An investigation of oxidation and reduction of C-60, the excited states, energy gaps and stability using semi-empirical and ab initio methods (original) (raw)
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Theoretical calculations for the fullerene cation are important for several aspects. Jahn-Teller vibronic interactions are symmetry-allowed in this ion and the expectation is that such interactions lead to static geometrical effects. In addition it is interesting to study the change of the vibrational spectrum of C 60 upon ionization. We have used semi-empirical AM1/UHF and PM3/UHF and density functional theoretical methods (B3LYP and LDA) to calculate the electronic ground state equilibrium geometry and vibrational frequencies for C 60 + . A small but significant reduction from icosahedral symmetry to D 5d obtained from DFT calculations without symmetry constraints supports the presence of static Jahn-Teller distortions. Structure optimizations constrained to D 5d and D 3d symmetry have also been carried out. The JT stabilization energy in the D 5d and D 3d structures is estimated according to two different methods. Vibrational frequencies calculated at B3LYP/6-31G level for the fullerene cation of D 5d geometry are reported and compared to literature values of neutral C 60 .
The Journal of Physical Chemistry A, 2001
The rate of oxidative quenching of 3 C 60 by chloranil (CA) in CH 2 Cl 2 is much enhanced by added trifluoroacetic acid (TFA) or hexafluoro-2-propanol (HFIPA). These additives have similar hydrogen-bonding powers but differ widely in their proton acidities. In both cases, quenching rate constants calculated for H-bonded CA increase sharply with additive concentration. H-bonded clusters around the quinone are postulated in which electron transfer is coupled to fast protonation of CA -• by TFA, and strong H-bonding or solvation of charged radicals by HFIPA. This is consistent with observed neutral semiquinone formation, higher radical yields, and much slower back reactions for TFA. The C 60 +• spectrum ( ) 25 000 ( 2000 M -1 s -1 at 980 nm) shows low absorption throughout the visible region. Charge-shift reactions of C 60 +• and arenes follow Rehm-Weller-Marcus kinetics and afford efficient preparation of arene +• cation radicals using visible light.
Analysis of occupied and empty electronic states of C60
Chemical Physics Letters, 1991
We calculated the electronic structure of solid Cd0 using a first principles pseudopotential local-density method. We present an analysis of the theoretical results and compare them to experimental photoemission and inverse photoemission spectra of solid Cbo-The agreement between theory and experiment is excellent. We give a simple interpretation of the electronic states of C,, based on its quasi-spherical shape.
Internet Electronic Journal of …, 2003
Theoretical calculations for the fullerene cation are important for several aspects. Jahn-Teller vibronic interactions are symmetry-allowed in this ion and the expectation is that such interactions lead to static geometrical effects. In addition it is interesting to study the change of the vibrational spectrum of C 60 upon ionization. We have used semi-empirical AM1/UHF and PM3/UHF and density functional theoretical methods (B3LYP and LDA) to calculate the electronic ground state equilibrium geometry and vibrational frequencies for C 60 +. A small but significant reduction from icosahedral symmetry to D 5d obtained from DFT calculations without symmetry constraints supports the presence of static Jahn-Teller distortions. Structure optimizations constrained to D 5d and D 3d symmetry have also been carried out. The JT stabilization energy in the D 5d and D 3d structures is estimated according to two different methods. Vibrational frequencies calculated at B3LYP/6-31G level for the fullerene cation of D 5d geometry are reported and compared to literature values of neutral C 60 .
J Phys Chem a, 1999
Photophysical properties of the excited singlet and triplet states of pentaphenylfulleren-2-ol (C 60 (C 6 H 5) 5 OH, PPF) and penta-4-fluorophenylfulleren-2-ol [C 60 (C 6 H 4 F) 5 OH, PFPF], two derivatives of buckminsterfullerene, C 60 , have been investigated in benzene and benzonitrile solutions using two complementary transient absorption techniques, namely, laser flash photolysis and pulse radiolysis. Singlet-singlet and triplet-triplet absorption spectra have been characterized. Quantum yields for formation of the triplet states by intersystem crossing from the singlet states, and also the intrinsic lifetimes of the singlet and triplet states, have been determined. In addition to the intrinsic decay of the triplet state, the evidences have been obtained for the contribution of the other two processes, namely, the self-quenching by the ground state and the T-T annihilation reaction, toward the decay of the triplet state, and the rate constants for these processes have been determined. The formation of charge transfer (CT) complexes with two aromatic amines, diphenylamine (DPA) and triphenylamine (TPA), in benzonitrile and the electron transfer reactions in the excited singlet and CT complexes have been studied.
