Fullerene Systems

Fullerenes are excellent electron acceptors, since the electron affinity of Cgo is exceptionally large (2.8 eV) and the LUMO is sixfold degenerate. Suggestions have been made to use fullerenes as storage of electrons, and indeed there is some sense in it. It has been possible to fill all six orbitals subsequently at an electrode, using cyclic voltammetry. The surface of the molecule is large, which permits solvent molecules to polarize and neutralize six electrons. 

The carotene or the porphyrin is excited to Sj. There is ET to the Cgo ligand from the porphyrin. Later, the hole moves to the carotene ligand. There is now a rather stable charge-separated state. Finally, this state decays by ET from to carotene. The triplet excited state of carotene is formed with long lifetime, before the whole complex retnms to the ground state. This system holds the promise as an artificial photosynthetic system. 

The molecular orbitals in the vicinity of the HOMO-LLIMO gap are localized on either of the three x-systems. Two HOMOs are found on porphyrine and the next two on carotene. The seven LUMOs are found on CgQ. However, it should be mentioned that information on the orbitals is not sufficient to explain the mechanism. Unfortunately, the system is too large to permit meaningful calculations of the excited states. 

Lemetyinen, J. Andreasson, and many others have studied other large x-systems including the Cgo molecule. After excitation, electrons or excitations can be seen in time-resolved transient spectroscopy jumping between the connected molecules. This type of work is useful in understanding natural photosynthetic processes. It deserves to be mentioned that ET or conductivity cannot occur without excitation. 

Other work of this type, for example, by M. R. Wasielewsky et al aim at finding x-bridges that permit ET over large distances. Even photoinduced conductivity over a large distance appears to be possible. 

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Rao CNR and Seshadri R 1994 Phase transitions, superoonduotivity and ferromagnetism in fullerene systems MRS Bulletin 12 28-30... 

Another example is a phthaloq anine-azacrown-fullerene system that can be synthesized with the same DCC supported esterification [153],... 

Some representative examples of fullerene-porphyrin dyads are shown in Scheme 9. In other examples, porphyrin analogs such as phthalocyanines and subphthalocyanines have been used for the construction of efficient dyads. Again, the most straightforward approach for their synthesis involved 1,3-dipolar cycloaddition of the appropriate azomethine ylides to C60 [203-205]. Also, with the aid of the Bingel reaction, other phthalocyanine-fullerene systems have been prepared [206,207] with the most prominent example being the one that contains a flexible linker possessing an azacrown subunit [208]. The novelty of this dyad can be found in the nature of the linker that could, in principle, induce conformational changes in the multicomponent system when certain ions (e.g., alkaline ions) are present. As a direct consequence this would potentially allow an external control over the electronic interactions between the phthalocyanine and fullerene units. 

A double bond 1.406 A), suggesting the present computational method is capable of providing accurate results for the fullerene systems. 

A review of Jahn-Teller effects in discrete fullerene systems... 

H-CIDNP and ESR techniques. A laser flash photolysis and time-resolved ESR study of the formation of phosphinoyl radicals from benzoyldiphenyl-phosphine oxide and 257 has appeared. The addition of dialkyIphosphoryl radicals to a fullerene system has also been studied. Interest in adducts of phosphine oxides with proton donors, notably phenols and other solvent guests ° has continued. 

New perspective of electron transfer chemistry (porphyrin and porphyrin-fullerene systems) 030BC609. 

PCBM, which represent the most often studied polymer-fullerene systems, are shown... 

This procedure was recently used to prepare other pyrrolino[ 60] fullerene systems - 2,5-disubstituted Ceo-pyrrolidine derivatives 25 and 26 - using microwave irradi-... 

The design of covalently linked donor-fullerene systems capable of undergoing photoinduced electron-transfer processes has been widely studied as a result of the remarkable photophysical [35] and electronic [36] properties of fullerenes. Porphyrins, phthalocyanines, tetrathiafulvalenes, carotenes, and ferrocene [37] have been covalently attached to the fullerene sphere, usually as pyrrolidine[ 60] fullerene derivatives by 1,3-dipolar cycloaddition reactions. 

Langa et al. [38] described the first synthesis of D-A dyads (30a-c) based on C o and used ruthenocene as the electron-donor fragment (Scheme 21.12). Synthesis of these pyrrolidine)60]fullerene systems was achieved by 1,3-dipolar cycloaddition of ruthenocenecarboxaldehyde (28), N-methylglycine, and C o in toluene under the action of microwave irradiation in a focused microwave oven. The adducts 30a-c were obtained in moderate yields (26-31%). 

Photophysical studies on a nanosecond time scale provided clear evidence of in-termolecular PET from TTF, an excellent electron donor, to the pyrazolino)60]-fullerene systems (58a,b). 

Figure 2. Schematic drawing of an open carbon tube (a) and a carbon onion (b) as examples for a particular configuration of fullerene systems. 

Fig. 1.6 The bivariate correlation of the parabolic- with n- energies as reported in Table 1.5 for Fullerene system...

Figure 12.5 Fullerene intercalation in different polymer/fullerene systems, (a) The expansion of the d-spacing ofthe pTT upon the addition of PC60BM and the inset shows how the PC60BM fits between the side chains, (b) The same situation exists for PQT. (c) There is insufficient...

In Figure 13.8, one of the first fullerene systems that was studied in detail regarding PIET is shown (Devens Gust et al.). A substituted porphyrin is connected via phenyl groups with Cgo on the right and a p-carotene on the left. 

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