Simple modification in hexakis-addition for efficient synthesis of c(60)-centered dendritic molecules bearing multiple aromatic chromophores

In the templated hexakis-addition reaction of malonic esters with C(60) to prepare dendritic macromolecules that are terminated symmetrically with 12 derivatized pyrenes, a simple modification to use a much larger excess of the bromination agent resulted in dramatic increases in the product yields. [structure: see text]     

Intra- and intermolecular heavy-atom effects on the fluorescence properties of brominated C60 polyads

A series of brominated mono-methano[60]fullerene malonate derivatives (two diads and one triad) are investigated for intramolecular and external heavy-atom effects on their fluorescence. Significant internal and external heavy-atom effects are observed in the three cases. It is shown that the internal effect doubles when going from the diads to the triad. In bromobenzene and in iodobenzene, the external effect is predominant, and diads and triad behave identically.     

Nanostructure origins of C60 fluorescence in pyridine

The nanostructure origins of three distinct and strong fluorescence bands of C60 in room-temperature pyridine are reported for the first time. Fluorescence study and in-situ TEM observation on C60-pyridine solutions with different setting times exhibit that the blue fluorescence peaks centered at 440 nm originate from C60 nanoparticles; the yellow-green fluorescence band located at 575 nm derives from C60 lace-like cluster; and the salmon pink fluorescence band around 700 nm arises from C60 microbulk in solution. The conclusions are supported further by investigation on the C60-toluene system as well.     

Photophysical properties of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor or acceptor substituents: their fluorescence solvatochromism and lightfastness

We prepared a series of 1,3,6,8-tetrakis(arylethynyl)pyrenes with donor or acceptor substituents and investigated their photophysical properties. Solvent polarity hardly affected on the UV/vis spectra of all of the tetrakis(arylethynyl)pyrenes used in this study. On the other hand, electron-donating groups, NMe₂ and NPh₂ groups imparted fluorescence solvatochromicity to the skeleton by intramolecular charge transfer in the excited state. Furthermore, a tetrakis(arylethynyl)pyrene showed better lightfastness upon exposure to laboratory weathering using a xenon long arc lamp than coumarin.     

Inclusion properties of 3-fluoromesotetraphenylporphyrin with C60 and C70

To improve the selectivity ratio of C70 over C60, a new designer molecule, viz., 3-fluoromesotetraphenylporphyrin (1) has been reported in the present investigations. Fluorescence studies reveal that the Q-absorption band of 1 gets sufficient quenching effect upon addition of both C60 and C70. Binding constants (K) of the C60/1 and C70/1 complexes are estimated to be 580 and 10,800 dm3 mol(-1), respectively. Thus, K(C70)/K(C60) is approximately 19 which is very large and even comparable with other macrocyclic host molecules like calix[5]arene, azacalix[m]arene[n]pyridine, cyclotriveratrylenophane and calixarene bisporphyrin. 1H NMR chemical shift measurements show that the -NH- proton of 1 suffers more shifts in presence of C70 compared to C60. This finding also offers a good support in favor of high K value for C70/1 complex as well as large selectivity ratio of C70 over C60.     

Spectral properties of the C60 complex with dibenzenechromium

The product of the interaction of fullerene C₆₀ with dibenzenechromium (DBC) was studied by ESR and IR spectroscopy. The ESR spectrum contains a signal of the radical cation DBC⁺. A signal of the C₆₀ ^? anion is virtually absent, which is most likely related to its broadening. The IR spectrum contains bands characteristic of the DBC⁺ cation in the (DBC)I molecule and four bands characteristic of C₆₀ ^?. The data obtained indicate the interaction of C₆₀ molecules with the environment in the crystal structure of the complex.     

Effects of substituents on silicon atoms upon absorption and fluorescence properties of 1,3,6,8-tetrakis(silylethynyl)pyrenes

Synthesis, UV–vis absorption, and fluorescence spectroscopic properties of 1,3,6,8-tetrakis(silylethynyl)pyrenes 2–10 were studied. Absorption maxima of CH₂Cl₂ solutions of these compounds appeared at 437–445?nm, and molar absorption coefficients (ε) of most of these compounds exceeded 10⁵?L?mol^?1?cm^?1. Fluorescence emissions measured in dilute CH₂Cl₂ solutions are observed in visible region, and their intensities remarkably increased compared with that of pyrene. Fluorescence spectra obtained from concentrated CH₂Cl₂ solutions exhibited broad excimer emissions when steric bulk of substituents on silicon atoms is sufficiently low. Molecular orbital calculations indicated that HOMO-LUMO energy gap decreased with increasing the number of phenyl groups on silicon atoms, and that the silyl groups act as electron-donating groups to tetraethynylpyrene core. Resonances in ²⁹Si NMR spectra shifts to upfield with increasing the number of phenyl groups on silicon atoms due to the shielding effect of phenyl groups.     

