Absorption fullerenes

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... 

The spectral dependence of the photoresponse of these bilayer heterojunction devices, illuminated from the 1TO side, is displayed in Figure 15-22. The onset of photocurrent at hv— 1.7 cV follows the absorption of the fullerene, indicating a symmetric hole transfer from the excited fullerene to the MEH-PPV. The minimum in the photocurrent at /iv=2.5 eV corresponds to the photon energy of maximum absorption of MEH-PPV. The MEH-PPV layer, therefore, acts as a filter, which reduces the number of photons reaching the MEH-PPV/C()0 interlace. Thus, the thickness of the MEH-PPV layer determines the anlibatic spectral be-... 

An approach for improving the response of conjugated polymcr/fullerene bilayer devices, which is based on an additional excitonic middle layer inserted into the D-A interface, was suggested by Yoshino el al. [94. In the middle layer light absorption produces electron-hole pairs, which migrate towards the interlace and... 

The dendritic effect evidenced for 1-8 might be useful to optimize the optical hmiting properties characteristic of fullerene derivatives. Effectively, the intensity dependant absorption of fuUerenes originates from larger absorption cross sections of excited states compared to that of the ground state [32], therefore the... 

Two redox states of one complex, (168) and (169), exhibit very similar respective values of ca. 0.6 J cm-2 and 0.7 J cm-2 with 32 ps pulses at 532 nm (in benzene).452 A 532 nm OL study of the two neutral complexes (170) and (171) using ns and ps pulses has also been reported.453-455 Low values of ca. 0.3 Jem-2 are observed with ps pulses in benzene, and both ps time-resolved pump-probe and Z-scan measurements reveal that RSA and nonlinear refraction are responsible for the OL behavior.453-455 Because (170) and (171) are transparent in the region 400-900 nm, their OL responses should cover a wider range than those of fullerenes and MPcs.453-455 Dai et al. have applied ps 532 nm DFWM to the tetrahedral Zn11 or Cd11 complexes (172) and (173), the modest 7 responses of which are resonance enhanced by the n- 7r transition at 512nm.456 The dimeric square pyramidal Zn11 complex (174) exhibits a broad n —> tt absorption with Amax = 497 nm in DMF and is shown by 532 nm Z-scan to exhibit SF behavior.457... 

Measurements of the optical properties in this range of wavelengths can probe the fundamental electronic transitions in these nanostructures. Some of the aforementioned effects have in fact been experimentally revealed in this series of experiments (90). As mentioned above, the IF nanoparticles in this study were prepared by a careful sulfidization of oxide nanoparticles. Briefly, the reaction starts on the surface of the oxide nanoparticle and proceeds inward, and hence the number of closed (fullerene-like) sulfide layers can be controlled quite accurately during the reaction. Also, the deeper the sulfide layer in the nanoparticle, the smaller is its radius and the larger is the strain in the nanostructure. Once available in sufficient quantities, the absorption spectra of thin films of the fullerene-like particles and nanotubes were measured at various temperatures (4-300 K). The excitonic nature of the absorption of the nanoparticles was established, which is a manifestation of the semiconducting nature of the material. Furthermore, a clear red shift in the ex-citon energy, which increased with the number of sulfide layers of the nanoparticles, was also observed (see Fig. 21). The temperature dependence of the exciton... 

We have shown, in a series of reported experiments that cationic fullerenes fulfill many, but not all the aforementioned criteria. Our laboratory was the first to demonstrate that the soluble functionalized fullerenes described above, especially the cationic compounds BF4-BF6, were efficient antimicrobial PS and could mediate photodynamic inactivation (PDI) of various classes of microbial cells (Tegos et al., 2005). We used a broadband-pass filter giving an output of the entire visible spectrum (400-700 nm) to excite the fullerenes that maximized the absorption. 

In should be noted that the same problem exists for both other photosensitizers and other methods for decontamination of the blood and its components (e.g. absorption) (Mohr, 2000). The use of fullerenes is to be preferred to the use of photoactive dyes because the former are water-soluble components. Due to its insolubility in water, fullerene may be easily removed from the liquid phase after the procedure of decontamination. 

After irradiation of fullerenes C60 in the cell medium, ROS production has been detected, and this index increased as follow fullerene C60 < fullerene C60-compos-ite-1 < fullerene C -composite-2. As one may see from the data presented in Table 6.1, the rate of ROS generation elevated nearly twice after absorption of light in predetermined range by fullerenes C60, if fullerene C60 was bound to the surface of aminopropylaerosyl, and threefold, if anthracenal that absorbs at X = 357nm was introduced to the content of composite. 

