Electronic Structure Of Fullerenes Research Articles

Electronic Correlations, Electronic and Vibrational Spectroscopy, and Dynamic Properties of С60 and С70 Fullerenes and their Condensed Phases

The article provides a critical analysis of the key spectroscopic data on the study of the structure and properties of various molecular solids and phases based on C60 and C70 fullerenes and their derivatives, such as endo- and exohedral complexes with metal ions, hydrogen, helium, and halogens, their electronic and magnetic resonance spectra and, in some cases, the dynamics of the atomic core. Key experimental data have been interpreted based on calculations of the electronic structure of fullerenes and their derivatives.

Optical Spectra and Electronic Structure of Fullerenes

Optical Spectra and Electronic Structure of Fullerenes

Energetics of H2O encapsulated in fullerenes under an electric field

Based on first-principles total energy calculations, we analyze the dipole energy U = −d · E of a water molecule encapsulated in fullerene isomers from C60 to C80, all of which satisfy the isolated pentagon rule. Our calculations show that the dipole energy exhibits unusual features not expected for an isolated water molecule in vacuum. The dipole energy depends sensitively on the electronic structure of fullerenes and their cage network topology when situated in an external electric field. We also demonstrate that the electrostatic potential inside the fullerene exhibits an anisotropic feature with respect to the applied field.

Passive optical switches based on endohedral fullerenes

Reverse saturable absorption in fullerenes has been widely used to realize excellent passive optical limiters for the visible region up to 650nm. However, there is still a need for passive optical switches and limiters with a low limiting threshold (<0.5J/cm2) and higher damage limits. The electronic structure of fullerenes can be modified either through doping or by the encapsulation of endohedral clusters to achieve exotic quantum states of matter such as superconductivity. Building on this ability, we show that the encapsulation of Sc3N, Lu3N or Y3N in C80 alters the HOMO–LUMO gap and leads to passive optical switches with a significantly low limiting threshold (0.3J/cm2) and a wider operation window (average pulse energy >0.3mJ in the ns regime).

Interfacial electronic structures between fullerene and calcium for high performance n-type organic semiconducting devices

The electronic structure of fullerene (C 60) deposited on calcium (Ca) was investigated using in-situ ultraviolet photoelectron spectroscopy. The energy level alignment at the C 60/Ca interface was estimated by combining both shifts of the highest occupied molecular orbital (HOMO) level and of the vacuum level during the step-by-step deposition of C 60 on Ca. The HOMO level of C 60 shows shifts relating to band-bending, resulting in an electron injection barrier of 0.2 eV with accumulation contact with the Ca substrate. The vacuum level reveals an interface dipole of 1.11 eV with negative poles on the C 60 side. Noticeably, gap states are formed at the interface region, which might pin the Fermi level and be responsible for the formation of the interface dipole. The complete interfacial energy level diagram of C 60/Ca is presented.

Electrical Transport and Electronic Delocalization of Small Fullerenes

We report the electrical transport properties of several small fullerenes sandwiched between two metallic electrodes and modulated by a gate electrode, calculated using an orthodox theory. The relationship between the charging energies and the structures of fullerenes is obtained. Bond types and molecular curvatures are observed to be important in determining charging energies. The calculated current−voltage and conductance characteristics are related to the electronic structures of fullerenes near energy gaps and are adjustable by the applied gate voltages, indicating that molecular devices with different functions can be designed by selecting fullerenes with proper bond types and curvatures, and by changing the applied gate voltages.

Electronic structure of fullerenes with defects

We report a systematic study of electronic structures in the Hückel approximation for fullerenes with symmetrically arranged defects. We show that these hypothetical molecules present a closed electronic structure in many cases. Furthermore, we compare energy gaps with those of defect-free fullerenes showing that, in most cases, these gaps are wider for fullerenes with symmetrically arranged defects, so they seem to be chemically stable.

A pyracylene model for the interaction of transition metals with fullerenes: a density functional study

Pyracylene, a polynuclear aromatic hydrocarbon which is made up of two benzene and two cyclopentadienyl rings, has been employed as a model to study the interaction of transition metal complexes with fullerenes. To reproduce adequately the geometric and electronic structure of fullerene with a pyracylene model, we had to impose suitable geometric constraints forcing the pyramidalisation angle on the two central carbon atoms to assume a value similar to that observed in C60. Density functional calculations were then performed on (PH3)2M(C14H8) (M = Ni, Pd, Pt) molecules. The results have been analysed in terms of the Chatt–Dewar–Duncanson model and show that the constrained pyracylene is a fairly good model to study the interaction of transition metals with fullerene: geometries are reproduced within 0.02 A and the bond dissociation energies are slightly underestimated by only 10–40 kJ mol−1.

Transformation of the electronic structure of fullerene C60 caused by complex formation in N-methylpyrrolidone solutions

Evolution of the electronic absorption and photoluminescence spectra of the fullerene C60 solutions with various concentrations in a polar solvent (N-methylpyrrolidone) was studied. Comparison with the electrooptical properties of these solutions shows that a slow (associative) fullerene-solvent interaction mechanism is operative at large (nearly saturating) concentrations (1×10−3 g/cm3), whereas the solutions of relatively low concentration (less than 5×10−4 g/cm3) exhibit fast complex formation between fullerene and the solvent molecules. The latter interaction significantly changes the electronic structure of fullerene.

Application of symmetry-adapted wavefunctions to systematic treatment of electronic structure of fullerenes

By constructing symmetry-adapted wavefunctions and investigating the topological structure, a systematic method is proposed for resolving the π-electron Hamiltonian of a fullerene with a certain symmetry and for treating second-neighbour hopping analytically. Calculations for fullerenes with different symmetries show that second-neighbour hopping has almost no influence for small molecules but may play an important role in the electronic and bonding properties of large carbon clusters.

SIMPLE APPROACHES TO FULLERENES AND BUCKONIONS ELECTRONIC STRUCTURE: GUTZWILLER AND SHELL-MODEL CALCULATIONS

The electronic structure of fullerenes and buckonions have been investigated using quantum-mechanical methods: the Gutzwiller and shell-model techniques. In the first part, fullerenes have been modeled with the Hubbard Hamiltonian and the electronic correlation has been examined within the Gutzwiller framework. It has been derived various characteristic energies of fullerenes ( C 60 and C 240) in the free state (first and second ionization energies, electron affinity, and singlet and triplet energies). The second part deals with buckonions. Fullerenes and buckonions have been modeled with the spherical shell-model approach. The calculation has led to the electronic structure of fullerenes and of buckonions. So if we compare the energy levels of the buckonions with those of the fullerenes which build the buckonions, only the buckonions energy levels coming from the outer shell are changed by the coupling between shells.