UV-Vis, fluorescence and NMR spectroscopic investigations on inclusion properties of a designed tetrahomocalix[8]arene with fullerenes C60 and C70 in solution

The present article reports the spectroscopic investigations on non-covalent interaction of fullerenes C(60) and C(70) with a macrocyclic receptor molecule, namely, 1,3,5,7-tetrahomo-p-tert-butylcalix[8]arene (1) in toluene. Jobs method of continuous variation reveals 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds selectively C(60) compared to C(70) as obtained from binding constant (K) data of C(60)-1 (K(C60-1)) and C(70)-1 (K(C70-1)) complexes which are enumerated to be 265,000 dm(3) mol(-1) and 63,43 dm(3) mol(-1), respectively, and selectivity in binding (K(C60-1)/K(C70-1)) is estimated to be 4.18 as obtained from UV-Vis study. Steady state fluorescence studies reveal quenching of fluorescence of 1 in presence of fullerenes and the K value of the C(60)-1 and C(70)-1 complexes are estimated to be 80,760 and 68,780 dm(3) mol(-1), respectively, with selectivity in binding (K(C60-1)/K(C70-1)) ~1.18. (1)H NMR analysis provides very good support in favor of strong binding between C(60) and 1. The high value of K value for C(60)-1 complex indicates that 1 forms an inclusion complex with C(60).     

The synthesis and fluorescence of a methoxy-phenyl substituted C_60-pyrrolidine derivative

A new 4-methoxyphenyl substituted C60-pyrrolidine derivative, C60(C10H13NO) (1), was prepared and its room-temperature fluorescence was studied. Its fluorescence intensity is three times stronger than that of C60. Its singlet energy was estimated to be 25 kJ/mol lower than that of C60. The fluorescence lifetime was determined to be 2.1+0.3 ns by using the frequency domain method. The fluorescence quenching by concentration and aromatic electron donor: N, N-dimethyl aniline (DMA) was investigated. Data show that its fluorescence could not be quenched by DMA.     

Physicochemical properties of Water-Soluble Fullerene C60-Carbohydrate Composites

Water-soluble composites of fullerene C60 with carbohydrates (saccharose, fructose, and dextrans) prepared by the mechanochemical procedure were analyzed by electronic absorption and ¹³C NMR spectroscopy, thin-layer chromatography, and differential scanning calorimetry.     

Absorption spectrophotometric, fluorescence and theoretical investigations on supramolecular interaction of a designed bisporphyrin with C60 and C70

The present article reports the spectroscopic and theoretical investigations on supramolecular interaction between fullerenes (C(60) and C(70)) and a designed bisporphyrin, namely 1, in toluene. Job's method of continuous variation establishes 1:1 stoichiometry of the fullerene/1 complexes. Both absorption spectrophotometric and steady-state fluorescence studies reveal effective and selective interaction between fullerenes and 1 as average binding constants (K) for the C(60)/1 and C(70)/1 complexes are enumerated to be 34,700 and 359,925 dm(3) mol(-1), respectively. Large selectivity ratio in K, i.e., K(C(70))/K(C(60)), indicates that 1 acts as an effective molecular tweezers for C(70) in solution. Time-resolved fluorescence study evokes that the quenching of fluorescence of 1 by fullerenes is of static type in nature. Molecular mechanics calculations in vacuo determine the energies and single projection structures of the supramolecular systems, which provide very good support in favor of strong binding between C(70) and 1.     

C(60)-based triads with improved electron-acceptor properties: pyrazolylpyrazolino[60]fullerenes.

A series of triad pyrazolylpyrazolino[60]fullerenes has been prepared in one pot from suitably functionalized hydrazones by 1,3-dipolar cycloaddition reactions under microwave irradiation. The electrochemical properties of the compounds obtained were investigated by cyclic voltammmetry, and they show better electron acceptor character than the parent C(60) in all cases. Fluorescence experiments and time-resolved transition spectroscopy indicate the existence of photoinduced charge-transfer processes with the C(60) triplet acting as the acceptor.     

Cytotoxicity and photocytotoxicity of a dendritic C(60) mono-adduct and a malonic acid C(60) tris-adduct on Jurkat cells

The cytotoxic and photocytotoxic effects of two water-soluble fullerene derivatives, a dendritic C(60) mono-adduct and the malonic acid C(60) tris-adduct were tested on Jurkat cells. Cell growth and vitality were determined by a cell counting and staining technique. After 2 weeks cultivation in the presence of the fullerene derivatives, it was found that only the dendritic mono-adduct inhibits cell growth (within 2 weeks the cell number decreased to 19%), whereas the tris-malonic acid adduct has little effect. The growth inhibition is reversible; cultivating the same cells further in the absence of fullerene, the cell number increased to 106.4%. Other experiments showed that these fullerene derivatives become toxic when irradiated with UVA or UVB light. The cell death is mainly caused by membrane damage and it is UV dose-dependent. Tris-malonic acid fullerene was found to be more phototoxic than the dendritic derivative. This result is in contrast to the singlet oxygen quantum yields determined for the two compounds. We propose that the two fullerene derivatives may interact with the cell membrane in different ways thus causing the observed effects. Further experiments will be done to determine the location and concentration of the two compounds in and on the cells.     

