Magnetic Circular Dichroism Spectra Research Articles

Magnetic Circular Dichroism of Luminescent Triarylmethyl Radicals.

Stable triarylmethyl radicals are the most common carbon radical building blocks and have recently attracted much attention for their luminescent properties. However, magnetic circular dichroism (MCD) discovered by Michael Faraday and magnetic circularly polarized luminescence (MCPL) have not been observed for simple triarylmethyl radicals, probably due to their photodegradability. Here we report the first observation of MCD and MCPL of triarylmethyl radicals in solution using racemic mixtures of (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) and (3,5-difluoro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (F2PyBTM), which are much more photostable than simple triphenylmethyl radical derivatives. Faraday B terms, which are at the origin of magnetic dichroism in nondegenerate systems, were calculated using TD-DFT, and the line shape of MCD spectra was well reproduced. This study provides new circular dichroism properties for luminescent triarylmethyl radicals in solution without separating enantiomers and also clarifies the origin of magnetic circular dichroism properties of stable organic radicals for the first time.

Magnetic circular dichroism of f-f electron transitions in Ho3+ and Nd3+ ions in antiferromagnetic crystal Ho0.75Nd0.25Fe3(BO3)4 in the region of spin-reorientation transition

Absorption and magnetic circular dichroism (MCD) spectra have been studied in the region of 5I8 → 5F2, 5S2, 5F3, and 5F5 absorption bands of the Ho3+ ion and in the region of 4I9/2→4G7/2, 2K13/2, 4S3/2, 4F7/2, 4F5/2 and 2H9/2 absorption bands of the Nd3+ ion in an antiferromagnetic trigonal crystal Ho0.75Nd0.25Fe3(BO3)4 in the temperature range from 5 to 90 K. A qualitative change in the shape of the MCD spectra of Ho3+ ion was revealed during the spin-reorientation transition at TR = 6.9 К. Below TR, in the easy-axis state of the crystal, the MCD spectrum has a shape typical for paramagnets, i.e., it consists of diamagnetic and paramagnetic parts. Just above TR, in the easy-plane state of the crystal, MCD of Ho3+ ion has a spectrum similar to the absorption spectrum, which is typical for the paramagnetic part of the MCD. It was shown, that in the easy-plane state the exchange field of iron, being perpendicular to the external field directed along the C3 axis, quenches the usual paramagnetic and diamagnetic MCD in Ho3+ ion, but creates a condition for the appearance of a large paramagnetic MCD of mixing (B-term). With temperature increasing, the MCD spectrum of Ho3+ ion gradually turns into a spectrum typical for paramagnets with the predominance of the sign-changing diamagnetic part, because the influence of the exchange field decreases. The shape of the MCD spectra of Nd3+ ions are typical for paramagnets but does not change during the reorientation transition in the rest of the crystal. This means that the magnetic moment of the Nd3+ ion does not make a reorientation transition simultaneously with the Fe3+ and Ho3+ ions of the rest of the crystal. This phenomenon is accounted for by a strong local magnetic anisotropy of the Nd3+ ion and by a weak exchange interaction Fe-Nd, which is not enough for rotation of the Nd3+ ion moment synchronously with that of the Fe3+ ion. The magneto-optical properties of neodymium are controlled by the easy-axis anisotropy of neodymium.

The visible magneto-optical response of RE1-xAxMnO3manganites: relationship with the charge component of the material.

Magnetic circular dichroism (MCD) spectroscopy for manganite films of various compositions and morphologies has been studied in the range of 1.2-3.7 eV. The primary focus was on the temperature behavior of the MCD spectra, as well as the magnetization and resistivity of the films. The data obtained were analyzed in comparison with magneto-optical spectroscopy of the Kerr rotation (KR) on both single crystal and thin film of manganites. It has been established that the MCD response at 2.3 eV is typical for manganites transitioning into a conducting state. Consequently, it reflects a change in the band structure of the material. This response is also observed in the KR spectrum of manganites in the range 2.3-2.6 eV below the metal-insulator transition temperature. These findings complement the understanding of the electronic structure of manganites in general. Moreover, they also provide a basis for the search for new functional materials.

