Molecular structure of trimethyl[(3-indole)ethoxy]silane cooled in a supersonic jet

Conformations of He-jet-cooled trimethyl[(3-indole)ethoxy]silane (TIES) have been studied using a laser spectroscopy technique in combination with quantum-chemical computations. Six probable conformers of the molecule were computed, of which only two conformations were observed. Based on an analysis of fluorescence excitation spectra, fluorescence spectra, shapes of rotational band contours at the electronic S₀–S₁ transition of TIES, and theoretical computations, the above conformers were assigned to steric structures. Twisted structures have the lowest energy due to intramolecular hydrogen bonds C - H ?O < _C^Si C - H \cdots O <_C^{Si} between hydrogen atoms of methyl groups and an oxygen atom and C–H···π between H and the π-electron cloud of the indole ring.     

Intramolecular electron transfer in mixed-valence complexes [(NH3)5Ru-L-Ru(NH3)5]5+ (L = N2, pyz, pym, 4,4’-bipy, bpa)

The dynamics of the intramolecular electron transfer from Ru(II) to Ru(III) in binuclear mixed-valence complexes [NH₃)₅Ru -L-Ru(NH₃)₅]⁵⁺ (L = N₂, pyz, bipy, pym, bpa) is analyzed by the semiempirical CINDO + CI method. Translated from ZhurnalStruktumoi Khimii, Vol. 39, No. 4, pp. 579–590, July–August, 1998.     

Functionalized perylenes: origin of the enhanced electrical performances

In this letter we compare the transistor performances of two solution-processed perylene derivatives: N,N′-bis (n-octyl)- dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN₂) and N,N′-1H,1H-perfluorobutyl dicyanoperylenediimide (PDIF-CN₂). Perylenediimide nitrogen functionalization with perfluoroalkyl vs. alkyl chains improves the electron mobility of solution-processed organic field effect transistors (OFETs) by one order of magnitude. Time resolved spectroscopy allows attributing this increment to a higher degree of co-facial arrangement of the fluorinated molecules. This supramolecular arrangement enhances the π–π overlap leading to more efficient electron transport.     

Crystal structure of ethyl (2Z)-2-(3-methoxy-4-acetyloxy benzylidene)-7-methyl-3-oxo-5-phenyl-2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine-6-carboxylate

The title compound, C₂₆H₂₄N₂O₆S, (I), crystallizes in the monoclinic space group, P2₁/c, with cell parameters a = 16.248(1), b = 7.927(1), c = 19.371(4) ?, β = 105.295(2)°, Z = 4. The central pyrimidine ring in the compound (I) is significantly puckered, assuming a screw-boat conformation. The C11–C16 benzene ring stands vertical while thiazole and C18–C23 benzene rings are coplanar to the mean plane of pyrimidine ring having dihedral angles of 87.48(12), 3.63(11) and 0.94(12)°, respectively. In the absence of potential hydrogen bonding interaction, the crystal packing is influenced by intramolecular C-H…S interaction and intermolecular C-H…π interactions.     

Azobenzene-functionalized alkanethiols in self-assembled monolayers on gold

Self-assembled monolayers (SAMs) of 4-trifluoromethyl-azobenzene-4′-methyleneoxy-alkanethiols (CF₃– C₆H₄–N=N–C₆H₄–O–(CH₂) _n –SH on (111)-oriented poly-crystalline gold films on mica were examined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The spectra are analyzed with the help of density-functional-theory calculations of the isolated molecule. Only one doublet is detected in the sulphur 2p spectra of the investigated SAMs, consistent with a thiolate bond of the molecule to the gold surface. The C 1s XP spectra and the corresponding XAS π ^* resonance exhibit a rich structure which is assigned to the carbon atoms in the different chemical surroundings. Comparing XPS binding energies of the azobenzene moiety and calculated initial-state shifts reveals comparable screening of all C 1s core holes. While the carbon 1s XPS binding energy lies below the π ^*-resonance excitation-energy, the reversed order is found comparing core ionization and neutral core excitation of the nitrogen 1s core-hole of the azo group. This surprising difference in core-hole binding energies is interpreted as site-dependent polarization screening and charge transfer among the densely packed aromatic moieties. We propose that a quenching of the optical excitation within the molecular layer is thus one major reason for the low trans to cis photo-isomerization rate of azobenzene in aromatic-aliphatic SAMs.     

