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The development and technological applications of molecular spin systems require versatile experimental techniques to characterize and control their static and dynamic magnetic properties. In the latter case, bulk spectroscopic and magnetometric techniques, such as AC magnetometry and pulsed electron paramagnetic resonance, are usually employed, showing high sensitivity, wide dynamic range, and flexibility. They are based on creating a nonequilibrium state either by changing the magnetic field or by applying resonant microwave radiation. Another possible source of perturbation is a laser pulse that rapidly heats the sample. This approach has proven to be one of the most useful techniques for studying the kinetics and mechanism of chemical and biochemical reactions. Inspired by these works, we propose an inductive detection of temperature-induced magnetization dynamics as applied to the study of molecular spin systems and describe the general design and construction of a particular induction probehead, taking into account the constraints imposed by the cryostat and electromagnet. To evaluate the performance, several coordination compounds of VO2+, Co2+, and Dy3+ were investigated using low-energy pulses of a terahertz free electron laser of the Novosibirsk free electron laser facility as a heat source. All measured magnetization dynamics were qualitatively or quantitatively described using a proposed basic theoretical model and compared with the data obtained by alternating current magnetometry. Based on the results of the research, the possible scope of applications of inductive detection and its advantages and disadvantages in comparison with standard methods are discussed. [ABSTRACT FROM AUTHOR]

The application of terahertz (THz) science in industrial technology and scientific research requires efficient THz detectors. Such detectors should be able to operate under various external conditions and conform to existing geometric constraints in the required application. Pyroelectric THz detectors are among the best candidates. This is due to their versatility, outstanding performance, ease of fabrication, and robustness. In this paper, we propose a compact pyroelectric detector based on a bioriented poled polyvinylidene difluoride film coated with sputtered metal electrodes for in situ absorption measurement at cryogenic temperature. The detector design was optimized for the registration system of the electron paramagnetic resonance (EPR) endstation of the Novosibirsk Free Electron Laser facility. Measurements of the detector response to pulsed THz radiation at different temperatures and electrode materials showed that the response varies with both the temperature and the type of electrode material used. The maximum signal level corresponds to the temperature range of 10–40 K, in which the pyroelectric coefficient of the PVDF film also has a maximum value. Among the three coatings studied, namely indium tin oxide (ITO), Au, and Cu/Ni, the latter has the highest increase in sensitivity at low temperature. The possibility of using the detectors for in situ absorption measurement was exemplified using two typical molecular spin systems, which exhibited a transparency of 20–30% at 76.9 cm−1 and 5 K. Such measurements, carried out directly in the cryostat with the main recording system and sample fully configured, allow precise control of the THz radiation parameters at the EPR endstation. [ABSTRACT FROM AUTHOR]

High‐spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and fundamental research, but those synthesized to date possess limited stability and processability. In this work, we have designed a tetraradical based on the Blatter's radical and nitronyl nitroxide radical moieties and successfully synthesized it by using the palladium‐catalyzed cross‐coupling reaction of a triiodo‐derivative of the 1,2,4‐benzotriazinyl radical with gold(I) nitronyl nitroxide‐2‐ide complex in the presence of a newly developed efficient catalytic system. The molecular and crystal structure of the tetraradical was confirmed by X‐ray diffraction analysis. The tetraradical possesses good thermal stability with decomposition onset at ∼150 °C under an inert atmosphere and exhibits reversible redox waves at −0.54 and 0.45 V versus Ag/AgCl. The magnetic properties of the tetraradical were characterized by SQUID magnetometry of polycrystalline powders and EPR spectroscopy in various matrices. The collected data, analyzed by using high‐level quantum chemical calculations, confirmed that the tetraradical has a triplet ground state and a nearby excited quintet state. The unique high stability of the prepared triazinyl‐nitronylnitroxide tetraradical is a new milestone in the field of creating high‐spin systems. [ABSTRACT FROM AUTHOR]

The binding of G-quadruplex structures (G4s) with photosensitizers is of considerable importance in medicinal chemistry and drug discovery due to their promising potential in photodynamic therapy applications. G4s can experience structural changes as a result of ligand interactions and light exposure. Understanding these modifications is essential to uncover the fundamental biological roles of the complexes and optimize their therapeutic potential. The structural diversity of G4s makes it challenging to study their complexes with ligands, necessitating the use of various complementary methods to fully understand these interactions. In this study, we introduce, for the first time, the application of laser-induced dipolar EPR as a method to characterize G-quadruplex DNA complexes containing photosensitizers and to investigate light-induced structural modifications in these systems. To demonstrate the feasibility of this approach, we studied complexes of the human telomeric G-quadruplex (HTel-22) with cationic 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphyrin tetra(p-toluenesulfonate) (TMPyP4). In addition to showcasing a new methodology, we also aimed to provide insights into the mechanisms underlying photoinduced HTel-22/TMPyP4 structural changes, thereby aiding in the advancement of approaches targeting G4s in photodynamic therapy. EPR revealed G-quadruplex unfolding and dimer formation upon light exposure. Our findings demonstrate the potential of EPR spectroscopy for examining G4 complexes with photosensitizers and contribute to a better understanding of G4s' interactions with ligands under light. [ABSTRACT FROM AUTHOR]

Copper(II)–nitroxide based Cu(hfac)2LR compounds exhibit unusual magnetic behavior that can be induced by various stimuli. In many aspects, the magnetic phenomena observed in Cu(hfac)2LR are similar to classical spin-crossover behavior. However, these phenomena originate from polynuclear exchange-coupled spin clusters Cu2+–O˙–N< or >N–˙O–Cu2+–O˙–N<. Such peculiarities may result in additional multifunctionality of Cu(hfac)2LR compounds, making them promising materials for spintronic applications. Herein, we investigate the Cu(hfac)2LMeMe material, which demonstrates a three-step temperature-induced magnetostructural transition between high-temperature, low-temperature, and intermediate states, as revealed by magnetometry. Two main steps were resolved using variable-temperature Fourier-transform infrared and Q-band electron paramagnetic resonance (EPR) spectroscopies. The intermediate-temperature states (∼40–90 K) are characterized by the coexistence of two types of copper(II)–nitroxide clusters, corresponding to the low-temperature and high-temperature phases. High-field EPR experiments revealed the effect of partial alignment of Cu(hfac)2LMeMe microcrystals in a strong (>20 T) magnetic field. This effect was used to unveil the structural features of the low-temperature phase of Cu(hfac)2LMeMe, which were inaccessible using single-crystal X-ray diffraction (XRD) technique. In particular, high-field EPR allowed us to determine the relative direction of the Jahn–Teller axes in CuO6 and CuO4N2 units. [ABSTRACT FROM AUTHOR]

Probes sensitive to mechanical stress are in demand for the analysis of pressure distribution in materials, and the design of pressure sensors based on metal–organic frameworks (MOFs) is highly promising due to their structural tunability. We report a new pressure-sensing material, which is based on the UiO-66 framework with trace amounts of a spin probe (0.03 wt%) encapsulated in cavities. To obtain this material, we developed an approach for encapsulation of stable nitroxide radical TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl) into the micropores of UiO-66 during its solvothermal synthesis. Pressure read-out using electron paramagnetic resonance (EPR) spectroscopy allows monitoring the degradation of the defected MOF structure upon pressurization, where full collapse of pores occurs at as low a pressure as 0.13 GPa. The developed methodology can be used in and ex situ and provides sensitive tools for non-destructive mapping of pressure effects in various materials. [ABSTRACT FROM AUTHOR]