Charge-Transfer Spectroscopy and Electrochemistry of Transition-Metal Phthalocyanines

Charge-transfer spectroscopy of the selected transition-metal phthalocyanines will be discussed in conjunction with their electrochemical properties. Specifically, UV-Vis and magnetic circular dichroism (MCD) spectra of the PcFe(II)L2, PcRu(II)L2, PcMn(III)LX, and PcCr(III)LX (L is a neutral and X is a monoanionic ligand) will be discussed in terms of their metal-to-ligand (MLCT) and ligand-to-metal (LMCT) charge-transfer spectroscopy determined by the experimental UV-Vis and MCD as well as theoretical (time-dependent density functional theory) methods. Lever's EL scale was used to predict and correlate the MLCT and LMCT transitions in transition-metal phthalocyanines.

Strong NIR-II Magneto-Optical Activity of a Chiral Sm15Cu54 Cage.

The magneto-optical response of chiral materials holds significant potential for applications in physics, chemistry, and biology. However, exploration of the near-infrared (NIR) magneto-optical response remains limited. Herein, we report the synthesis and strong NIR-II magneto-optical activity of three pairs of chiral 3d-4f clusters of R/S-Ln15Cu54 (Ln = Sm, Gd, and Dy). Structural analysis reveals that R/S-Ln15Cu54 features a triangular prism cage with C3 symmetry. Interestingly, magnetic circular dichroism (MCD) spectra exhibit remarkable magneto-optical response in the NIR-II region, driven by the f-f transition. The maximum g-factor of R/S-Sm15Cu54 reaches 5.5 × 10-3 T-1 around 1300-1450 nm, surpassing values associated with DyIII and CuII ions. This remarkable NIR-II magneto-optical activity may be attributed to strong magnetic-dipole-allowed f-f transitions and helix chirality of the structure. This work not only presents the largest Ln-Cu clusters to date but also demonstrate the key role of magnetic-dipole-allowed transitions on magneto-optical activity.

Magnetic bilayer qubits: A bipartite quantum system

An exfoliated monolayer CrI3 possessing the ferromagnetic (FM) nature of out-of-plane Ising spin-up (or spin-down) electrons can be considered as a qubit with a quantum state of |ѱ>=|↑>=|0> (or |ѱ>=|↓>=|1>) due to the theory of the Bloch sphere. Therefore, here a bipartite quantum system of the antiferromagnetic (AFM) and FM bilayer CrI3 is proposed for four fundamental two-qubit (2Q) quantum states (≡|ѱѱ>) of |↑↓>=|01>, |↓↑>=|10>, |↑↑>=|00> and |↓↓>=|11>, respectively. Energy-resolved magnetic circular dichroism (MCD) spectropolarimetry was used to detect d-d transitions of the FM and AFM bilayer CrI3 for the four fundamental quantum states. The obtained MCD spectra of the d-d transitions with spin-frustration and spin-parallelism possess quantum signals of the four fundamental 2Q quantum states at θB = 0, where θB is the angle between the magnetic field and the surface normal. Hence, the bilayer CrI3 is a potential candidate for use in quatum computer.

Electronic Structures of an Annulated meso-Tetraphenylchlorin and a Related Chlorin Analogue Incorporating an 8-Membered Ring through MCD Spectroscopy and DFT Calculations.

