Gels of ionic liquid [C4mim]PF6 formed by self-assembly of gelators and their electrochemical properties

Three types of gelators, bis(4-octanoylaminophenyl) ether (BODE), bis(4-octanoylaminophenyl) methane (BODM) and 2,4′-bis(octanureido) toluene (BOUT) were utilized as gelators for the gelation of ionic liquid 1-butyl-3-menthyl-imidazolium hexafluorophosphate ([C₄mim]PF₆). The mean minimum gelator concentrations (MGCs) for the [C₄mim]PF₆ were found to be less than 2 wt%. The polarized optical microscopy image of [C₄mim]PF₆ gels reveals the formation of spherical crystallites resulting from the fibrillar aggregates of the gelators. The cyclic voltammograms of the [C₄mim]PF₆ gels indicate a good electrochemical stability over the range from ?3.0 to 3.0 V. The impedance spectra of the [C₄mim]PF₆ gels show good linear relationships between ion conductivity and temperature, indicating that the temperature dependence of the conductivity follows the classical Arrhenius equation.     

Unique Separation Behavior of a C60 Fullerene‐Bonded Silica Monolith Prepared by an Effective Thermal Coupling Agent

Herein, we report a newly developed C₆₀ fullerene‐bonded silica monolith in a capillary with unique retention behavior due to the structure of C₆₀ fullerene. N‐Hydroxysuccinimide (NHS)‐conjugated C₆₀ fullerene was successfully synthesized by a thermal coupling agent, perfluorophenyl azide (PFPA), and assigned by spectroscopic analyses. Then, NHS‐PFPA‐C₆₀ fullerene was attached onto the surface of a silica monolith in a capillary. The capillary provided specific separation ability for polycyclic aromatic hydrocarbons in liquid chromatography by an effective π–π interaction. Furthermore, corannulene, which has a hemispherical structure, was selectively retained in the capillary based on the specific structural recognition due to the spherical C₆₀ fullerene. This is the first report revealing the spherical recognition ability by C₆₀ fullerene in liquid chromatographic separation.     

BaxC60 fullerides: π Electronic peculiarities of the C60 molecule and their consequences for the solid state

The electronic structure of Ba_xC₆₀ fullerides was studied theoretically under special consideration of π electronic effects in the C₆₀ molecule. Band structure data were derived by an intermediate neglect of differential overlap (INDO) crystal orbital (CO) approach. Different electronic configuration were evaluated in the Ba-doped C₆₀ fullerides. Ba_xC₆₀ solids with x=0, 3, 4, 6 are insulators. For a Ba₅C₆₀ model extrapolated from the crystal structure of Ba₆C₆₀, a finite band gap is also predicted. For a Ca₅C₆₀-like structure of Ba₅C₆₀, a quasi-degeneracy between a metallic configuration and an insulating Mott-like state was found. With an increasing Ba-to-C₆₀ charge transfer (CT), sizable changes in the π system of C₆₀ occur. In the neural molecule and for not too high an electron count, the π electrons form more or less electronically isolated hexagon–hexagon (6–6) “double” bonds with only minor hexagon–pentagon (6–5) “double-bond” admixtures. In the vicinity of C₆₀¹²⁻, the 6–6 bonds have lost most of their double-bond character while it is enhanced for the 6–5 bonds. In highly charged anions, the π electron system of the soccer ball approaches a configuration with 12 decoupled 6π electron pentagons. For electron numbers between C₆₀ and C₆₀¹²⁻, the net π bonding is not weakened. The INDO CO results of the Ba_xC₆₀ solids are supplemented by INDO MO and ab initio (3-21 G* split-valence basis) calculations of molecular C₆₀ and some highly charged anions. Ab initio geometry optimizations show that the bond alternation of C₆₀ with short 6–6 and long 6–5 bonds is inverted in C¹²⁻₆₀. The high acceptor capability of C₆₀ is explained microscopically on the basis of quantum statistical arguments. In the π electron configurations of C₆₀ and C₆₀¹²⁻, the influence of the Pauli antisymmetry principle (PAP) is minimized. The quantum statistics of (π) electron ensembles with a deactivated PAP is of the so-called hard-core bosonic (hcb) type. In these ensembles, the on-site interaction is fermionic while the intersite interaction is bosonic. Energetic consequences of the quantum statistical peculiarities of π systems are explained with the aid of simple model systems; we selected annulenes and polyenes. Computational tools in this step are Green's function quantum Monte Carlo (GF QMC) and full configuration interaction (CI) calculations for the π electrons of the model systems. These many-body techniques were combined with a Pariser–Parr–Pople (PPP) Hamiltonian. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 333–373, 1997     

