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1.
A standard EPR technique has been applied to perform temperature studies of polycrystalline samples of C60 fullerene. A comparison of the three main parameters of EPR spectra obtained for a C60 sample before and after (solvent free) purification has been made in temperatures from 4 to 300 K. When compared to the spectrum of the as-obtained (crude) sample the spectrum of the purified sample revealed considerable changes i.e. an increase in the EPR signal intensity and evidence of a phase transition at about 90 K. This transition is proved to be related to the two processes: freezing of the orientational motion of C60 molecules and redistribution of the positive and negative charge observed as paramagnetic centres localized on C60 molecules.  相似文献   

2.
The structure and phase transitions of C60 crystals doped with lithium by injecting metal ions from the superionic crystal-C60 single crystal heterojunction under electrodiffusion conditions are reported. The sample experienced irreversible transitions resulting in the virtually complete disappearance of EPR signals and MW conduction in the temperature range 320–370 K. In this temperature interval, a new C60 phase was formed; the phase contained polymeric chains of C60 molecules along the crystallographic c axis and lithium clusters. The structure of this phase was determined. Annealing at 620 K restored the EPR signal and, according to the X-ray data, the initial cubic structure of pure C60. The X-ray pattern, however, contained additional diffraction peaks, which was evidence of the presence of one more phase with a structure yet unknown.  相似文献   

3.
In this work, by using the respective advantages of W- and X-band electron paramagnetic resonance (EPR) spectroscopy techniques to investigate electron transport processes, we have studied the light-induced redox transients of the primary electron donor P700 and the secondary acceptor A1 in photosystem (PS) I complexes of intact cyanobacterial cellsSynechocystis sp. PCC 6803. We found that the kinetic behavior of the cation radical P700 ·+ generated by illumination with continuous light, and the EPR intensity of the radical pair P700 ·+A 1 ·? generated upon laser pulse illumination strongly depend on the illumination prehistory (either the sample was frozen in the dark or during illumination). Both these processes were sensitive to the presence of electron transport inhibitors which block electron flow between the two photosystems. In line with our X-band EPR data on the kinetics of light-induced redox transients of P700, our high-field W-band EPR study of the radical-pair state P700 ·+A 1 ·? shows that photosynthetic electron flow through the PS I reaction center is controlled both on the donor and on the acceptor side of PS I.  相似文献   

4.
We have discovered a selective and efficient method for the synthesis of previously unknown 1,9-(1′,4′-oxathiano)-1,9-dihydro-(C60-Ih)[5,6]fullerene, a compound with the direct attachment of the sulfur atom to the fullerene core. The method is based on the reaction of C60 with 1,2-hydroxythiols in the presence of inorganic bases in air under ultrasonication. The significance of ultrasound has been exemplified with the comparative conventional methods. The title compound has been identified with mass-(MALDI TOF/TOF), one- and two-dimensional NMR 1H and 13C (COSY, HSQC, HMBS), IR, UV–Vis spectroscopic techniques. Using the direct EPR method, we have detected radical anion C60 (g = 2.0046 and ΔH = 2 G) as a key reaction intermediate of the sonochemical reaction. Based on the experimental results and quantum chemical calculations, we have proposed a mechanism for the conversion of C60 and 2-mercaptoethanol to the C60–1,4-oxathiane adduct.  相似文献   

5.
A comparative electron paramagnetic resonance (EPR) study has been performed on a series of structurally related molecular triads which undergo photoinduced electron transfer and differ one from the other in terms of the acceptor or donor moieties. The molecular triads, C-P-C60, TTF-P-C60 and C-P-PF, share the same free-base, tetraarylporphyrin (P) as the primary electron donor, which after light excitation initiates the electron transfer process, but differ either in terms of the electron acceptor (fullerene derivative, C60, versus fluorinated free-base porphyrin, PF), or in terms of the final electron donor (carotenoid polyene, C, versus tetrathiafulvalene, TTF). All these molecular triads can be considered artificial photosynthetic reaction centers in their ability to mimic several key properties of the reaction center primary photochemistry. Photoinduced charge separation and recombination have been followed by time-resolved EPR in a glass of 2-methyltetrahydrofuran and in the nematic phase of the uniaxial liquid crystal E-7. All the triads undergo photoinduced electron transfer, with the generation of charge-separated states in both the low-dielectric environment of the 2-methyl-tetrahydrofuran glass and in anisotropic E-7 medium. Different photochemical pathways have been recognized depending on the specific donor and acceptor moieties constituting the molecular triads. In the presence of the tetrathiafulvalene electron donor singlet- and triplet-initiated electron transfer routes are concurrently active. Recombination to the low-lying carotenoid triplet state occurs in the carotene-based triads, while singlet recombination is the only active route for the TTF-P-C60 triad, where a low-lying triplet state is lacking. Long-lived charge separation has been observed in the case of TTF-P-C60: about 8 μs for the singlet-born radical pair in the glassy isotropic matrix and about 7 μs for the triplet-born radical pair in the nematic phase of E-7. For all the molecular triads, a weak exchange interaction (J?1 G) between the electrons in the final spin-correlated radical pair has been evaluated by simulation of the EPR spectra, providing evidence for superexchange electronic interactions mediated by the tetraarylporphyrin bridge.  相似文献   

