Chiralité et magnétisme
Chirality and magnetism have a common history which date back to the nineteen century. It is based on the similar optical response of chiral and magnetized media when exposed to circularly polarized light. This similarity has raised many attempts, often vains, on the possibility to control chiral systems with magnetic fields.
On the basis of symmetry arguments, the interaction between chirality and magnetism is possible if the magnetic field is associated with another physical entity, such as electric current or light, even unpolarized. This association induces a “true chiral” influence, as defined by L. D. Barron. These two ways of associating light and electric current with magnetic fields are studied at the LNCMI since several years. They result in a different response of two enantiomers of a chiral system when unpolarized light (Magneto-Chiral Dichroism, MChD) or electric current (Magneto-Chiral Anisotopy, eMChA) are parallel/antiparallel applied with respect to the applied magnetic field.
More recently, we are focusing also on the inverse effect, notably, the generation of enantiomeric excesses under a true chiral influence (Magneto-Chiral Photochemistry, MChPh) or falsely chiral, or the generation of a magnetization by light irradiation in a magnetic field (inverse Magneto-Chiral Dichroism, iMChD).
Topics
Magneto-Chiral Dichroism (MChD):
Magneto-Chiral Dichroism (MChD) represents the differential absoprtion (or emission) that chiral materials show when light is transmitted (or emitted) along a magnetic field applied parallel or antiparallel with respect to the light wavevector.
The first experimental demonstration of this effect was done at the LNCMI on enantiopure emissive Eu(III) complexes. Since then, we experimentally investigate the parameters that drives MChD in chiral molecular and nanostructured systems based on transition metals or lanthanide ions. Theoretical support is provided by external collaborators.
A new method to probe magnetic memories
M. S. Raju, K. Paillot, I. Breslavetz, G. Novitchi, G. L. J. A. Rikken, C. Train, M. Atzori
J. Am. Chem. Soc. 2024, 146, 23616
Press communication CNRS Chimie
Magneto-Chiral Photochemistry (MChPh):
Given that the “direct” effect of unpolarized light and magnetic fields on chiral systems, such as MChD, have been clearly demonstrated, the inverse effects, such as the generation of an enantiomeric excess (ee) when a racemic mixture or a prochiral system are exposed to an external chiral influence, are also possible.
On the basis of the results achieved through the investigation of MChD in the visible range, we are now investigating Magneto-Chiral Photochemistry (MChPh), that is, photochemistry of chiral systems under magnetic field. The irradiation of a racemic mixture with a unpolarized laser beam in magnetic fields has provided an ee of the tris(oxalato)chromate(III) complex and this mechanism proposed as one of the possible origins of moleculear homochirality of life on Earth.
These studies have been recently reinitiated with measurements under much higher magnetic fields and it will be extended to biological relevant molecular systems in the frame of the project ANR JCJC PRINCIPE.
Response to a falsely chiral influence :
Effects comparable to magneto-chiral effects have been predicted when a certain system is subjected to an influence defined by L. D. Barron as “falsely chiral”. Thus, the Curie-de Gennes conjecture predicts that the application of a collinear magnetic and electric field is likely to produce an enantiomeric excess from an initially racemic mixture. We try to demonstrate this conjecture experimentally. We have obtained encouraging preliminary results, but these need to be reproduced and extended in order to establish the relevance of this more than century-old conjecture.
Experimental Techniques
Magneto-Chiral Dichroism (MChD) measurements
To measure the Magneto-Chiral Dichroism associated with the electronic transitions in the UV-Vis-NIR, an experimental setup based on a signal detection synchronized with magnetic field change has been developed at LNCMI. The measurment probe is mobile. It can be placed in a superconducting magnet or in resistive magnets, enabling measurements up to 9 T. Measurements can be taken over a very wide range of wavelengths, from 2.2 K to 290 K.
Natural Circular Dichroism (NCD) and Magnetic Circular Dichroism (MCD) measurements
Pour étudier les propriétés chiroptiques des systèmes chiraux et magnétiques, nous disposons de deux spectrophotophotomètres (JASCO J1500, Olis DSM17). Un cryostat optique permet d’étudier le Dichroïsme Circulaire Naturel (NCD) sur une large gamme de longueurs d’onde jusqu’à 5K. Nous développons actuellement l’implémentation du champ magnétique afin de pouvoir mesurer le Dichroïsme Circulaire Magnétique (MCD) dans les mêmes conditions.
We have two spectrophotometer to study the chiroptical properties of chiral and magnetic systems (JASCO J1500, Olis DSM17). An optical cryostat enables us to study Natural Circular Dichroism (NCD) over a wide range of wavelengths down to 5 K. We are currently developing a Magnetic Circular Dichroism (MCD) setuot under the same conditions and magnetic fields up to 6 T.
Publications
Selected Publications
Optical Readout of Single-Molecule Magnetic Memories with Unpolarized Light
M. S. Raju, K. Paillot, I. Breslavetz, G. Novitchi, G. L. J. A. Rikken, C. Train*, M. Atzori*
J. Am. Chem. Soc. 2024, 146, 23616
Multifunctional Helicene-Based Ytterbium Coordination Polymer Displaying Circularly Polarized Luminescence, Slow Magnetic Relaxation and Room Temperature Magneto-Chiral Dichroism
K. Dhbaibi, H. Douib, M. Grasser, V. Dorcet, L. Favereau, O. Cador, B. Le Guennic, F. Riobé, O. Maury, S. Guy, A. Bensalah‐Ledoux, B. Baguenard, C. Train, G. Rikken, M. Atzori,* F. Pointillart,* J. Crassous*
Angew. Chem. Int. Ed. 2022, e202215558
Magnetic 3d-4f Chiral Clusters Showing Metal-site Selective Magneto-Chiral Dichroism
X. Wang, S.-Q. Wang, J.-N. Chen, J.-H. Jia, C. Wang, K. Paillot, I. Breslavetz, L.-S. Long, L.-S. Zheng, G. L. J. A. Rikken, C. Train, X.-J. Kong* and M. Atzori*
J. Am. Chem. Soc. 2022, 144, 8837
Validation of Microscopic Magneto-Chiral Dichroism Theory
M. Atzori, H. Ludowieg, Á. Valentín-Pérez, M. Cortijo, I. Breslavetz, K. Paillot, P. Rosa, C. Train, J. Autschbach, E. A. Hillard, G. L. J. A. Rikken*
Sci. Adv. 2021, 7, eabg2859
A Chiral Prussian Blue Analogue Pushes Magneto-Chiral Dichroism Limits
M. Atzori*, I. Breslavetz, K. Paillot, K. Inoue, G. L. J. A. Rikken, C. Train*
J. Am. Chem. Soc. 2019, 141, 20022
All publications (HAL server)