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.     

Mixing of triply degenerated molecular orbitals in C602− and C603−

Mixing of triply degenerated lowest unoccupied molecular orbitals (LUMO; t_1u) and the next LUMO (NLUMO; t_1g) of a neutral C₆₀ molecule was estimated when it becomes dianionic (C₆₀²⁻) and trianionic (C₆₀³⁻) species. The electronic structure of the basic C₆₀ was obtained by a semiempirical (INDO type) Hartree-Fock scheme and the mixing of the t_1u and t_1g MOs by the conventional configuration interaction (CI) method assuming I_h structural symmetry of a C₆₀ for the sake of simplicity. The most favorable electronic states of C₆₀²⁻ and C₆₀³⁻ are predicted to be triplet and doublet, respectively. Furthermore, in C₆₀²⁻, the energy difference of this triplet state and the first excited singlet state is very close, which agrees well with the experimental observation. © 1997 John Wiley & Sons, Inc.     

Gelation Behavior of N-Decane Organogels with Gelators C28 and C40

Organogel formation during paraffin crystallization is one of the causes of oilfield problems. We investigated the formation of n-alkane organogels having C₁₀ as liquid phase and n-octacosane (C₂₈) and n-tetracontane (C₄₀) as solid gelators. It was seen that C₁₀/C₂₈ and C₁₀/C₄₀ form organogels with onset gelation temperatures of 33°C and 48°C respectively, while C₁₀/C₂₈/C₄₀, gelify at 52°C. Replacement of C₂₈ by n-heneicosane (C₂₁) reduced the crystallization rate of C₄₀. This result indicates that the onset temperatures and crystallization rates of organogels with gelators in the range of C₂₈ to C₄₀ could be modulated through the introduction of shorter chain n-alkanes.     

Dependence of the dispersion behavior of [60]fullerene in aqueous media on the chain length of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) as a dispersing agent

We have investigated the effect of the chain length of temperature-sensitive poly(N-isopropylacrylamide) (PIPAAm) on the dispersion of [60]fullerene (C₆₀) in aqueous media through an interaction between PIPAAm and C₆₀ below the lower critical solution temperature (LCST) of PIPAAm. UV–vis absorption spectral measurements showed that the saturated amount of the dispersed C₆₀ increased in proportion to the chain length of the PIPAAm. Additionally, an absorption band at around 430 nm was observed in the dispersed C₆₀ solution and was assigned to a C₆₀/PIPAAm complex. The complex formed an amorphous molecular assembly between C₆₀ molecules and PIPAAm chains, the structure of which was confirmed in a transmission electron microscopy image. Dynamic light scattering measurements indicated that the particle size of the C₆₀/PIPAAm complex increased with the chain length of the PIPAAm. From electrophoretic laser light scattering measurements, the zeta potential of the C₆₀/PIPAAm complex was found to be shifted from a negative value to zero with an increase in the chain length of PIPAAm. Longer PIPAAm chains, however, gave rise to a higher dispersion stability of the complex. Similar to the dispersion behavior of PIPAAm-C₆₀ conjugates in aqueous solutions, the aqueous C₆₀ dispersion with PIPAAm exhibited rapid, and reversible dispersion–aggregation changes in response to temperature alternation across the LCST.     

Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY−Fullerene C60 Dyad as Potential Antimicrobial Agent

A covalently linked BODIPY−fullerene C₆₀ dyad (BDP−C₆₀) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C₆₀ to inactivate bacteria. The absorption spectrum of BDP−C₆₀ was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C₆₀. Spectroscopic, calculations, and redox studies indicate a competence between photoinduced energy and electron transfer. Protonating the dimethylaminophenyl substituent through addition of an acidic medium led to a substantial increase in the fluorescence emission, triplet excited state formation, and singlet molecular oxygen production. At physiological pH, photosensitized inactivation of Staphylococcus aureus mediated by 1 μM BDP−C₆₀ exhibited a 4.5 log decrease of cell survival (>99.997 %) after 15 min irradiation. A similar result was obtained with Escherichia coli using 30 min irradiation. Moreover, proton-activated photodynamic action of BDP−C₆₀ turned this dyad into a highly effective photosensitizer to eradicate E. coli. Therefore, BDP−C₆₀ is an interesting photosensitizing structure in which the light-harvesting antenna effect of the BODIPY unit combined with the protonation of dimethylaminophenyl group can be used to improve the photoinactivation of bacteria.     

Investigation on the interaction on and the rotation of C60 in alkali-doped complexes AXA′3-XC60 (X = 1, 2, 3; A,A′ = alkali)

The interaction on and the rotation of C₆₀ in akali-doped C₆₀ solids, A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = alkali), have been calculated with Buckingham potential model. The results show that the total interaction on C₆₀ changes dramatically when the pure C₆₀ solid is alkali-doped into K₃C₆₀. The interaction on C₆₀ in K₃C₆₀ is about 20 times greater than that in pure C₆₀. And the main component in the former, occupying > 90% is electrostatic, while in the latter, the main components, occupying > 90%, are dispersive and repulsive. The results also show that in contrast to the whole-region free rapid rotation of C₆₀ molecule in its pure solid, the rotation of C₆₀ in K₃C₆₀ is mostly forbidden due to a 10 times increase (reaching about 300 kJ/mol) in potential barrier, except for the region from 0° to 50° where a broad, smooth, and shallow potential well exists. Calculations for alkali-doped complexes other than K₃C₆₀, i.e., A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = K, Rb, Cs), come to the same conclusion. Finally, an interesting and meaningful result is that the superconducting transition temperatures of A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = K, Rb, Cs) change inversely with the total interactions on C₆₀. © 1995 John Wiley & Sons, Inc.     

Electrochemical behavior of fullerene C60 and substituted fullerenes immobilized on an electrode surface

The effect of substituents with different donor capabilities, which are inserted into a molecule of fullerene C₆₀, on the kinetics and thermodynamics of redox conversions of fullerenes that are immobilized on an electrode, is studied for the first time. To this end, redox conversions that occur with rubbed-on films of fullerene and fulleropyrrolidines are studied using cyclic voltammetry in 0.5 M KCl/H₂O and a 0.1 M (C₄H₉)₄NBF₄/AN solution in acetonitrile. A hypothesis that the kinetics of redox conversions occurring with films of individual fullerenes is defined largely by changes in the structure of initial films in the process of their cathodic doping is used. The effect of the substituents is explained in the framework of this hypothesis by a transition from a dense crystalline structure of nonsubstituted fullerene C₆₀ to an amorphous structure of substituted fullerenes. It is demonstrated that the formal potentials corresponding to redox conversions of fullerenes in a solid cationic lipid matrix are defined by the energy of interaction of anions, which are products of reduction of fullerenes, with cations of the matrix. As a result of this interaction, the formal potentials of the process of cathodic doping shift to less negative values. It is established that the insertion of a donor substituent and increase in its donor capability amplify the energy of interaction of the fullerene anions with the lipid cations.     

