Solid-State Properties of Fullerenes and Their Compounds

In this article, we present a resume of experimental activities performed at the Research Center Karlsruhe in the field of fullerene solid-state physics. Central issues are the rotational order-disorder phase transitions in pure fullerene crystals and the electronic properties of undoped and doped fullerenes. The major part deals with C₆₀ but selected results for solid C70 and C₈₄ are also given. The experimental methods comprise X-ray diffraction, inelastic neutron scattering, dilatometry, magnetometry and photo-electron spectroscopy.     

洋葱状富勒烯的制备及摩擦性能研究

通过水下电弧放电法制备出洋葱状富勒烯(OLFs).采用高分辨透射电镜(HRTEM)、X射线衍射(XRD)分析了OLFs的晶体结构和形貌,并通过热重(TGA)考察了OLFs的热稳定性.在MRS-10A型四球摩擦试验机上测试了OLFs作为长城牌SE级15W-40汽油机油添加剂的摩擦性能.结果表明,所制备的OLFs具有较高的石墨化程度,直径约25nm,外形呈球状并具有一定的空心结构;在空气中的热稳定性维持到600℃以上.在不同的质量分数和载荷下,OLFs作为润滑油添加剂在减摩性能上均优于碳纳米管(CNTs).     

Solid-State Properties of Fullerenes and Their Compounds

Abstract

In this article, we present a resume of experimental activities performed at the Research Center Karlsruhe in the field of fullerene solid-state physics. Central issues are the rotational order-disorder phase transitions in pure fullerene crystals and the electronic properties of undoped and doped fullerenes. The major part deals with C₆₀ but selected results for solid C70 and C₈₄ are also given. The experimental methods comprise X-ray diffraction, inelastic neutron scattering, dilatometry, magnetometry and photo-electron spectroscopy.     

星形三苯胺衍生物的合成及其光物理性能

以三苯胺、芴酮等为原料,合成了一种新型星形三苯胺衍生物三(4-亚芴基肼基-5-亚甲基-2-噻吩基)苯胺(TFMTA)。用FTIR、1 HNMR、元素分析对TFMTA的结构进行了表征,并考察了其光物理性能。结果表明:TFMTA的薄膜显示较强的红色荧光;且具有明显的聚集诱导发光(Aggregation-induced emission,AIE)性能;其电离势(5.75eV)与正电极(ITO)的功函数(4.8eV)相匹配,可有效降低空穴注入的能垒,有利于空穴的传输;TFMTA的热分解温度是355℃,具有良好的热稳定性。     

Short Communication: Some Photophysical Properties of Nanotubes

The absorption spectra of (10,10) nanotubes are reported at varying concentrations. In addition, we have found that nanotubes are unable to photosensitize formation of singlet oxygen (¹O₂) and do not significantly quench it. These results imply that nanotubes are not able to form long-lived or localized excited states.     

Short Communication: Some Photophysical Properties of Nanotubes

Abstract

The absorption spectra of (10,10) nanotubes are reported at varying concentrations. In addition, we have found that nanotubes are unable to photosensitize formation of singlet oxygen (¹O₂) and do not significantly quench it. These results imply that nanotubes are not able to form long-lived or localized excited states.     

Time-Resolved Mass Spectrometric Studies of Fullerenes and Endohedral Fullerenes

Abstract

The energetics and dynamics of C₂ evaporations from fullerene radical cations C_n ^?+ were studied with and without ion trapping techniques. Electron space charge trapping was applied in electron ionization experiments. RF trapping in a Paul type ion source was applied for Laser MPI. Appearance energies, kinetic energy releases and metastable fractions were determined. the experimental data were modeled by finite heat bath theory (FHBT) and by RRKM/QET. Evaporation (binding) energies as well as conventional and intrinsic kinetic shifts were deduced. Our results support the following conclusions: (a) C₆₀ sits on the leading edge of a magic shell, with C₅₈ only slightly less stable and C₆₂ considerably less stable than C₆₀; (b) Dissociative decay is able to compete with radiative decay of C₆₀ ^?+ only at internal energies in excess of 37.6 eV (T_b>2300 K); (c) a Ne endohedral atom has a slightly stabilizing effect on the C₆₀ ^?+ cage whereas La is strongly stabilizing the C₈₂ ^?+ cage; (d) C₂ loss is a true evaporation in the sense of having a loose transition state with no reverse activation energy; (e) the C₂ evaporations are statistical in nature and theories such RRKM/QET and FHBT are in excellent agreement with experimental observations.     

Environment Effects on the Electronic Properties of Carbon Fullerenes: A Local Approach

The electronic structure of some relevant carbon fullerenes are determined by using a sp-electron tight-binding Hamiltonian including Coulomb interactions in the Hartree-Fock approximation. Surfaces with positive, non-positive and mixed curvatures are considered in order to study the effect of the local environment on the relevant electronic properties. Nanotubes having different diameters and helicities are analyzed and the results are compared with previous calculations. In each case, the equilibrium bond-length R is optimized by maximizing the cohesive energy E_coh(N). The perspectives and extensions of this study are also discussed.     

Fullerenes and Viruses

Abstract

It is well known that any, sometimes very small, changes in the chemical structure can lead to the dramatic changes in biological properties. Therefore it is necessary to divide into two different topics the studies of biological properties of fullerene and fullerene‐like compounds. In the enormous variety of data on the biological activity of fullerenes it is possible to select some with defined mechanism of action. This selection showed that in case of using the fullerene‐containing compositions the main mechanisms of drug action, namely unspecific, specific (ligand–receptor) interaction and membranotropic can be obtained. Therefore fullerenes as compounds with broad biological potential are very promising not only for the design of antiviral compounds, but also for the design of various types of drugs.     

