Narrow Results

We have investigated the decomposition of C₆₀ molecules with low and high coverages on Si(100)(2×1) surface at elevated temperatures. We also investigated the decomposition of an isolated C₆₀ molecule. We employed molecular-dynamics simulation using a model potential. It has been found that C₆₀ decomposes on Si(100) surface after 1000 K in the case of low coverage (0.11), however in high coverage case (0.67), C₆₀ molecules decompose after 900 K. On the other hand, isolated C₆₀ molecule decomposes after 7500 K, interestingly it shows a phase change from 3D to 2D at higher temperatures.

We have prepared three C₆₀ polymers under high-temperature and high-pressure conditions, and confirmed them to be orthorhombic (1D), tetragonal and rhombohedral (2D) polymer by XRD method, respectively. The ¹³C MAS NMR spectra of both orthorhombic and rhombohedral polymer have been measured and two resonance peaks observed. One resonance at 73 ppm resulted from the sp³ carbons with an intermolecular bonding, the other at 145 ppm is from the inequivalent sp² carbons on the C₆₀ molecule. For 1D polymer, the fine structure of the main peak at 145 ppm has been analyzed. By simulation of the ¹³C MAS NMR peak shape of the inequivalent carbons, we propose that there exist nine inequivalent carbons on a C₆₀ molecule in the orthorhombic (1D) polymer.

High harmonic generation (HHG) has attracted tremendous attention over two decades. This paper presents a brief review of high harmonic generation in atoms, molecules and nanostructures. Through a simple classical model, we first review a few important concepts in HHG. We then discuss how the electric field initial phase affects the harmonic yield, and explain the reason behind the cutoff law. We focus on HHG in nanostructures. As an example, a detailed calculation in C₆₀ is presented.

A mixture of TNT (Trinitrotoluene) and natural graphite was detonated in a vacuum container which was immersed into cooling water; detonation products were collected for detecting. The results of mass spectroscopy, high performance liquid chromatography showed significant signals of C₆₀, which proved that C₆₀ could be synthesized by detonating the mixture of TNT/graphite and the detonation pressure was around 12.3 GPa and the detonation temperature was around 1985 K.

To explore the practicability of C₆₀ synthesis under extreme conditions (high pressure and high temperature), trinitrotoluene (TNT), trinitramine (RDX) and graphite mixtures of different proportions were detonated in a vacuum container, and the detonation products were collected for detecting. The results of mass spectroscopy, high performance liquid chromatography showed significant signals of C₆₀, which proved that C₆₀ could be synthesized by detonating the mixture of TNT and graphite (in 6:4 and 7:3 mass ratio, respectively), the detonation pressure and temperature were calculated around 13 GPa and 2000 K, respectively. Both experiment results and theoretical analysis showed the importance of detonation pressure and cooling temperature in detonation synthesis of C₆₀.

The Au ultra-fine films were grown by MBE or magnetron sputtering on Al₂O₃ or MgO single crystals which were annealed at 1000°C to obtain smooth surfaces with a step-terrace structure. A one-dimensional alignment of Au particles was partially observed around the steps on Al₂O₃(0001), surfaces at about 600°C. On the other hand, Au ultra-fine films were also deposited by magnetron sputtering on MgO(100). The two processes were proceeded to obtain C₆₀ monolayers on the above Au films. Only C₆₀ molecules adsorbed on Au remained and the others were re-evaporated by annealing at 350°C. By this re-evaporation method the nanostructured C₆₀ monolayers were fabricated. In addition self-assembly monolayers of a C₆₀ derivative, C₆₀-O-C₈SH, (C₆₀-SAM) were synthesized on the Au/MgO by soaking in benzene solution of the C₆₀ derivative. The C₆₀-SAM was obtained only along the step edges. In the case of C₆₀-SAM on ultra-fine Au films/MgO several samples showed the resistivity anomalies at 150–250 K accompanying with specific deviation from metallic linear dependences on temperature.

We have performed the ab initio molecular orbital calculations for combinations of the fullerene-fragments as the models of the nonbonding interaction of C₆₀ dimer at the preferred configurations in the simple cubic phase. The intermolecular interaction potentials have been calculated using several basis sets with MP2 level of the electron correlation energy and the basis set superposition error correction. The strong dispersion attractions that is dominant in the van der Waals interaction has been found for the combinations of the fullerene-fragments. The equilibrium intermolecular distances obtained are in good agreement with the corresponding experimental value. The repulsive region of the intermolecular interaction calculated by ab initio method is found to be express by an atom–atom interaction potential with an anisotropic exponential type repulsive term, which is less steep than the conventional Lennard–Jones type potential.

