Indium(I) iodide as a radical initiator: intramolecular cyclization of functionalized bromo-alkynes to substituted tetrahydrofurans

Aryl substituted α-carbonyl bromo-alkynes undergo facile cyclizations to the corresponding substituted 4-methylene-tetrahydrofurans using indium(I) iodide in acetonitrile under sonication in high yields. The reaction is predicted to proceed via a radical process initiated by InI and a plausible radical pathway is suggested.     

Indium(I) iodide-promoted cleavage of diaryl diselenides and disulfides and subsequent condensation with alkyl or acyl halides. One-pot efficient synthesis of diorganyl selenides, sulfides, selenoesters, and thioesters

Diphenyl diselenides and disulfides undergo facile cleavages by indium(I) iodide and the corresponding generated selenate and thiolate anions condense in situ with alkyl or acyl halides present in the reaction mixture. Thus, a simple, efficient, and general procedure has been developed for the synthesis of unsymmetrical diorganyl selenides, sulfides (thioethers), selenoesters, and thioesters by this one-pot reaction at room temperature.     

Copper(II) Complexes of 3,4,5‐Trisubstituted Pyrazolates: In Situ Formation of Pyrazole Rings from Different Carbon Centers

The synthesis and characterization of two pyrazolate‐bridged dicopper(II) complexes, [Cu₂(L¹)₂(H₂O)₂](ClO₄)₂ ( 1 , HL¹=3,5‐dipyridyl‐4‐(2‐keto‐pyridyl)pyrazole) and [Cu₂(L²)₂(H₂O)₂](ClO₄)₂ ( 2 , HL²=3,5‐dipyridyl‐4‐benzoylpyrazole), are discussed. These copper(II) complexes are formed from the reactions between pyridine‐2‐aldehyde, 2‐acetylpyridine (for compound 1 ) or acetophenone (for compound 2 ), and hydrazine hydrate with copper(II) perchlorate hydrate under ambient conditions. The single‐crystal X‐ray structure of compound 1? 2 H₂O establishes the formation of a pyrazole ring from three different carbon centers through C? C bond‐forming reactions, mediated by copper(II) ions. The free pyrazoles (HL¹ and HL²) are isolated from their corresponding copper(II) complexes and are characterized by using various analytical and spectroscopic techniques. A mechanism for the pyrazole‐ring synthesis that proceeds through C? C bond‐forming reactions is proposed and supported by theoretical calculations.     

Intercommutation of semilocal strings and Skyrmions

We study the intercommuting of semilocal strings and Skyrmions for a wide range of internal parameters, velocities, and intersection angles by numerically evolving the equations of motion. We find that the collisions of strings and strings, strings and Skyrmions, and Skyrmions and Skyrmions all lead to intercommuting for a wide range of parameters. Even the collisions of unstable Skyrmions and strings lead to intercommuting, demonstrating that the phenomenon of intercommuting is very robust, extending to dissimilar field configurations that are not stationary solutions. Even more remarkably, at least for the semilocal U(2) formulation considered here, all intercommutations trigger a reversion to Nielsen-Olesen strings.     

Ionothermal Synthesis of Imide‐Linked Covalent Organic Frameworks

Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time‐consuming process and restricted to well‐soluble precursor molecules. Synthesis of polyimide‐linked COFs (PI‐COFs) is further complicated by the poor reversibility of the ring‐closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI‐COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene‐based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high‐temperature XRPD analysis hints to the formation of precursor–salt adducts as crystalline intermediates, which then react with each other to form the COF.     

511 keV photons from superconducting cosmic strings

We show that a tangle of light superconducting strings in the Milky Way could be the source of the observed 511 keV emission from electron-positron annihilation in the Galactic bulge. The scenario predicts a flux that is in agreement with observations if the strings are at the approximately 1 TeV scale, making the particle physics within reach of planned accelerator experiments. The emission is directly proportional to the galactic magnetic field, and future observations should be able to differentiate the superconducting string scenario from other proposals.     

Boojum and stripe textures in long-range orientationally ordered monolayers on solid substrates

Long-range organization of molecular tilt azimuth is a striking feature in monolayers at the air-water interface. We show that the boojum and stripe textures of pentadecanoic acid (PDA) with the continuous variations of molecular tilt azimuth formed at the air-water interface at temperatures lower than room temperature can be preserved after being transferred to glass substrates at low dipping speeds. The long-range tilt order in the transferred boojums and stripes is resolved by frictional force microscopy at room temperature, suggesting that the tilt order is "frozen" through the interaction of PDA molecules with the glass surface. The transferred stripe structure can be used as a unique alignment layer to induce a continuously azimuthal orientation of nematic liquid crystals.     

Analytical model of transient compressive stress evolution during growth of high diffusivity thin films on substrates

We present an analytical model of transient compressive stress evolution during growth of thin films with high surface and grain boundary diffusivities on substrates. The model provides a closed-form analytical solution which compares well with numerical analysis as well as recent experimental data on transient stress evolution during electrodeposition of Sn films on substrates.     

Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks

Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However, the response of such materials toward laser‐induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)‐based porous COFs—Por‐COF‐HH and its dual metalated congeners Por‐COF‐ZnCu and Por‐COF‐ZnNi—have been prepared and present excellent NLO properties. Notably, intensity‐dependent NLO switching behavior was observed for these Por‐COFs, which is highly desirable for optical switching and optical limiting devices. Moreover, the efficient π‐conjugation and charge‐transfer transition in ZnCu‐Por‐COF enabled a high nonlinear absorption coefficient (β=4470 cm/GW) and figure of merit (FOM=σ₁/σ_o, 3565) value compared to other state‐of‐the‐art materials, including molecular porphyrins (β≈100–400 cm/GW), metal–organic frameworks (MOFs; β≈0.3–0.5 cm/GW), and graphene (β=900 cm/GW).     

Thermally exfoliated graphene oxide reinforced stress responsive conductive nanocomposite hydrogel

Lightweight and flexible biosensors that can sustain mechanical deformation and can be adhered to human skin is an interesting field of study. In the current article, a systematic study on development of thermally exfoliated graphene oxide (TEGO)–reinforced poly(vinyl alcohol) (PVA)–based conductive hydrogel nanocomposites has been reported. The free‐standing hydrogels were synthesized using controlled and repetitive freeze‐thaw cycles. The samples were then studied for their mechanical as well as electrical properties. The hydrogels were characterized for their microstructural, chemical, and rheological properties to understand the observed macroscopic properties. Additionally, a study on the behavior of hydrogels immersed in phosphate‐buffered saline (PBS) was carried out to investigate their hydrolytic stability within simulated biological environment. Overall, the nanocomposite hydrogels demonstrated excellent static and dynamic mechanical performance, stability in PBS, considerable electrical conductivity, and significant electrical response to applied external stress, establishing their potential for use as flexible biosensors.