6.
The single crystals of triphenylphosphinselenid [C18H15PSe] were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to 60Co gamma (γ) rays with a dose speed of 0.980 kGy/h at the room temperature for 72 h. The free radical over the sample was observed using electron paramagnetic resonance (EPR)–X band spectrometer. The EPR spectra were recorded between 120 and 400 K. Furthermore, the sample irradiated was rotated in steps of 10° and analyzed for different orientations of the crystal in the magnetic field. Only one radical structure was determined on the molecule. The hyperfine constants of the sample were found to be anisotropic. The average values of these constants and value of g were calculated as following: g=2.007656, aSe=37.47 G, aP=27.44 G, aHa=17.28 G, and aHb=18.16 G.  相似文献   

7.
The temperature dependence of the EPR spectra of the recently discovered Ag6S3O4 phase in the Ag-O-S system prepared by two methods, the known method of co-precipitation from aqueous solution and a new method depending on the interaction of Ag2S and Ag2SO4 solid reagents, has been investigated. No EPR spectra were observed at room temperature, while at liquid helium temperature a number of EPR spectra have been recorded, which disappeared upon increasing temperature up to liquid nitrogen temperature. The sample obtained by the co-precipitation method revealed an intense, rich EPR spectrum that has been tentatively interpreted assuming the presence of at least two different Ag2+ ion complexes, one monomer resulting in an intense anisotropic, rhombic EPR powder pattern with g1 = 1.93(1), g2 = 2.025(3), g3 = 2.094(5), hyperfine constants A1 = = A2 = 60(5) · 10?4 cm?1,A 3 = 90(5) · 10?4 cm?1 and one dimer EPR pattern presumably involving a pair of Ag2+ ions with internuclear separation of 4.3 Å. However, the presence of larger clusters could not be excluded. On the other hand, the sample obtained by a solid state reaction method has given rise to two rather weak EPR lines centered at geff = 2.105(3) and geff = 4.213(3), respectively.  相似文献   

8.
Simultaneous electrochemical and electron paramagnetic resonance experiments have been carried out on the reduced C60 fullerene to examine theg-factor assignment of the radical species. C 60 1? and C 60 3? show the following EPR characteristics at room temperature: C 60 1? :g 1?=2.0002±0.0001, 2ΔB 1s=0.17 mT, and C 60 3? :g 3?=2.0008±0.0002, 2ΔB 1s=0.07 mT. EPR linewidths are apparently narrower compared to those in most of the spectra previously reported. Variable temperature EPR study on solution containing C 60 1? has shown thatg 1? value is not while the linewidth is only slightly temperature dependent.  相似文献   

9.
The radiative quantum efficiencies η of the CdSe/ZnS core-shell nanoparticles embedded into polymethyl methacrylate (PMMA) and suspended in three different solvents: chloroform (CHCl3), toluene (C6H5CH3) and tetrahydrofuran (C4H8O) were measured using thermal lens (TL) technique. The mode-mismatched pump-probe TL measurements were accomplished in function of the CdSe/ZnS quantum-dot concentration (12-60 mg/ml) at λe = 594 nm (pump) and λp = 632.8 nm (probe). The values obtained for η were higher for CdSe/ZnS nanoparticles suspended in tetrahydrofuran and chloroform, as compared to the values for toluene. Thermal diffusivity (D) and the absolute nonradiative quantum efficiency (φ) were determined.  相似文献   

10.
Intermediate products of radical reactions of chlorohydrocarbons catalyzed by copper chloride complexes were synthesized by the photolysis of solutions of [(C4H9)3BzN+]2[CuCl4]2? in chlorobenzene and chloroform at the wavelength corresponding to Cl → Cu charge transfer. It was shown by the EPR method that the products of photolysis were alkyl radicals formed by organic fragments of the quaternary ammonium cation and Cu(II) complexes (supposedly organocopper compounds). The total content of paramagnetic centers decreased. The mechanisms of photoreduction of quaternary ammonium tetrachlorocuprates and possible reasons for the decay of paramagnetic particles were considered.  相似文献   