The non-bonded interactions between a porphyrin molecule and a C₆₀ molecule, in the gas-phase, has been systematically investigated using various theoretical models. These are: (1) wavefunction-based methods, Hartree-Fock SCF (HF), second-order Møller-Plesset (MP2) theory, and the localized MP2 (LMP2) theory using the diatomics in molecules (DIM-LMP2) and triatomics in molecules (TRIM-LMP2) methods; (2) density functional theory (DFT), using non-local (BLYP, PW91), hybrid (B3LYP), and local (SVWN) functionals. Of the HF and DFT methods examined, corrected for BSSE using the counterpoise (CP) method, only the SVWN method predicts a close separation (2.5 Å) between the porphyrin and the C₆₀ molecules, in line with close contacts observed in crystal structures of cocrystallates of porphyrins and fullerenes (2.7-3.0 Å). The MP2 and LMP2 methods also predict a close contact between the two molecules although the MP2 and TRIM-LMP2 methods overestimate the interaction giving a separation < 2.5 Å while the DIM-LMP2 method gives a satisfactory separation of 2.9 Å. The SVWN and DIM-LMP2 methods also predict a reasonable complexation energy of ca. −13 kcal/mol (SVWN and DIM-LMP2 CP-uncorrected) and −7.9 kcal/mol (SVWN CP-corrected), whereas the MP2 and TRIM-LMP2 methods probably strongly overestimate the complexation energy. The remaining methods underestimate the complexation energy. The CP-uncorrected DIM-LMP2/6-31G(d) method gave the best estimate of the porphyrin-C₆₀ separation (2.9 Å) with a complexation energy of −13.3 kcal/mol; however, the more cost-effective SVWN functional gives satisfactory values for these quantities with the SVWN/6-311+G(d) level providing the best estimate for the complexation energy (−16.5 kcal/mol). The porphyrin-C₆₀ interaction was investigated in the giant triad 1 in which a zinc porphyrin, a dimethoxynaphthalene and a C₆₀ fullerene are separated by two norbornylogous bridge sections of six and five bond lengths, respectively. All methods predict the existence of a compact form of the molecule in which the porphyrin and C₆₀ moieties are only 2.9-4.3 Å apart (contact distance). This finding is consistent with certain photophysical properties of 1.

Photochemical and photophysical properties of self-assembling 5-(4-pyridyl)-10,15,20-triphenylporphinatozinc (Znpyp₃) have been studied by steady-state and time-resolved absorption in addition to time-resolved fluorescence spectroscopy. Self-assembling oligomers (Znpyp₃)_n(n = 3 at 0.1 mM) were synthetically generated and assigned to a zigzag chain oligomeric structure, where n is dependant on the concentration and temperature. The lifetimes of the singlet and triplet excited states of (Znpyp₃)_n depend on n and the axial ligation. The rate-constant of (Znpyp₃)_n for the intermolecular T-T annihilation process was smaller than that of monomeric porphyrins. In the photoinduced electron-transfer to fullerenes (C₆₀ and C₇₀), it was revealed that the rate-constants and efficiencies for (Znpyp₃)_n were essentially the same as those of the monomer. In the back electron transfer, the rate-constants of oligomers were smaller than that of the monomeric porphyrin, which suggests hole-delocalization along the porphyrin chain.

