Quasi-fullerenes

Its open structure involving a 13-atom orifice, not counting the bridging -COO-moieties, was assigned on the basis of NMR and IR data. The precursor compound 35 exhibits a reactive [5,6]-double bond, which is very susceptible to O2 addition. 

The intermediate dioxetane 36 is probably formed via ring opening and subsequent Baeyer-Villiger-type oxidation [2]. 

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In our opinion, heterofullerenes with divalent heteroatoms, like O and S, are potentially interesting compounds because they could possibly exist as neutral ylide structures with > C-0+< and > C-S+< bonds, respectively. Alternative structures for C59O and C59S are less ionic truncated quasi-fullerene structures bearing a carbonyl or thiocarbonyl moiety, as shown in Fig. 35. 

Fig. 35. Possible structures for C59O and C59S ylide heterofullerenes or open-cage (thio)car-bonyl quasi-fullerenes...

High-resolution transmission electron microscopy (HREM) is the technique best suited for the structural characterization of nanometer-sized graphitic particles. In-situ processing of fullerene-related structures may be performed, and it has been shown that carbonaceous materials transform themselves into quasi-spherical onion-like graphitic particles under the effect of intense electron irradiation[l 1],... 

We hope that macroscopic samples of quasi-spherical onion-like particles will soon become available, and then we will be able to characterize these systems in detail. Probably a new generation of carbon materi-aks can be generated by the three-dimensional packing of quasi-spherical multi-shell fullerenes. 

The synthesis of molecular carbon structures in the form of C q and other fullerenes stimulated an intense interest in mesoscopic carbon structures. In this respect, the discovery of carbon nanotubes (CNTs) [1] in the deposit of an arc discharge was a major break through. In the early days, many theoretical efforts have focused on the electronic properties of these novel quasi-one-dimensional structures [2-5]. Like graphite, these mesoscopic systems are essentially sp2 bonded. However, the curvature and the cylindrical symmetry cause important modifications compared with planar graphite. 

Except for Ceo, lack of sufficient quantities of pure material has prevented more detailed structural characterization of the fullerenes by X-ray diffraction analysis, and even for Ceo problems of orientational disorder of the quasi-spherical molecules in the lattice have exacerbated the situation. At room temperature Cgo crystallizes in a face-centred cubic lattice (Fm3) but below 249 K the molecules become orientationally ordered and a simple cubic lattice (Po3) results. A neutron diffraction analysis of the ordered phase at 5K led to the structure shown in Fig. 8.7a this reveals that the ordering results from the fact that... 

For 10 and 11 four quasi-reversible reduction waves were found, which are attributed to the reduction of the C60 moieties leading correspondingly to the mono-, di-, tri- and tetraanion. Nevertheless, the reduction potentials were all shifted toward more negative values relative to pristine Cgo- Saturation of a double bond in the fullerene skeleton raises the LUMO energy in 10 and 11. Furthermore, two oxidation waves stemming from oligomer centered processes were found. 

In the first part of present work specific conductivity of fullerene C60 crystals has been measured under smooth quasi-isentropic loading conditions up to 15 GPa at initial temperatures T=293 K and 77 K. We have registered the sharp increase of conductivity more than 6 orders of magnitude in a range of pressure from 0 to 15 GPa, Fig. 1. Value of conductivity regains initial properties after dynamic load is removed. The results received testified about sharply decreasing of band-gap of C6o under compression. However the experimental temperature dependence of... 

The purpose of the second part of the present research is measurement of conductivity of fullerene C6o crystals under high pressures more than at the former experiments to find out metallization C(, is possible. In the latest experiments we used a mode of multi-step quasi-isentropic compression of fullerene crystals by series of consecutive flat shock waves which enables us to reach much higher... 

Table 5.2. Redox potentials (V vs. NHE) of Ceo and fullerene derivatives. Experimental conditions reference electrode quasi-Ag/AgCl wire (calibrated with ferrocene), working and counter electrodes Pt foils, supporting electrolyte Bu4NPF6 (0.1 M), solvent ODCB/MeCN (4/1), scan rate 100 mV/s, room temperature...

This view of Voc generation is additionally supported by the fact that the values of the temperature coefficient dUoc/dT = -(1.40-1.65) mVK-1 for the cells under the present study (with bilayer LiF/Al and ITO/PEDOT contacts) coincide with those for polymer/fullerene bulk heterojunction solar cells of the previous generation (with the same components of the active layer but without LiF and PEDOT contact layers) [156]. In this picture, the temperature dependence of Voc is directly correlated with the temperature dependence of the quasi-Fermi levels of the components of the active layer under illumination, i.e., of the polymer and the fullerene. Therefore, the temperature dependence of Voc over a wide range, and in particular V),c(0 K), are essential parameters for understanding bulk hetero junction solar cells. 

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