Michinori Sumimoto

Theoretical investigation of the molecular and electronic structures and excitation spectra of iron phthalocyanine and its derivatives, FePc and FePcLn (L = Py, CN−; n = 1, 2)

The effects of axial ligands on the ground-state geometries, electronic structures and the characteristic optical properties of iron phthalocyanine and its derivatives, FePc and FePcL(n) (L = pyridine (Py) and cyanide (CN(-)); n = 1, 2), were investigated using the density functional theory (DFT) method. The geometries of FePc with a triplet spin state and of FePc(Py), FePc(Py)(2), FePc(CN(-)) and FePc(CN(-))(2) with singlet spin states were optimized under D(4h), C(2v), D(2h), C(4v), and D(4h) molecular symmetries, respectively. The highest occupied molecular orbitals (HOMOs) of FePc, FePc(Py), FePc(Py)(2), and FePc(CN(-)) are pi-type orbitals, which have no contribution from the p(z) atomic orbitals of all nitrogen atoms, whereas the HOMO of FePc(CN(-))(2) is the 7e(g) orbital, which has contributions from the d(xz) and the d(yz) orbitals of the Fe atom mixing with the pi-orbitals of the axial CN(-) ligands. The time-dependent (TD) DFT method gives many optically allowed excitations for FePc, FePc(Py), FePc(Py)(2), FePc(CN(-)), and FePc(CN(-))(2) in the UV-VIS region. Our calculated bands corresponded well with the experimental results. In FePc(Py)(2), the metal-ligand charge transfer (MLCT) transitions from the metal d to the axial-ligand pi*-type orbitals contributed to the B band region. In FePc(CN(-))(2), the MLCT transitions from the metal d to the Pc-ring pi*-type orbitals contributed mainly to the first B band region, but those from the metal d to the axial-ligand pi*-type orbitals did not appear in the energy regions of the Q and B bands. Thus, the axial ligands caused a spectral change in FePc through orbital mixing.

Theoretical investigation of the molecular, electronic structures and vibrational spectra of a series of first transition metal phthalocyanines by Z. Liu et al.

A recent paper by Lui et al. [Z. Liu, X. Zhang, Y. Zhang, J. Jiang, Spectrochim. Acta A 67 (2007) 1232] reported on the theoretical investigations of the fully optimized geometries and electronic structures of iron (II) phthalocyanine (FePc) with the singlet spin state carried out with the restricted density functional theory (DFT) method, where the B3LYP functional was adopted for the exchange-correlation term; however, the triplet spin state was experimentally reported, and we also obtained the triplet spin state by the unrestricted DFT calculations.

Stereoselective synthesis of 1-nitrobicyclo[3.1.0]hexanes and fused isoxazoline-N-oxides from primary nitro compounds.

The one-step preparation of 1-nitrobicyclo[3.1.0]hexane and bicycloisoxazoline-N-oxide was readily achieved from conjugate adducts of nitro alkenes and allylmalonates by treatment with Ag(2)O and iodine under basic conditions. We observed that when a primary alkyl group was present at the β-position of the nitro group, bicyclo[3.1.0]hexane was preferentially formed, whereas if a secondary alkyl group occupied that position, isoxazoline-N-oxide was predominantly produced. High cis-selectivity was observed for the formation of cyclopentane units for both reactions. An iodomethyl adduct, considered an intermediate of the cyclization, was isolated, and its conversion to isoxazoline-N-oxide was successfully achieved. The isoxazoline-N-oxide underwent 1,3-dipolar cycloaddition with alkenes to yield tricycloheterocyclic compounds, which were readily converted to spirolactam in good yield by reductive cleavage of N-O bonds using Raney-Ni. On the other hand, 1,3-dipolar cycloaddition of the isoxazoline-N-oxide to terminal alkynes yielded tricyclic aziridines stereoselectively.

Theoretical study on the molecular structures of X-, α-, and β-types of lithium phthalocyanine dimer

We report here the results from theoretical calculations of the potential energy curves, the geometry optimizations, and the electronic structures for three dimers of lithium phthalocyanine (LiPc) by using three types of functional systems: PBE1PBE, B3LYP, and M06. The results were discussed in comparison with those obtained for the dimers of magnesium phthalocyanine (MgPc). The long‐range dispersive interactions were considered in part using these functional systems in the increasing order of PBE1PBE, B3LYP, and M06. The mechanism whereby the dispersive interactions affect the geometric and electronic structures of the LiPc and MgPc dimers is discussed. The calculated results provide insight into the computational methods for both open‐ and closed‐shell metal phthalocyanine (MPc) dimers: Although the PBE1PBE and B3LYP functional systems cannot evaluate a weak dispersion interaction appropriately, the M06 functional can estimate a weak dispersion interaction well in both open‐ and closed‐shell MPc dimers. Basis set superposition error (BSSE) corrections play an important role for the quantitative analysis; however, the calculation results without BSSE corrections may be sufficient for the qualitative discussion on the properties of these dimers such as geometries, stabilities, electronic structures, and so on.

Photoelectron Spectroscopic Study of Electronic Structures of L-Cysteine

The valence band structure of L -cysteine films was investigated by ultraviolet photoelectron spectroscopy (UPS) in the photon energy range of 40–100 eV. Smooth thin films were produced by vacuum evaporation and characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and Raman scattering spectroscopy. The photon energy dependence of the UPS spectra indicates that electronic states close to the valence band maximum may be attributed to sulfur, while the other states in the higher-binding-energy region may be attributed to carbon, nitrogen, and oxygen. Molecular orbital calculation was performed on seven possible geometries of L -cysteine. The observed UPS spectrum is in good agreement with the simulated one in terms of the C3 geometry of L -cysteine. It is concluded that the sulfur-originated electronic state is located at the valence-band maximum, indicating that cysteine is one of the useful and promising materials in future bioelectronics.

