Fluorine Donor Research Articles

Supercharging green chemistry: Unleashing 1, 4‐NADH regeneration and unprecedented C(sp3)‐F bond activation via NiS‐NiO/S‐g‐C3N4 nanocomposite photocatalyst under solar light

AbstractFluorinated and enzymatic chemicals are widely used in society due to their chemical, physical, and biological qualities. Nevertheless, despite their vital importance, present approaches to adding fluorine to molecules and regenerating enzyme cofactors have serious flaws. For instance, numerous approaches are photocatalytic and employ stoichiometric counterparts of heavy metals. Prevailing photocatalytic approaches, on the other hand, show very poor activity, and selectivity has not been attained by heterogeneous photocatalysis, despite the several benefits such a method would provide. Here, we show how heterogeneous photocatalysis may be used to selectively create C(sp3)‐F bonds and 1,4‐NADH regeneration cofactor. Employing NiS‐NiO/S‐g‐C3N4 nanocomposite photocatalyst as a photocatalyst, NAD+ and Selectfluor as an acceptor and mild fluorine donor, effective 1,4‐NADH regeneration, and decarboxylative fluorination of carboxylic acids can be attained in very short reaction times. Furthermore, NiS‐NiO/S‐g‐C3N4 nanocomposite photocatalyst exhibits outstanding levels of robustness and photo‐catching capacity. These aspects, attached to the mild environment of the reaction scheme, exhibit a breakthrough toward the sustainable cofactor of 1,4‐NADH regeneration and synthesis of fluorinated compounds.

High-performance lithium metal batteries enabled by fluorinated aromatic diluent assisted nonflammable localized high-concentration electrolytes

Localized high concentration electrolytes (LHCEs) possess low viscosity, good wettability, sufficient ionic conductivity and good compatibility with lithium metal anodes. However, diluents of LHCEs suffer from high density, high-cost and low activity in the formation of robust SEIs. Herein, we developed a trimethyl phosphate (TMP)-based nonflammable LHCE diluted by 1,2-difluorobenzene (DFB), which lower density, lower cost, lower LUMO and better fluorine-donating property. With the addition of DFB, 3.2 M LiFSI/TMP/DFB (LiFSI/TMP/DFB 0.75:1:0.5) exhibits reduced viscosity (49.2 mPa s) and improved ionic conductivity (1.27 mS cm−1), while the local high-concentration solvation structure of TMP-Li+-FSI− is retained. DFB can fabricate LiF-rich SEI on lithium metal anodes owing to its low LUMO and fluorine donor properties, and efficiently inhibits lithium dendrites. Remarkably, the battery performance of the LHCE is significantly improved by DFB. 3.2 M LiFSI/TMP/DFB endows LiNi0.8Co0.1Mn0.1O2/Li cells with excellent long-term cycle performance (capacity retention of 80.1% after 500 cycles). LiFePO4/Li cells with 3.2 M LiFSI/TMP/DFB demonstrate high rate capability (discharge capacity of 112.7 mAh g−1 at 5 C rate) and outstanding long-term cycle performance (capacity retention of 80.9% after 850 cycles).

Spectral, structural, and pharmacological studies of perillaldehyde and myrtenal based benzohydrazides

