Matteo Atzori

Chiral materials, integrating structural breaking of mirror-symmetry, exhibit physical properties that cannot be observed in centrosymmetric analogues. Among these properties, optical magneto-chiral anisotropy, the nonreciprocal absorption of light shown by chiral magnetized systems, is emerging as an enabling technology in magneto-optics and photonics. Here, we report on enantiopure chiral molecular crystals based on the erbium(III) rare-earth ion that display nonreciprocal, wavelength-selective, magnetic field-induced variations of the optical absorption coefficients up to ca. 200% for the intrashell f–f electronic transition falling in the 1.5 μm telecom wavelength range. Such a response is associated with an exceptionally high Magneto-Chiral Dichroism induced by the strong spin–orbit coupling of the Er(III) and the helical chirality at the lanthanide center, exalted by the magnetic-dipole-allowed character of the electronic transition. This chirality-induced nonreciprocal magneto-optical response represents a proof of concept for the use of these chiral crystalline molecular materials as potential components in magneto-optical diodes.

Here we report on the preparation and investigation of a pair of enantiopure chiral complexes of chromium(III) featuring the chiral (1 R ,2 R )‐diaminocyclohexane and (1 S ,2 S )‐diaminocyclohexane ligands. Single‐crystal X‐ray crystallography reveals an octahedral tris‐chelated propeller‐like coordination geometry. Natural circular dichroism spectroscopy in solution and in the solid state indicates that both spin‐allowed and spin‐forbidden d–d electronic transitions of the Cr(III) ion are optically active. Variable temperature and variable magnetic field magneto‐chiral dichroism spectroscopy reveals that the spin‐forbidden absorption bands are MChD active and provide low‐temperature g _MChD dissymmetry factors comparable to those of tris(oxalato)chromate(III). On these bases, magneto‐chiral photochemistry experiments aimed at inducing a preferential enantiomeric excess of one enantiomer over the other by irradiating a racemic solution of the complexes with unpolarized light under an applied magnetic field have been conducted.

The first ab initio simulation of Magneto-Chiral Dichroism (MChD) for a lanthanide-based complex is reported. The previously experimentally studied [Yb(hfac)3(P–H6bpy)] complex is investigated with multireference wavefunction-based methods using complete active space self-consistent field (CASSCF) calculations, further refined by second-order perturbation theory (CASPT2) and state-interaction spin–orbit approach (RASSI-SO), in combination with the microscopic MChD theory developed by Barron and Vrbancich (BV). The simulations enable a detailed analysis of the 2F5/2 ← 2F7/2 electronic transitions. At 4 K, the MChD response is found to be dominated by the MChD Cterm contribution, arising from electric dipole-magnetic dipole interactions and population differences within the ground state, split by the magnetic field. Overall, the simulated spectrum shows good agreement with experiment in terms of both relative transition energies and band-sign assignments. Zeeman splitting was explicitly evaluated and found to be negligible under the experimental conditions, indicating that vibronic coupling is the most likely origin of the remaining discrepancies. By providing a quantitative and physically grounded description of the MChD spectrum of a lanthanide complex, this work goes beyond the current state of the art in theoretical simulations of MChD and fills a crucial gap, at a time when the growing body of experimental data on lanthanide complexes calls for direct theory–experiment comparisons to enable deeper interpretation.

In this work, we report the preparation of a chiral Er(III) complex specifically designed to assess the influence of the magnetic anisotropy axes orientation on its magneto‐chiral dichroism (MChD). High resolution MChD measurements performed along the three principal crystallographic axes revealed pronounced anisotropic effects on both MChD signal line shapes and intensities. By combining, for the first time, angle‐resolved torque magnetometry, comprehensive magneto‐optical spectroscopy on oriented single crystals, absorption measurements under magnetic fields up to 30 T and theoretical calculations, we provide clear experimental insight into the anisotropic nature of the MChD in lanthanide complexes. Specifically, we evaluate the extent to which Er moderate anisotropy enables signal persistence across a wide range of crystallographic orientations. These results allow the identification of the key role played by both the orientation and the magnitude of magnetic anisotropy in the MChD response of chiral lanthanide complexes, representing a significant step toward the directional control of magneto‐chiroptical responses in lanthanide‐based molecular materials.

