111 and 1121, deserves special attention. 

In contrast to the relative ease of reduction, oxidation of fullerenes requires more severe conditions [113, 114]. Not only does the resonance stabilization raise the level of the corresponding oxidation potential (1.26 V versus Fc/Fc ), but also the reversibility of the underlying redox process is affected [115]. 

Thin films of fullerenes, which were deposited on an electrode surface via, for example, drop coating, were largely heterogeneous, due to the entrapping of solvent molecules into their domains. Consequently, their electrochemical behaviour displayed different degrees of reversibility and stability depending on the time of electrolysis and the... 

Another interesting physical feature relates to the cliromophoric character of fullerenes. Based on the symmetry prohibitions, solutions of [60]fullerene absorb predominantly in the UV region, with distinct maxima at 220, 260 and 330 nm. In contrast to extinction coefficients on the order of 10 cm at these wavelengths, the visible region shows only relatively weak transitions (X at 536 nm s =710 cm ) [142]. 

There are, indeed, many biological implications that have been triggered by the advent of fullerenes. They range from potential inhibition of HIV-1 protease, synthesis of dmgs for photodynamic therapy and free radical scavenging (antioxidants), to participation in photo-induced DNA scission processes [156, 157, 158, 159, 160, 161, 162 and 163]. These examples unequivocally demonstrate the particular importance of water-soluble fullerenes and are summarized in a few excellent reviews [141, 1751. 

Figure C 1.2.10. Representative examples of fullerene based donor-bridge-acceptor dyads and triads.

Meijer G and Bethune D S 1990 Laser deposition of oarbon olusters on surfaoes-a new approaoh to the study of fullerenes J. Chem. Rhys. 93 7800-2... 

Campbell E B and Hertel I V 1992 Molecular beam studies of fullerenes Carbon 8 1157-65... 

Eohegoyen L and Eohegoyen L E 1998 Eleotroohemistry of fullerenes and their derivatives Accou/rfs. Chem. Res. 31 593-601... 

Tanigaki K, Kuroshima S and Ebbesen T W 1995 Crystal growth and structure of fullerene thin films Thin Soiid Fiims 257 154-65... 

Fisoher J, Heiney P A and Smith A B III 1992 Solid-state ohemistry of fullerene-based materials Accounts. Chem. Res. 25 112... 

Bulhoes LOS, Obeng Y S and Bard A J 1993 Langmuir-Blodgett and electrochemical studies of fullerene films Chem. Mater. 5 110-14... 

Leigh D A, Moody A E, Wade F A, King T A, West D and Bahra G S 1995 Second harmonic generation from Langmuir-Blodgett films of fullerene-aza-crown ethers and their potassium ion complexes Langmuir 11 2334-6... 

Goldenberg L M 1994 Eleotroohemioal properties of Langmuir-Blodgett films J. Electroanal. Chem. 379 3-19 Chlistunoff J, Cliffel D and Bard A J 1995 Eleotroohemistry of fullerene films Thin Solid Films 257 166-84... 

Bezmelnitsin V N, Eletskii A V and Stepanov E V 1994 Cluster origin of fullerene solubility J. Phys. Chem. 98 6665-7... 

Andriesvsky G V, Kloohkov V K, Karyakina E L and Mohedlov-Petrossyan N O 1999 Studies of aqueous oolloidal solutions of fullerene Cgg by eleotron miorosoopy Chem. Phys. Lett. 300 392-6... 

Yamakoshi Y N, Yagami T, Fukuhara K, Sueyoshi S and Miyata N 1994 Solubilization of fullerenes into water with polyvinylpyrrolidone applioable to biologioal tests J. Chem. Soc., Chem. Common. 517-18... 

Jensen A W, Wilson S R and Schuster D I 1996 Biological applications of fullerenes—a review Bioorg. Med. Chem. 4 767-79... 