N-Acylhydrazones have been an interesting scaffold due to their diverse biological activities toward different therapeutic targets. We synthesized seven new N'‐[(E)‐[(4S)‐4‐(prop‐1‐en‐2‐yl)cyclohex‐1‐en‐1‐yl]methylidene]benzohydrazides as well as seven new N'-[(E)-{6,6-dimethylbicyclo[3.1.1]hept-2-en-2-yl}methylidene]benzohydrazides. The structure of synthesized hydrazides has been studied by using X-ray analysis, FT-IR, NMR, and HRMS spectra. Derivatives containing fluorine atoms in position 2 of the phenyl ring display versatile structures in solution and the solid state. The 1H NMR spectra of 3c and 5c measured in DMSO-d6 display at ambient temperature two unequally populated sets of signals. These facts confirm the existence of the two conformers of 3c and 5c of different stability which interconvert by rotation about their C―N bond slowly enough to lead to discrete sets of signals in 1H NMR spectra at room temperature. The kinetics of the conformational interconversion of derivatives 3c and 5c in DMSO-d6 were studied by two-dimensional exchange spectroscopy (2D EXSY). In 1H NMR spectra of 3c and 5c measured in CDCl3 and acetone-d6 was observed the strong splitting of the H-2 signal into a doublet because of H-bond formation between organic fluorine and NH donor. The FT–IR spectra of 3a–g and 5a–g confirmed the presence of the H-bonds N–H···O=C and N–H···N. Hydrazones 3f, 5a, and 5c crystallize in the P1 space group and the asymmetric units contain two pairs of pseudo-centrosymmetric molecules. Hydrazone 5b crystallizes in the P41 space group and the asymmetric units contain only one molecule. In the crystal, the molecules in 3f, 5a and 5b are linked through N―H···O hydrogen bonds, in 5c also N―H···N hydrogen bonds are present. In contrast to the NMR, the X-ray and IR spectra did not give unambiguous evidence of the F···H−N H-bond. The synthesized hydrazones 3c and 3g exhibited excellent antiproliferative effects in Jurkat cells with IC50 values of 3.8 and 4.2 μM, respectively. Our findings indicate that these compounds are promising antitumor agents.

A structural and spectroscopic study on heterometallic sodium(I)–europium(III) β-diketonate complexes

In order to gain insight into heterometallic alkali–lanthanide systems, a series of Na(I)–Eu(III)/La(III) β-diketonate complexes were synthesized and structurally characterized by single crystal X-ray diffraction. The Eu(III) and La(III) complexes are found to be isostructural in both monomeric and polymeric forms. Adjusting β-diketonate ligands from TFPB to TFNB in monomeric complexes results in Na(I) ion being coordinated by 2-acetonaphthone instead of water due to the unexpected hydrolysis of HTFNB. Transformation of monomeric form into polymeric one can be achieved by simple recrystallization in less polar solvents. The X-ray structures of the complexes describe β-diketonate fragments as bidentate ligands towards Na(I) ion using oxygen and fluorine donor atoms in both forms. Photoluminescence studies highlight the largest emission quantum yield for [Eu(TFNB)4Na(MeOH)2(2-acetonaphthone)] (1a-m) which possibly has an additional sensitization of coordinated 2-acetonaphthone. Polymeric Eu(III) complexes show moderate emissions due to the scrambling process in solution as suggested by NMR results.

Compacted Magnesium Fluoride: Preparation, Characterization, and Optics

The electronic structure and the effect of defects on the optical properties of magnesium fluoride are studied by X-ray photoelectron spectroscopy (XPES). A deviation from fluorine stoichiometry in MgF2−x is shown to give rise to a long-wavelength shift of the absorption edge. The color of a defective magnesium fluoride caused by the absorption in the range 215–300 nm, low mechanical strength, and optical instability are related to the defectiveness of the fluorine sublattice. A way to reduce the defectiveness is to use specific synthetic procedures and dope the material to be vaporized with a fluorine donor.

Catalytic Formation of C(sp3)–F Bonds via Heterogeneous Photocatalysis

Due to their chemical, physical, and biological properties, fluorinated compounds are widely employed throughout society. Yet, despite their critical importance, current methods of introducing fluorine into compounds suffer from severe drawbacks. For example, several methods are noncatalytic and employ stoichiometric equivalents of heavy metals. Existing catalytic methods, on the other hand, exhibit poor activity, generality, selectivity and/or have not been achieved by heterogeneous catalysis, despite the many advantages such an approach would provide. Here, we demonstrate how selective C(sp3)–F bond synthesis can be achieved via heterogeneous photocatalysis. Employing TiO2 as photocatalyst and Selectfluor as mild fluorine donor, effective decarboxylative fluorination of a variety of carboxylic acids can be achieved in very short reaction times. In addition to displaying the highest turnover frequencies of any reported fluorination catalyst to date (up to 1050 h–1), TiO2 also demonstrates excellent level...