Herein, we compare the electronic structures of the metal-free and nickel(II) derivatives of an annulated meso-tetraphenyldihydroxychlorin with those of the (metallo)chlorin analogues derived by pyrroline β,β'-ring cleavage of the annulated (metallo)chlorins. These (metallo)chlorin analogues incorporate 8-membered heterocycles in place of the pyrroline, carry oxo-functionalities on the former pyrroline β-carbon atoms, and were previously shown to possess drastically ruffled (twisted) nonplanar conformations. The magnetic circular dichroism spectra of all chromophores investigated feature chlorin-like UV-vis spectra and correspondingly reversed (positive-to-negative in ascending energy) sign sequences in the Q-band region, indicative of ΔHOMO < ΔLUMO relationships. Density functional theory (DFT) calculations indicate that the HOMOs in all compounds are a1u-type molecular orbitals (in traditional for the porphyrin spectroscopy D4h point group). Time-dependent DFT calculations correlate well with the experimental spectra and indicate that Gouterman's four-orbital model can be applied to these chromophores. This work highlights to which degree synthetic chlorin analogues can deviate from the structural parameters of natural chlorins without losing their electronic chlorin characteristics.

Pure Spin Transport in YIG Films with Amorphous‐to‐Crystalline Transformation

AbstractMagnetic insulators, especially Y3Fe5O12 (YIG), are considered promising candidates for spin‐based device applications due to their ultralow damping, high spin injection efficiency, and long‐distance spin propagation. However, these intriguing features are widely studied based on crystallization YIG films. Pure spin phenomena, like spin transport in YIG films with structural evolution, remain unclear. Herein, pure spin transportation is systematically investigated in the sandwich structure formed by YIG, the inserted layer‐nominal YIG (n‐YIG) with a varied crystalline structure and heavy metal Platinum (Pt). By applying ferromagnetic resonance (FMR)‐driven inverse spin Hall effect (ISHE) measurement, the detected ISHE voltage signal presented a strong correlation with the thickness of n‐YIG and its crystalline phase. A significant increasement in spin transportation is obtained for the crystallized n‐YIG via a high‐temperature annealing. These results demonstrate that pure spin current is transported availably in the structural evolution of YIG films. Furthermore, the element‐specific X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD) spectra on the n‐YIG films showed a distinction for the crystallized n‐YIG which indicates that the spin propagation is correlated to its magnetic order. These findings are instructive for low‐dissipation spin‐based devices.

Nature of magnetic circular dichroism and absorption spectra of f-f transitions in Na0.4Ho0.6F2.2 single crystal

We present first study of magnetic circular dichroism (MCD) spectra of Ho3+ ion in C4v local symmetry, which it has in fluorite Na0.4Ho0.6F2.2. Optical absorption and MCD spectra were studied in this single crystal in the region of 5I8→ 5F3, 5F2, 3K8 and 5G5 transitions in the temperature range 3.6–––90 K. It was revealed, that number of transitions observed in the MCD and absorption spectra coincides with the number of transitions only from the doublet E state to singlet excited states. The E-E type transitions are not active in MCD, but they are not observed in the absorption spectra either. Paramagnetic magneto-optical activities (MOA) of the absorption bands and their temperature dependences were measured and interpreted with the help of the theory based on the nature of f-f transitions allowance. The MCD spectra were also analyzed in approximation of the J,±MJ wave functions of the free atom. It was shown in particular, that the lowest initial state of the transitions observed at T > 10 K had MJ = 7, but this is not the lowest state of the holmium ion in the crystal. A little lower there is a quasi-doublet with MJ = 8 and, accordingly, with a higher magneto-optical activity of transitions from it. However, the intensity of transitions from this state is low.

Fine-tuning of radiative properties by "mild" substituents: searching for a perfectly soft chromophore.

Controlling spectral properties to achieve desired characteristics is an attractive goal in application-oriented research, e.g., in the design of fluorescence sensors. "Soft" chromophores, molecules with strong spectral responses to internal or external perturbations are good candidates for such studies. In this work, absorption, fluorescence, and magnetic circular dichroism (MCD) spectra were obtained for a series of porphyrins, substituted at the meso-positions with n-hexyl groups. As the number of substituents increases from 1 to 4, significant changes are observed. The intensity of the S0-S1 transition (Qx) in the 0-0 region strongly decreases in mono-substituted porphyrin, but upon additional substitutions it increases to values larger than in the parent, unsubstituted molecule. Such behavior can be explained, using the perimeter model, by changes in the energy splittings between the two highest (HOMO) and two lowest (LUMO) frontier molecular orbitals. Single substitution makes porphyrin a nearly perfect soft chromophore, but upon introduction of a larger number of n-hexyl groups it is transformed into a hard one. DFT simulations incorrectly predict a continuous transition from a soft to hard chromophore, because the calculated ordering of two HOMO orbitals is opposite to that obtained by experiment. On the other hand, for those porphyrins that can be classified as hard chromophores, the calculations nicely reproduce contributions of Franck-Condon and Herzberg-Teller terms to absorption and fluorescence spectra.

