ANALYSIS OF DEAD CORE FORMATION IN CATALYTIC REACTION AND DIFUSION PROCESSES WITH GENERALIZED DIFUSION FUX

Dead-core and non-dead-core solutions to the nonlinear diffusion–reaction equation based on the generalized diffusion flux with gradient-dependent diffusivity and the power-law reaction kinetics in catalyst slabs are established. The formation of dead zones where the reactant concentration vanishes is characterized by the critical Thiele modulus that is derived as a function of reaction order and diffusion exponent in the generalized diffusion flux. The effects of reaction order and diffusion exponent on the reactant concentration distribution in the slab and dead-zone length are analyzed. It is particularly demonstrated that by contrast to the model based on the standard Fick’s diffusion, dead-core solutions exist in the case of first-order reactions. Also, the relationship between critical Thiele moduli for models based on the generalized and standard Fick’s diffusion fluxes is established

Impact of Halogen Termination and Chain Length on π-Electron Conjugation and Vibrational Properties of Halogen-Terminated Polyynes

: We explored the optoelectronic and vibrational properties of a new class of halogen-terminated carbon atomic wires in the form of polyynes using UV-vis, infrared absorption, Raman spectroscopy, X-ray single-crystal diffraction, and DFT calculations. These polyynes terminate on one side with a cyanophenyl group and on the other side, with a halogen atom X (X = Cl, Br, I). We focus on the effect of different halogen terminations and increasing lengths (i.e., 4, 6, and 8 sp-carbon atoms) on the π-electron conjugation and the electronic structure of these systems. The variation in the sp-carbon chain length is more effective in tuning these features than changing the halogen end group, which instead leads to a variety of solid-state architectures. Shifts between the vibrational frequencies of samples in crystalline powders and in solution reflect intermolecular interactions. In particular, the presence of head-to-tail dimers in the crystals is responsible for the modulation of the charge density associated with the π-electron system, and this phenomenon is particularly important when strong I··· N halogen bonds occur

Spectral dependence of nonlinear optical properties of symmetrical octatetraynes with p-substituted phenyl end-groups

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Palladium End-Capped Polyynes via Oxidative Addition of 1‑Haloalkynes to Pd(PPh₃)₄

Reported here is the use of 1-haloacetylenes and 1-halopolyynes as synthons for the preparation of new palladium­(II) end-capped polyynes. The 1-haloalkynes were obtained in a series of transformations from <i>para</i>-substituted bromoarenes that included Sonogashira coupling followed by halogenation and chain elongation via Cadiot–Chodkiewicz protocol. The key step for the synthesis of metal complexes was oxidative addition of 1-haloalkynes to Pd­(PPh₃)₄, which allowed obtaining a series of metal compounds <b>1</b>–<b>5</b>-C_<i>n</i>X with carbon chains up to hexatriyne in 75–100% yield. All the compounds were characterized by NMR and HRMS or elemental analysis. The ¹³C spectra of the 1-haloalkynes showed interesting, although expected, shifts of the carbon chain atoms close to the halogen termini. X-ray crystal structures were obtained for three polyynestwo butadiynes (<b>2</b>-C₄[Pd]Br and <b>3</b>-C₄[Pd]­Br) and one hexatriyne (<b>1</b>-C₆[Pd]­Br)and the latter is the first reported X-ray crystal structure of palladium end-capped hexatriyne

Polyynes as Precursors of Photoluminescent Solvent Polarity Probes

A simple and convenient synthesis of substituted thiophenes from pyrrole end-capped polyynes is being reported. The method allows one to obtain a variety of different fluorescent oligo­(hetero)­aryles from polyyne precursors. The resulting thiophenes exhibit strong emission solvatochromism in a wide scope of different solvents which makes them promising candidates for fluorescent solvent polarity probes

Porous Silsesquioxane–Imine Frameworks as Highly Efficient Adsorbents for Cooperative Iodine Capture