In this work, we report the preparation of a chiral Er(III) complex specifically designed to assess the influence of the magnetic anisotropy axes orientation on its magneto‐chiral dichroism (MChD). High resolution MChD measurements performed along the three principal crystallographic axes revealed pronounced anisotropic effects on both MChD signal line shapes and intensities. By combining, for the first time, angle‐resolved torque magnetometry, comprehensive magneto‐optical spectroscopy on oriented single crystals, absorption measurements under magnetic fields up to 30 T and theoretical calculations, we provide clear experimental insight into the anisotropic nature of the MChD in lanthanide complexes. Specifically, we evaluate the extent to which Er moderate anisotropy enables signal persistence across a wide range of crystallographic orientations. These results allow the identification of the key role played by both the orientation and the magnitude of magnetic anisotropy in the MChD response of chiral lanthanide complexes, representing a significant step toward the directional control of magneto‐chiroptical responses in lanthanide‐based molecular materials.

The combination of single‐molecule magnet (SMM) behavior with chiroptical and magneto‐(chiro)optical properties allows for the preparation of functional materials responsive to light and magnetic fields. Herein, we report on novel enantiopure chiral lanthanide (Ln) SMMs derived from the [Ln(bbpen)] ⁺ scaffold (bbpen = N,N′‐bis(2‐hydroxybenzyl)‐N,N′‐bis(2‐methylpyridyl)ethylenediamine), formulated as [Dy(bbpen)((1 S ,2 S )/(1 R ,2 R )‐ chxn )](BPh ₄ ) ( Dy‐ S / R ) ( chxn = 1,2‐diaminocyclohexane). These chiral complexes exhibit SMM behavior associated with effective energy barriers over 800 K and strong room‐temperature NCD and MCD responses, as evidenced by the g _NCD and g _MCD dissymmetry factors. CPL measurements at room temperature reveal | g _lum | values of 0.23(2) for the ⁴ F _9/2 → ⁶ H _11/2 magnetic dipole‐allowed transition, setting a new record value in the realm of chiral SMMs. Furthermore, variable‐temperature and variable‐field MChD spectroscopy measurements reveal among the strongest magneto‐chiral optical responses reported so far for Dy ^III chiral complexes, despite the electric‐dipole induced nature of the Dy ^III f‐f electronic transitions. Dynamic MChD measurement at low temperature allowed us to optically trace the magnetic hysteresis cycles for both enantiomers and for different electronic transitions. Overall, this study establishes the bbpen scaffold as an ideal building block for the preparation of multifunctional materials and open great perspectives for the preparation of novel chiral materials with enhanced magneto‐(chiro)optical responses by chemical design.

The combination of single‐molecule magnet (SMM) behavior with chiroptical and magneto‐(chiro)optical properties allows for the preparation of functional materials responsive to light and magnetic fields. Herein, we report on novel enantiopure chiral lanthanide (Ln) SMMs derived from the [Ln(bbpen)] ⁺ scaffold (bbpen = N,N′‐bis(2‐hydroxybenzyl)‐N,N′‐bis(2‐methylpyridyl)ethylenediamine), formulated as [Dy(bbpen)((1 S ,2 S )/(1 R ,2 R )‐ chxn )](BPh ₄ ) ( Dy‐ S / R ) ( chxn = 1,2‐diaminocyclohexane). These chiral complexes exhibit SMM behavior associated with effective energy barriers over 800 K and strong room‐temperature NCD and MCD responses, as evidenced by the g _NCD and g _MCD dissymmetry factors. CPL measurements at room temperature reveal | g _lum | values of 0.23(2) for the ⁴ F _9/2 → ⁶ H _11/2 magnetic dipole‐allowed transition, setting a new record value in the realm of chiral SMMs. Furthermore, variable‐temperature and variable‐field MChD spectroscopy measurements reveal among the strongest magneto‐chiral optical responses reported so far for Dy ^III chiral complexes, despite the electric‐dipole induced nature of the Dy ^III f‐f electronic transitions. Dynamic MChD measurement at low temperature allowed us to optically trace the magnetic hysteresis cycles for both enantiomers and for different electronic transitions. Overall, this study establishes the bbpen scaffold as an ideal building block for the preparation of multifunctional materials and open great perspectives for the preparation of novel chiral materials with enhanced magneto‐(chiro)optical responses by chemical design.