Phenomenological πN→ππN amplitude and the modelling of the Olsson–Turner and Chew–Low approaches

The phenomenological amplitude for the reaction πN→ππN fixed by fittings to the experimental data in the energy region 0.300 ≤P _Lab≤ 500 MeV/c is used for modelling the Chew–Low extrapolation and Olsson–Turner threshold approach. It is shown that the uncritical application of the former results in enermous theoretical errors, the extracted values being in fact random numbers. The results of the Olsson–Turner method are characterized by significant systematic errors coming from unknown details of the isobar physics. Received: 10 December 1997     

What can we learn from the decay of NX(1625) in the molecule picture?

Considering two assumptions on the molecular state, i.e. the S-wave Λ̄–K^- and S-wave Σ̄⁰–K^- molecular states, we study the possible decays of N̄_X(1625) that include N̄_X(1625)→K^-Λ̄,π⁰p̄,ηp̄,π^-n̄. Our results indicate that (1) if N̄_X(1625) is the Λ̄–K^- molecular state, K^-Λ̄ is the main decay mode of N̄_X(1625), and the branching ratios of the rest decay modes are tiny; (2) if N̄_X(1625) is the Σ̄⁰–K^- molecular state, the branching ratio of N̄_X(1625)→K^-Λ̄ is one or two orders smaller than that of N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄. Thus the search for N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄ will be helpful to shed light on the nature of N̄_X(1625). PACS 13.30.Eg, 13.75.Jz     

Europium-sensitized Chemiluminescence of System Tetracycline–H<Subscript>2</Subscript>O<Subscript>2</Subscript>–Fe(II)/(III) and Its Application to the Determination of Tetracycline

Chemiluminescence (CL) of the reaction system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III) was used for the determination of tetracycline hydrochloride in water, pharmaceutical preparations, and honey. The CL spectrum registered for this system shows emission bands typical of Eu(III) ions, with a maximum at λ ∼ 600 nm, corresponding to the electronic transitions of ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂. A strong chemiluminescence intensity characteristic of europium(III) ions in the system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III), as contrasted to the emission of the system tetracycline–H₂O₂–Fe(II)/(III) without Eu(III), proves that the Eu(III) ion plays the role of a chemiluminescence sensitizer, accompanying tetracycline oxidation in the Fenton system (H₂O₂–Fe(II)/(III)). A linear dependence was observed for the integrated CL light intensity on the tetracycline concentration in the range of 2 × 10⁻⁷ to 3 × 10⁻⁵ mol l⁻¹ with the detection limit of 5 × 10⁻⁸ mol l⁻¹ in aqueous solution.     

Synthesis, thermal and optical properties of metal(II) complexes with a novel ligand derived from pyrazolone-5

Three novel metal(II) complexes, CoL₂, NiL₂ and CuL₂ (L = (Z)-4-(2-(1,3-dimethyl-5-oxo-1H-pyrazol-4(5H)-ylidene)hydrazinyl)-1,5-dimethyl-2-phenyl-1,2-dihydropyrazol-3-one were synthesized. Their structures were postulated based on elemental analyses, ¹H NMR, ESI-MS, FT-IR spectra and UV-vis spectra. The effect of different central metal(II) ions on absorption bands of the metal(II) complexes in CHCl₃ solutions was researched. The result indicates that the bathochromic shift is CuL₂ > NiL₂ > CoL₂. The absorption properties of thin films and thermal stability of these complexes are also discussed. In addition, the optical constants (complex refractive index N=n+ik) and thickness of the complex thin films on polished single-crystal silicon substrates were measured by spectroscopic ellipsometry. Results indicate that the metal(II) complexes would be a promising recording medium candidate for blu-ray recordable optical storage system due to good absorption at 405 nm, high thermal stability and sharp thermal decomposition, and a high n values of 1.35–1.45 and a low k values of 0.33–0.39.     