Crystal solvate of C60 with tricloroethylene,C60 · C2HCl3

Extraction of fullerenes from carbon soot by trichloroethylene has been studied. We have found that C₆₀ forms a solvate with trichloroethylene (C₆₀ · C₂HCl₃:a=31.31(1);b= 10.156(4);c=10.146(4) Å;V=3228.6 ų,Z=4,d _calc=1.752 g cm^–3, orthorhombic symmetry). Its thermal stability has been studied using TG and DSC. A phase transition of the first order at 167 K has been detected.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1248–1250, July, 1994.The authors are grateful to V. P. Bubnov and I. S. Krainskii for providing them with the samples of fulle-rene-containing carbon soot, and to M. G. Kaplunov and A. V. Zvarykina for assistance in the work.This work was carried out with the financial support of the Russian Foundation for Basic Research, Project Nos. 93-03-18705 and 93-03-5650.     

Some properties of the adduct of benzenesulfinyl chloride with myrcene

Conclusion The reaction of PhSOCl with myrcene at high pressure leads to the cis-1,4 addition product.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5 pp. 1143–1145, May, 1987.     

Synthesis and properties of water-soluble derivatives of fullerene C60

Procedures for synthesized of water-soluble forms of fullerene C₆₀ and its derivatives were developed.     

Study on the intermolecular interaction of C60 and simulations on the orientational properties of C60 in crystals

We developed the new intermolecular interaction model of C(60) with the quantitative accuracy for the molecular orientational properties in crystals. The energy difference (DeltaE) and the activation barrier (E(barrier)) between the two stable orientations (P and H orientations) in crystals are in the values of +14.7 and +260 meV in our model, respectively; these values are in fairly good agreement with the experimental values (DeltaE approximately +11 meV, E(barrier)=+235-+290 meV in experiments). The relaxation calculation for C(60) crystals using our model revealed that there is the reversal of the stable orientations between the P and H orientations under the high H-orientation occupancy (p(H)) in crystals, when p(H)>0.83, DeltaE<0. From the molecular dynamics calculations for C(60) crystals using our model, it is found that the phase transition is induced at T(C)=200-260 K, which is consistent with the experimental value of 260 K. Immediately below T(C), we found a great variety of molecular rotational jumps involving that between the P and H orientations every about 10(-9) s due to the thermal activation. In the high temperature phase (>T(C)), all molecules rotate irregularly like in Brownian motion involving the rotational "slumber" for approximately 10(-12)-10(-11) s.     

Structure and electronic properties of highly charged C60 and C58 fullerenes

We present a theoretical study of the structure and electronic properties of positively charged C60(q+) and C58(q+) fullerenes (q = 0-14). Electronic energies and optimum geometries have been obtained using density-functional theory with the B3LYP functional for exchange and correlation. We have found that closed- and semiclosed-shell C60(q+) ions (q = 0, 5, and 10) preserve the original icosahedral symmetry of neutral C60. For other charges, significant distortions have been obtained. The C58(q+) fullerenes are, in general, less symmetric, being C58(8+) the closest to the spherical shape. Most C60(q+) fullerenes follow Hund's rule for spin multiplicity, while most C58(q+) fullerenes are more stable with the lowest spin multiplicity. The calculated ionization potentials for both kinds of fullerenes increase almost linearly with charge, except in the vicinity of C60(10+) and C58(8+). We have also explored the region of the potential-energy surface of C60(q+) that leads to asymmetric fission. Minima and transition states corresponding to the last steps of the fission process have been obtained. This has led us to conclude that, for 3 < or = q < or = 8, C2(+) emission is the preferred fragmentation channel, whereas, for higher q values, emission of two charged atomic fragments is more favorable. The corresponding fission barrier vanishes for q > 14.     

Preparation and properties of polyethoxysilsesquioxane‐C60 hybrids

Free‐standing films of C₆₀‐polyethoxysiloxane hybrids were prepared, and their optical limiting properties were evaluated. Triethoxysilylated C₆₀, with a formula of H₃C₆₀[Si(OEt)₃]₃, was synthesized by the hydrolysilylation of C₆₀ with triethoxysilane in the presence of platinum catalyst. C₆₀‐polyethoxysiloxanes were prepared by a cohydrolytic polycondensation of triethoxysilylated C₆₀ with tetraethoxysilane in a molar ratio of Si/C₆₀ = 10–1000 under nitrogen flow. The molecular weight of C₆₀‐polyethoxysiloxane increased with a decrease of Si/C₆₀. Transparent and flexible free‐standing films were prepared by aging an ethanol solution of C₆₀‐polyethoxysiloxane at 80 °C for 6–8 days. The mechanical strength and Young's modulus increased with a decrease in Si/C₆₀. These free‐standing films showed an optical limiting property, for which the threshold value decreased from 1163 mJ/cm² (Si/C₆₀ = 1000) to 130 mJ/cm² (Si/C₆₀ = 10) with a decrease of Si/C₆₀. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3273–3279, 2007