[Show abstract][Hide abstract] ABSTRACT: We have applied the pulse ELDOR detected NMR (EDNMR) technique to determine the tensors of the transferred Cu(S = 1/2) - 14N (I = 1) hyperfine (HF) interaction in single crystals of diamagnetically diluted mononuclear o phenylenebis(N(R)-oxamides) complexes of [nBu4N]2[Cu(opboR2)] (R = Et 1, nPr 2) (%1) in host lattice of [nBu4N]2[Ni(opboR2)] (R = Et 3, nPr 4) (%99) (1@3 and 2@4). ). To facilitate the analysis of our EDNMR data and to analyze possible manifestations of the nuclear quadrupole interaction in the EDNMR spectra we have treated a model electron-nuclear system of the coupled S = 1/2 and I = 1 spins using the spin density matrix formalism. It appears that this interaction yields a peculiar asymmetry of the EDMR spectra which manifests not only in the shift of the positions of the EDNMR lines which correspond to the forbidden EPR transitions, as expected, but also in the intensities of the EDNMR lines. The symmetric shape of the experimental spectra has enabled a conclusion that in the studied complexes the quadrupole interaction is negligible. This has simplified the analysis of the spectra. The HF tensors of all four N donor atoms could be accurately determined. Based on the HF tensors, an estimate of the spin density transferred from the central paramagnetic Cu(II) ion to the N donor atoms reveals its unequal distribution. We discuss possible implications of our estimates for the magnetic exchange paths and interaction strengths in respective trinuclear complexes [Cu3(opboR2)( pmdta)2](NO3)2 (R = Et 6, nPr 7).
The Journal of Physical Chemistry B 07/2015; 119(43). DOI:10.1021/acs.jpcb.5b03987 · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electron spin dynamics of the photoexcited state of a new porphyrin system built of a zinc porphyrin molecule with a linked complex of copper ion (ZnPCu) was studied using electron paramagnetic resonance (EPR) methods. The time-resolved continuous-wave and echo-detected EPR data show that electron spins of the ZnPCu system are polarized. The shape of the EPR spectrum and the echo-detected nutation spectroscopy data indicate that there is a relatively small spin–spin interaction between two subunits, namely, less than the zero-field splitting parameter of the excited triplet ZnP molecule. Results have been interpreted assuming that the S = 1 Zn porphyrin subunit electron spins are polarized via the triplet mechanism and this polarization is transferred to the S = 1/2 copper subunit via a flip-flop process induced by the exchange interaction between these subunits. The formation of the integral spin polarization in the triplet–doublet system as a function of the value and type of the triplet–doublet interaction was analyzed.
Applied Magnetic Resonance 07/2015; 46(11):1-22. DOI:10.1007/s00723-015-0705-0 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The energy transfer mechanism, which provides the feeding of the excited 5D4 level of Tb(III), has been studied by photoluminescence spectroscopy in the Tb(III) complex with p-sulfonato-thiacalixarene doped into the silica nanoparticles. The quantitative evaluation of the rate constants of each energy transfer step highlights two channels of the energy transfer from the singlet ligand-centered level to the 5D4 level. The channel one occurs via the triplet ligand level S1→T1→5D4, the second channel comes about via the higher levels of Tb(III) S1→5D3→5D4. The latter channel determines the rate of the luminescence decay of the 5D4 level. The high luminescence efficiency and enhanced thermo- and photo-stabilities make the Tb(III) complexes doped into the silica nanoparticles a promising nanomaterial for medical and bioanalytical applications.
Journal of Luminescence 01/2015; 157:158–162. DOI:10.1016/j.jlumin.2014.08.050 · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Kinetic equations for the spin density matrix which take into account binary collisions and a method of calculating the spin exchange effective radius have been generalized to the case of dilute solutions of charged paramagnetic particles. The effective radius of the spin exchange and rate constant of the bimolecular spin exchange between charged paramagnetic particles in solutions have been calculated numerically. Calculations have been performed under the assumption that the exchange interaction is isotropic and decays exponentially with the increase in the distance between radicals, and the solution has a given dielectric permittivity and Debye screening radius. Dependences of the spin exchange rate constant on the mutual diffusion coefficient, exchange and electrostatic interactions parameters have been found numerically. The theory has been applied to experimental results taken from the literature. The rate constant of the spin exchange between radicals of like charge found from the experiment and calculated within the developed theory are in good qualitative agreement
Applied Magnetic Resonance 10/2014; 45(7):911. DOI:10.1007/s00723-014-0571-1 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The study of the terbium(III) and gadolinium(III) βdiketonate complexes by
photoluminescence spectroscopy reveals considerable changes of the photophysical properties of the complexes under UV laser irradiation. The measurements show the enhancement of the luminescence intensities in the vitrified transparent film of the terbium(III) complex as well as the gadolinium(III) complex under the 337 nm laser irradiation at room temperature. The irradiated film of the terbium(III) complex restores the initial photophysical properties after heating close to the melting temperature (~353 K) and cooling. We did not observe any change of the luminescent properties of the irradiated film for months. These features can be used for the design of new lanthanide-based photostable systems with laser control of the luminescence intensity.