Matériaux moléculaires fonctionnels avec des propriétés magnétiques et de conduction électronique basé sur les ligands anilate: Ce travail de thèse explore la capacité des ligands anilates d’être employés pour la préparation de nouveaux matériaux moléculaires fonctionnels avec des propriétés magnétiques et de conduction électrique. Les anilates, qui sont les dérivés du 2,5-dihydroxy-1,4- benzoquinone substitués sur les positions 3 et 6, ont été sélectionnés comme ligands puisque leurs caractéristiques électroniques et structurales, leurs modalités de coordination et leur capacité de médiation des interactions de super-échange magnétique en font d’excellents ligands pour la préparation de ces matériaux. Plusieurs ligands anilates ont été utilisés pour le design et la préparation d'une nouvelle classe de complexes paramagnétiques octaédriques tris-chélates de formule générale [MIII(X2An)3]3- (MIII = Cr, Fe; X = Cl, Br, I, H, Cl/CN, An = C6O4 2- = anilate). Ces complexes métalliques paramagnétiques ont été complètement caractérisés et utilisés comme briques moléculaires pour la préparation de i) une nouvelle classe de ferriaimants moléculaires, dans laquelle la modification des substituants sur le ligand permet de modifier les interactions entre les centres métalliques, et, par conséquent, les propriétés magnétiques, ii) des conducteurs paramagnétiques moléculaires obtenus par combinaison avec le donneur organique BEDT-TTF, iii) une série de conducteurs moléculaires chiraux obtenus par combinaison du donneur organique TM-BEDT-TTF avec des couches hétéro-bimétalliques anioniques obtenues par association in situ de complexes tris(chloranilate)ferrate(III) et des ions potassium. En outre, ont été synthétisés de nouveaux dérivés anilates avec des propriétés electroactives et de luminescence, afin de démontrer la capacité du motif anilate d’être fonctionnalisé avec différents substituants comme porteurs de propriétés physiques spécifiques.

Single-molecule toroics, materials that combine spin and chirality at the molecular level, are promising candidates for applications in data storage, chiral spintronics and magnetoelectric devices. Over the past two decades, substantial progress has been made in the design of toroidal spin states via ligand design and coordination chemistry strategies. However, achieving homochiral magnetic vortex configurations across both molecular and unit-cell scales—a key prerequisite to induce the toroidal polarization using a homogeneous magnetic field—remains challenging. Here we report enantiopure chiral dysprosium triangles in which introduction of structural chirality induces spin homochirality. µ-SQUID magnetometry and ab initio calculations evidence a non-coplanar spin texture that exhibits a toroidal ground state at low temperature. Furthermore, magneto-chiral dichroism spectroscopy, a technique sensitive to both chirality and magnetization, reveals unusual behaviours below 4.5 K, the temperature at which the coupling between Dy(III) ions favours the generation of a toroidal spin state.

In this work, the wavelength range of magneto-chiral dichroism (MChD) based optical readout of magnetic hysteresis is extended to the near-infrared (NIR) telecom communication range where optical fibers have the smallest transmission loss. To achieve this goal, we have prepared and investigated a new air-stable chiral single-molecule magnet (SMM) formulated as (S)- and (R)-[Dy(bbppn)Cl] (bbppn = N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-pyridylmethyl)-X-1,2-propanediamine, X = S, R). We demonstrate that the magnetic hysteresis of this SMM, despite exhibiting rapid quantum tunneling of magnetization (QTM) at zero field, can be optically detected using unpolarized light through MChD. Complementary to our seminal study limited to the visible spectral range, we demonstrate that the MChD-based readout is also effective for the Dy(III) f-f transitions in the NIR region, confirming the robustness of this method across a broader spectral window. These findings establish MChD as a generalizable optical readout method for molecular magnetic materials, reinforcing its potential for future applications in polarization-free optical data readout technologies and optical communication at telecom wavelengths.