Studies of the photoexcited states of the fullerenes, C60 and C70

The spectra of C₆₀ and C₇₀ were examined using low-temperature photoluminescence and quasi-elastic light scattering spectroscopy. A detailed vibronic analysis of the lowest triplet and singlet excited states of C₇₀ is obtained. The lowest triplet state is identified as a ³E₁′ state and the vibronic structure consists primarily of Herzberg-Teller active e₂′ modes. The intensity of the electronic origin is comparable to the vibronically induced intensity and is extraordinarily solvent sensitive. The spectrum of monosubstituted C₆₀ is shown to be qualitatively similar to that of C₆₀ in polar or strongly complexing solvents. The principal effect of solvent interaction or substitution is to induce dipole intensity in the orbitally forbidden electronic origins of the luminescent states of C₆₀ and C₇₀. The Rayleigh scattering of fullerene solutions illustrates that solute aggregation occurs easily and that aggregate nucleation is strongly affected by surfaces in contact with the solution.     

Bowl-Assisted Ball Assembly for Solvent-Processing the C60 Electron Transport Layer of High-Performance Inverted Perovskite Solar Cell

Pristine fullerene C₆₀ is an excellent electron transport material for state-of-the-art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high-quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl-shaped additive, corannulene, to assist in C₆₀-assembly into a smooth and compact film through the favorable bowl-ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C₆₀, it also plays a critical role in forming C₆₀-corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution-processed-C₆₀ (SP-C₆₀) ETL. Moreover, the stability of the CC device is far superior to that of the C₆₀-only device because corannulene can retard and curb the spontaneous aggregation of C₆₀. This work establishes the bowl-assisted ball assembly strategy for developing low-cost and efficient SP-C₆₀ ETLs with high promise for fully-SP PSCs.     

Nature of C60 and C70 fullerene encapsulation in a porphyrin- and metalloporphyrin-based cage: Insights from dispersion-corrected density functional theory calculations

The search for efficient synthetic hosts able to encapsulate fullerenes has attracted attention with regard to the purification and formation of ordered supramolecular architectures. This study of a porphyrin-based cage as an extension of the well-described ExCage⁶⁺ and BlueCage⁶⁺, involving viologen as sidearms, provides an interesting scenario where the oblate C₇₀ fullerene is preferred in comparison to the spherical C₆₀. Our results expose the nature of the fullerene-cage interaction involving ∼50% of dispersion-type interactions evidencing the strong π⋯π surface stacking, with a complementary contribution by the electrostatic and orbital polarization character produced by a charge reorganization with a charge accumulation facing the porphyrin macrocycles and a charge depletion along the equator formed by the viologens sidearms. Interestingly, the central N₄H₂ ring from each porphyrin contributes to the dispersion term via N-H⋯π interactions, which is decreased when the metallate N₄Zn is evaluated. Thus, the formation of stable and selective fullerene encapsulation can be achieved by taking into account two main driving forces, namely, (a) the extension of the π⋯π and X-H⋯π stacking surface and (b) charge reorganization over the fullerene surfaces, which can be used to control fine tuning of the encapsulation thanks to the introduction of more electron-deficient and electron-rich groups within the host cage.     

Ab-initio molecular dynamics simulation of monolayer C60 thin film on silicon (100) surface

Two dimensional band structure is calculated for a triangular lattice of C₆₀ molecules by using a mixed-basis approach in which wave functions are expanded with not only plane waves but also 1s and 2p atomic orbitals of carbon atoms. The present analysis modeling a charge transfer from Si dimers of the Si (100) surface suggests the existence of a small Fermi-surface. The resulting partial charge distribution is consistent with the recent STM observation of specific stripes, the direction of which is parallel to that of the topmost double bond of C₆₀, regardless of the intermolecular interaction. It is concluded that the orientation of C₆₀ on the Si surface is mainly determined by the direction of dimer arrays and not by the interaction between C₆₀ molecules.ACKNOWLEDGEMENT The authors are very grateful to the Institute for Supercomputing Research of RECRUIT Co. for the use of the NEC SX-2 supercomputer. Authors also thank IBM Japan and Japan IMSL Inc. for supporting them a good computer environment.     