[Show abstract][Hide abstract] ABSTRACT: The current theory of three-pulse electron double resonance (PELDOR) has been generalized to the case, when paramagnetic particles (spin labels) in pairs or groups have the electron paramagnetic resonance (EPR) spectra, which overlap essentially or coincide. The PELDOR signal modulation induced by the dipole–dipole interaction between paramagnetic spin ½ particles in pairs embedded in disordered systems has been analyzed comprehensively. It has been shown that the PELDOR signal contains additional terms in contrast to the situation considered in the current theory, when the EPR spectra of the spin labels in the pairs do not overlap. In disordered systems, the pairs of spin labels have the characteristic dipolar interaction frequency. According to the current theory for pairs of spin labels, the PELDOR signal reveals the modulation with this characteristic frequency. The additional terms, which are obtained in this work, do not change the modulation frequency of the PELDOR signal for pairs of spin labels. However, these additional terms should be taken into account when analyzing the amplitude of the PELDOR signal and the amplitude of the modulation of the PELDOR signal. The consistent approach to treating the PELDOR data for the groups containing three or more spin labels has been outlined on the basis of the results for pairs of spin labels. It has been also analyzed how the spin flips and molecular motion or molecular isomerization can affect the manifestation of the interaction between the spin labels in PELDOR experiments. PELDOR experiments for the stable biradicals (biradicals I containing 1-oxyl-2,2,5,5-tetramethylpyrroline-3-yl spin labels and biradicals II containing 3-imidazoline spin labels) have been performed. The results have been interpreted within the theory developed in this work.
Applied Magnetic Resonance 06/2014; 45(6):573-619. DOI:10.1007/s00723-014-0541-7 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper we study the method of distinguishing the substances by measuring their nuclear paramagnetic longitudinal and transverse relaxation times and the diffusion coefficient of molecules. Experiments performed using a commercial high magnetic field NMR spectrometer show the possibility to use this method for reliable identification of liquids. Observables in these experiments rather often cannot be described by a single exponential function. In the article we discuss how to utilize the non-single exponential experimental dependences for a quantitative processing of the NMR experimental results.
Magnetic Resonance for the Detection of Explosives Workshop (MRDE) was; 01/2014
[Show abstract][Hide abstract] ABSTRACT: The current theory of the four-pulse electron double resonance (PELDOR) has been extended to take into account two effects: (1) overlapping of the electron paramagnetic resonance (EPR) spectra of paramagnetic spin ½ particles (spin labels) in pairs and (2) overlapping of the excitation bands by the pump and echo-forming pulses. It has been shown that the PELDOR signal contains additional terms in contrast to the situation considered in the current theory, when the EPR spectra of the spin labels in the pairs and the excitation bands do not overlap. All terms oscillate with the same frequency, which is the characteristic dipolar interaction frequency. The largest additional terms originate from the fact that both spins in pairs can be excited by the echo-forming pulses when the EPR spectra of the partners in pairs overlap essentially. The results of the numerical calculations, which illustrate the possible scale of the effect of these additional terms on the PELDOR signal, are presented.
Applied Magnetic Resonance 01/2014; 46(1):67-83. DOI:10.1007/s00723-014-0609-4 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate a possibility to enhance the coherence time of electron spins in magnetic molecular complexes by application of the Carr-Purcell-Meiboom-Gill (CPMG) multiple microwave pulse sequence. Our theoretical analysis shows that the CPMG sequence can efficiently suppress the spin decoherence channel arising due to spectral diffusion induced by a random modulation of the hyperfine interaction which is an important source of the spin dephasing in molecular magnets. We confirm this by employing the CPMG protocol in pulse electron spin resonance experiments on model binuclear 1,2-diphosphacyclopentadienyl manganese complexes.We show that, compared to the standardly used two-pulse primary spin-echo technique, the CPMG experiment can boost the phase memory time up to one order of magnitude, bringing it to above 10 μs at low temperatures. This finding may be important for the implementation of quantum computation protocols on molecular magnets.We discuss a possible interesting analogy with the Zeno’s paradox in quantum theory (the Zeno quantum effect), which could be implicit in the CPMG experiment.
