White CsPbBr3: Characterizing the One-Dimensional Cesium Lead Bromide Polymorph

Inorganic lead halide perovskites have gained immense scientific interest for optoelectronic applications. In this work, we present a one-dimensional polymorph of cesium lead bromide (δ-CsPbBr₃) synthesized through a simple anion-exchange reaction, wherein distorted edge-sharing PbBr₆ octahedra form 1D chains isolated by Cs ions. δ-CsPbBr₃ was characterized by Raman spectroscopy, X-ray diffraction, ²⁰⁷Pb and ¹³³Cs solid-state NMR, and by optical emission and absorption spectroscopies. This non-perovskite material irreversibly transforms into the well-known three-dimensional perovskite phase (γ-CsPbBr₃) upon heating to above 151 °C. The indirect bandgap was determined by absorption measurements and calculation to be 2.9 eV. δ-CsPbBr₃ exhibits broadband yellow photoluminescence with a quantum yield of 3.2 %±0.2 % at room temperature and 95 %±5 % at 77 K, and this emission is attributed to the recombination of self-trapped excitons. This study emphasizes that the metastable δ-CsPbBr₃ may be a persistent, concomitant phase in Cs−Pb-Br-containing materials systems, such as those used in solar cells and LEDs, and it showcases the characterization tools used for its detection.     

Role of propagating slit mode in enhanced transmission through slit arrays in a metallic films

The mechanisms responsible for enhanced transmission of electromagnetic wave through an array of subwavelength slits in a metallic film are analyzed. Theoretical model of the enhanced transmission which takes into account the penetration of electromagnetic field into real metal is developed. Semi-analytical model based on Fabry–Perot formula is considered. Comparison of theoretical model, semi-analytical model and results of numerical simulation of Maxwell equations in time-dependent form (FDTD method) for silver with various geometric parameters is presented. The roles of surface plasmons and plasmon localized along slits are studied.     

Hybrid Metal Halides with Multiple Photoluminescence Centers

Very little is known about the realm of solid‐state metal halide compounds comprising two or more halometalate anions. Such compounds would be of great interest if their optical and electronic properties could be rationally designed. Herein, we report a new example of metal halide cluster‐assembled compound (C₉NH₂₀)₉[Pb₃Br₁₁](MnBr₄)₂, featuring distinctly different anionic polyhedra, namely, a rare lead halide cluster [Pb₃Br₁₁]^5? and [MnBr₄]^2?. In accordance with its multinary zero‐dimensional (0D) structure, this compound is found to contain two distinct emission centers, 565 nm and 528 nm, resulting from the formation of self‐trapped excitons and ⁴T₁‐⁶A₁ transition of Mn²⁺ ions, respectively. Based on the high durability of (C₉NH₂₀)₉[Pb₃Br₁₁](MnBr₄)₂ upon light and heat, as well as high photoluminescence quantum yield (PLQY) of 49.8 % under 450 nm blue light excitation, white light‐emitting diodes (WLEDs) are fabricated, showcasing its potential in backlight application.     

Synthesis of azachromones and azachromanones

Chemistry of Heterocyclic Compounds - This minireview highlights known methods for the synthesis of azachromones and azachromanones, including the earliest and the latest examples of their...     

Highly Emissive Self‐Trapped Excitons in Fully Inorganic Zero‐Dimensional Tin Halides

The spatial localization of charge carriers to promote the formation of bound excitons and concomitantly enhance radiative recombination has long been a goal for luminescent semiconductors. Zero‐dimensional materials structurally impose carrier localization and result in the formation of localized Frenkel excitons. Now the fully inorganic, perovskite‐derived zero‐dimensional Sn^II material Cs₄SnBr₆ is presented that exhibits room‐temperature broad‐band photoluminescence centered at 540 nm with a quantum yield (QY) of 15±5 %. A series of analogous compositions following the general formula Cs_4?xA_xSn(Br_1?yI_y)₆ (A=Rb, K; x≤1, y≤1) can be prepared. The emission of these materials ranges from 500 nm to 620 nm with the possibility to compositionally tune the Stokes shift and the self‐trapped exciton emission bands.     