The efficient capture and storage of radioactive iodine (¹²⁹I or ¹³¹I), which can be formed during nuclear energy generation or nuclear waste storage, is of paramount importance. Herein, we present highly efficient aerogels for reversible iodine capture, namely, porous silsesquioxane–imine frameworks (PSIFs), constructed by condensation of octa­(3-aminopropyl)­silsesquioxane cage compound and selected multitopic aldehydes. The resulting PSIFs are permanently porous (Brunauer–Emmet–Teller surface areas up to 574 m²/g), thermally stable, and present a combination of micro-, meso-, and macropores in their structures. The presence of a large number of imine functional groups in combination with silsesquioxane cores results in extremely high I₂ affinity with uptake capacities up to 485 wt %, which is the highest reported to date. Porous properties can be controlled by the strut length and rigidity of linkers. In addition, <b>PSIF-1a</b> could be recycled at least four times while maintaining 94% I₂ uptake capacity. Kinetic studies of I₂ desorption show two strong binding sites with apparent activation energies of 77.0 and 89.0 kJ/mol. These energies are considerably higher than the enthalpy of sublimation of bulk I₂

Palladium End-Capped Polyynes via Oxidative Addition of 1‑Haloalkynes to Pd(PPh₃)₄

Reported here is the use of 1-haloacetylenes and 1-halopolyynes as synthons for the preparation of new palladium­(II) end-capped polyynes. The 1-haloalkynes were obtained in a series of transformations from <i>para</i>-substituted bromoarenes that included Sonogashira coupling followed by halogenation and chain elongation via Cadiot–Chodkiewicz protocol. The key step for the synthesis of metal complexes was oxidative addition of 1-haloalkynes to Pd­(PPh₃)₄, which allowed obtaining a series of metal compounds <b>1</b>–<b>5</b>-C_<i>n</i>X with carbon chains up to hexatriyne in 75–100% yield. All the compounds were characterized by NMR and HRMS or elemental analysis. The ¹³C spectra of the 1-haloalkynes showed interesting, although expected, shifts of the carbon chain atoms close to the halogen termini. X-ray crystal structures were obtained for three polyynestwo butadiynes (<b>2</b>-C₄[Pd]Br and <b>3</b>-C₄[Pd]­Br) and one hexatriyne (<b>1</b>-C₆[Pd]­Br)and the latter is the first reported X-ray crystal structure of palladium end-capped hexatriyne

Use of Stable Amine-Capped Polyynes in the Regioselective Synthesis of Push–Pull Thiophenes

The reactions of a series of 1-halopolyynes with secondary amines led to novel amine end-capped polyynes exhibiting surprisingly high stability toward moisture. The new compounds were characterized by NMR spectroscopy, ESI-MS spectrometry, and X-ray single-crystal diffractometry. The use of amine end-capped polyynes as precursors to substituted push–pull thiophenes was next presented. The results show the firstto the best of our knowledgetransformation of ynamine to thiophene and the first regioselective transformation of a longer polyynes to butadiyne-substituted thiophene. Photophysical studies of the resulting compounds show that some of the substituted thiophenes have high quantum yield photoluminescence upon UV light irradiation

Use of Stable Amine-Capped Polyynes in the Regioselective Synthesis of Push–Pull Thiophenes

The reactions of a series of 1-halopolyynes with secondary amines led to novel amine end-capped polyynes exhibiting surprisingly high stability toward moisture. The new compounds were characterized by NMR spectroscopy, ESI-MS spectrometry, and X-ray single-crystal diffractometry. The use of amine end-capped polyynes as precursors to substituted push–pull thiophenes was next presented. The results show the firstto the best of our knowledgetransformation of ynamine to thiophene and the first regioselective transformation of a longer polyynes to butadiyne-substituted thiophene. Photophysical studies of the resulting compounds show that some of the substituted thiophenes have high quantum yield photoluminescence upon UV light irradiation