Understanding the Supramolecular Self‐Assembly of the Fullerene Derivative PCBM on Gold Surfaces

We report a DFT study on the self‐assembly of the fullerene derivative PCBM on the Au(111) surface. Recent STM experiments (Angew. Chem. 2007 , 119, 8020–8023^[1]) show a coverage‐dependent transition of the adsorption and self‐assembly of PCBM on this surface. To understand the origin of this observation, we compute the geometries and relative energies of ten PCBM dimers and four tetramers. The calculations show that the self‐assembly of PCBM at high coverage is mainly controlled by hydrogen bonding between the PCBM tails. Due to the large size of the fullerene cage, the hydrogen bonds are formed far away from the surface; hence they are very similar to those found in the gas phase. This picture successfully explains the observed site‐insensitive adsorption at high coverage and the 2D arrangement of PCBM on the surface.     

The structure of fullerene films and their metallocene doping

Hexagonal close-packed (HCP) C₆₀ and C₇₀ films have been prepared by the Langmuir method and examined by electron microscopy and electron-diffraction analysis. It has been shown that the vacuum deposition of a C₆₀+C₇₀ mixture results in the formation of a film with small sized grains and a distorted C₆₀-HCP structure. The simultaneous deposition of C₆₀ and ferrocene results in the formation of a film with a changed morphology and an electron-diffraction pattern that contains a variable amount of ferrocene depending on the experimental conditions. The electron-diffraction pattern corresponds to the presence of the known molecular complex C₆₀[(C₅H₅)₂Fe]₂. The analogous simultaneous deposition of fullerene C₆₀ and cobaltocene results in the formation of a C₆₀ film stable in air and water, which contains carbon and cobalt (from the data of X-ray fluorescence, electron microscopy and microdiffraction). It has a different morphology and different diffraction patterns than pure C₆₀ films and, depending on the cobaltocene content (relative to that of fullerene), appears to be a fullerite film doped with various amounts of cobaltocenium fullende, which is an ionic compound.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1379–1383, August, 1994.The work was financially supported by the Russian Foundation for Basic Research (Projects 93-03-4676 and 93-03-18368).     

Electrochemistry of fullerenes immobilized on the electrodes

The main methods of fullerene immobilization on solid electrodes are briefly reviewed. The effect of the procedures of immobilization and introduction of donor substituents into fullerene on the electrochemical (and spectral) characteristics is considered. A general classification of fullerene coatings is proposed. The coatings can be grouped as (i) the phase films of individual fullerenes and (ii) the composite films of fullerenes, which are dispersed in/on the matrixes of various natures. It is concluded that the main parameters of redox conversions of phase films are determined by the retardation of matrix restructurization in the doping and, in the case of dispersed fullerenes, by the character of their interaction with other components of composition. The correct results for the dispersed systems can be obtained only by using the reference electrode with a potential virtually independent of solvent nature.     

Synthesis of fullerene adducts with terpyridyl- or pyridylpyrrolidine groups in trans-1 positions

Two C(60) hexakis-adducts (2 and 3) were synthesized by using a protection-deprotection strategy. The symmetric fullerene tetrakis-adduct 8 was obtained by anthracene removal from the hexakis-adduct 7. Reaction of 8 with terpyridylglycine or pyridylglycine afforded two hexakis-adducts, 2 and 3. By using the retro-cyclopropanation reaction, the four malonate addends located on the equatorial belt of the hexakis-adducts were removed to afford two trans-1 bis-adducts, 4 and 5, with terpyridyl- or pyridylpyrrolidine groups. The structures of 2 and 3 were confirmed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and (1)H, (13)C, and COSY NMR, and UV-visible spectroscopy. The cyclic voltammograms of fullerene multiadducts 2, 3, and 9 show irreversible reductions. Self-assembled monolayers (SAMs) of 1 and 3 were formed on gold surfaces through nitrogen adsorption. SAMs of 3 represent the first example of a fullerene hexakis-adduct formed on gold surfaces through nitrogen adsorption. Controlled potential electrolyses (CPE) were conducted to prepare trans-1 bis-adducts 4 and 5 modified with terpyridyl and pyridyl groups.     

纳米富勒烯(nC60)的生态毒性效应

随着纳米技术的飞速发展,纳米材料的应用日趋广泛.同时,纳米材料的大规模生产和应用对人体健康与生态环境可能产生的安全风险也引起了人们的普遍关注.富勒烯是应用最广泛的纳米材料之一,在水中能形成稳定的水溶性纳米颗粒,进而增大其在环境中的迁移性与生物暴露几率.然而目前对纳米富勒烯(nC60)的环境和毒性效应还知之甚少.本文综合评述了水溶性nC60纳米颗粒的制备、稳定机制、在环境中的迁移特性及其与环境中污染物的相互作用,并着重阐述了nC60可能产生的生物毒性效应.分析表明,nC60的生物毒性效应主要与nC60的表面化学特性和颗粒大小有关,同时环境介质也影响nC60的毒性.最后讨论了nC60生态环境效应研究中应加强的若干方面.     