Quantum Chemical Study of the Reactivity of C 60 HR and C 60 (CHR) Derivatives
The Journal of Organic Chemistry, 2004
In the present work a quantum chemical study of a series of substituted hydrofullerenes, C 60 HR, and a series of methanofullerenes, C 60 (CHR), is presented. Their reactivity and geometrical, energetic, electronic, and magnetic properties, as well as the influence of the substituent, are discussed. As a probe of the reactivity, the acidic properties of these fullerene derivatives were predicted, based on the calculated deprotonation energies, with a previously set up scheme. The electronic delocalization upon deprotonation was described, and the global (magnetizabilities) and local aromaticity (nucleus-independent chemical shifts) was analyzed and compared with respect to the group properties for the series of functional groups. The geometries of both acidic and basic forms were fully optimized at the AM1 level, and all property calculations were performed at the HF/3-21G and the B3LYP/6-31G* level of theory.
Normal vibrational analysis of the triplet excited state ofC60
Physical Review B, 2001
The vibrational frequencies and infrared intensities for the lowest triplet excited state (T 1) of the C 60 molecule have been calculated using a density-functional theory. Despite the fact that the I h to D 5d structural distortion on the ground state (S 0) to T 1 electronic transition was not large, the calculated infrared stick spectrum of T 1 is very different from that of S 0. The change in the geometry and vibrational structures from S 0 to T 1 reflects the difference between their potentials. The difference was discussed in consideration of both the translation and rotation of the normal coordinates for T 1 relative to S 0 .
Electronic structure and bonding of C60 to metals
Synthetic Metals, 1993
The electron distribution and orbital interactions of C60 with metals coordinated at different sites on the outside of the fuUerene are evaluated with the Fenske-Hall molecular orbital method. The characters and nodal properties of the frontier orbitals of C60 are first evaluated in terms of basis transformations to the C2 units that join the pentagons and to the C5 units of the pentagons in the Cso molecule. The highest occupied molecular orbital (HOMO, hu symmetry) of C60 is largely ~r bonding between the carbon atom pairs that join adjacent pentagons. The lowest unoccupied molecular orbital (LUMO, tlu symmetry) is predominantly ~-antibonding between these carbon atom pairs. These orbital characters and energies are well situated for synergistic bonding of a metal atom to the carbon-caxbon pair between the pentagons, in which the HOMO of C60 donates a electron density to the metal, and the LUMO of C60 accepts ~r electron density from the metal. The electron donation and acceptance between the individual molecular orbitals of the C60 molecule and the orbitals of a metal at different possible bonding sites of C~o are probed with a Ag ÷ ion. It is found that the bonding is favored at the site between the pentagons and that many different orbitals of C~o are involved in the interaction. The net bonding of Ag ÷ to C60 is weaker than to ethylene. Calculations are also carried out on the organometallic complexes C60Pt(PHa)2 and (C2H4)Pt(PH3)2. The net bonding of ethylene and C80 to platinum is found to be very similar in these cases. A significant difference in this case is that the net negative charge on C60 is more delocalized in the carbon cluster in contrast to the localized charge on ethylene.
Photoionization of C60: a model study
Journal of Physics B: Atomic, Molecular and Optical Physics, 2008
Time-dependent density functional theory is used to calculate the total and subshell photoionization cross sections of C 60. The core of 60 C 4+ ions is smeared into a classical jellium shell before treating the correlated motion of the 240 valence electrons quantum mechanically. The calculation reveals two collective plasmon resonances in the total cross section in agreement with the experiment. It is found that a phase-coherent superposition of amplitudes leading to enhancements in the ionization from various C 60 subshells in two distinct energy regions essentially builds the plasmons. While the result shows good qualitative agreement with the experiments, the limitation of the model to describe the data in quantitative detail is discussed.