Doping fullerene

I he results of their calculations were summarised in two rules. The first rule states that at least one isomer C with a properly closed p shell (i.e. bonding HOMO, antibonding I. U.MO) exists for all n = 60 - - 6k (k = 0,2,3,..., but not 1). Thus Qg, C72, Cyg, etc., are in lhi-< group. The second rule is for carbon cylinders and states that a closed-shell structure is lound for n = 2p(7 - - 3fc) (for all k). C70 is the parent of this family. The calculations Were extended to cover different types of structure and fullerenes doped with metals. 

Another interesting applications area for fullerenes is based on materials that can be fabricated using fullerene-doped polymers. Polyvinylcarbazole (PVK) and other selected polymers, such as poly(paraphcnylene-vinylene) (PPV) and phenylmethylpolysilane (PMPS), doped with a mixture of Cgo and C70 have been reported to exhibit exceptionally good photoconductive properties [206, 207, 208] which may lead to the development of future polymeric photoconductive materials. Small concentrations of fullerenes (e.g., by weight) lead to charge transfer of the photo-excited electrons in the polymer to the fullerenes, thereby promoting the conduction of mobile holes in the polymer [209]. Fullerene-doped polymers also have significant potential for use in applications, such as photo-diodes, photo-voltaic devices and as photo-refractive materials. 

Y Wang, Photoconductivity of fullerene-doped polymers, Nature, 356 585-587, 1992. 

Li G, Mianami N (2003) Increase of photoluminescence from fullerenes-doped poly (alkyl methacrylate) under laser irradiation. Journal of Photoluminescence 104 207. 

N.V. Kamanina, Mechanisms of optical limiting in p-conjugated organic system fullerene doped polyimide, Synthetic Metals, vol. 127, pp. 121-128, 2002. 

These examples demonstrate the well-known process of polymerization initiated by anion-radicals. Our next consideration is devoted to an unusual case of initiation. Intercalation of fullerenes by metals results in the formation of fullerene-metal derivatives. Paramagnetic metallofullerenes (anion-radicals) are the fullerenes doped with endohedral metal. According to calculations and structural studies, LaCs2, for example, contains La in the center of one hexagonal ring of the fuller-ene cage (Akasaka et al. 2000, Nishibori et al. 2000, Nomura et al. 1995). Intrafullerene electron transfer in metallofullerenes is possible (Okazaki et al. 2001). 

Interestingly, if the C50 fullerene doped by alkali metals is rapidly cooled down to the liquid nitrogen temperature, polymerization does not occur. Only monomeric anion-radical salts are obtained. Warming up these monomers to 80-160 K results in dimerization polymerization does not take place. The dimer (KCgo)2 is dielectric (Pekker et al. 1995). It has been shown that the tris(anion)-radical Cgo can polymerize too. Particularly, Na2CsCgo forms a polymer that maintains superconducting properties (Mizuki et al. 1994). 

Aviram A, Ratner MA (1974) Molecular rectifiers. Chem Phys Lett 29 277-283 Viani L, dos Santos MC (2006) Comparative study of lower fullerenes doped with boron and nitrogen. Solid State Commun 138 498-501... 

Keywords Fullerene, doping, infrared spectroscopy, mass spectrometry, X-ray diffraction, crystallite size, lattice constant, gas storage, phase transitions. 

Wang Y (1992) Photoconductivity of Fullerene-Doped Polymers, Nature 356 585-587... 

The fullerenes used were synthesized according to the electric arc method, giving a mixture of Qo and C o in the ratio —85 15. Thin films of the fullerene-doped polymer are prepared by spin-coating fullerene and PVK (molecular weight —5x10 ) from solution in toluene (typically 40 mg of fullerene and 1.5 g of PVK in 12 ml of toluene) onto aluminium substrates. The samples are dried in an oven at 100 °C for several hours before use. The film thickness can be varied from 1 to 30 xm, by changing the concentration of PVK and the spin speed. The films are optically clear and air-stable for at least several months. 

Photoconductivity of Fullerene-doped Polymers Y. Wang, Nature 356, 585-587 (1992). 

Fullerene-Doped Polyvinylcarbazole. Fullerenes are known to be good electron acceptors. In the presence of electron donors such as aromatic amines, weakly bonded charge-transfer complexes can be formed [115]. Through virtual excitation, the existence of charge-transfer interaction can enhance the second-order optical nonlinearity of fullerenes [116], With direct excitation, excited state electron transfer between fullerenes and various electron donors such as aromatic amines [115,117], semiconductor colloids [118], porphyrin [119], and polymers [101, 103, 120] can occur. This electron-accepting property led to the development of fullerene-doped polymeric photoconductors [101,103]. 

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