Fullerene trimer

Fig. 3 STM images of fraction A containing fullerene trimers 6a-6d and fraction B containing 6e, together with the calculated energy relative to that of equatorial isomer...

The Raman spectra of the products of y-irradiation of solid Cm showed the formation of dimers and trimers. IR evidence has been reported for the formation of a fullerene trimer, Ciso." ... 

Since there are 30 double bonds to react in fullerene Cgo, the [2-1-2] cycloaddition of Cgo molecules at these bonds results in the formation of so-called fullerene polymers [19]. Although it seemed important to clarify the structure and properties of the most basic unit of these polymers such as dimers and trimers, the method for preparation of these polymers such as high-pres-sure/high-temperature treatment or photoirradiation was not suitable to stop the [2-1-2] reaction at the stage of dimerization or trimerization. 

A possible explanation for the lack of electron-transfer characteristics in the trimer 9d is derived when extrapolating the linear relationship in Fig. 9.8 to the distance of the trimer. As a matter of fact, the charge-separation would not be able to compete with the intrinsic singlet lifetime of C6o (i.e. dashed line). This, in turn, explains the lack of fullerene emission quenching in 9d. Nevertheless, the photophysical assays clearly established that oPPE bridges effectively mediate electron-transfer processes over distances up to 20 A. These findings were further corroborated by quantum mechanical calculations. 

The finding of the presence of a trimer form of Sc]1 in the fullerene cage, rather than that of three mutually separated Sc2+ ions, is somewhat unexpected in the light of the discandium (Sc2+)2 C]4 fullerene [4], where the two individual Sc2+ ions are separated by 3.9(1) A in the C84 cage. Obviously, the formation of the Sc3+ trimer should be much more energetically favorable than that of three... 

Fig. 13.16 Multi-step photoinduced electron [50] and (b) ferrocene-meso, meso-linked transfer in (a) a ferrocene-zinc porphyrin-free porphyrin trimer-fullerene pentad [Fc-base porphyrin-C60 tetrad (Fc-ZnP-H2P-C60) (ZnP)3-C60] Ar = 3,5-Bu 2C6H3 [51].

The best molecule mimicking multi-step electron-transfer processes in the photo synthetic reaction center so far reported is a ferrocene-meso, meso-linked porphyrin trimer-fullerene pentad [Fc-(ZnP)3-C60] in Fig. 13.16b, where the C60 and the ferrocene (Fc) are tethered at both the ends of (ZnP)3 (R = 46.9 A)... 

Scheme 5. Multistep photoinduced ET in a ferrocene-mcio.mcio-linked porphyrin trimer-fullerene pentad [Fc—(ZnP)3 C6o] Ar = 3,5-/-BuC5Fl3 (48).

The triscandium endohedral fullerene Sc3 C82 has been isolated and studied by ESR.96 Synchrotron X-ray studies indicate that the three scandium atoms form a triangle and this trimer has a formal charge of three allowing formulation of the compound as (Sc3)3+C323-.113 The temperature-dependent metal cluster position inside the C82 cage has been studied.114... 

Simple redox solutes, ferrocene, N, N, N, JV-tetramethyl-l,4-phenylenediam-ine, decamethylferrocene, bis(i-propylcyclopentadienyl) iron(ll), [Ru(phen)j] (0104)2, [Fe(bpy)3](0104)2, [Co(bpy)3](0104)2, and iodine have been studied at electrodes modified with polymeric fullerene films. FuUerene-modified electrodes were prepared by electropolymerization of Cjq initiated by traces of dioxygen or by simultaneous electroreduction of fullerene and Pd(ll) acetate trimer. For the former films, the electrochemical activity decreases upon potential cycling. The electrochemical activity of the film is stabihzed by the redox solute added to the electropolimerization stage due to the catalytic oxidation of the fullerene film by the oxidized form of the redox system. Similarly, positively charged species can also be incorporated into the structure of the film. The reversible behavior of redox solutes decreases with the increase in the thickness of the Pd/C q film. This film also incorporates ferricinium ion, N, N, N, N-tetramethyl-l,4-phenylenediamine cation, decamethylferricinium ion, and to a smaller degree [Co(bpy)3]"+ [53]. 