Luminescence Characterisation of the Reaction System Histidine–KBrO3–Tb(III)–H2SO4

Chemiluminescence of the system containing Tb(III) ions, histidine and bromate ions in acid solution was studied. The kinetic curves and CL emission spectra of the system were discussed. The emission spectrum of the histidine–Tb(III)–KBrO₃–H₂SO₄ system revealed two emission maxima at ∼490 and 550 nm, characteristic of Tb(III) ions. Values of lifetimes of the Eu(III) excited states in Eu(III)–histidine system have shown that the histidine formed ML and ML₂ complexes in neutral solution and did not make them in acidic environment. On the basis of the results, a possible mechanism of reaction system: histidine–Tb(III)–KBrO₃–H₂SO₄ is presented.     

A study in depth of f<Subscript>0</Subscript>(1370)

Claims have been made that f₀(1370) does not exist. The five primary sets of data requiring its existence are refitted with suitable Breit–Wigner amplitudes. Major dispersive effects due to the opening of the 4π threshold are included for the first time; the σ→4π amplitude plays a strong role. Crystal Barrel data on p̄p→3π⁰ at rest require f₀(1370) signals of at least 32 and 33 standard deviations (σ) in ¹S₀ and ³P₁ annihilation respectively. Furthermore, they agree within 5 MeV for mass and width. Data on p̄p→ηηπ⁰ agree and require at least a 19σ contribution. This alone is sufficient to demonstrate the existence of f₀(1370). BES II data for J/Ψ→φπ⁺π^- contain a visible f₀(1370) signal >8σ. In all cases, a resonant phase variation is required. Cern–Munich data for ππ elastic scattering are fitted well with the inclusion of some mixing between σ, f₀(1370) and f₀(1500). Values of Γ_2π for f₂(1565), ρ₃(1690), ρ₃(1990) and f₄(2040) are determined. PACS 13.25.Gv; 14.40.Gx; 13.40.Hq     

Novel approach to pion and eta production in proton-proton collisions near threshold

We evaluate the threshold matrix–element for the reaction pp→ppπ⁰ in a fully relativistic Feynman diagrammatic approach. We employ a simple effective range approximation to take care of the S–wave pp final–state interaction. The experimental value for the threshold amplitude A = (2.7 −i0.3) fm⁴ can be reproduced by contributions from tree level chiral (long–range) pion exchange and short–range effects related to vector meson exchanges, with ω-exchange giving the largest individual contribution. Pion loop effects appear to be small. We stress that the commonly used heavy baryon formalism is not applicable in the NN–system above the pion production threshold due to the large external momentum, |p|≃ (Mm _π)^−1/2, with M and m _π the nucleon and the pion mass, respectively. We furthermore investigate the reaction pp→pnπ⁺ near threshold within the same approach. We extract from the data the triplet threshold amplitude as B = (2.8 −i1.5) fm⁴. Its real part can be well understood from (relativistic) tree level meson–exchange diagrams. In addition, we investigate the process pp→ppη near threshold. We use a simple factorization ansatz for the ppη final–state interaction and extract from the data the modulus of the threshold amplitude, |C|= 1.32 fm⁴. With g _ηN= 5.3, this value can be reproduced by (relativistic) tree level meson–exchange diagrams and η–rescattering, whose strength is fixed by the ηN scattering length. We also comment on the recent near threshold data for η^′–production. Received: 27 November 1998     

ωN final state interactions and ω-meson production from heavy-ion collisions

We calculate the elastic and inelastic ωN→ωN, →πN, →ρN, →ρπN, →ππN, →σN reactions within a boson exchange approximation where the ωρπ coupling constant and form factor are fixed by the reaction πN→ωN in comparison to the experimental data. We find rather large ωN cross sections at low relative momenta of the ω-meson which leads to a substantial broadening of the ω-meson width in nuclear matter. The implications of the ωN final state interactions are studied for ω production in ¹²C +¹²C, ⁴⁰Ca +⁴⁰Ca and ⁵⁸Ni +⁵⁸Ni reactions at about 2 · A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative to a general m _T-scaling (for π⁰ and η mesons) might be controlled experimentally by the TAPS Collaboration. Received: 28 April 1999 / Revised version: 7 June 1999     

Infrared ion dip and ultraviolet spectroscopy of 4-phenyl imidazole, its tautomer, 5-phenyl imidazole, and its multiply hydrated clusters

