新型功能碳材料的高压截获

高性能功能材料在诸多领域具有广泛的应用前景,是人们一直关注的研究热点。高压可以有效地改变物质的原子间距和成键方式,是获得新型功能材料的重要途径。在碳材料的高压研究中,许多有趣的功能碳材料,如光学透明碳、高强度弹性碳和超硬非晶碳等,已经通过不同的碳前驱体合成。本文简要介绍了作者近年来在低维碳基纳米复合材料高压研究中取得的进展,基于设计的不同低维碳前驱体,高压下截获了具有超硬特性、新型压致共价聚合及发光增强的碳材料。     

Investigation into the molecular structure and energetic stability of endohedral and exohedral metallofullerene derivatives of C24

Density-functional theory was applied to the investigation of the structural and electronic properties of C₂₄ fullerene derivatives. Transition metals (TMs) from groups 11 and 12, in various oxidation and spin-states, are inserted at either endohedral (TM@C₂₄) or exohedral (TM-C₂₄) sites and their subsequent energetic stabilities are assessed. With the exception of Ag@C₂₄, all derivatives are predicted to occupy a minimum on the potential energy surface. The optimized exohedral TM-C₂₄ geometries yield TM-C bond lengths that are consistent with comparable carbon-metal bond lengths, and the overwhelming majority of the derivatives result in a slight deformation of the C₂₄ cage as the bonding carbon takes on more sp³ character. All of the TM@C₂₄ equilibrium structures maintain the integrity of the cage structure with a moderate increase in the diameter. All neutral exohedral and endohedral complexes favor the low spin-state; conversely, all of the charged exohedral complexes prefer the high spin-state, with the exception of Cu-C₂₄¹⁺ molecular ion. The Group 12 charged endohedral derivatives prefer the low spin-state, whereas the Group 11 molecular ions do not necessarily exhibit a definitive trend. Analysis of the energetic data predicts that of the lowest energy endohedral molecular species only four are predicted to be energetically favorable in terms of insertion energy and an advantageous HOMO-LUMO gap: Cu@C₂₄²⁺, Ag@C₂₄¹⁺, Au@C₂₄³⁺, and Zn@C₂₄²⁺.     

Encapsulation of glycine inside C60 fullerene: Impact of confinement

Confinement of glycine inside C₆₀ fullerene (gly@C₆₀) is analyzed via geometrical, energetic and deformation density of intermolecular interaction. Results show that both fragments are significantly deformed due to the compression imposed by the confinement. Also kinetic energy pressure and relaxation deformation density analyses are used to describe the nature of interaction between components, and topological analysis of the steric deformation density in gly@C₆₀ was carried out to find the critical points of the charge deformation due to steric effects. The relevance between different types of energies and charge displacement show almost identical sensitivity of energies to the repulsive interaction.     

Aromatic character of Oh-C24N24. A cavernous nitride fullerene bearing N4-macrocycle motifs

Spherical fullerenes offer noteworthy structures usually involving six- and five-membered faces, with application in technological issues. In this sense, cavernous spherical-like structures bearing larger holes provide interesting examples for further understanding of structure-properties relationship. Here, we explored the magnetic response of a proposed cavernous nitride fullerene, C₂₄N₂₄, which has a O_h-symmetry with six N₄-macrocyclic and eight 1,3,5-triazine faces displaying 48-π electrons. C₂₄N₂₄ exhibits a local aromatic behavior owing to the contrasting antiaromatic response of the N₄-macrocyclic faces and the aromatic character of the 1,3,5-triazine faces. Thus, the overall structure is ascribed as a local aromatic species, where the triazine faces exhibit the characteristic shielding cone for aromatic rings. Furthermore, the constructive combination of local shielding cones in C₂₄N₂₄ delivers a related shielding-cone response, as expected for a perfect aromatic cage. Hence, the local aromatic/nonaromatic/antiaromatic sections exhibit an additive or subtractive interaction, leading to a characteristic response inherent to the nature of the spherical cage. We expect that further study of the interplay between different aromatic and antiaromatic faces in fullerene-like cages can deliver interesting pseudo-aromatic or pseudo-antiaromatic spherical species.     