The complexes of cobalt(II) tetraphenylporphyrin (Co^IITPP) with fullerenes C₆₀, C₇₀ and C₆₀(CN)₂ are presented. It is shown that Co^IITPP forms complexes with fullerenes in different solvents: [Co^IITPP•fullerene•solvent] (solvent = C₆H₆, C₆H₅Me, C₆H₄Cl₂, CS₂, CHCl₃). The use of additional donors (Cp₂Fe, Cr⁰(C₆H₆)₂, and TDAE) in the synthesis of Co^IITPP/fullerene complexes allows one to obtain multi-component complexes ranging from neutral [(Co^IITPP•Py)₂•Cp₂Fe•fullerene•solvent] to ionic [Co^IITPP•(D₂^•+)•(fullerene^•−)•solvent] (D₂ = Cr^I(C₆H₆)₂, TDAE). The interaction of Co^IITPP with neutral and negatively charged fullerenes is considered. The neutral Co^IITPP/fullerene complexes are characterized by a secondary M…C(fullerene) bonding with the shortest Co…C contacts in the 2.69-2.82 Å range and noticeable changes in the electronic structure of the parent components. At the same time, σ-bonding is observed in ionic complexes between Co^IITPP and fullerene radical anions with the shortened Co…C contacts being in the 2.28-2.32 Å range. The resulting (Co^IITPP•fullerene⁻) anions are diamagnetic. The σ-bonding is relatively weak and the (Co^IITPP•fullerene⁻) anions begin to dissociate above 200 K.

This article reviews recent developments that have taken place in research related to new porphyrin architectures and their host-guest chemistry, as described in a microsymposium bearing the same name held during the 3^rd International Conference on Porphyrins and Phthalocyanines (ICPP-3). The usefulness of representative arrays, aggregates, donor-acceptor systems, and receptor motifs based on porphyrin architectures is highlighted as it applies to the fabrication of molecular devices, understanding the biomimetic electron transfer processes, and recognition of bioorganic substrates.

In situ scanning tunneling microscopy (STM) was employed to investigate the adsorption of C₆₀ on a Ni(II) octaethylporphyrin (NiOEP) adlayer at liquid/Au(111) interface. It was found that C₆₀ molecules tend to form small islands without defined coordination to the underlying NiOEP array. Moreover, increasing the surface coverage of C₆₀ resulted in the formation of multilayers. The mixture of C₆₀ and NiOEP prepared in solution formed separated domains. The results suggested that the C₆₀–C₆₀ interaction is stronger than that of C₆₀–NiOEP and dominated the adsorption of C₆₀ on NiOEP-modified Au(111) surface. This work provides a direct evidence at molecular scale for the coordination of C₆₀ with NiOEP in a two-dimensional assembly, demonstrating that immobilizing C₆₀ at the geometric center of NiOEP on an Au(111) surface in solution is complicated.

The effect of ultraviolet, visible and near-infrared irradiation on the yield and morphology of single crystalline C₆₀ fullerene nanowhiskers (FNWs) and nanotubes (FNTs) was investigated in an effort to produce large-scale quantities of FNWs and FNTs. These fullerene nanomaterials were synthesized by the liquid–liquid interfacial precipitation method using pyridine and isopropyl alcohol (IPA) as solvents. The C₆₀–pyridine solution was illuminated using different wavelengths for 24 h at ambient pressure and temperature before addition of IPA. High yields (30–38 mg/L) were obtained upon irradiation using wavelengths in the ultraviolet region in accordance with the increased photoabsorption signal of solid C₆₀ and C₆₀ dissolved in pyridine acquired by a UV-VIS-NIR spectrophotometer. However, elevated yields (21–27 mg/L) were also obtained in the 600–800 nm regions, where C₆₀ absorption is particularly weak. Such an enhanced yield of FNTs and FNWs is probably related to the reported rise in transient absorption of the triplet excited state of C₆₀ in the 740 nm region formed by the decay of the photoexcited singlet C₆₀ through intersystem crossing. The formation of photopolymerized fullerene nanofibers was also observed by Raman spectroscopy, it is attributed to ultraviolet and visible light irradiation. SEM and TEM observations suggest that preparation of FNWs and FNTs by irradiation using different wavelengths of light does not produce apparent morphological transformations on the surface of these fullerene materials.

The growth rate of C₆₀ fullerene nanowhiskers (C₆₀NWs) prepared by the liquid–liquid interfacial precipitation method is measured and the growth mechanism is discussed. The growth of C₆₀NWs is investigated from the data obtained at the growth temperatures of 5, 10, 15 and 20°C. It is found that the convection of the solution scarcely influences the growth rate, suggesting that a surface reaction of C₆₀ molecules dominates the growth process. The activation energy of C₆₀NWs' growth is estimated at about 52.8 kJ/mol from their initial stage of growth. This activation energy is much greater than that of C₆₀ diffusion in solutions found in the literature. This result suggests that the desolvation process of C₆₀ on the whisker surface governs the growth of C₆₀NWs.