Mass-resolved resonant two photon ionisation (R2PI) and infrared ion dip spectra have been recorded for 4-phenylimidazole (4PI) and its singly and multiply hydrated clusters 4PI(H₂O)_{n = 0 - 4}, under supersonic expansion conditions. In the case of 4PI(H₂O)_0,1, it has also been possible to record infrared spectra in both the ground (S₀) and excited (S₁) states. Combining the experimental data with the results of ab initio calculations has led to the structural assignment of each cluster. In each case, the water molecules bind primarily to the NH site of the imidazole ring. Clusters with n≥ 2 incorporate linear water chains, in which the proton donating terminus bridges either to the π-electron system (n = 2) or to the >N: atom site (n = 3, 4) on the imidazole ring. Despite the creation of a “water wire”, connecting the donor and acceptor sites of imidazole, there is no evidence of proton transfer in either the ground or excited state. Received 20 December 2001 Published online 13 September 2002     

Luminescent Donor-Acceptor β-Diketones: Modulation of Emission by Solvent Polarity and Group II Metal Binding

A class of aryl trifluoromethyl-containing β-diketones were synthesized via one step Claisen condensation. These π-conjugated diketones exhibit strong solvatochromism from intramolecular donor-acceptor charge transfer (CT). In addition, fluorescence quantum yields (ϕ_f) and lifetimes (τ_f) were measured in different solvents. Diketones exhibit bathochromic shifts in emission spectra with increasing solvent polarity. Fluorescence changes upon Group II metal binding were also studied. Despite the relatively simple structure, the anthracene-CF₃ diketone, atm, has strong binding affinity for Mg²⁺. A 70 nm blue shift and sixfold increase in intensity were observed upon addition of only one equivalent MgCl₂ in ethanol solution. It also shows selectivity for Mg²⁺ binding even in the presence of excess Ca²⁺. Association constant (K_a) calculations suggest atm has two orders of magnitude stronger chelation for divalent magnesium than for calcium. These findings make atm an attractive starting point for molecular probe and light emitting material design.     

Process πp → ππN at high energies and moderate momenta transferred to the nucleon and the determination of parameters of the f0(980) and f0(1300)

We present the results of simultaneous analysis of the S-wave ππ spectra in the reactions π ⁻ p → (ππ)_S n at p _lab=38 GeV/c (GAMS) and π ⁻ p → (ππ)_S n at p _lab=18 GeV/c (E852 Collaboration) at moderate momenta transferred to the nucleon, |t| ≲ 1.5 (GeV/c)². The t distributions are described by the Reggeized π and a ₁ exchanges provided by the leading and daughter trajectories, while the M _ππ spectra are determined by a set of scalar-isoscalar resonances. With M _ππ distributions averaged over different t intervals, we have found several solutions given by different t-channel-exchange mechanisms at |t| ∼ (0.5–1.5) (GeV/c)², with resonance parameters close to each other. We conclude that, despite a poor knowledge of the structure of the t exchange, the characteristics of resonances such as masses and widths can be reliably determined using the processes under discussion. As to pole positions, we have found (1031±10)−i(35±6) MeV for f ₀(980) and (1315±20)−i(150±30) MeV for f ₀(1300). From Yadernaya Fizika, Vol. 66, No. 5, 2003, pp. 960–972. Original English Text Copyright ? 2003 by Anisovich, Sarantsev. This article was submitted by the authors in English.     

Two-pion production in proton-proton collisions with a polarized beam

The two-pion production reaction pp → ppπ⁺π⁻ was measured with a polarized proton beam at T _p ≈ 750 and 800MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed-pulse technique for Quirl and central calorimeter provided positive π⁺ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1–4 overconstraints. Total and differential cross-sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing-power values up to A _y = 0.3. The data taken in the energy region of the excitation of the Roper resonance confirm that its dominant ππ decay channel is N ^* → Nσ.     

The electronic structure and magnetic property of μ-hydroxo bridged manganese porphyrin dimer

The electronic structure and effective exchange integrals (J _ab) between two manganese (III) ions of porphyrin dimer (PPMn(III)–OH–Mn(III)PP) were examined by using unrestricted hybrid DFT (UHDFT) methods. The dependence of J_ab on bond angle between two manganese ( Mn–OH–Mn) is also calculated to elucidate orbital overlap effect for J_ab value in the system. Natural orbital analysis is performed to explain the overlap effect in terms of the instability of the π, σ and δ orbitals by using diradical character.