3-Fluoroalkyl (CF3, CHF2, CH2F) Cyclobutane-Derived Building Blocks for Medicinal Chemistry: Synthesis and Physicochemical Properties

Synthesis and physicochemical characterization of all possible cis- and trans-1,3-disubstituted cyclobutane-derived amines and carboxylic acids bearing mono-, di- and trifluoromethyl groups at the C-3 position is disclosed. Tetramethylammonium fluoride (TMAF)- or morpholinosulfur trifluoride (Morph-DAST)-mediated nucleophilic fluorination of appropriate cis- and trans-diastereomeric substrates was used as the key step for the preparation of CH₂F- and CHF₂-substituted derivatives. To obtain the corresponding cis- and trans-isomeric CF₃-substituted derivatives, resolution of known 3-(trifluoromethyl)cyclobutanecarboxylic acid (obtained as a mixture of diastereomers) was applied. The proposed procedures were suitable for the preparation of corresponding fluoroalkyl-substituted cyclobutane-derived amines and carboxylic acids on up to 50 g scale. All 12 building blocks obtained were characterized by measuring dissociation constants (pK_a) and lipophilicities (LogP, for model derivatives) to evaluate the effect of the fluoroalkyl substituents on their physicochemical properties relevant to further drug discovery applications.     

Quantification of local hydration at the surface of biomolecules using dual-fluorescence labels

By using four labels of the 3-hydroxyflavone family displaying selective sensitivity to hydrogen bond (HB) donors and poor response to other polar molecules, we developed an approach for measuring local water concentration [H(2)O](L) (or partial volume of water: W(A) = [H(2)O](L)/55.6) in the label surrounding both in solvent mixtures and in biomolecules by the intensity ratio of two emissive forms of the label, N*/T*. Using a series of binary water/solvent mixtures with limited preferential solvation effects, a linear dependence of log(N*/T*) on the local concentration of HB donor was obtained and then used as a calibration curve for estimating the W(A) values in the surroundings of the probes conjugated to biomolecules. By this approach, we estimated the hydration of the labels in different peptides and their complexes with DNAs. We found that W(A) values for the label at the peptide N-terminus are lower (0.63-0.91) than for free labels and depend strongly on the nature of the N-terminal amino acid. When complexed with different DNAs, the estimated hydration of the labels conjugated to the labeled peptides was much lower (W(A) = 0-0.47) and depended on the DNA nature and linker-label structure. Thus, the elaborated method allows a site-specific evaluation of hydration at the surface of a biomolecule through the determination of the partial volume of water. We believe the developed procedure can be successfully applied for monitoring hydration at the surface of any biomolecule or nanostructure.     

On some integral-consistent methods for calculating magnetohydrodynamic phenomena in problems of computational astrophysics

When constructing difference schemes for calculating complex problems of computational astrophysics considering magnetohydrodynamic and gravitational phenomena, the processes of matter overcompression (with a change in density by several orders of magnitude) should be taken into account, and it is important at a discrete level to take into account the corresponding energy transformations of magnetohydrodynamic, gravitational, kinetic, and internal energy during the evolution of a star. This problem is solved by constructing completely conservative difference schemes in a view of these magnetohydrodynamic processes and self-gravitating phenomena. In this work, to study and apply the difference methods for solving problems of magnetic gas dynamics, a discrete representation of symmetrized spatial deformations of the medium was obtained. The representation is consistent with changes in the magnetic, kinetic, and internal energies and does not lead to their distortions when the matter is overcompressed.     

Transition absorption as a mechanism of surface photoelectron emission from metals

Transition absorption of a photon by an electron passing through a boundary between two media with different permittivities is described both classically and quantum mechanically. Transition absorption is shown to make a substantial contribution to photoelectron emission at a metal/semicon‐ductor interface in nanoplasmonic systems, and is put forth as a possible microscopic mechanism of the surface photoelectric effect in photodetectors and solar cells containing plasmonic nanoparticles.