Theoretical and experimental investigation on the electronic properties of the shuttlecock shaped and the double-decker structured metal phthalocyanines, MPc and M(Pc)2 (M = Sn and Pb)

The molecular geometries, electronic structures, and excitation energies of tin and lead phthalocyanine compounds, SnPc, PbPc, Sn(Pc)(2), and Pb(Pc)(2), were investigated using the B3LYP method within a framework of density functional theory (DFT). The geometries of SnPc, PbPc, Sn(Pc)(2), and Pb(Pc)(2) were optimized under C(4v), C(4v), D(4d), and D(4d) molecular symmetries, respectively. The excitation energies of these molecules were computed by the time-dependent DFT (TD-DFT) method. The calculated results for the excited states of three compounds other than the unknown Pb(Pc)(2) corresponded well with the experimental results of electronic absorption spectroscopy. The non-planar C(4v) molecular structure of SnPc and PbPc influences especially on the orbital energy of the HOMO-1 through mixing of the s-type atomic orbital of the central metal atom to the π system of the Pc ring in an anti-bonding way; however, the HOMO and the LUMO have little effect of the deviation from the planar structure because they have no contribution from the atomic orbital of the central metal. This orbital mixing pushes up the orbital energy of the HOMO-1, and reduces the energy of the metal-to-ligand charge transfer band of SnPc and PbPc. The calculated results also reproduced well the excitation profile of Sn(Pc)(2), which was quite different from that of SnPc. The strong interactions between the π-type orbitals of two Pc moieties altered the electronic structure resulting in the characteristic excitation profile of Sn(Pc)(2). In addition, this caused a reduction of about 0.8 eV in the ionization potential as compared to usual MPcs including SnPc, which was consistent with the experimental results.

A free-energy perturbation method based on Monte Carlo simulations using quantum mechanical calculations (QM/MC/FEP method): application to highly solvent-dependent reactions.

This study describes the framework of the quantum mechanical (QM)/Monte Carlo (MC)/free‐energy perturbation (FEP) method, a FEP method based on MC simulations using quantum chemical calculations. Because a series of structures generated by interpolating internal coordinates between transition state and reactant did not produce smooth free‐energy profiles, we used structures from the intrinsic reaction coordinate calculations. This method was first applied to the Diels–Alder reaction between methyl vinyl ketone and cyclopentadiene and produced ΔG  sol‡ values of 20.1 and 21.4 kcal mol−1 in aqueous and methanol solutions, respectively. They are very consistent with the experimentally observed values. The other two applications were the free‐energy surfaces for the Cope elimination of N,N‐dimethyl‐3‐phenylbutan‐2‐amine oxide in aqueous, dimethyl sulfoxide, and tetrahydrofuran solutions, and the Kemp decarboxylation of 6‐hydroxybenzo‐isoxazole‐3‐carboxylic acid in aqueous, dimethyl sulfoxide, and CH3CN solutions. The calculated activation free energies differed by less than 1.8 kcal mol−1 from the experimental values for these reactions. Although we used droplet models for the QM/MC/FEP simulations, the calculated results for three reactions are very close to the experimental data. It was confirmed that most of the interactions between the solute and solvents can be described using small numbers of solvent molecules. This is because a few solvent molecules can produce large portions of the solute–solvent interaction energies at the reaction centers. When we confirmed the dependency on the droplet sizes of solvents, the QM/MC/FEP for a large droplet with 106 water molecules produced a ΔG  sol‡ value similar to the experimental values, as well as that for a small droplet with 34 molecules.

Theoretical and experimental study on the excited states of the X-, α- And β-forms of lithium phthalocyanine

The electronic structures and absorption spectra for three different types (X, α and β) of model dimers of lithium phthalocyanine (LiPc) were investigated by the density functional theory (DFT) and compared with a LiPc monomer. We quantitatively investigated the excited states of the three LiPc dimers using time-dependent DFT calculations. The differences and similarities of the observed absorption spectra in the solution and the polymorphic solids of LiPc were clearly interpreted by the calculated excited states of the monomer and dimers. The calculated results for the dimers presumed that the X-form showed a different electronic spectral pattern from the monomer and the other two forms, whereas the α- and β-forms presented similar electronic absorption profiles to each other and to the monomer. The calculated excited states also explained the differences in absorption profiles between LiPc and typical phthalocyanine compounds. These characteristic features of LiPc would be closely related to its molecular orbitals, especially those which originated from the singly occupied molecular orbital (SOMO) of the LiPc monomer. It was shown that the next highest occupied π-type orbital to the SOMO of the monomer reduced the energy of the low-lying excited states, which corresponded to the Q- and B-bands of the dimers.

Photoelectron spectroscopic study on the electronic structures of the dental gold alloys and their interaction with L-cysteine

The valence electronic structures of the dental gold alloys, type 1, type 3, and K14, and their interaction with L-cysteine have been studied by ultraviolet photoelectron spectroscopy with synchrotron radiation. It was found that the electronic structures of the type-1 and type-3 dental alloys are similar to that of polycrystalline Au, while that of the K14 dental alloy is much affected by Cu. The peak shift and the change in shape due to alloying are observed in all the dental alloys. It is suggested that the new peak observed around 2 eV for the L-cysteine thin films on all the dental alloys may be due to the bonding of S 3sp orbitals with the dental alloy surfaces, and the Cu–S bond, as well as the Au–S and Au–O bonds, may cause the change in the electronic structure of the L-cysteine on the alloys.

Theoretical investigation of the molecular structures and excitation spectra of triphenylamine and its derivatives

The molecular geometries, electronic structures, and excitation energies of NPh(3), NPh(2)Me, NPhMe(2), and NMe(3), were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region.