Near infrared electronic spectrum of TCNQ mono-valent anion

The high resolution near infrared electronic spectrum of TCNQ anion dissolved in 2-methyltetrahydrofuran glass at 77 K has been determined. The absorption bands are interpreted as simple progressions of two molecular vibrations in a single electronic excited state with ν₀₀ = 11661 cm^?1. The molecular vibrations (ω′₁ = 1264 ± 3 cm^?1, ω′₂ = 335 ± 3 cm^?1) of the vibrational progression agree well with observed Raman active transitions. The experimental data do not require the presence of two electronic transitions in the 1.3 to 2.1 eV region, contrary to what had been assumed previously on the basis of less well resolved room temperature spectra.     

Contracted and expanded meso-alkynyl porphyrinoids: from triphyrin to hexaphyrin

The boron trifluoride-catalyzed Rothemund condensation of triisopropylsilyl (TIPS) propynal 1 with 3,4-diethylpyrrole in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a mixture of products, including [15]triphyrin(1.1.3) H3, corrole H(3)4, porphyrin H(2)2, [24]pentaphyrin(1.1.1.1.1) H(4)5, [28]hexaphyrin(1.1.1.1.1.1) H(4)6, and two linear tripyrromethenes H(2)7 and H(2)8. We report the spectroscopic characteristics of these unusual chromophores, together with the crystal structures of triphyrin H3 (and its zinc complex ZnCl3), porphyrin H(2)2 (and its metal complexes Zn2, Ni2 and Pt2), hexaphyrin H(4)6, and tripyrromethene nickel(II) complex Ni7. When the condensation is catalyzed with trifluoroacetic acid, rather than boron trifluoride, the triphyrin H3 become the main product (26% yield). This novel macrocycle is linked with a TIPS-substituted exocyclic double bond. This C=C bond makes an eta(2)-interaction with the zinc center in ZnCl3 with C-Zn distances of 2.863 and 3.025 A. The porphyrin H(2)2 is severely ruffled, and its absorption spectrum is red-shifted and broadened compared with the analogous compound without ethyl substituents. The hexaphyrin H(4)6 adopts a figure-of-eight conformation with virtual C(2) symmetry in the solid state and C(2) symmetry in solution on the NMR time scale. Oxidation with DDQ appears to convert this nonaromatic [28]hexaphyrin into an aromatic [26]hexaphyrin with a strongly red-shifted absorption spectrum, but the oxidized macrocyle is too unstable to isolate.     

Vibrational spectroscopy of perfluorocarboxylic acids from the infrared to the visible regions

We report here the gas-phase mid-IR, near-IR, and visible vibrational spectra of perfluoropropionic, perfluorooctanoic, and perfluorononanoic acids using Fourier transform and cavity ring-down spectroscopy. The impetus for this work was to provide insight into the behavior of environmentally persistent perfluorocarboxylic acids. Although the most intense transition for all three perfluorocarboxylic acids in the fundamental spectra is the CF3 stretch, the O-H stretch carries the most intensity in the overtone region. We record the O-H stretching transition frequencies and absorption cross-sections in the DeltavOH = 1-5 regions. Our work suggests that perfluorocarboxylic acids have more harmonic O-H bonds, smaller transition frequencies, and smaller intensities as compared to shorter-chain hydrocarbon acids, alcohols, and peroxides.     

生命色素研究: 细菌中新卟啉类化合物

发现了一些细菌血红蛋白卟啉辅基, 它们的结构与无处不在的原血红蛋白素。这些新色素在芳核和侧链包含有引人注目的改性, 样品有血红蛋白素α, ο和α1,讨论了这些大环的合成途径和它们可能的生物合成途径。     

Regularity and asymptotic properties of the discrete spectrum of electronic hamiltonians

We analyze the electronic part of diatomic molecular Hamiltonians as a function of the internuclear distance, x. We prove analyticity outside x ≠ 0 of eigenvalues in the discrete spectrum and differentiability up to second order for the associated projection operators. Furthermore, it is shown that for large internuclear distances they converge to eigenvalues and eignprojectors of the separated atoms.     