Dynamics of nuclear spin polarization induced and detected by coherently precessing electron spins in fluorine-doped ZnSe

We study the dynamics of optically-induced nuclear spin polarization in a fluorine-doped ZnSe epilayer via time-resolved Kerr rotation. The nuclear polarization in the vicinity of a fluorine donor is induced by interaction with coherently precessing electron spins in a magnetic field applied in the Voigt geometry. It is detected by nuclei-induced changes in the electron spin coherence signal. This all-optical technique allows us to measure the longitudinal spin relaxation time $T_{1}$ of the $^{77}\text{Se}$ isotope in a magnetic field range from 10 to 130~mT under illumination. We combine the optical technique with radio frequency methods to address the coherent spin dynamics of the nuclei and measure Rabi oscillations, Ramsey fringes and the nuclear spin echo. The inhomogeneous spin dephasing time $T_{2}^{*}$ and the spin coherence time $T_{2}$ of the $^{77}\text{Se}$ isotope are measured. While the $T_{1}$ time is on the order of several milliseconds, the $T_{2}$ time is several hundred microseconds. The experimentally determined condition $T_{1}\gg T_{2}$ verifies the validity of the classical model of nuclear spin cooling for describing the optically-induced nuclear spin polarization.

Inhomogeneous nuclear spin polarization induced by helicity-modulated optical excitation of fluorine-bound electron spins in ZnSe

Optically-induced nuclear spin polarization in a fluorine-doped ZnSe epilayer is studied by time-resolved Kerr rotation using resonant excitation of donor-bound excitons. Excitation with helicity-modulated laser pulses results in a transverse nuclear spin polarization, which is detected as a change of the Larmor precession frequency of the donor-bound electron spins. The frequency shift in dependence on the transverse magnetic field exhibits a pronounced dispersion-like shape with resonances at the fields of nuclear magnetic resonance of the constituent zinc and selenium isotopes. It is studied as a function of external parameters, particularly of constant and radio frequency external magnetic fields. The width of the resonance and its shape indicate a strong spatial inhomogeneity of the nuclear spin polarization in the vicinity of a fluorine donor. A mechanism of optically-induced nuclear spin polarization is suggested based on the concept of resonant nuclear spin cooling driven by the inhomogeneous Knight field of the donor-bound electron.

Optically controlled initialization and read-out of an electron spin bound to a fluorine donor in ZnSe

Here we report photon antibunching and magneto-spectroscopy of a single electron spin bound to a fluorine donor in a ZnMgSe/ZnSe QW nanostructure. The results confirm the presence of an optically controllable lambda-system which allows the optical manipulation of the electron bound to the neutral fluorine donor as a spin qubit. Moreover, we achieved optical spin pumping of the qubit by resonant excitation of each of the four allowed transitions of the lambda system. We verified the spin transfer by detecting single photons when the bound electron decays into the opposite spin state. The results presented here constitutes an elegant initialization and the read-out procedure of the electron spin qubit bound to a fluorine donor which are prerequisite for coherent optical control of an impurity based solid-state spin qubit.

Optical Pumping of a Single Electron Spin Bound to a Fluorine Donor in a ZnSe Nanostructure

Here we demonstrate optical pumping of a single electron within a semiconductor nanostructure comprised of a single fluorine donor located within a ZnSe/ZnMgSe quantum well. Experiments were performed to detect optical pumping behavior by observing single photons emitted from the nanostructure when the electron changes spin state. These results demonstrate initialization and read-out of the electron spin qubit and open the door for coherent optical manipulation of a spin by taking advantage of an unconventional nanostructure.

