Magnetochiral Dichroism Research Articles

A novel aspect of spectroscopy for porphyrinic compounds under magnetic fields

The spectroscopies of a range of porphyrinic compounds performed under a magnetic field are reviewed, focusing on the molecular functions of the compounds. Characteristic molecular magneto-optical effects, such as the Kerr effects and magnetochiral dichroism (MChD), as well as time-resolved electron paramagnetic resonance (TREPR) are reviewed. A novel molecular magneto-optical memory is described on the basis of the results of a Kerr spectroscopic study of Si phthalocyanine coupled with a ferromagnetic substrate. The results of TREPR analyses of low-symmetry tetraazaporphyrin derivatives are discussed in order to determine the relationship between molecular symmetry and singlet oxygen yield, as knowing this relationship is essential for photodynamic therapy. Finally, the MChD of porphyrins is introduced as a new way of elucidating the asymmetry in biological systems. Further, it can lead to new asymmetric synthesis methods and form the basis for novel magneto-optical devices.

Interplay of Chiral Auxiliary Ligand and Azide Bridging Ligand during the Coordination Network Formation with Copper(II)

Self-assembly formation of a bridging ligand and chiral auxiliary ligand with a metal center, in general, gets dominated by the former interaction. We report here that introduction of weak noncovalent interactions, away from the chiral center, can manifest molecular chirality in an auxiliary ligand into the self-assembled structure, a strategy useful for observing a magnetochiral dichroism effect. Structural details of azido bridged copper(II) coordination networks with enantiomerically pure, racemic, and admixtures of chiral benzylamine derivatives are discussed.

Magnetochiral dichroism resonant with electromagnons in a helimagnet.

Cross-coupling between magnetism and electricity in a solid can be hosted by multiferroics with both magnetic and ferroelectric orders. In multiferroics, the collective spin excitations active for both electric and magnetic fields, termed electromagnons, play a crucial role in the elementary process of magnetoelectric (ME) coupling. Here we report the colossal dynamical (optical) ME effect, or more specifically the magnetochiral (MCh) effect, in the electromagnon resonance for the screw spin helimagnet CuFe(1-x)Ga(x)O2 (x = 0.035). The MCh effect shows up as the nonreciprocal directional dichroism; the extinction coefficient is different for counter-propagating lights, as large as by 400%. The MCh effect derived from the screw spin order is proved by control of the magnetic helicity of helimagnetism and its magnetization. The results point to the general presence of the MCh effect in helimagnets, paving a way to the ME control of electromagnetic wave in the giga- to tera-hertz region.

A multichannel magneto-chiral dichroism spectrometer.

In this work, we describe a multichannel magneto-chiral dichroism spectrometer for the visible and near infrared wavelength ranges. The optical signal acquisition is based on commercially available Czerny-Turner spectrograph systems equipped with solid state detector arrays. The signal analysis method is based on post-processing phase sensitive detection, where the optical properties of the sample are modulated by an alternating external magnetic field. As an illustration of the performance of this spectrometer, magneto-chiral dichroism was measured in crystals of α - NiSO4 · 6H2O and good agreement with literature results was obtained.

Homochirality Origin in Nature: Possible Versions

Homochirality and related problems have been reviewed. Relative probability of different versions of homochirality arising were estimated on the example of processes, synthesis of organic compounds in space, asymmetric photolysis under circularly polarized light, synthesis of optically active compounds as a result of parity violation, magnetochiral dichroism, chiral amplification, optical active amino acids synthesis and theirs isotope ratios in meteorites, and some other determinate and indeterminate processes. It has been estimated handedness of moving objects as source of chirality. Possible contributions of these processes in homochirality origin in nature have been evaluated. The view is justified that homochirality (and life) origin may be not an accidental event. Keywords: Asymmetric in vitro and in vivo reactions, enantioselectivity, homochirality.

Magneto-chiral dichroism in chiral mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker SMMs

Two new chiral mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes with both (R)- and (S)-enantiomers were synthesized and structurally characterized. The significant magneto-chiral cross effect revealed for the dysprosium compound suggests the great potential of sandwich-type tetrapyrrole rare earth systems in the research field of magneto-chiral dichroism.

Strong magnetochiral dichroism of helical structures of garnet particles

We report on the occurrence of strong nonreciprocal magnetochiral dichroism in helical structures of magnetic garnet spheres, which emerges as a result of the simultaneous lack of time-reversal and space-inversion symmetries, by means of rigorous full-electrodynamic calculations using the layer-multiple-scattering method. It is shown that a strong effect appears in flat band regions associated with enhanced natural and magnetic optical activity.