A Highly Efficient Self‐Assembly of Responsive C2‐Cyclohexane‐Derived Gelators

The rational design and synthesis of a family of effective low‐molecular‐weight gelators (LMWGs) with a modular architecture based on a C₂‐1,4‐diamide cyclohexane core are reported. Due to the high symmetry, the gelators are initially well distributed in solution and no trapped aggregates are formed before the assembly is triggered. The subsequent self‐assembly process, which results in the formation of versatile gels, is highly efficient and can be triggered and tuned due to its remarkable dependence on the pH of solution. The assembly of different gelators is found to be closely related to the pK_a of the corresponding functional substituents on the LMWGs. Primary cell culture experiments reveal that the hydrogels made under physiological conditions are promising as potential tailor‐made microenvironments.     

Selective reduction of fullerene C60 by metals in neutral and alkaline media. Interaction of C60 with KOH

The reduction of fullerene C₆₀ by Zn and Mg in DMF was studied both in the presence and absence of KOH. Fullerene C₆₀ was reduced in these systems to form the C₆₀ ^n– (n = 1, 2, and 3) anions. The anions were detected by optical and ESR spectroscopies. It was found that Mg reduced C₆₀ to the monoanion, Mg/KOH and Zn reduced C₆₀ to the dianion, and Zn/KOH reduced C₆₀ to the trianion. Like KCN, potassium hydroxide adds to fullerene upon interaction with C₆₀ in DMF. The reaction of C₆₀ with KOH in benzonitrile was accompanied by the generation of the fullerene monoanion. A possible mechanism of the formation of fullerene monoanions in the presence of KOH is discussed. The degradation of the C₆₀ ^n– anions in air was studied.     

Thermal and thermo-oxidative degradation of high density polyethylene/fullerene composites

Fullerene (C₆₀)/high density polyethylene (HDPE) composites were studied in order to understand for their behaviors on thermal and thermo-oxidative degradation. Under different atmosphere, the influences of C₆₀ on the thermal stability of HDPE are different. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) demonstrate that in N₂ the addition of C₆₀ increases the onset decomposition temperature by about 10 °C with more heavy compounds (more than 34 carbon). Also the thermal stability of HDPE in air is remarkably improved with the addition of C₆₀. When the content of C₆₀ is 2.5 wt% the onset decomposition temperature increases by about 91 °C. The results of viscoelastic behavior and gel content reveal that C₆₀ can trap the alkyl radicals and alkyl peroxide radicals to inhibit hydrogen abstraction to suppress the chain scission and preserve the long chain structure. However, in the absence of C₆₀ or with low C₆₀ concentration, hydrogen abstraction occurs, resulting in the formation of a series of alkyl radicals and alkyl peroxide radicals, which accelerates the chain scission and plays a leading role in the thermal oxidative degradation.     

Interaction in fullerene—ammonia system at 423—773 K

The interaction of C₆₀ fullerite and C₆₀—NH₄Cl mixture (8 wt. % of NH₄Cl, promoter of reaction) with ammonia was investigated at a starting NH₃ pressure of 0.6—0.7 MPa in the temperature range 423—773 K. Raising the temperature to 723 K is accompanied by hydrogenation and nitrogenation of the C₆₀ matrix. Treatment of fullerite with ammonia at 773 K is followed by the decomposition of the fullerene framework and formation of X-ray amorphous product. The physico-chemical properties of hydride-nitride phases formed during the interaction were investigated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 217—219, February, 2006.     

Cycloaddition of C60 fullerene to stable 2-RSO2-benzonitrile oxides

The interaction of stable 2-RSO₂-benzonitrile oxides1a−c (R=Ph, Bu^t, or PhMeN) with C₆₀ fullerene proceeds at the double (6,6)-bond of fullerene as the [3+2] cycloaddition to form the corresponding isoxazolines2a−c. The molecular structure of compound2b was established by X-ray structural analysis. The interaction of C₆₀ fullerene with 2-(5-methyl-4-nitrothiophene)carbonitrile sulfide, which was obtained by thermolysis of 5-(5′-methyl-4′-nitro-2′-thienyl)1,3,4-oxathiazol-2-one, affords only unstable products. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 118–126, January, 1997.