The method of preparation of this complex is simple enough and consists of mixing of fullerene solution in toluene with solution of PVP in chloroform with the following evaporation of organic solvents and dissolution of the residue in water. It was shown that the complex formation caused the bathochromic and hypochromic shifts of the fullerene absorption bands in UV-VIS spectra (Yamakoshi et al., 1994). 

The most convenient method for the evaluation of fullerene molecules aggregation is the comparison of UV-VIS absorption spectra in various solvents and for Langmuir-Blodgett films (Bensasson et al., 1994). Some preliminary conclusions about the state of aggregation can be made basing only the absorption maximum of fullerene C60 in the region of 3 30-340 nm concern. 

Thus, if mentioned above is to be taken into consideration that absorption band in the region of 330-340 nm reflects to a certain extent the degree of fullerene molecules association in solution, we can come to the conclusion that the less the PVP molecular mass and the less the fullerene contents is the more fullerene molecules are in low associated state. It is quite probable that the increase of the fullerene contents in the complex brings to the formation of adducts, where not single fullerene C60 molecules are bonded with PVP but their associates. It can be one of the reasons of the observed fact of the difference of UV-VIS spectra of C60/PVP complex with PVP of different molecular mass (up to spectra crossover, which is a singular evidence that these compounds are nonidentical). 

Fig. 13.3 Electronic absorption spectra of C60 fullerene dissolved in (A) brassica oilseeds methyl ester (biodiesel) (B) olive oil (C) sunflower oil (D) soybean oil (E) linseed oil (F) linseed oil and C60 fullerene after heating at 150°C for 15 minutes...

The new absorption band at 435 ran in the C60 spectrum has been attributed to the 1,2 addition to the fullerene cage to the fatty acid chains either across to the double bonds by a Diels-Alder addition or, more simply, by radical addition (Cataldo and Braun, 2007). Thus, fatty acid esters are able to not only dissolve C60, but also react with this molecule causing the addition of the fatty chain to the fullerene cage. In fact, the bands at 435 ran shown in Fig. 13.3 appear only when C60 is stirred at 75°C for a couple of hours in the esters of fatty acids. Only for olive oil the new band appears much weaker than in the other cases and displaced at 450 ran (Fig. 13.3B). Since this oil contains chlorophyll, the displacement may be probably due also to a charge-transfer interaction between C60 and chlorophyll or with other impurities. 

The solubility of C60 and C70 fullerenes in vegetable oils will permit to employ these molecules for topical use in creams, lotions and ointments, which are adsorbed by skin. Vegetable oils, especially olive oil, are considered excellent excipients for injectable preparation where the active principle is soluble in fats. Their absorption in the subcutaneous tissues is slow and limited and ensures a gradual release of the active principle (Adami, 1960). 

It has also been found a certain level of reactivity between C60 and C70 with the unsaturated fatty acids. The electronic absorption spectra show evidences that C60 or C70 are grafted onto the fatty chains when the fullerene solutions in vegetable oils are left for days in air, by heating the solutions under N2, Ar and air, or by UV irradiation of the solutions in inert atmosphere. 

There have been several developments in this area since this manuscript was prepared. The heat of combustion of corannulene was determined by microbomb combustion calorimetry and its gas-phase enthalpy of formation was estimated at 110.8 kcal/mol. All anionic oxidation states of corannulene were observed by optical absorption, EPR, and NMR spectroscopies. More support for the an-nulene-within-annulene model of the corannulene tetraanion was presented. An alternative pyrolysis route to corannulene was reported, as well as some attempts toward the synthesis of bowl-shaped subunits of fullerenes. And in contrast with previous semiempirical studies," ab initio calculations predicted a general concave preference for the metal cation binding to semibuckminsterfullerene 2%. ... 

Fullerenes can be easily chemically reduced by the reaction with electropositive metals [1, 97-99], for example, alkali- and alkaline earth metals. The anions Cjq"" (n = 1-5) can be generated in solution by titrating a suspension of in liquid ammonia with a solution of Rb in liquid ammonia [100], whereupon the resulting anions dissolve. Monitoring of this titration is possible by detecting the characteristic NIR absorption of each anion by UV/Vis/NIR spectroscopy. The solubility of the alkali metal fullerides in the polar solvent NHj demonstrates their salt character. 

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