Li原子掺杂C28单分子器件的热自旋输运性质

利用第一性原理对Li原子掺杂C₂₈的分子器件的热自旋输运性质进行了计算。在不同的温度场下,上下自旋分别为Li原子掺杂C₂₈的分子器件中的空穴和电子提供了输运通道,在MJ₁和MJ₃分子器件中,热自旋电流随着温度增加而增大,但在MJ₂分子器件中,热自旋电流先增大再减小。三种分子器件都出现了自旋塞贝克效应,MJ₂还出现了负微分电阻现象,利用费米-狄拉克分布和自旋输运谱对其物理机理进行了解释。根据Li掺杂C₂₈的单分子器件的热自旋输运性质,可设计新的自旋纳米器件。     

Role of the Bridge in Photoinduced Electron Transfer in Porphyrin–Fullerene Dyads

The role of π‐conjugated molecular bridges in through‐space and through‐bond electron transfer is studied by comparing two porphyrin–fullerene donor–acceptor (D–A) dyads. One dyad, ZnP–Ph–C₆₀ (ZnP=zinc porphyrin), incorporates a phenyl bridge between D and A and behaves very similarly to analogous dyads studied previously. The second dyad, ZnP–EDOTV–C₆₀, introduces an additional 3,4‐ethylenedioxythienylvinylene (EDOTV) unit into the conjugated bridge, which increases the distance between D and A, but, at the same time, provides increased electronic communication between them. Two essential outcomes that result from the introduction of the EDOTV unit in the bridge are as follows: 1) faster charge recombination, which indicates enhanced electronic coupling between the charge‐separated and ground electronic states; and 2) the disappearance of the intramolecular exciplex, which mediates photoinduced charge separation in the ZnP–Ph–C₆₀ dyad. The latter can be interpreted as a gradual decrease in electronic coupling between locally excited singlet states of D and A when introducing the EDOTV unit into the D–A bridge.     

Enhanced electronic and nonlinear optical responses of C24N24 cavernous nitride fullerene by decoration with first row transition metals; A computational investigation

The electronic (energy gap and work function) as well as electrical properties (dipole moment, polarizability, and first hyperpolarizabilities) of the first-row transition metals decorated C₂₄N₂₄ cavernous nitride fullerene were explored using DFT calculations. The transition metals are decorated at N4 cavity of C₂₄N₂₄ fullerene. According to our spin polarized computations, the most stable spin state monotonically increases to sextet for Mn@C₂₄N₂₄ and thereafter dropped off gradually to singlet state for Zn@C₂₄N₂₄ system. The findings demonstrate that transition metals can remarkably decrease the HOMO-LUMO energy gap and work function values up to 63% and 21% of bare C₂₄N₂₄, respectively. As can be seen, when the Sc and Ti metals are located above the N4 cavity of fullerene, systems of enhanced static hyperpolarizabilities (β₀) are delivered. These findings might provide an effective strategy to design high performance eletcro-optical materials based on carbon- nitride fullerene.     

Fused-Pentagon Isomers of C60 Fullerene Isolated as Chloro and Trifluoromethyl Derivatives

The carbon cage of buckminsterfullerene I_h-C₆₀, which obeys the Isolated-Pentagon Rule (IPR), can be transformed to non-IPR cages in the course of high-temperature chlorination of C₆₀ or C₆₀Cl₃₀ with SbCl₅. The non-IPR chloro derivatives were isolated chromatographically (HPLC) and characterized crystallographically as ¹⁸⁰⁹C₆₀Cl₁₆, ¹⁸¹⁰C₆₀Cl₂₄, and ¹⁸⁰⁵C₆₀Cl₂₄, which contain, respectively two, four, and four pairs of fused pentagons in the carbon cage. High-temperature trifluoromethylation of the chlorination products with CF₃I afforded a non-IPR CF₃ derivative, ¹⁸⁰⁷C₆₀(CF₃)₁₂, which contains four pairs of fused pentagons in the carbon cage. Addition patterns of non-IPR chloro and CF₃ derivatives were compared and discussed in terms of the formation of stabilizing local substructures on fullerene cages. A detailed scheme of the experimentally confirmed non-IPR C₆₀ isomers obtained by Stone–Wales cage transformations is presented.     

Fullerene compounds with general formulae C60Ox (x = 1–3): Isomerism,stability and polarizability

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