Time-resolved transient optical and electron paramagnetic resonance spectroscopic studies of electron donor-acceptor thermally activated delayed fluorescence emitters based on naphthalimide-phenothiazine dyads.

The photophysics of naphthalimide (NI)-phenothiazine (PTZ) dyads were investigated as electron donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) emitters. Femtosecond transient absorption (fs-TA) spectra show that the photophysical processes in non-polar solvents are in singlet localized state (LE, = 0.8 ps) → Franck-Condon singlet charge separation state (CS, = 7.

The Photophysics of Naphthalimide-Phenoselenazine Electron Donor-Acceptor Dyads: Revisiting the Heavy-Atom Effect in Thermally Activated Delayed Fluorescence.

We prepared thermally activated delayed fluorescence (TADF) emitter dyads, NI-PTZ, NI-PTZ-2Br and NI-PSeZ, with naphthalimide (NI) as electron acceptor and 10H-phenothiazine (PTZ) or 10H-phenoselenazine (PSeZ) as electron donor to study the heavy-atom effect on the intersystem crossing (ISC) and reverse ISC (rISC) in the TADF emitters. The delayed fluorescence lifetimes of the dyads containing heavy atoms ( =5.9 μs for NI-PSeZ and =16.

Intersystem Crossing, Photo-Induced Charge Separation and Regioisomer-Specific Excited State Dynamics in Fully Rigid Spiro Rhodammine-Naphthalene/Anthraquinone Electron Donor-Acceptor Dyads.

We prepared a series fully rigid spiro electron donor-acceptor orthogonal dyads, with closed form of rhodamine (Rho) as electron donor and naphthalene (Np)/anthraquinone (AQ) as electron acceptor, to access the long-lived triplet charge separation (CS) state, via the electron spin control method. We found strong dependency of the photophysical property of the dyads on the amino substitution positions of the Np chromophores in the dyads 1,8-DaNp-Rho and 2,3-DaNp-Rho. Nanosecond transient absorption (ns-TA) spectra show the population of the LE state (lifetime: 47 μs) for 2,3-DaNp-Rho, however, long-lived CS state was observed (τ=0.

Kinetics of Electron Transfer between Redox Cofactors in Photosystem I Measured by High-Frequency EPR Spectroscopy.

The kinetics of the primary electron donor P and the quinone acceptor A redox transitions were simultaneously studied for the first time in the time range of 200 μs-10 ms using high-frequency pulse Q-band EPR spectroscopy at cryogenic temperatures in various complexes of photosystem I (PSI) from the cyanobacterium PCC 6803. In the A-core PSI complexes that lack 4Fe4S clusters, the kinetics of the A and P signals disappearance at 100 K were similar and had a characteristic time of τ ≈ 500 μs, caused by charge recombination in the PA ion-radical pair in the branch of redox cofactors. The kinetics of the backward electron transfer from A to P in the branch of redox cofactors with τ < 100 μs could not be resolved due to time limitations of the method.

"Nutation" of electron spins in biradicals.

In this work, the nutation of the spins of unpaired electrons in the nitroxide biradical of bis‑methano[60]fullerene was experimentally studied. Nutation frequencies were found in a wide range of microwave field power. To interpret the obtained results, numerical calculations of the nutation of biradicals were carried out for a set of parameters of the spin-spin interaction of a pair of unpaired electrons and for different values of the Rabi frequency of the microwave field.

Photoisomerization of two 2-hydroxy-5-arylazobenzaldehydes in solvents of different polarities.

Two azo dyes 2-hydroxy-5-(4-nitrophenylazo)benzaldehyde and 2-hydroxy-5-(4-chlorophenylazo)benzaldehyde dissolved in carbon tetrachloride, hexane, acetone and acetonitrile were irradiated with 365 nm UV light, and processes, occurring in them, were studied by NMR and UV-vis spectroscopy. It was established that reversible trans/cis photoisomerization of the molecules occurs in the non-polar solvents and is not observed in the polar solvents. 2D NOESY NMR spectroscopy was used to identify isomers of the azo compounds.

Electron Spin Dynamics of the Intersystem Crossing in Aminoanthraquinone Derivatives: The Spectral Telltale of Short Triplet Excited States.

We studied the excited state dynamics of two bis-amino substituted anthraquinone (AQ) derivatives, with absorption in the visible spectral region, which results from the attachment of a electron-donating group to the electron-deficient AQ chromophore. Femtosecond transient absorption spectra show that intersystem crossing (ISC) takes place in 190-320 ps, and nanosecond transient absorption spectra demonstrated an unusually short triplet state lifetime (2.06-5.

