Mono- and dicarbonyl-bridged tricyclic heterocyclic acceptors: synthesis and electronic properties

A series of trialkylsilyl-substituted 2,2'-dithiophene, 4,4'-di-n-hexyl-2,2'-dithiophene, 5,5'-dithiazole, and 2,2'-diselenophene with carbonyl (2a-d) and α-dicarbonyl bridges (3a-d) were prepared from readily available dihalides, using double lithiation followed by trapping with N,N-dimethylcarbamoyl chloride or diethyl oxalate (or N,N-dimethylpiperazine-2,3-dione), respectively. Cyclic voltammetry reveals that the first half-wave reduction potentials for this series of compounds span a wide range, from -1.87 to -0.97 V vs the ferrocene/ferrocenium couple at 0 V (0.1 M (n)Bu(4)NPF(6) in THF). A significant increase of the first half-wave reduction potential (by 0.50-0.67 V) was observed on substitution of the monocarbonyl bridge with α-dicarbonyl. Adiabatic electron affinity (AEA, gas phase) trends determined via density functional theory (DFT) calculations are in good agreement with the electrochemical reduction potentials. UV-vis absorption spectra across the series show a weak absorption band in the visible range, corresponding to the HOMO→LUMO transition within a one-electron picture, followed by a more intense, high-energy transition(s). Single-crystal X-ray structural analyses reveal molecular packing features that balance the interplay of the presence of the bulky substituents, intermolecular π-stacking interactions, and S···O intermolecular contacts, all of which affect the DFT-evaluated intermolecular electronic couplings and effective charge-carrier masses for the crystals of the tricyclic cores.     

Kinetic Magnetic‐Field Effect Involving the Small Biologically Relevant Inorganic Radicals NO and O2.−

Oxidation of dihydrorhodamine 123 (DHR) to rhodamine 123 (RH) by oxoperoxonitrite (ONOO^?), formed through recombination of NO and O₂^.? radicals resulting from thermal decomposition of 3‐morpholinosydnonimine (SIN‐1) in buffered aerated aqueous solution at pH 7.6, represents a kinetic model system of the reactivity of NO and O₂^.? in biochemical systems. A magnetic‐field effect (MFE) on the yield of RH detected in this system is explored in the full range of fields between 0 and 18 T. It is found to increase in a nearly linear fashion up to a value of 5.5±1.6 % at 18 T and 23 °C (3.1±0.7 % at 40 °C). A theoretical framework to analyze the MFE in terms of the magnetic‐field‐enhanced recombination rate constant k_rec of NO and O₂^.? due to magnetic mixing of T₀ and S spin states of the radical pair by the Δg mechanism is developed, including estimation of magnetic properties (g tensor and spin relaxation times) of NO and O₂^.? in aqueous solution, and calculation of the MFE on k_rec using the theoretical formalism of Gorelik at al. The factor with which the MFE on k_rec is translated to the MFE on the yield of ONOO^? and RH is derived for various kinetic scenarios representing possible sink channels for NO and O₂^.?. With reasonable assumptions for the values of some unknown kinetic parameters, the theoretical predictions account well for the observed MFE.     

Molecular dynamics simulation studies of absorption in piperazine activated MDEA solution

Development of more efficient solvent solutions for removal of CO(2) from natural gas and flue gases is a major task, which contributes to improved design of process plants and leads to decreased costs for its removal. Understanding the mechanisms of CO(2) absorption as well as analysis of undesired simultaneous processes is crucially important in this regard. In this work, we have applied Molecular Dynamics (MD) to investigate the absorption of CO(2) from a binary mixture of CO(2) and CH(4) into aqueous piperazine activated MDEA solution. The MD simulations were performed at a constant temperature of 298 K for five different systems with a loading factor of 0.07 to provide insight into molecular distribution in the amine solution and to enhance understanding of absorption mechanisms on the molecular scale. Force field parameters that were missing from the OPLS-AA force field, as well as charge distribution of piperazine (PZ), protonated piperazine (PZH(+)), piperazine carbamate (PZCOO(-)) and MDEA were obtained by QM calculations. The results of our simulations emphasize the importance of piperazine and piperazine carbamate in accelerating the absorption process. For the first time, we have shown the undesirable trapping of CH(4) by the amine solution and revealed that amine groups are mainly responsible for both absorption of CO(2) and the undesired trapping of CH(4).     

Glycinium semi‐malonate and a glutaric acid–glycine cocrystal: new structures with short O—H...O hydrogen bonds

Glycinium semi‐malonate, C₂H₆NO₂⁺·C₃H₃O₄⁻, (I), and glutaric acid–glycine (1/1), C₂H₅NO₂·C₅H₈O₄, (II), are new examples of two‐component crystal structures containing glycine and carboxylic acids. (II) is the first example of a glycine cocrystal which cannot be classified as a salt, as glutaric acid remains completely protonated. In the structure of (I), there are chains formed exclusively by glycinium cations, or exclusively by malonate anions, and these chains are linked with each other. Two types of very short O—H...O hydrogen bonds are present in the structure of (I), one linking glycinium cations with malonate anions, and the other linking malonate anions with each other. In contrast to (I), no direct linkages between molecules of the same type can be found in (II); all the hydrogen‐bonded chains are heteromolecular, with molecules of neutral glutaric acid alternating with glycine zwitterions, linked by two types of short O—H...O hydrogen bonds.     

