A number of consecutive generations of bithiophenesilane dendrimers and their precursors are studied by the methods of the equilibrium electro-optical Kerr effect, dielectric polarization, and ...absorption spectroscopy in dilute toluene solutions. It is shown that the molecules of hybrid dendrimers containing bithiophene fragments covalently linked via silicon atoms are not kinetically rigid and feature the small-scale mechanism of interaction with external electric fields. A tris(bithiophene)methylsilane fragment is found to be the subunit responsible for the electro-optical and optical spectral properties of the above hybrid dendrimers. It is revealed that the polarization of bithiophensilane dendrimers predominantly shows the deformation pattern.
In this work, a versatile synthetic method for preparation of linear phenyloxazoles and their organosilicon derivatives under mild conditions via a combination of van Leusen and direct CH arylation ...reactions is reported. It was used for the synthesis of a novel trimethylsilyl (TMS) derivative of blue laser dye 1,4-bis(5-phenyloxazol-2-yl)benzene (POPOP) and its structural isomer 1,4-bis(2-phenyloxazol-5-yl)benzene (isoPOPOP) with and without TMS substituents. All of the compounds demonstrated high photoluminescence quantum yields and large molar extinction coefficients, which further increased for their TMS derivatives. Measurements of accelerated photodegradation of the dyes in diluted THF solutions revealed that POPOP-type compounds are twice more stable than their isoPOPOP-type isomers, independent of the presence or absence of TMS substituents. Cyclic voltammetry (CV) investigations revealed that POPOP-type dyes are more electrochemically stable as compared to their isoPOPOP-type isomers. Quantum chemical TD DFT calculations of the frontier energy levels of the dyes were in a good agreement with the experimental data obtained by CV. Single-crystal X-ray diffraction experiments revealed significant structural differences between crystal lattices of the dyes. Due to facile synthesis and excellent optical properties as well as high photo- and thermo- stability the novel luminescent dyes may find wide application in organic photonics.
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•A mild synthesis of phenyloxazoles and their trimethylsilyl derivatives is reported.•All phenyloxazoles synthesized have high PLQYs and molar extinction coefficients.•POPOP-type compounds are more stable than their structural isomers.•X-ray diffraction revealed important structural differences between the lattices.
The luminescence spectral properties of oligothiophenesilane dendrite macromolecules were studied. It was found that the chromophores responsible for the formation of the absorption and luminescence ...spectra were dendrimer fragments separated by silicon atoms; all the chromophores are equally involved in the formation of the absorption spectra of dendritic macromolecules of the zero, first, second, and third generations. It was shown that for dendrites of the first, second, and third generations, the luminescence spectrum is mainly formed by the chromophore fragments lying in the internal layers of the dendritic macromolecule due to the induction resonance energy transfer of electronic excitation from peripheral to internal chromophore fragments. The conclusion was drawn that synthesis of dendritic macromolecules with internal chromophore fragments possessing a high quantum yield of fluorescence can give actively luminescing nanosized objects with the molar extinction coefficient proportional to the number of fragments ɛ
max
≈ 10
6
l/(mol cm). These compounds can find wide application in transducers for converting various types of ionizing radiation into optical radiation in electroluminescent devices.
The last 10–15 years have been marked by a rapid increase in the volume of knowledge about the role of the intestinal microbiota in the regulation of various physiological processes. In particular, ...the interrelations between disturbances in the composition of the intestinal microflora and an increase in the risk of developing cardiovascular diseases were noted. There are also emerging works that demonstrate the possibility of reducing the severity of myocardial ischemia-reperfusion injury as a result of various effects on the composition of intestinal microbiota. This review analyzes the recent literature on the influence of intestinal microbiota on myocardial resistance to ischemia-reperfusion injury. It has been shown that modulation of the intestinal microbiome by changing the nature of nutrition, probiotics, antibiotics, and intestinal microflora transplantation leads to a reduction in the size of myocardial infarction. Normalization of increased permeability of intestinal epithelial barrier with reduction of manifestations of systemic inflammation, changes in the level of secretion of some hormones, increased production of short-chain fatty acids and modulation of bile acid metabolism under the action of intestinal bacterial enzymes are considered as possible mechanisms of cardioprotection mediated by changes in the functional state of microbiota. The concept of increasing myocardial resistance to ischemia-reperfusion injury by modulating the composition of the intestinal microbiota is a completely new scientific direction that requires detailed study in experiment with the possibility of rapid implementation of the results obtained in clinical practice.
The synthesis of new dendrimers and branched oligothiophene silanes containing bithiophene groups at the periphery and quaterthiophene fragments at the center of the molecule is described. Specific ...features of bithiophene silane bromination were shown, and the conditions for the efficient synthesis of methyltris(5-bromo-2,2′-bithiophen-5-yl)silane have been found for the first time. The optical properties of the synthesized compounds were studied. The efficiency of the electron excitation energy transfer between the fragments of branched bi-and quaterthiophene silanes was measured.
A SensL MicroFC-SMT-60035 6x6 mm\(^2\) silicon photo-multiplier coated with a NOL-1 wavelength shifter have been tested in the liquid xenon to detect the 175-nm scintillation light. For comparison, a ...Hamamatsu vacuum ultraviolet sensitive MPPC VUV3 3x3 mm\(^2\) was tested under the same conditions. The photodetection efficiency of \(13.1 \pm 2.5\)% and \(6.0 \pm 1.0\)%, correspondingly, is obtained.
Particle separation based on size in the cross section of a rotating drum with a packing is investigated as a function of the size of the blades, their number, the rotational speed of the drum, and ...its filling. A significant relationship is established between the effect of separation and the rotational speed of the drum and the space factor of its material. A conclusion is drawn concerning the possibility of utilizing the effect of particle separation with respect to size in the cross section of a rotating drum to control the grain-size distribution of the product in drum granulators-dryers, mixers, and separators.
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