Modified porphyrinoids from carbazates and hydrazones and the first crystal structure of a di-iminoporphodimethene

Novel porphyrinoids with interrupted conjugation (di-iminoporphodimethenes) result from the Pd-catalyzed coupling of meso-bromo porphyrins and their metal complexes with carbazates and hydrazones, followed by aerial oxidation. X-ray crystallography revealed a saddle shape for molecules of the nickel(II) complex of a di-iminoporphodimethene.     

Structural and electronic properties of tungsten trioxides: from cluster to solid surface

Geometries and electronic structures of WO₃(001) surface and a series of stoichiometric (WO₃) _n clusters (n = 1–6) have been systematically investigated using first-principles density functional calculations. Six possible reconstructured models of WO₃(001) surface with cubic phase are explored, and the most stable configuration is the \( (\sqrt 2 \times \sqrt 2 )R45^{\circ} \) surface. The main feature of WO₃(001) surface is that the top of valence band is dominated by the 2p states of the bridging oxygen atom, rather than the top terminal oxygen. By comparing the geometrical parameters, from the structural point of view, the W₃O₉ cluster can be used as the smallest molecular prototype of the WO₃ surface. However, in terms of the electronic structure, only until W₆O₁₈, the cluster begins to appear the electronic feature of the WO₃(001) surface. This may be due to the reason that the W₆O₁₈ cluster and the top layer of WO₃(001) surface show similar “stoichiometry” if we treat two kinds of oxygen atoms as different “elements”. In addition, for the chemical reactivity, using BH₃ as a probe molecule, the W₆O₁₈ cluster also bears general resemblance to the WO₃(001) surface, and the bridging oxygen atoms in two systems are the preferred sites for the nucleophilic reaction. Therefore, our results indicate that the W₆O₁₈ cluster with a spherical buckyball structure can be viewed as the smallest molecular model to understand the properties such as catalytic activity of WO₃(001) surface.     

Modulating membrane properties: the effect of trehalose and cholesterol on a phospholipid bilayer

The protective properties of trehalose on cholesterol-containing lipid dipalmitoylphosphatidylcholine (DPPC) bilayers are studied through molecular simulations. The ability of the disaccharide to interact with the phospholipid headgroups and stabilize the membrane persists even at high cholesterol concentrations and restricts some of the changes to the structure that would otherwise be imposed by cholesterol molecules. Predictions of bilayer properties such as area per lipid, tail ordering, and chain conformation support the notion that the disaccharide decreases the main melting transition in these multicomponent model membranes, which correspond more closely to common biological systems than pure bilayers. Molecular simulations indicate that the membrane dynamics are slowed considerably by the presence of trehalose, indicating that high sugar concentrations would serve to avert possible phase separations that could arise in mixed phospholipid systems. Various time correlation functions suggest that the character of the modifications in lipid dynamics induced by trehalose and cholesterol is different in the hydrophilic and hydrophobic regions of the membrane.     

Bias effects on the electronic spectrum of a molecular bridge

In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectral analysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of the electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level.     

7-甲氧基香豆素-3-甲酰二乙醇胺的电子结构和光谱性质的理论研究

采用密度泛函的B3LYP和单激发组态相互作用(CIS)方法分别对基态和第一、第二单重激发态(S1和S2)结构进行优化,均采用6-31G(d)基组.在优化的基态和第一单重激发态的结构基础上,用含时密度泛函理论(TD-DFT),成功模拟了7-甲氧基香豆素-3-甲酰二乙醇胺的吸收光谱和荧光发射光谱,并用极化连续模型考虑了溶剂的影响.利用前线轨道、电荷密度差(CDD)和态密度(DOS)图分析了电子跃迁的特性.计算结果与实验结果吻合得很好.该量子计算方法对此类化合物的定性和定量研究是有效的.     

Interaction-induced contribution to changes in the infrared spectrum of hydrogen-bonded complexes

An attempt to include interaction-induced effects into the study of absorption in H-bonded complexes is presented. The IR band shapes of the ν_s(OH) mode in phenol, 2,4,6-trimethylphenol, 2,6-dichloro-4-nitrophenol, and dimethylamine with nitriles or pyridine derivatives have been studied in terms of the dipolar coupling theory.     