Interfacial long traveling waves in a two‐layer fluid with variable depth

Long wave propagation in a two‐layer fluid with variable depth is studied for specific bottom configurations, which allow waves to propagate over large distances. Such configurations are found within the linear shallow‐water theory and determined by a family of solutions of the second‐order ordinary differential equation (ODE) with three arbitrary constants. These solutions can be used to approximate the true bottom bathymetry. All such solutions represent smooth bottom profiles between two different singular points. The first singular point corresponds to the point where the two‐layer flow transforms into a uniform one. In the vicinity of this point nonlinear shallow‐water theory is used and the wave breaking criterion, which corresponds to the gradient catastrophe is found. The second bifurcation point corresponds to an infinite increase in water depth, which contradicts the shallow‐water assumption. This point is eliminated by matching the “nonreflecting” bottom profile with a flat bottom. The wave transformation at the matching point is described by the second‐order Fredholm equation and its approximated solution is then obtained. The results extend the theory of internal waves in inhomogeneous stratified fluids actively developed by Prof. Roger Grimshaw, to the new solutions types.     

Femtosecond laser interactions with dielectric materials: insights of a detailed modeling of electronic excitation and relaxation processes

Electronic excitation–relaxation processes induced by ultra-short laser pulses are studied numerically for dielectric targets. A detailed kinetic approach is used in the calculations accounting for the absence of equilibrium in the electronic subsystem. Such processes as electron–photon–phonon, electron–phonon and electron–electron scatterings are considered in the model. In addition, both laser field ionization ranging from multi-photon to tunneling one, and electron impact (avalanche) ionization processes are included in the model. The calculation results provide electron energy distribution. Based on the time-evolution of the energy distribution function, we estimate the electron thermalization time as a function of laser parameters. The effect of the density of conduction band electrons on this time is examined. By using the average electron energy, a new criterion is proposed based on determined damage threshold in agreement with recent experiments (Sanner et al. in Appl. Phys. Lett. 96:071111, 2010).     

Observations of surface modifications induced by the multiple pulse irradiation using a soft picosecond x-ray laser beam

To study the interactions between picosecond soft x-ray laser (SXRL) beams and material surfaces, gold (Au), copper (Cu), and silicon (Si) surfaces were irradiated with SXRL pulses having a wavelength of 13.9 nm and a duration of ～7 ps. Following irradiation, the surfaces of the substrates were observed using a scanning electron microscope and an atomic force microscope. With single pulse irradiation, ripple-like structures were formed on the Au and Cu surfaces. These structures were different from previously investigated conical structures formed on an Al surface. In addition, it was confirmed that the development of modified structures, i.e., growth of hillocks on the Au and Cu surfaces, was observed after multiple SXRL pulse exposures. However, on the Si surface, deep holes that seemed to be melted structures induced by the accumulation of multiple pulses of irradiations were found. Therefore, it was concluded that SXRL beam irradiation of various material surfaces causes different types of surface modifications, and the changes in the surface behaviors are attributed to the differences in the elemental properties, such as the attenuation length of x-ray photons.     

First hybrid oximehydrazonate phthalocyaninoclathrochelates: The synthesis and properties of lutetium phthalocyanine-capped cage iron(II) complexes

Ditopic oximehydrazonate iron(II) phthalocyaninoclathrochelates were synthesized by a transmetallation (a capping group exchange) reaction of the initial labile triethylantimony-capped clathrochelate iron(II) oximehydrazonates with lutetium(III) phthalocyanine as a Lewis acid. The complexes obtained were characterized using elemental analysis, PD and MALDI-TOF mass spectrometries, IR, UV–Vis, ⁵⁷Fe Mössbauer, and ¹H, ¹³C{¹H} NMR spectroscopies. An encapsulated iron(II) ion was found to be in a low-spin state. The cyclic voltammograms show oxidation and reduction waves assignable to Fe^2+/3+ couples of macrobicyclic framework and to phthalocyanine macrocycles.     

First-order optical systems with real eigenvalues

It is shown that a lossless first-order optical system whose real symplectic ray transformation matrix can be diagonalized and has only real eigenvalues, is similar to a separable hyperbolic expander in the sense that the respective ray transformation matrices are related by means of a similarity transformation. Moreover, it is shown how eigenfunctions of such a system can be determined, based on the fact that simple powers are eigenfunctions of a separable magnifier. As an example, a set of eigenfunctions of a hyperbolic expander is determined and the resemblance between these functions and the well-known Hermite-Gauss modes is exploited.