Methylazacalixpyridines: remarkable bridging nitrogen-tuned conformations and cavities with unique recognition properties

Methylazacalix[n]pyridines (n = 4, 8) and methylazacalix[m]arene[n]pyridines (m = n = 2, 4) have been synthesized by a convenient fragment coupling approach starting from 2,6-dibromopyridine, 2,6-diaminopyridine, and benzene-1,3-diamine. Thanks to the intrinsic electronic nature of nitrogen, which can adopt mainly sp(2) hybridization, allowing it variously to conjugate, partially conjugate, or not conjugate with the adjacent one or two pyridine rings, the resulting nitrogen-bridged calixpyridine derivatives act as a unique class of macrocyclic host molecules with intriguing conformational structures offering fine-tunable cavities and versatile recognition properties. Whilst in solution it is fluxional, in the solid state methylazacalix[4]pyridine adopts a 1,3-alternate conformation with a C(2v) symmetry in which every two bridging nitrogen atoms conjugate with one pyridine ring. After protonation, the methylazacalix[4]pyridinium species has a different conjugation system of its four bridging nitrogen atoms, yielding the similar twisted 1,3-alternate conformations with an approximate S(4) symmetry. The cavity of each protonated methylazacalix[4]pyridine, however, varies finely to accommodate guest species of different size and geometry, such as planar DMF or HO(2)CCO(2) (-) ion, a twisted HO(2)CCO(2) (-) ion, and a tetrahedral ClO(4) (-) ion. As giant macrocyclic hosts, both methylazacalix[8]pyridine and methylazacalix[4]arene[4]pyridine interact efficiently with fullerenes C(60) and C(70) through van der Waals forces. Their ease of preparation, versatile conformational structures, and recognition properties make these multinitrogen-containing calixarenes or cyclophanes unique and powerful macrocyclic hosts in supramolecular chemistry.     

Host-guest interactions in the supramolecular incorporation of fullerenes into tailored holes on porphyrin-modified gold nanoparticles in molecular photovoltaics

Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics.     

A theoretical investigation of the interaction between H,Li, Na,K, and fullerenes

We studied the interaction between H, Li, Na, and K with one and two C₆₀ molecules using unrestricted Hartree–Fock (UHF) methods. We investigated the effects of distances between the doping atoms and the C₆₀ clusters, total charges, interaction energies, stabilities, HOMO‐LUMO energy differences, charge distribution, and potential energy surfaces. The effect of each doping atom was analyzed and potential technological applications discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Methane as a Selectivity Booster in the Arc‐Discharge Synthesis of Endohedral Fullerenes: Selective Synthesis of the Single‐Molecule Magnet Dy2TiC@C80 and Its Congener Dy2TiC2@C80

The use of methane as a reactive gas dramatically increases the selectivity of the arc‐discharge synthesis of M‐Ti‐carbide clusterfullerenes (M=Y, Nd, Gd, Dy, Er, Lu). Optimization of the process parameters allows the synthesis of Dy₂TiC@C₈₀‐I and its facile isolation in a single chromatographic step. A new type of cluster with an endohedral acetylide unit, M₂TiC₂@C₈₀, is discovered along with the second isomer of M₂TiC@C₈₀. Dy₂TiC@C₈₀‐(I,II) and Dy₂TiC₂@C₈₀‐I are shown to be single‐molecule magnets (SMM), but the presence of the second carbon atom in the cluster Dy₂TiC₂@C₈₀ leads to substantially poorer SMM properties.     

Capturing C90 Isomers as CF3 Derivatives: C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18

High‐temperature trifluoromethylation of a C₉₀ isomeric mixture with CF₃I followed by HPLC separation of C₉₀(CF₃)_n isomers resulted in the isolation of several individual C₉₀(CF₃)_14?18 compounds. Single crystal X‐ray diffraction with the use of synchrotron radiation resulted in the structure determination of C₉₀(30)(CF₃)₁₄, C₉₀(35)(CF₃)_16/18, and C₉₀(45)(CF₃)_16/18. Their addition patterns are discussed and compared with the known isomers C₉₀(30)(CF₃)₁₈ and C₉₀(35)(CF₃)₁₄, respectively. The presence of the most stable C₉₀ isomer, C₉₀(45), in the fullerene soot has been confirmed for the first time.