Photon antibunching and magnetospectroscopy of a single fluorine donor in ZnSe

We report on the optical investigation of single electron spins bound to fluorine donor impurities in ZnSe. Measurements of photon antibunching confirm the presence of single, isolated optical emitters, and magneto-optical studies are consistent with the presence of an exciton bound to the spin-impurity complex. The isolation of this single-donor-bound-exciton complex and its potential homogeneity offer promising prospects for a scalable semiconductor qubit with an optical interface.

Fluorine donors andTi3+ions inTiO2crystals

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) are used to identify and characterize neutral fluorine donors in ${\text{TiO}}_{2}$ crystals having the rutile structure. The fluorine ions substitute for oxygen and are present as unintentional impurities. Isolated singly ionized fluorine donors in an as-grown (fully oxidized) crystal convert to their neutral charge state during exposure to 442 nm laser light at 6 K. These donors return to the singly ionized charge state within a few seconds when the light is removed. In contrast, the neutral fluorine donors are observed at 6 K without photoexcitation after a crystal is reduced at $600\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ in flowing nitrogen gas. The angular dependences of the EPR and ENDOR spectra provide a complete set of spin-Hamiltonian parameters (principal values are 1.9746, 1.9782, and 1.9430 for the $g$ matrix and $\ensuremath{-}0.23$, 0.47, and 5.15 MHz for the $^{19}\text{F}$ hyperfine matrix). These matrices suggest that the unpaired electron is localized primarily on one of the two equivalent neighboring substitutional titanium ions, i.e., the ground state of the neutral fluorine donor in rutile-structured ${\text{TiO}}_{2}$ is a ${\text{Ti}}^{3+}$ ion adjacent to a ${\text{F}}^{\ensuremath{-}}$ ion.

Indistinguishable Photons from Independent Semiconductor Nanostructures

We demonstrate quantum interference between photons generated by the radiative decay processes of excitons that are bound to isolated fluorine donor impurities in ZnSe/ZnMgSe quantum-well nanostructures. The ability to generate single photons from these devices is confirmed by autocorrelation experiments, and the indistinguishability of photons emitted from two independent nanostructures is confirmed via a Hong-Ou-Mandel dip. These results indicate that donor impurities in appropriately engineered semiconductor structures can portray atomlike homogeneity and coherence properties, potentially enabling scalable technologies for future large-scale optical quantum computers and quantum communication networks.

Investigation of excitons bound to fluorine donors in ZnSe

The electrical and optical properties of fluorine impurities in ZnSe have been studied. Bulk and delta-doped ZnSe:F layers were grown by molecular beam epitaxy. Electrical measurements reveal evidence that a majority of fluorine impurities act as shallow donors. In delta-doped samples, we find strong photoluminescence due to the radiative recombination of fluorine donor bound excitons. We measured a fluorescence lifetime of less than 250 ps and determined the inhomogeneous line width to be below 2 meV at liquid helium temperature.

Influence of physicochemical properties of solvents on swelling behavior of fluoropolymers

The experimental data are available on the swelling of carbon-black-filled fluorine-containing polymers (Viton) in a number of solvents. However, the quantitative relation between the physicochemical parameters of the solvents and the degree of swelling of the polymers is still unclear. It has been shown that this relation may be determined in terms of the linear free energy concept via solvation of linear equations with due regard for various characteristics of solvents. The polarizability and basicity of solvents are factors governing the degree of polymer swelling. This fact makes it possible to assume the existence of donor-acceptor interaction between fluorine atoms and donor solvents.