Methods for Controlling Structure and Photophysical Properties in Polyfluorene Solutions and Gels

Knowledge of the phase behavior of polyfluorene solutions and gels has expanded tremendously in recent years. The relationship between the structure formation and photophysics is known at the quantitative level. The factors which we understand control these relationships include virtually all important materials parameters such as solvent quality, side chain branching, side chain length, molecular weight, thermal history and myriad functionalizations. This review describes advances in controlling structure and photophysical properties in polyfluorene solutions and gels. It discusses the demarcation lines between solutions, gels, and macrophase separation in conjugated polymers and reviews essential solid state properties needed for understanding of solutions. It gives an insight into polyfluorene and polyfluorene beta phase in solutions and gels and describes all the structural levels in solvent matrices, ranging from intramolecular structures to the diverse aggregate classes and network structures and agglomerates of these units. It goes on to describe the kinetics and thermodynamics of these structures. It details the manifold molecular parameters used in their control and continues with the molecular confinement and touches on permanently cross‐linked networks. Particular focus is placed on the experimental results of archetypical polyfluorenes and solvent matrices and connection between structure and photonics. A connection is also made to the mean field type theories of hairy‐rod like polymers. This altogether allows generalizations and provides a guideline for materials scientists, synthetic chemists and device engineers as well, for this important class of semiconductor, luminescent polymers.     

Synthesis and Properties of Platinum Complexes of Fullerenes (C60 and C70)

Platinum complexes of C60 and C70 were synthesized and characterized by using spectroscopic analysis. The X-ray data of the C60-platinum complex containing no solvent of crystallization afforded the definite bond lengths and angles.     

On the Formation and Stability of Fullerenes

Abstract

Fullerenes (especially the higher ones) degrade to an insoluble material on storage in air. The C _2v(II) isomer of [78]fullerene is completely degraded after storage for 5 months. The extreme instability may account for the variable yields of this isomer obtained by different research groups. Strong heating of KBr discs of these insoluble materials produces CO₂ showing that they are oxygen containing. Given this inherent instability of fullerenes, the question arises as to why they are formed in the first place. It is argued that the formation is not a unique consequence of the need to eliminate dangling bonds produced during carbon vaporisation by the arc-discharge procedure. Rather, fullerene formation is favoured by a higher intramolecular dangling-bond collision frequency (i.e. much higher Arrhenius A-factor) for cage closure compared to the intermolecular collisions that lead to the more stable graphitic sheets.     

Terrestrial and Extraterrestrial Fullerenes

This paper reviews reports of occurrences of fullerenes in circumstellar media, interstellar media, meteorites, interplanetary dust particles (IDPs), lunar rocks, hard terrestrial rocks from Shunga (Russia), Sudbury (Canada) and Mitov (Czech Republic), coal, terrestrial sediments from the Cretaceous-Tertiary-Boundary and Permian-Triassic-Boundary, fulgurite, ink sticks, dinosaur eggs, and a tree char. The occurrences are discussed in the context of known and postulated processes of fullerene formation, including the suggestion that some natural fullerenes might have formed from biological (algal) remains.     

On the Formation and Stability of Fullerenes

Fullerenes (especially the higher ones) degrade to an insoluble material on storage in air. The C_2v(II) isomer of [78]fullerene is completely degraded after storage for 5 months. The extreme instability may account for the variable yields of this isomer obtained by different research groups. Strong heating of KBr discs of these insoluble materials produces CO₂ showing that they are oxygen containing. Given this inherent instability of fullerenes, the question arises as to why they are formed in the first place. It is argued that the formation is not a unique consequence of the need to eliminate dangling bonds produced during carbon vaporisation by the arc-discharge procedure. Rather, fullerene formation is favoured by a higher intramolecular dangling-bond collision frequency (i.e. much higher Arrhenius A-factor) for cage closure compared to the intermolecular collisions that lead to the more stable graphitic sheets.     

Shungite Carbon and Fullerenes

Thermpgravimetry method applied to shungite carbon (ShC) was the next step which testified its similarity with fullerenes. Fullerene-like approach suggested earlier was helpful in understanding shungite nature. ShC behavior under heating in air confirmed the structure ordering and its metastability.     

Shungite Carbon and Fullerenes

Abstract

Thermpgravimetry method applied to shungite carbon (ShC) was the next step which testified its similarity with fullerenes. Fullerene-like approach suggested earlier was helpful in understanding shungite nature. ShC behavior under heating in air confirmed the structure ordering and its metastability.     

EPR of Graphite and Fullerenes

Analysis of the EPR results for graphite and fullerenes has led to the development of a model for the g-factor in follerene based on the analogy between graphite and fullerene. Pressure dependence of g-factor in C₆₀ powder confirms the validity of this model. ¹³C hyperfine splitting of_a0.36 mT in pristine fullerene is also reported. The g-factors of C₆₀^-1 and C₆₀^-3 in a solution and in a different K°C₆₀ fullerides are presented. C₆₀⁺ⁿ states should be described by the spectroscopic splitting factor larger than that of a free spin.     

Theory for the Growth of Fullerenes

Abstract

In view of recent experiments we extend our previous growth model for fullerene formation. It becomes clear how a high efficiency of C₆₀ formation is achieved. We estimate the size dependence of intermediate structures along the most efficient growth route and furthermore the stability of Si_2o, Ge_2o vs. the unstable C_20-     

纳米TiO2的光化学特性及其在环境科学中的应用

纳米ＴｉＯ２是一种优异的光电功能材料。介绍了其奇特的表面结构、优异的光化学特性及其光催化作用的机理,并概述了纳米ＴｉＯ２在环境科学中有机污染物的光催化降解、重金属离子的光催化还原及光催化杀菌等方面的应用。