A comparison of pulse and CW EPR T-relaxation measurements of an inhomogeneously broadened nitroxide spin probe undergoing Heisenberg spin exchange 2. The intercept discrepancy.

Experimental confirmation of a theoretical prediction of a non-linear broadening of the spin packets of nitroxide free radicals due to Heisenberg spin exchange at low concentrations, C, is presented. A recent demonstration that spectra with resolved proton hyperfine structure may be analyzed efficiently and accurately was utilized to confirm the theory. As C→0, a plot of the spin-packet line width (SPW) curves downward due to the presence of proton hyperfine couplings that increase the number of distinguishable quantum spin states.

Evaluation of Nitric Oxide-Donating Properties of 11-indeno[1,2-]quinoxalin-11-one Oxime (IQ-1) by Electron Paramagnetic Resonance Spectroscopy.

IQ-1 (11-indeno[1,2-]quinoxalin-11-one oxime) is a specific c-Jun N-terminal kinase (JNK) inhibitor with anticancer and neuro- and cardioprotective properties. Because aryloxime derivatives undergo cytochrome P450-catalyzed oxidation to nitric oxide (NO) and ketones in liver microsomes, NO formation may be an additional mechanism of IQ-1 pharmacological action. In the present study, electron paramagnetic resonance (EPR) of the Fe complex with diethyldithiocarbamate (DETC) as a spin trap and hemoglobin (Hb) was used to detect NO formation from IQ-1 in the liver and blood of rats, respectively, after IQ-1 intraperitoneal administration (50 mg/kg).

Analysis of the Intensity of Nitric Oxide Production in Different Parts of the Spinal Cord after Modeling Combined Cerebral and Spinal Injury.

Using the method of electron paramagnetic resonance spectroscopy, we showed that NO production decreases by 60% (p<0.05) in the region located rostral to the spinal cord injury 7 days after combined injury to the brain and spinal cord. At the same time, NO production did not change in the site of spinal cord injury and caudal to the injury.

Influence of divalent metal cations on α-lactalbumin fibril formation.

The effect of binding of divalent metal cations (Ca, Cu, Mg, Mn, Zn) on the kinetics of fibril formation of bovine α-lactalbumin at acidic conditions is considered. The kinetic parameters of the process were determined using a thioflavin T fluorescence assay. The DSC thermograms of bovine α-lactalbumin in the presence and absence of cations were recorded.

Impact of Zeeman and hyperfine interactions on the magnetic properties of paramagnetic metal Ions: I. Local interactions of the electron spin.

The anisotropic Zeeman interaction of an ion, and the strong hyperfine interaction with its own nucleus, can significantly influence its interactions with the local environment. These effects, including the reduction of the effective magnetic moment of the electron spin and the phase memory decay rate, are studied theoretically. Analytical expressions describing the mean magnetic moment of the electron spin are obtained.

Photophysics and photochemistry of thermally activated delayed fluorescence emitters based on the multiple resonance effect: transient optical and electron paramagnetic resonance studies.

The photochemistry of two representative thermally activated delayed fluorescence (TADF) emitters based on the multiple resonance effect (MRE) (DABNA-1 and DtBuCzB) was studied. No significant TADF was observed in fluid solution, although the compounds have a long-lived triplet state ( 30 μs). We found that these planar boron molecules bind with Lewis bases, , 4-dimethylaminopyridine (DMAP) or an -heterocyclic carbene (NHC).

Impact of Zeeman and hyperfine interactions on the magnetic properties of paramagnetic metal ions: II. Super-hyperfine interactions with surrounding nuclei.

The anisotropic Zeeman and strong hyperfine interactions of a Kramers ion can significantly affect its magnetic properties as well as the interactions with the nearby nuclei. The interactions with the local environment are described in the preceding article. In the current work, the change of the spin states of distant nuclei is studied.

Impact of Zeeman and hyperfine interactions on the magnetic properties of paramagnetic metal Ions: III. Analysis of the local interactions in a single crystal of Yb doped YSiO.

The electron spin echo envelope modulation (ESEEM) technique is a direct method to probe the nuclear spin coherences induced by electron spin transitions. Recently, this approach was used to study an isotopically pure YSiO crystal doped with Yb ions, and the presence of the Fermi contact interaction was proposed to explain the frequency comb detected in the two-pulse ESEEM experiment [Solovarov N. K.

Experimental confirmation of the formation of collective modes of the magnetization motion of paramagnetic particles in dilute solutions due to spin exchange.