Czochralski growth, optical and magneto-optical properties of Ce9.33(SiO4)6O2 crystal

Ce9.33(SiO4)6O2 (CSO) crystals were grown by the Czochralski (Cz) method. Rietveld refinement of XRD patterns confirmed the oxyapatite structure of CSO, XPS analysis revealed the valence of Ce ions in CSO crystals. Magnetization curve and temperature dependencies of the magnetic susceptibility were measured, paramagnetic behavior and magnetic anisotropy have been observed. Photoluminescence and Faraday rotation characteristics of the CSO crystal were investigated at room temperature. Verdet constants of CSO were about 1.6 times as large as those of TGG. Baesd on Van Vleck–Hebb theory, the effective transition wavelength and probability of CSO crystal were calculated and compared with other Ce3+-containing crystals. The absorption and magnetic circular dichroism (MCD) spectra of 4f→5d transitions in Ce3+ ions in CSO crystal were studied.

Faraday rotation enhancement for colloidal spherical Au and Ag nanoparticles and their mixtures

So far, magnetooptical (MO) properties of silver nanoparticles (AgNPs) have been studied only by magnetic circular dichroism (MCD) spectroscopy at the surface plasmon resonance (SPR) band. However, direct knowledge of the Faraday rotation effect (FR) is very important in fundamental research and applications. In the present work, we study an enhancement of FR of individual gold nanoparticles (AuNPs) and AgNPs and their mixture of colloidal aqueous suspension. The Au and Ag spherical NPs were synthesized independently as colloids in an aqueous suspension and then such mixtures were studied (AgNPs were also studied as a suspension in hexane). The noble metal NPs were characterized by TEM, UV–Vis, and refraction methods. The enhancement of FR of individual NPs was observed and it is consistent with available MCD results. For the mixtures, observed changes of magnitude of FR is small, and coupling of both SPR is rather weak. The obtained FR spectra associated with SPR band have been successfully converted to MCD spectra using the Kramers-Kronig transformation. Calculated MCD spectra are consisted with that obtained by direct measurements.

Electronic structure analysis of phthalocyanine complexes using magnetic circular dichroism and magnetic circularly polarized luminescence spectroscopy.

In the study of phthalocyanine complexes using magnetic circular dichroism (MCD) spectroscopy, the electronic structure of excited states is generally discussed based on the rigid-shift approximation, in which the band profiles for left-handed circularly polarized (lcp) and right-handed circularly polarized (rcp) light are assumed to be the same. This assumption may not necessarily be valid for cases where there are multiple initial states having different geometries. Magnetic circularly polarized luminescence (MCPL) from phthalocyanine complexes can be regarded as an example of such cases, since the two degenerate emission states are split in a magnetic field and can undergo a structural deformation. Here, we investigated an alternative approach, where the lcp and rcp components are independently determined. This method, which we refer to as the direct-separation approach, allows direct determination of the distribution of the two emission states as well as the orbital angular momentum . Using this approach, and the distribution were determined from MCD and MCPL spectra of a series of phthalocyanine complexes. Comparison of the two methods shows that the rigid-shift and the direct-separation approaches give practically equivalent results for the systems under study, but the latter is advantageous for systems where the former is not applicable.

Measurement of the Induced Magnetic Polarisation of Rotated-Domain Graphene Grown on Co Film with Polarised Neutron Reflectivity.