Zeng Y, Biczok L and Linschitz H 1992 External heavy atom induced phosphorescence emission of fullerenes the energy of triplet Cgg J. Phys. Chem. 96 5237-9... 

Tokuyama H, Yamago S, Nakamura E, Shiraki T and Sugiura Y 1993 Photoinduoed bioohemioal aotivity of fullerene oarboxylio aoid J. Am. Chem. See. 115 7918-9... 

Kato T, Kodama T, Shida T, Nakagawa T, Matsui Y, Suzuki S, Shiromaru H, Yamauehi Kand Aehiba Y 1991 Eleetronie absorption speetra of the radioal anions and eations of fullerenes Cgg and C g Chem. Phys. Lett. 180 446-50... 

Stasko A, Brezova V, Biskupie S, Dinse K-P, Sehweitzer P and Baumgarten M 1995 EPR study of fullerene radieals generated in photosensitized TiOg suspensions J. Phys. Chem. 99 8782-9... 

Cagle D W, Kennel S J, Mirzadeh S, Alford J M and Wilson L J 1999 In vivo studies of fullerene-based materials using endohedral metallofullerene radiotraoers Proc. Natl Acad. Sc/. USA 96 5182-7... 

Figure C 1.2.6. Summary of fee [ ] fullerene stmeture and alkali-interealation eomposites of [ ] fullerene.

The field of fullerene chemistry expanded in an unexpected direction in 1991 when Sumio lijima of the NEC Fundamental Research Laboratories in Japan discovered fibrous carbon clusters in one of his fullerene preparations This led within a short time to substances of the type portrayed in Figure 11 7 called single-walled nanotubes The best way to think about this material IS as a stretched fullerene Take a molecule of Ceo cut it in half and place a cylindrical tube of fused six membered carbon rings between the two halves... 

Carbon soot from resistive heating of a carbon rod in a partial helium atmosphere (0.3bar) under specified conditions is extracted with boiling C H or toluene, filtered and the red-brown soln evapd to give crystalline material in 14% yield which is mainly a mixture of fullerenes C q and C70. Chromatographic filtration of the crude mixture with allows no separation of components, but some separation was observed on silica gel... 

Physical properties of Fullerene C q. It does not melt below 360°, and starts to sublime at 300° in vacuo. It is a mustard coloured solid that appears brown or black with increasing film thickness. It is soluble in common organic solvents, particularly aromatic hydrocarbons which give a beautiful magenta colour. Toluene solutions are purple in colour. Sol in (5mg/mL), but dissolves slowly. Crysts of C o are both needles and plates. 

Physical properties of Fullerene Cyg It does not melt below 360°, and starts to sublime at 350° in vacuo. A reddish-brown solid, greenish black in thicker films. Solns are port-wine red in colour. Mixtures of Csq and C70 are red due to C70 being more intensely coloured. It is less soluble than Cso in but also dissolves... 

Further reading Kroto, Fischer and Cox Fullerenes Pergamon Press, Oxford 1993 ISBN 0080421520 Kadish and Ruoff (Eds) Fullerenes Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials The Electrochemical Soc. Inc, Pennington, NJ, 1994 ISBN 1566770823]... 

Drcssclhaus, M.S., Dresselhaus, G. and Eklund, P.C., Science of Fullerenes and Carbon Nanotubes, 1996, Academic Press, San Diego. 

The structure-property relations of fullerenes, fullerene-derived solids, and carbon nanotubes are reviewed in the context of advanced technologies for carbon-hased materials. The synthesis, structure and electronic properties of fullerene solids are then considered, and modifications to their structure and properties through doping with various charge transfer agents are reviewed. Brief comments are included on potential applications of this unique family of new materials. 

Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

Since the structure and properties of fullerene solids are strongly dependent on the structure and properties of the constituent fullerene molecules, we first review the structure of the molecules, which is followed by a review of the structure of the molecular solids formed from Ceo, C70 and higher mass fullerenes, and finally the structure of Cgo crystals. 

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