Symmetry conditions for nonreciprocal light propagation in magnetic crystals

Recent studies demonstrated the violation of reciprocity in optical processes in low-symmetry magnetic crystals. In these crystals the speed of light can be different for counter-propagating beams. Correspondingly, they can show strong directional anisotropies such as direction dependent absorption also called directional dichroism[S. Bord\'acs et al., Nat. Phys. 8, 734 (2012); M. Saito et al., J. Phys. Soc. Jpn. 77, 013705 (2008)]. Based on symmetry considerations, we identify the magnetic point groups of materials which can host such directional anisotropies and also provide a list of possible candidate materials to observe these phenomena. In most of these cases, the symmetry of the crystal allows directional anisotropy not only for optical processes but also for the propagation of beams of particles and scalar waves. We also predict new types of directional optical anisotropies -- besides the optical magnetoelectric effect and the magnetochiral dichroism investigated so far -- and specify the magnetic point groups of crystals where they can emerge.

Strong Hard X‐ray Magnetochiral Dichroism in Paramagnetic Enantiopure Molecules

Experimental evidence of magnetochiral dichroism is found in the hard X-ray absorption spectra of paramagnetic enantiopure molecules. An isotropic sample of a {Tb[Ni(pro)2]6}3+ salt (pro = L- or D-prolinate) shows up to a 1% difference in absorbance when a magnetic field (1 T) is applied parallel or anti-parallel to the incident X-ray beam at room temperature. This represents the largest magnetochiral dichroism ever observed in absolute and relative value. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Magneto-chiral dichroism of artificial light-harvesting antenna

We have demonstrated the presence of magneto-chiral dichroism (MChD) of chiral J-aggregates of zinc chlorins. To the best of our knowledge, this is the first observation of MChD in artificial light-harvesting antennas.

Magnetochiral Effects in Amphiphilic Porphyrin J‐Aggregates

The detection of magnetochiral dichroism (MChD; CD: circular dichroism) in a suspension of J-aggregate particles of an achiral amphiphilic nonmetalated porphyrin renews the interest for porphyrins in supramolecular chemistry and reinforces the concept that novel advanced materials can be obtained through self-assembly and auto-organization processes (see picture).

Magneto‐Chiral Dichroism of Organic Compounds

Direction decides: Magneto-chiral dichroism describes the dependence of the absorbance of a chiral molecule on the direction of a magnetic field to which it is exposed, and it may help to explain the homochirality of life. This phenomenon was now observed in organic compounds using porphyrin J-aggregates.

The fruitful introduction of chirality and control of absolute configurations in molecular magnets

In this critical review, it is shown how the introduction of chirality and the control of the absolute configurations of chiral elements in molecular magnets allow obtaining enantiopure chiral magnets (ECM), an archetype of multifunctional materials. This task has been recognised as a major challenge for both chemists and physicists of molecular magnetism. To reach this goal, the former have combined the rational approaches towards molecular-based magnets and of enantiopure metal-organic frameworks. They have used enantiopure stable radicals, ligands from the chiral pool, enantiopure coligands associated with achiral connectors or enantioselective self-assembly to successfully reach their synthetic targets. They were motivated by the will to obtain suitable systems for the experimental demonstration of the influence of enantiomeric purity on the physico-chemical properties. This influence can be found in the magnetic properties themselves but, most interestingly, in the coexistence and interaction between the properties arising from controlled non-centrosymmetry. Thus the combination of natural circular dichroism, second harmonic generation or ferroelectricity with long-range magnetic ordering can give birth to new properties like magneto-chiral dichroism, magnetisation induced second harmonic generation or multiferroicity. The two former synergetic effects have already been demonstrated in enantiopure chiral magnets. The third one remains a challenging target that can be reached by adapting strategies developed towards enantiopure molecular ferroelectrics (119 references).

Chirality and magnetism II: Free electron on an infinite helix, inverse Faraday effect and inverse magnetochiral effect

The interplay of chirality and magnetism is of fundamental physical interest. A free electron on a helix with periodic boundary conditions is possibly the simplest model exhibiting both chirality and orbital paramagnetism. In a previous report we have studied with this model the relation between natural circular, magnetic circular and magnetochiral dichroism. Here we extend our investigation to the second-order nonlinear optical phenomena designated as the inverse Faraday effect and as the inverse magnetochiral effect. Both effects manifest themselves as a radiation-induced time-independent magnetic field which lifts the magnetic degeneracy of the system. While the inverse Faraday effect is circular differential, the comparatively much weaker inverse magnetochiral effect is independent of the polarization of the incident radiation.