Multisectional KrF laser with a pulse repetition rate of 4 kHz and inductive-capacitive discharge stabilisation

An electric-discharge KrF laser with an inductive-capacitive discharge stabilisation and a pulse repetition rate up to 4 kHz is developed. The multisectional discharge gap with a total length of 25 cm is formed by 25 pairs of anode-cathode plates. A discharge width of no more than 1 mm is realised. Ne and He are used as the buffer gases, and F2 serves as the fluorine donor. The maximum output pulse energy is ∼6 mJ for the Ne—Kr—F2 mixture at a total pressure of 1.6—3.2 atm. The maximum efficiency of the laser is ∼1.4%. An original optical technique is worked out for measuring the gas velocity in the working gap. The maximum gas velocity in the gap between the electrodes is found to be 19 ms-1 in the experiments. The average output power of the laser for a pulse repetition rate of 3—4 kHz is ∼12 W, while the relative rms deviation of the laser pulse energy lies in the range 2%—3.8%. It is shown that the refractive index gradient of the active medium, which is related to the free electron concentration in the discharge plasma, plays a significant role in the formation of laser radiation field in the resonator. The characteristic value of the refractive index gradient is found to be no less than 10-5 cm-1 for the KrF laser wavelength.

Compact 4-kHz XeF laser with a multisectional discharge gap

A XeF electric-discharge laser with a pulse repetition rate f of up to 4 kHz is developed. The laser electrode unit is based on plate electrodes with inductive—capacitive discharge stabilisation. He and Ne are used as buffer gases, and NF3 serves as a fluorine donor. A narrow (∼1 mm) discharge is achieved; the specific energy deposition per unit length of the active volume is as high as 2 J m-1. The maximum energy in a laser pulse is ∼3 mJ for NF3—Xe—He and NF3—Xe—Ne mixtures at total pressures of 0.8 and 1.2 atm, respectively, and the maximum lasing efficiency is ∼0.73%. The maximum gas velocity in the working gap is 19 m s-1. The laser-pulse energy at a high pulse repetition rate (4 kHz) virtually coincides with that obtained at a low repetition rate. The mean output pulse power at f = 4 kHz reaches 12 W, and the rms deviation of the laser-pulse energy is ∼2.5%.

Thermodynamic Parameters of the Formation of 3d Transition Metal Complexes as Model Systems for Description of Substrate-Receptor Interaction

The thermodynamic characteristics of the doubly charged ions of 3d metals with ligands containing oxygen, nitrogen, and fluorine donor atoms are analyzed. The complexing reactions are separated into three main groups on the basis of the changes in the enthalpy and entropy components of the Gibbs free energy. It was shown that the assignation of a reaction to a particular group is determined by the nature of the donor atoms in the ligands. The correlations between the enthalpy and entropy components of the Gibbs free energy and the atomic number of the 3d elements are studied.

High-power HF laser pumped by an electron-beam-initiated chemical nonchain reaction

The development of a high-power HF laser pumped by a chemical nonchain reaction initiated by a radially converging electron beam is reported. A radiation energy of ∼ 115 J with an efficiency of ∼ 8% in terms of deposited energy has been achieved in a mixture with an active volume of ∼ 30 liters. It is shown that because of the high SF6 density, the total pressure jump in SF6–H2(D2) mixtures caused by the electron beam injection and the chemical reactions is several times smaller than that in the active mixtures of exciplex lasers for the same input energies. This factor considerably facilitates the development of wide-aperture HF and DF lasers with an SF6 fluorine donor pumped by an electron-beam-initiated chemical nonchain reaction.

High efficiency multikilojoule HF chemical lasers using an electron beam initiated low-pressure mixture of H2/F2/NF3 or H2/F2/SF6

High electrical and high chemical efficiencies were simultaneously achieved for the multikilojoule HF chemical laser using a Lambda-type (inclined type) electron beam initiation scheme. The optimum addition of NF3 or SF6 fluorine donor could increase both efficiencies and could reduce the total pressure of the laser gas mixture. The laser output obtained from the low-pressure mixture of H2/F2/O2/NF3=30/208/62.5/70 (Torr) was 4.5 kJ in a 50-ns FWHM pulse width with an electrical laser efficiency of 226% and a chemical efficiency of 18.5%.