Experimental confirmation of the manifestations of new spin exchange paradigm in EPR spectra of N nitroxide radical solutions is presented. It was shown that in the region of relatively low concentrations of radicals, the two side components of the spectrum have a mixed shape (the sum of the absorptive line and dispersive line). The dispersion contributions in these two lines have opposite signs.

Superconducting spin valve effect in Co/Pb/Co heterostructures with insulating interlayers.

We report the superconducting properties of Co/Pb/Co heterostructures with thin insulating interlayers. The main specific feature of these structures is the intentional oxidation of both superconductor/ferromagnet (S/F) interfaces. We study the variation of the critical temperature of our systems due to switching between parallel and antiparallel configurations of the magnetizations of the two magnetic layers.

LiV(PO) Cathode Material: Synthesis Method, High Lithium Diffusion Coefficient and Magnetic Inhomogeneity.

LiV(PO) cathodes for Li-ion batteries (LIBs) were synthesized using a hydrothermal method with the subsequent annealing in an argon atmosphere to achieve optimal properties. The X-ray diffraction analysis confirmed the material's single-phase nature, while the scanning electron microscopy revealed a granular structure, indicating a uniform particle size distribution, beneficial for electrochemical performance. Magnetometry and electron spin resonance studies were conducted to investigate the magnetic properties, confirming the presence of the relatively low concentration and highly uniform distribution of tetravalent vanadium ions (V), which indicated low lithium deficiency values in the original structure and a high degree of magnetic homogeneity in the sample, an essential factor for consistent electrochemical behavior.

Estimation of Heisenberg exchange interaction in rigid photoexcited chromophore-radical compound by transient EPR.

The magnetic field dependence of the spin polarization in a photoexcited rigid chromophore-radical conjugate is theoretically investigated. The excitation of the chromophore-radical conjugate often populates the metastable doublet and quartet states formed by the interactions of the unpaired electrons of the triplet chromophore and the radical. The intensities of the +1/2 ↔ - 1/2 transitions of the doublet and quartet manifolds are sensitive to the ratio jω = 3J/ω0 between the triplet-doublet exchange interaction J and the Zeeman energy ω0.

A Rational Way to Control the Triplet State Wave Function Confinement of Organic Chromophores: Effect of the Connection Sites and Spin Density Distribution-Guided Molecular Structure Design Principles in Bodipy Dimers.

To study the intersystem crossing (ISC) and the spatial confinement of the triplet excited states of organic chromophores, we prepared a series of Bodipy dimers. We found that the connection position of the two units has a significant effect on the absorption and fluorescence. Singlet oxygen quantum yields of 3.

Sorption-oxidation mechanism for the removal of arsenic (III) using Cu-doped ZnO in an alkaline medium.

1-D oxides Zn1-xCuxO and spherical composites Zn1-xCuxO/CuO were obtained by thermolysis of formate-glycolate complexes Zn1-xCux (HCOO)(OCH2CH2O)1/2 (0 ≤ x ≤ 0.15). The structural and property characteristics showed that Cu was introduced into the Zn site of the ZnO lattice to form the Zn0.

The effect of thionation of the carbonyl group on the photophysics of compact spiro rhodamine-naphthalimide electron donor-acceptor dyads: intersystem crossing, charge separation, and electron spin dynamics.

Herein, a spiro rhodamine (Rho)-thionated naphthalimide (NIS) electron donor-acceptor orthogonal dyad (Rho-NIS) was prepared to study the formation of a long-lived charge separation (CS) state the electron spin control approach. The transient absorption (TA) spectra of Rho-NIS indicated that the intersystem crossing (ISC) occurs within 7-42 ps to produce the NIS state the spin orbit coupling ISC (SOC-ISC). The energy order of CS (2.

Low-temperature motion of the scandium bimetal in endofullerene Sc@C(CHPh).

The spin decoherence of the scandium bimetal in Sc@C(CHPh) is studied at low temperatures (20-120 K) by the electron spin echo technique. The correlation between the magnetic quantum number of the total spin state of the scandium nuclei and the decay rates is established. For the total spin = 5, a decrease of the phase relaxation time by a factor of two is observed by changing the transition from = -1 to = +1 and = -3 at 120 K.

Investigation of NO Role in Neural Tissue in Brain and Spinal Cord Injury.

Nitric oxide (NO) production in injured and intact brain regions was compared by EPR spectroscopy in a model of brain and spinal cord injury in Wistar rats. The precentral gyrus of the brain was injured, followed by the spinal cord at the level of the first lumbar vertebra. Seven days after brain injury, a reduction in NO content of 84% in injured brain regions and 66% in intact brain regions was found.