Theoretical infrared spectrum of the ethanol hexamer

The hydrogen bond network of ethanol clusters is among the most complex hydrogen bond networks of molecular clusters. One of the reasons of its complexity arises from the number of possible ethanol monomers (there are three isoenergetic isomers of the ethanol monomer). This leads to difficulties in the exploration of potential energy surfaces (PESs) of ethanol clusters. In this work, we have explored the PES of the ethanol hexamer at the MP2/aug-cc-pVDZ level of theory. We have provided structures and their relative stability at 0 K and for temperatures ranging from 20 to 400 K in the gas phase. These structures are used to compute the theoretical infrared (IR) spectrum of the ethanol hexamer at the MP2/aug-cc-pVDZ level of theory. As a result, 98 different structures have been investigated, and six isomers are reported to be the most isoenergetically stable structures of the ethanol hexamer. These isomers are folded cyclic structures in which the stability is enhanced by the implication of CH⋯O interactions. Our investigations show that the PES of the ethanol hexamer is very flat, yielding several isoenergetic structures. Furthermore, we have noted that several isomers contribute to the population of the ethanol hexamer at high temperatures. As far as the IR spectroscopic study is concerned, we have found that the IR spectra of the most stable structures are in good agreement with the experiment. Considering this agreement, these structures are used to assign the experimental peaks in the CH-stretching region. We concluded that the stability of the structures of the ethanol hexamer is related both to OH⋯O hydrogen bonds and CH⋯O interactions. Overall, we have found that the IR spectrum of the ethanol hexamer, calculated from the contribution of all the possible stable structures weighted by their probability, excellently reproduce the experimental spectrum of the ethanol hexamer.     

Microsolvation effects on the optical properties of crystal violet

We present a joint experimental and theoretical study of the photoabsorption and photodissociation behavior of crystal violet, that is, the tris[p-(dimethylamino)phenyl]methyl cation. The photodissociation spectra of isolated and microsolvated crystal violet have been measured. A single band is observed for the bare cation. This is in good agreement with the calculated vibronic absorption spectrum based on time-dependent density functional theory calculations. The interaction of crystal violet with a single water molecule shifts and broadens the photodissociation spectrum, so that it approaches the spectrum obtained in solution. Theoretical calculations of the structure of the complex suggest that the shift in the absorption spectrum originates from a water molecule bonding with the central carbon atom of crystal violet.     

The electronic spectrum of AuO: a combined theoretical and experimental study

The near-infrared electronic spectrum of AuO(1) has been re-examined in light of the new microwave data on the v = 0 and v = 1 vibrations of the X(2)Pi(3/2) state of AuO. The two observed bands in the spectrum, with red-degraded bandheads located at 10726 and 10665 cm(-1), have been reanalyzed. New theoretical work on AuO clarifies the electronic structure, and the bands in the infrared are now assigned as the (0,1) and (1,2) bands of the a(4)Sigma(-)(3/2) - X(2)Pi(3/2) transition, respectively.     

Calculations on the electronic spectrum of water

Ab initio SCF and CI calculations are reported for excitation energies, oscillator strengths and geometry of upper states in the low-energy electronic transitions of water. Good agreement is obtained with experimental data where available, both with regard to the location and intensity of the various spectral bands for this system. In addition several transitions of either weakly allowed or forbidden character respectively are predicted which have not yet been unambiguously identified via experimental techniques.     

The electronic spectrum of the triethylamine-perfluoro-tert-butanol complex

The far-ultraviolet absorption spectrum of the triethylamine-perfluoro-tert-butanol complex has been measured in the gas phase. The photoelectron band of lowest energy has also been determined. It is about 13000 cm^?1 higher than for free triethylamine. Up to at least 60000 cm^?1, the UV spectrum is readily interpreted as a triethylamine spectrum shifted to higher frequencies by about 13000 cm^?1. The bands of lowest frequency are the 3s and 3p Rydberg bands which follow the ionization potential. Up to 60000 cm^?1, no charge transfer type band has been found.