In this paper, we determine the magnetic moment induced in graphene when grown on a cobalt film using polarised neutron reflectivity (PNR). A magnetic signal in the graphene was detected by X-ray magnetic circular dichroism (XMCD) spectra at the C K-edge. From the XMCD sum rules an estimated magnetic moment of 0.3 μB/C atom, while a more accurate estimation of 0.49 μB/C atom was obtained by carrying out a PNR measurement at 300 K. The results indicate that the higher magnetic moment in Co is counterbalanced by the larger lattice mismatch between the Co-C (1.6%) and the slightly longer bond length, inducing a magnetic moment in graphene that is similar to that reported in Ni/graphene heterostructures.

Photophysical Exploration of Two Isomers of Octaethyltrioxopyrrocorphin.

The introduction of three β-oxosubstituents to octaethylporphyrin by means of an oxidation/rearrangement reaction generates the trioxopyrrocorphin chromophore. Pyrrocorphins (hexahydroporphyrins) are generally nonaromatic, but we recently demonstrated trioxopyrrocorphins to possess considerable aromatic character. This contribution explores the photophysical characteristics of these unusual chromophores. In agreement with density functional theory modeling, the UV-vis and magnetic circular dichroism spectra of the two─out of the four possible─triketone regioisomers investigated conform to the Gouterman model of porphyrinoid optical spectra, in alignment with their aromaticity. Their excited-state dynamics shed further light on the degree to which β-oxo substitutions tune the photophysical properties of porphyrinoids. Introduction of β-oxo functionalities increases the rate and yield of intersystem crossing and shortens the triplet state lifetime. Unexpectedly, the singlet oxygen generation yield of both pyrrocorphins remains relatively high, with modes of distortion from planarity likely enhancing triplet energy transfer. This work thus expands our understanding of a rare class of porphyrinoids and further characterizes them as sustaining aromatic porphyrinic π-systems. Our findings suggest triple β-oxo substitution as a viable route toward the development of novel, high-singlet oxygen yield porphyrinic photosensitizers.

Efficient Protocol for Computing MCD Spectra in a Broad Frequency Range Combining Resonant and Damped CC2 Quadratic Response Theory.

Coupled cluster response theory offers a path to high-accuracy calculations of spectroscopic properties, such as magnetic circular dichroism (MCD). However, divergence or slow convergence issues are often encountered for electronic transitions in high-energy regions with a high density of states. This is here addressed for MCD by an implementation of damped quadratic response theory for resolution-of-identity coupled cluster singles-and-approximate-doubles (RI-CC2), along with an implementation of the MCD term from resonant response theory. Combined, damped and resonant response theory calculations provide an efficient strategy to obtain MCD spectra over a broad frequency range and for systems that include highly symmetric molecules with degenerate excited states. The protocol is illustrated by application to zinc tetrabenzoporphyrin in the energy region of 2-8 eV and comparison to experimental data. Timings are reported for the resonant and damped approaches, showing that a greater part of the calculation time is consumed by the construction of the building blocks for the final MCD ellipticity. A recommendation on how to use the procedure is outlined.

DIBENZOCYCLOOCTADIENE LIGNANS ISOLATED FROM THE ROOTS OF SCHISANDRA CAULIFLORA AND THEIR NITRIC OXIDE INHIBITION ACTIVITY ON LPS STIMULATED RAW 264.7 CELLS

Objectives: To isolate and determine the chemical structure of some compounds from the roots of Schisandra Cauliflora and their inhibitory activity on nitric oxide production. Methods: The roots of Schisandra cauliflora, which were collected in Vinh Phuc in April 2022, were processed before being extracted and isolated to obtain compounds. Compounds structures were elucidated based on extensive spectroscopic analyses, including 1D- and 2D-nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (HR-ESI-MS), and CD spectra. The obtained compounds were evaluated for inhibitory activity on nitric oxide production on LPS stimulated RAW 264.7 cells. Results and conclusion: From the methanol extract of the roots of Schisandra cauliflora, three dibenzocyclooctadiene lignans were isolated, including ananonin J, ananolignan F, and ananolignan C. Their structures were elucidated. All the compounds inhibited nitric oxide productions on LPS stimulated RAW 264.7 cells with IC50 values of 45.24 ± 1.46, 41.32 ± 1.45, and 48.71 ± 1.34µM, respectively, compared to that of the positive control of dexamethasone (IC50 14.20 ± 0.54µM). This is the first time these lignan compounds have been isolated from the roots of Schisandra cauliflora.