11.
We present preliminary results on the preparation and structure of Mg4C60, a new fulleride polymer. A series of MgxC60 compositions (0<x<6) were prepared by solid state reaction. While most samples were multiphase, a single phase material was obtained at the nominal composition Mg4C60. The X-ray diffraction pattern of Mg4C60 was successfully indexed and fitted to a rhombohedral structure based on two-dimensional polymeric sheets of C60 ions. This result extends the family of fulleride polymers to the salts of multiply charged cations and thus opens a new direction in this field.  相似文献   

12.
王晓雄  李宏年 《物理学报》2006,55(8):4259-4264
用X射线光电子能谱研究了Sm掺杂的固态C60相衍变和芯电子态.在SmxC60中Sm的含量x小于0.5时,样品是固溶相;在x=0.5和x=2.75之间的掺杂阶段,样品是这两个相的混合.在x=2.75和x=6之间的高掺杂阶段未观察到相分离的X射线光电子能谱证据.Sm 4f, 4d的实验数据表明Sm的价态是+2.二价Sm 3d5/2芯态谱线存在两个子峰. 关键词: 60的Sm填隙化合物')" href="#">C60的Sm填隙化合物 相结构 电子态 X射线光电子能谱  相似文献   

13.
The amorphous polymer surfaces of polystyrene (PS, M n=200 kg/mol, M w/M n=1.05) and poly(methyl methacrylate) (PMMA, M n=51.9 kg/mol, M w/M n≤1.07) were brought into contact at 21°C to form PS‐PS (for 54 days) and PMMA‐PMMA auto‐adhesive joints (for 11 days). After contact at that temperature corresponding to T g‐bulk ?81°C for PS and to T g‐bulk–88°C for PMMA, where T g‐bulk is the calorimetric glass transition temperature of the bulk sample, the bonded interfaces were fractured and their surfaces were analyzed by atomic force microscopy (AFM). The surface roughness, R q, of the fractured interfaces was larger by a factor of 3–4 than was that of the free PS and PMMA surfaces aged for the same period of time. A similar increase in R q was found by comparison of the free PS surface aged at T g‐bulk+15°C for 1 h and of the surface of the PS‐PS interface fractured after healing at T g‐bulk+15°C for 1 h. These observations, indicative of the deformation of the fractured interfaces, suggest the occurrence of some mass transfer across the interface even below T g‐bulk ?80°C.  相似文献   

14.
Polymer alkyl-fullerene (P-C60) radical adducts produced by ultraviolet (UV) photoinitiated reactions between low-density polyethylene (LDPE) and C60 in the presence of benzophenone (BP) as a photoinitiator have been detected and identified for the first time by electron spin resonance (ESR) and confirmed by simulation analysis of the spectrum. A well-resolved ESR spectrum was recorded in situ upon UV irradiation of the LDPE/BP/C60 sample in the molten state (413 K). Detailed analysis of hyperfine structures shows that the observed spectrum is composed of three components: a broad singlet atg = 2.0025 from the C60 radical anion; an innermost pair of13C satellites; and a 12-line spectrum superposed on the broad singlet. The simulation analysis of the spectrum shows that the 12-line spectrum is due to the overlapping of two kinds of radical adducts of tertiary carbon-C60 (A) and secondary carbon-C60 (B), which have slightly differentg-values and almost the same integral intensity IA/IB (48.4/51.6). The spectrum simulated on the basis of the1H and13C hyperfine interaction parameters is in good agreement with the observed spectrum. These results provide positive evidence that the C60-bound LDPE materials can be obtained directly by a simple method of BP-photoinitiated reaction of the LDPE/C60 system.  相似文献   

15.
EPR and Vis-NIR absorption spectra have both been measured for clarification of contradictory statements about the para-and diamagnetic states of fullerenes. Thereby identification of one sharp EPR signal in solution at room temperature to C 60 ? (g=2.000±4.0001; ΔB=0.07±0.01 mT) could be made upon using different fullerene sources (TechnoCarbo, Hoechst) and methods of anion generation (chemically, electrochemically, and photochemically). This fact is also supported by the similar observation for a monosubstituted derivative (g=1.9999; ΔB=0.10 mT), in which a small broadening of this sharp signal is found originating from additional1H hyperfine interactions. Furthermore theg-values of the radical anions of C60 increase with charge (g(C 60 ? <g(C 60 2? ) < <g(C 60 3? ) <g(C 60 5? )) indicating largest contributions from spin-orbit coupling for the monoanion. No diamagnetic states for the dianions of [60]- and [70]- fullerenes could be found so far but biradical species with largest zero field splittingsD=2.7 mT (C 60 2? ), andD=3.1 mT (C 70 2? ), respectively. The cation formation of C60 (g=2.0023-2.0029; ΔB=0.15-0.20 mT) with antimony pentachloride was controlled by mass spectrometry. Stable cations were found only in methylenechloride. In other solvents like toluene addition reactions seem to occur.  相似文献   