Coherent magneto-optical polarisation dynamics in a single chiral carbon nanotube

We propose a theoretical framework and a dynamical model for the description of the natural optical activity and the Faraday rotation in an individual chiral single-walled carbon nanotube in the highly nonlinear coherent regime. The model is based on a discrete-level representation of the optically active states near the band edge. Chirality is modelled by a system Hamiltonian corresponding to energy-level configurations, specific for each handedness, that are mirror reflections of each other. An axial magnetic field is introduced through the Aharonov–Bohm and Zeeman energy-level shifts.The time evolution of the quantum system following an ultrafast circularly polarised optical excitation is studied using the coherent vector Maxwell pseudospin equations. Giant natural and magneto-optical gyrotropy, exceeding the one of the artificial photonic metamaterials, is numerically demonstrated for a single (5, 4) carbon nanotube and an estimate of the magnitude of the natural and magneto-chiral circular dichroism and specific optical rotatory power is obtained. The model provides a framework for the investigation of chirality and magnetic field dependence of the ultrafast nonlinear optical response of a single carbon nanotube.

Quantum theory of natural circular, magneto-chiral and non-reciprocal linear dichroism

For dichroic signals produced by parity-odd absorption events, we expose, in correct and concise form, electron degrees of freedom that participate in correlations between spin and orbital variables. Additionally, and for the first time, we prove sum rules for integrated dichroic signals, analogous to the celebrated work by Thole et al (1992 Phys. Rev. Lett. 68 1943) for parity-even events. Natural circular dichroism is a standard method for characterizing chiral materials, and the photon magneto-chiral effect is an important candidate for the origin of the homo-chirality of life.

Chirality and magnetism: Free electron on an infinite helix, NCD, MCD, and magnetochiral dichroism

The free electron on a helix with periodic boundary conditions is undoubtedly one of the simplest quantum chemical models exhibiting both chirality and orbital angular momentum. Subjected to a light beam traveling parallel to the helix axis, the model exhibits natural circular dichroism and, assuming a lifting of the magnetic degeneracy by an external static magnetic field, also magnetic circular dichroism and magnetochiral dichroism. We believe that the model illustrates well the interplay of chirality and magnetism in a pure magnetic state, and that it could also be of interest in the study of the recently discovered chiral ferromagnets.

Magnetic Control of Crystal Chirality and the Existence of a Large Magneto-Optical Dichroism Effect inCuB2O4

The possibility of a magnetic field controlling the chirality of matter has been debated for a long time. Here, we report the successful induction of chirality in the noncentrosymmetric canted antiferromagnet, CuB2O4, by application of a low intensity static magnetic field. The chirality is reversed by a 90 degrees rotation of the direction of the magnetic field. The induction of chirality by a magnetic field gives rise to a gigantic enhancement of magnetochiral dichroism in this material. The ability to switch handedness in combination with this large magnetochiral optical effect allows us to design new optical devices such as a magnetically controllable isolator.

Strong magneto-chiral dichroism in enantiopure chiral ferromagnets

As materials science is moving towards the synthesis, the study and the processing of new materials exhibiting well-defined and complex functions, the synthesis of new multifunctional materials is one of the important challenges. One of these complex physical properties is magneto-chiral dichroism which arises, at second order, from the coexistence of spatial asymmetry and magnetization in a material. Herein we report the first measurement of strong magneto-chiral dichroism in an enantiopure chiral ferromagnet. The ab initio synthesis of the enantiopure chiral ferromagnet is based on an enantioselective self-assembly, where a resolved chiral quaternary ammonium cation imposes the absolute configurations of the metal centres within chromium-manganese two-dimensional oxalate layers. The ferromagnetic interaction between Cr(III) and Mn(II) ions leads to a Curie temperature of 7 K. The magneto-chiral dichroic effect is enhanced by a factor of 17 when entering into the ferromagnetic phase.

Are optically active three-dimensional oxalate-based ferromagnets good candidates for theobservation of x-ray magnetochiral dichroism? A neutron diffraction study

Neutron diffraction studies have been performed on[Ru(bpy)2(ppy)][MnCr(ox)](bpy = 2, 2′bipyridine;ppyH = 2-phenylpyridine;ox = oxalate), a3D oxalate-based compound in one of its optically active forms. The diffraction pattern matches withthe P 213 space group found by x-ray diffraction. The magnetic structure has been studied in themagnetically ordered phase of the compound, e.g. below 5.5 K. The compound ordersferromagnetically. Owing to the most probable orientation of the spins, the magnetic space group isP 2121′21′. The Shubnikovgroup is then 22′2′. Such a magnetic point group is compatible with the observation of x-ray magnetochiraldichroism, the occurrence of a ferromagnetic ordering being an important factor toenhanced the forecast effect.