Unusual Pathways of Triplet State Dynamic Relaxation in Meso-Aryl-Substituted Porphyrins and Their Chemical Dimers at 295 K

It was found that mono- and di-meso-phenyl substitution in octaethylporphyrins (OEP)and their chemical dimers with the phenyl ring as a spacer manifests itself in the dramatical shortening of T₁ state lifetimes at 295 K (from 1.5 ms down to 2–5 s in degassed toluene solutions). On the other hand, this substitution does not influence spectral-kinetic parameters of S₀ and S₁ states. The enhancement of the T₁ state non-radiative deactivation is explained by torsional librations of the phenyl ring around a single C-C bond in sterically encumbered OEP molecules leading to non-planar dynamic distorted conformations in the excited T₁ states. For these compounds with electron-accepting NO₂-groups in the meso-phenyl ring the strong non-radiative deactivation of S₁ and T₁ states (by 2–3 orders of magnitude) is observed upon the displacement of NO₂-group from para-to ortho-position of the phenyl ring. The S₁ state quenching is caused by the direct intramolecular electron transfer to low-lying CT state of the radical ion pair (the normal region, non-adiabatic case presumably, V = 130–190 cm^–1 in dimethylformamide). The additional deactivation of the T₁ state is connected with thermally activated transitions to upper-lying CT states as well as the strengthening of intersystem crossing probabilities.     

Mode shapes at the boundaries of the transmission zones for plane-polarized bulk waves in a regularly layered medium

International Applied Mechanics -     

Design of small-molecule thrombin inhibitors based on the <Emphasis Type="Italic">cis</Emphasis>-5-phenylproline scaffold

The design of novel organic compounds containing no strongly basic amidine or guanidine functional groups typical of serine protease inhibitors was performed to develop an oral anticoagulant drug. A three-dimensional computational model for thrombin active site was constructed and optimized for docking of small-molecule organic compounds and calculating the energies of inhibitor-enzyme interactions. Novel racemic derivatives of 1-[2-(4-chlorophenylthio)acetyl]-5-phenylpyrrolidine-2,4-dicarboxylic acids were synthesized for which Cl-π interactions between the inhibitors and the S1 pocket of thrombin active site are predicted by modeling. The compounds synthesized deactivate thrombin in vitro and the inhibition properties show good correlations with the results of calculations.     

Waveguide technique for measuring thin film parameters

A waveguide technique for measuring the absorption coefficient, refractive index, and thickness of thin films is suggested. It is based on taking the angular dependence of the light beam reflection coefficient in an optical scheme involving a prism coupler. Application of the technique to determining the parameters of thin-film waveguides, insulating coatings, and metal films is considered.     

Interaction of low-energy Cu2 dimers with copper clusters on the graphite surface

The sputtering of clusters consisting of 13, 27, and 75 copper atoms from the (0001) graphite surface under bombardment by Cu₂ dimers with energies of 100, 200, and 400 eV has been simulated using the molecular dynamics method. A comparative analysis of the distributions of backscattered particles and their energies over polar angles and the energy distributions of sputtered atoms has been performed. The factors responsible for the large sputtering yield from surface clusters under their bombardment with dimers as compared to copper and xenon monomers have been discussed. It has been demonstrated that, in the case of bombardment with dimers, the substantial role in the sputtering of surface clusters is played by the overlap of collision cascades initiated by each atom of the incident dimer. The differences in the sputtering under cluster and atom bombardments are especially pronounced in the case of large surface clusters.     

Effects of W and Mo crystalline texture on the angular distribution of sputtered atoms

The effects of W and Mo surface crystalline texture on the angular distribution of sputtered atoms were investigated experimentally and by computer simulation. A small-sized planar DC magnetron was used to sputter the target by 200–300 eV Ar⁺ ions. The crystalline texture was formed under rolling of metal foils and during the preparation of metal bars and was controlled by X-ray diffraction analysis. For W and Mo foils, a strong anisotropy of the angular distribution was found. The character of angular distribution was different in the planes oriented perpendicularly and in parallel to the direction of rolling. In the first case, the angular distribution was peaked at the polar angle θ=0, while in the second case, the angular distribution, in addition to a maximum at θ=0, revealed a pronounced maximum at θ≈ 57° and ≈60° for Mo and W, respectively. For bars, no azimuthal anisotropy was observed, but the angular distribution was peaked at θ=37° (Mo) and θ=45° (W). This is in contrast to the case of non-textured Mo and W polycrystals, for which the angular distribution had a maximum at θ=0. Computer simulation technique in combination with the results of X-ray analysis was used to clarify the above experimental findings. It was demonstrated that the angular distribution of sputtered atoms can be successfully used for the determination of the crystalline texture of metals.     

Angular distribution of atoms sputtered from germanium by 1–20 keV Ar ions

The angular distribution of atoms sputtered from germanium under 1–20 keV Ar⁺ ion bombardment (normal incidence) has been studied experimentally and using computer simulations. A collector technique combined with Rutherford backscattering to analyze the distribution of collected material was used. In addition, the surface topography was under control. It was found that the experimental angular distribution of sputtered atoms (E ₀=3–10 keV) could be approximated by the function cos ⁿ θ with n≈ 1.65. Such a high value of n is connected with the surface scattering of ejected atoms and a noticeable contribution of backscattered ions to the formation of the sputter flux (the mass effect). The target surface was found to be practically flat even at ion fluencies ～10¹⁸ ions/cm². The results obtained are compared with data from the literature, including our recent data on Si sputtering.