16.
The authors experimentally observed the superluminal propagation at negative group velocity in C60 polymethyl methacrylate (PMMA) firstly. The largest time advancement of 7.61 ms was obtained at 1 mg/cm3 of sample concentration, the corresponding group velocity was −0.657 m/s. Fast light in C60 PMMA offers several advantages over liquids or vapors for a variety of possible applications: (i) easy for experimental measurement and practical applications (ii) easy for manufacture, (iii) sample concentration is another convenient parameter to vary the signal delay.  相似文献   

17.
The temperature dependence of EPR spectrum of La@C82 in the powder of empty C60 and C70 mixed crystals was studied by EPR spectroscopy employing X- and Q-band microwave frequencies. The rigid limit spectra (at 4.2 K for the X-band and at 132 K for the Q-band) could be analyzed by static spectral simulation which yielded the EPR parameters,g =2.0021,g =1.9970,La A =7.8 MHz,La A ~0 MHz and an isotropic13C coupling value of about 3 MHz. For higher temperatures an appreciable motional averaging effect was observed and the spectra were analyzed by using dynamic spectral simulation based on the stochastic Liouville equation, where we assumed an isotropic rotational motion with the Brownian diffusion. The calculated spectra reproduced the dominant feature of the temperature dependence of the spectra almost satisfactorily for both the X-and Q-band frequencies with the appropriate rotational correlation times. The Arrhenius plots of the correlation time gave two activation energies of 0.9 kcal/mol and 2.9–3.8 kcal/mol for the temperatures below and above 200 K, respectively.  相似文献   

18.
Electron paramagnetic resonance (EPR) spectroscopy was used to examine free radical properties of model neuromelanins obtained by oxidative polymerization of noradrenaline, adrenaline and dopamine. We compared the lineshape of the experimental spectra, type and concentration of free radicals in the analyzed samples. The effect of different concentrations of Cu2+ on free radicals in melanins was studied. The total concentration of free radicals (about 1018 to 1019 spin/g) in the studied melanins increases as follows: adrenaline-melanin < dopamine-melanin < noradrenaline-melanin. EPR spectra of dopamine-melanin and adrenaline-melanin were a single EPR line (ΔB pp, 0.50 and 0.55 mT, respectively). o-Semiquinone free radicals with the characteristicg-value of 2.0040 exist in these melanins. EPR spectra of noradrenaline-melanin were a superposition of two lines (ΔB pp, 0.45 and 0.81 mT). o-Semiquinone free radicals were responsible for the narrower component. Nitrogen free radicals with ag-factor of 2.0030 were probably responsible for the broader component. Paramagnetic copper ions quenched the EPR signals of melanin free radicals in the studied samples. For melanin-Cu2+ complexes, broad EPR lines (ΔB pp, 10–32 mT) of copper ions with ag-value of about 2.1 appeared. The influence of the microwave power on the EPR spectra of these complexes demonstrated the fast spin-lattice relaxation in the copper system in melanins.  相似文献   

19.
The radio-frequency muon spin resonance technique (RF-μSR) is described, with examples drawn from muon studies of fullerences. Two distinct species can be detected by RF-μSR when solid C60 is irradiated with positive muons. Endohedral muonium (Mu@C60) is characterized by a muon hyperfine constant (A μ) close to the vacuum value. A remarkable feature of the RF-μSR spectrum is the double quantum transition, which appears when the allowed transitions are saturated. The exohedral muonium adduct (C60Mu) is also detected, and has a much smaller value ofA μ typical of a carbon-centred organic radical. It has been studied by RF-μSR in dilute solution, which is not possible for transverse field muon spin rotation (TF-μSR). There is a significant difference inA μ of C60Mu in the solid and in solution, a result of great import to the analysis of avoided-level crossing experiments on13C60Mu.  相似文献   

20.
Sputtering of organic materials using a C60 primary ion beam has been demonstrated to produce significantly less accumulated damage compared to sputtering with monatomic and atomic-cluster ion beams. However, much about the dynamics of C60 sputtering remains to be understood. We introduce data regarding the dynamics of C60 sputtering by evaluating TOF-SIMS depth profiles of bulk poly(methyl methacrylate) (PMMA). Bulk PMMA provides an ideal test matrix with which to probe C60 sputter dynamics because there is a region of steady-state secondary ion yield followed by irreversible signal degradation. C60 sputtering of PMMA is evaluated as a function of incident ion kinetic energy using 10 keV C60+, 20 keV C60+ and 40 keV C60++ primary ions. Changes in PMMA chemistry, carbon accumulation and graphitization, and topography as a function of total C60 ion dose at each accelerating potential is addressed.  相似文献   

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