Fig. 2 The types of arrangements of fullerenes (van der Waals contacts) in their host-guest complexes (host molecules not shown). These cover finite structures, (a) monomeric (encapsulated), (b) dimeric, and (c) the proposed trimeric complex involving p-Bu -calixa[8]arene, and higher aggregates, and continuous structures, all of which were established in parts (d-j), with scope for structures of higher complexity. (View this a t in color at www.dekker.com,)...

Spectacular trimeric assemblies 11 of cavitands functionalized with four dithiocarbamate units were obtained upon their mixing with Zn(II) and Cd(II) salts in EtOH/ H2O (Fig. 4). In apolar solvents, the H-NMR spectra were broad, but the complexes nicely crystallized from pyridine/H20 they were characterized by x-ray crystallography. Trimers 11 form stable 1 1 complexes with fullerene Cgo in benzene and toluene solutions the log fass values are within the range 3.5-6 (UV/Vis spectroscopy). 

Fluorescence quenching studies carried out on the first series of porphyrin dimer 53a, trimer 53b, and tetramer 53c show that fluorescence of the porphyrin arrays is quenched approximately 100 times compared to arrays not bearing fullerenes. Due to the properties of the arrays, namely strong excitonic coupling and red shifted, split Soret bands, no conclusions are drawn about the mechanism (ET or eT) of the quenching. 

Nuclear applications of nanocapsules are related to the emitting physical properties of the encapsulated material. Emitted radiation can be electromagnetic of high energy (y), electrons or positrons (/3), alpha particles (" He nucleus), or fission products [67]. These emitters can be in themselves radioactive or can be activated by a nuclear reaction, usually a neutron capture. The particular advantage of carbon nanocapsules in nuclear applications is related to the protective characteristics that the carbon capsule confers to the interior product. Experiments on irradiation of fullerenes have shown that knocked carbon atoms from one cage are foimd in another fuUerene and even form dimers and trimers by a recoil-implantation mechanism [68]. The observed major damage of capsules in nanoencapsulated molybdenum irradiated in a nuclear reactor was produced by... 

A recently reported cyclic porphyrin trimer, 9, shows an extremely high binding affinity for Ceo, with a on the order of 2.1 x 10 in cyclohexane and 1.6 x 10 in toluene. For C70, the affinity in tolnene is even greater with a of 2 X 10 M-i, and is one of the highest reported affinities for C70. The binding constant is even larger for higher fullerenes, which may be due to the increased interaction between all three of the porphyrin walls. 

Figure 9 Recently developed tripod systems for fullerene encapsulation. 8 is a tripod on a rigid scaffold. 9 is a cyclic trimer. 10 is a trimer with flexible arms.

Recently, Anderson has reported a rigid tri-porphyrin host able to associate with Cgo, C70, and also Cg6 with extremely high binding constant values such as logX = 6.2, 8.2, and >9, respectively (Figure 2.9c). The strong affinity of this trimer to bigger fullerenes cannot be measured by fluorescence titration, and it has been demonstrated with some advanced experiments. ... 

Another approach to trap fullerenes involves the use of Cgo as a template for the formation of its own porphyrin host. The fullerene is, thus, able to preorganize the MP subunits before the in situ cyclization reaction that carries out the formation of the macrocycle host. In the example reported by Langford et al., the porphyrin subunits involved in a metathesis reaction form mainly a dimer without the presence of Qo in a dichloromethane solution while they are preferentially forming the host trimer when the fullerene is exploited as the template. "... 

Mulholland, A. R., Woodward, C. P. and Langford, S. J. Fullerene-templated synthesis of a cyclic porphyrin trimer using olefin metathesis. Chem. Commun. 47, 1494-1496, 2011. 

Fig. 4 Monomer structures for a series of DA copolymers used as the HTMs in combination with fullerene-based ETMs in high-performance BHJ organic solar cells. The stmcture of a trimer of P3HT is provided for reference. All alkyl chains have been truncated to methyl groups...

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