Physical Review B 09/2013; 88(9):094418. DOI:10.1103/PhysRevB.88.094418 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electron Paramagnetic Resonance (EPR) spectra of the nitroxide spin probe 3β-doxyl-5α-cholestane (CSL) are studied as functions of the molar concentration, c, and the temperature, T, in a series of n-alkanes. The results are compared with a similar study of a much smaller spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDT). The Heisenburg spin exchange (HSE) rate constants, K(ex) , of CSL are similar in hexane, octane and decane, and are about one-half of those for pDT in the same solvents. They are also about one-half of the Stokes-Einstein-Perrin (SEP) prediction. This reduction in HSE efficiency is attributed to an effective steric factor, f(eff) , which was evaluated by comparing the results with the Stokes-Einstein-Perrin prediction or with pDT is f(eff) = 0.49 ± 0.03, independent of temperature. The unpaired spin density in CSL is localized near one end of the long molecule, so the exchange integral, J , leading to HSE, is expected to be large in some collisions and small in others; thus, J is modeled by an ideal distribution of values of J =J(0) with probability f and J = zero with probability (1-f). Due to rotational and translation diffusion during contact and between re-encounters of the probe, the effective steric factor is predicted to be f(eff) = f(1/2) . Estimating the fraction of the surface of CSL with rich spin density, yields a theoretical estimate of f(eff) = 0.59 ± 0.08, in satisfactory agreement with experiment. HSE is well described by simple hydrodynamic theory, with only a small dependence on solvent-probe relative sizes at the same value of T/η, where η is the viscosity of the solvent. This result is probably due to a fortuitous interplay between long- and short-range effects that describe diffusion processes over relatively large distances. In contrast, dipole-dipole interactions (DD) as measured by the line broadening, B(dip) , and the mean time between re-encounters within the cage, τ(RE), vary significantly with the solvent-probe size ratio at the same value of T/η. For these phenomena, dominated by short-range diffusion, the reciprocal fractional free volume ,V(0)/V(f) provides a better description of the diffusion. Thus B(dip) and τ(RE) form common curves when plotted vs. V(0)/V(f). As a result, the fractional broadening by DD occurs at an order of magnitude higher values of T/η for CSL compared with pDT.
The Journal of Physical Chemistry A 11/2012; 116(51). DOI:10.1021/jp310297d · 2.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) are very prospective methods of the
bulk detection of explosives and illicit substances. Both methods are based on use of apparatus, which are very similar
technically and in some cases could be applied simultaneously. We report our experimental works on NQR/NMR
techniques for explosives detection. In addition of classical single-frequency NMR/NQR we also explored a potential of
double resonance (NMR/NQR) and multifrequency NQR approaches as well as magnetic resonance imaging (MRI)
techniques. Multifrequency (two/three) NQR technique involves various (two or three) transitions in the three energy
level system of 14N nuclei. It is shown that this kind of NQR technique allows filtering spurious signal after
radiofrequency pulses and increases the sensitivity of NQR detection. On the other hand, various liquids can be detected
using NMR. We shown that reliable discrimination among extended set of liquids reveal a need in use of additional
NMR parameters or complimentary techniques. It is demonstrated that MRI is also feasible method for detection of
[Show abstract][Hide abstract] ABSTRACT: A method of elaborating pulse sequences performing unitary transformations on the basis of their transformation matrices has been developed. For the first time the pulse protocols performing two-qubit quantum logical operations in electron spin systems have been obtained.
Applied Magnetic Resonance 12/2011; 41(2-4). DOI:10.1007/s00723-011-0297-2 · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report a pulse electron spin resonance study of binuclear Mn molecular complexes whose magnetic properties are controlled by the ligand substitution. An electron spin echo in these complexes in the solid phase and also diluted in a frozen solution matrix was detected, and the spin decoherence time T2 of Mn spins at different temperatures was determined. We observe a simple exponential T2 relaxation in the latter samples and a nonexponential relaxation process in the former ones. The data analysis establishes the hyperfine coupling to the protons as an important source of the electron spin decoherence. Furthermore, the data clearly suggest an important role of the intermolecular spin-spin coupling for the T2 relaxation. The influence of both mechanisms should be considered as limiting factors for coherent spin manipulation in molecular magnets with regard to their possible application for quantum computing.
[Show abstract][Hide abstract] ABSTRACT: This report presents a comprehensive analysis of the contributions of the Heisenberg exchange and dipole–dipole interactions
in diluted solutions of nitroxide radicals to the shape of their electron paramagnetic resonance (EPR) spectra taking into
account all coherence transfer processes. It is shown that these contributions interfere. The approaches to obtain the molecular-kinetic
and exchange integral parameters by analyzing the EPR spectrum dependence on the radical concentration and the solvent viscosity
Applied Magnetic Resonance 05/2010; 38(2):237-256. DOI:10.1007/s00723-010-0128-x · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The phase behavior of a self-organizing system based on the nonionic surfactant of decaethylene glycol monodecyl ether-lanthanum
nitrate hexahydrate-water and decanol is presented. A system phase diagram was constructed. The concentration, temperature
ranges of existence and types of liquid crystal phases were established. Analysis of structural changes during the phase transitions
hexagonal phase-lamellar phase-isotropic liquid was made on the basis of data obtained by viscosimetry and self-diffusion