Variable spin texture in Mn3Sn/Pt heterostructures revealed by magnetic circular dichroism

Non-collinear antiferromagnets with a D019 hexagonal structure have attracted tremendous attention for their potential applications in topological spintronics. Exploring the relationship between spin texture and electronic band structure is crucial for understanding the physical nature of these chiral antiferromagnets. Here, we systematically investigated the variation of topological spin texture of the non-collinear antiferromagnet Mn3Sn film using magnetic circular dichroism (MCD) spectroscopy. The evolution of Mn spin texture from coplanar inverted triangular structure to swirling spin texture was achieved in Mn3Sn/Pt heterostructures through introducing an interfacial Dzyaloshinskii–Moriya interaction (DMI) at room temperature. Correspondingly, unconventional zero-crossing points in energy-resolved MCD spectra as well as a gradual shift of a zero-crossing point to longer wavelength were observed. Our work provides a spin texture modulation approach via interfacial DMI and an effective non-contact magneto-optical detection method to reveal the spin texture in the non-collinear antiferromagnet/heavy metal system.

Magnetic Circular Dichroism of Porphyrinoid Silver Complexes: Evidence of the Electronic Structure Inversion upon Protonation of the N-Confused Core.

We report a systematic investigation of a series of Ag(II) and Ag(III) complexes of porphyrins and their analogues using UV-vis magnetic circular dichroism (MCD) spectroscopies and theoretical calculations. Ag(II) and Ag(III) octaethyl- and tetraarylporphyrins show the usual sign sequence in the Q-band region (i.e., negative to positive intensities with increasing energy) of their MCD spectra, indicative of the ΔHOMO > ΔLUMO relationship (ΔHOMO is the energy difference between Michl's a and s orbitals, and ΔLUMO is the energy difference between Michl's -a and -s pair of MOs). In contrast, Ag(II) complexes of β,β'-pyrrole-modified porphyrins (with an effective chlorin-type π-system) and Ag(III) corroles have sign reverse features in the MCD spectra of their Q-band region (ΔHOMO < ΔLUMO relationships). The Ag(III) complex of N-confused porphyrin shows the ΔHOMO > ΔLUMO relationship in the neutral state and the ΔHOMO < ΔLUMO relationship in the protonated form.

Plasmon-exciton coupling in Au nanosphere/carbocyanine J-aggregate hybrids assessed by magnetic circular dichroism (MCD) spectroscopy

In this study, we evaluate plasmon-exciton coupling in Au nanosphere/carbocyanine J-aggregate hybrids by magnetic circular dichroism (MCD) spectroscopy. The carbocyanine dye we used is JC-1, which adsorbs onto Au nanospheres to form J-aggregates. The hybrids exhibit a double-peaked extinction spectrum, and a shallow dip appears at the resonance position of the native J-aggregates, indicating the presence of plasmon-exciton interactions. MCD spectra of the hybrids show a derivative-like profile originated from the surface plasmon resonance of Au nanospheres accompanied by an additional distinct dip (or bump) caused by the exciton resonance of the adsorbed J-aggregates. Importantly, the MCD dip (or bump) position does not correspond to that of the observed new extinction peak, but agrees well with the extinction dip. Moreover, we find that the linewidths of the MCD dip (or bump) are narrow and comparable to that of the J-band of the dye aggregates. All the results suggest that the present hybrid systems are categorized in a weak-coupling regime. Hence we believe that MCD will be a useful spectroscopic method to effectively assess the plasmon-exciton interactions in various kinds of plasmonic-excitonic nanohybrid systems.