Highly Axial Magnetic Anisotropy in a N3O5Dysprosium(III) Coordination Environment Generated by a Merocyanine Ligand

Photochromic Dysprosium Single-Molecule Magnet Featuring Reversible Redox Transformation of Polyoxomolybdate Moiety

A photochromic dysprosium-based single-molecule magnet [Dy(CyPh2PO)2(H2O)5](PMo12O40) ⋅ 3CyPh2PO⋅H2O (1-Dy) is synthesized via cocrystal engineering of a polyoxomolybdate (POMo) anion and an Ising-type cation with pseudo pentagonal bipyramidal geometry. Upon ultraviolet irradiation, MoVI-to-MoV single-electron photoreduction occurs in the POMo moiety, resulting in significant changes of optical and magnetic properties. The emergence of intervalence charge-transfer transitions in heteropoly blue state 1-Dy* facilitates photothermal conversion in near-infrared region. Meanwhile, the coercive field of hysteresis loop is altered from 0.72 T (1-Dy) to 0.04 T (1-Dy*) at 2 K, which might be contributed to the magnetic interaction between DyIII and MoV. After dark treatment, 1-Dy* can convert to the initial state with the recovery of magnetic memory effect. These results presented herein provide a blueprint for developing versatile opto-magnetic materials via the coupling of photochemical regulation and magnetic interaction.

A Modern Look at Spiropyrans: From Single Molecules to Smart Materials

Photochromic compounds of the spiropyran family have two main isomers capable of inter-switching with UV or visible light. In the current review, we discuss recent advances in the synthesis, investigation of properties, and applications of spiropyran derivatives. Spiropyrans of the indoline series are in focus as the most promising representatives of multi-sensitive spirocyclic compounds, which can be switched by a number of external stimuli, including light, temperature, pH, presence of metal ions, and mechanical stress. Particular attention is paid to the structural features of molecules, their influence on photochromic properties, and the reactions taking place during isomerization, as the understanding of the structure-property relationships will rationalize the synthesis of compounds with predetermined characteristics. The main prospects for applications of spiropyrans in such fields as smart material production, molecular electronics and nanomachinery, sensing of environmental and biological molecules, and photopharmacology are also discussed.

Metal complexes bearing photochromic ligands: photocontrol of functions and processes

Metal complexes associated with photochromic molecules are attractive platforms to achieve smart light-switching materials with innovative and exciting properties due to specific optical, electronic, magnetic or catalytic features of metal complexes and by perturbing the excited-state properties of both components to generate new reactivity and photochemical properties. In this overview, we focus on selected achievements in key domains dealing with optical, redox, magnetic properties, as well as application in catalysis or supramolecular chemistry. We also try to point out scientific challenges that are still faced for future developments and applications.

A Complete Ab Initio View of Orbach and Raman Spin-Lattice Relaxation in a Dysprosium Coordination Compound

The unique electronic and magnetic properties of lanthanide molecular complexes place them at the forefront of the race toward high-temperature single-molecule magnets and magnetic quantum bits. The design of compounds of this class has so far being almost exclusively driven by static crystal field considerations, with an emphasis on increasing the magnetic anisotropy barrier. Now that this guideline has reached its maximum potential, a deeper understanding of spin-phonon relaxation mechanisms presents itself as key in order to drive synthetic chemistry beyond simple intuition. In this work, we compute relaxation times fully ab initio and unveil the nature of all spin-phonon relaxation mechanisms, namely Orbach and Raman pathways, in a prototypical Dy single-molecule magnet. Computational predictions are in agreement with the experimental determination of spin relaxation time and crystal field anisotropy, and show that Raman relaxation, dominating at low temperature, is triggered by low-energy phonons and little affected by further engineering of crystal field axiality. A comprehensive analysis of spin-phonon coupling mechanism reveals that molecular vibrations beyond the ion's first coordination shell can also assume a prominent role in spin relaxation through an electrostatic polarization effect. Therefore, this work shows the way forward in the field by delivering a novel and complete set of chemically sound design rules tackling every aspect of spin relaxation at any temperature.

Mononuclear Dysprosium Alkoxide and Aryloxide Single-Molecule Magnets

Recent studies have shown that mononuclear lanthanide (Ln) complexes can be high‐performing single‐molecule magnets (SMMs). Recently, there has been an influx of mononuclear Ln alkoxide and aryloxide SMMs, which have provided the necessary geometrical control to improve SMM properties and to allow the intricate relaxation dynamics of Ln SMMs to be studied in detail. Here non‐aqueous Ln alkoxide and aryloxide chemistry applied to the synthesis of low‐coordinate mononuclear Ln SMMs are reviewed. The focus is on mononuclear Dy^III alkoxide and aryloxide SMMs with coordination numbers up to eight, covering synthesis, solid‐state structures and magnetic attributes. Brief overviews are also provided of mononuclear Tb^III, Ho^III, Er^III and Yb^III alkoxide and aryloxide SMMs.

Redox-Modulations of Photophysical and Single-molecule Magnet Properties in Ytterbium Complexes Involving Extended-TTF Triads

The reaction between the 2,2’-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate triad (H₂SQ) and the metallo-precursor [Yb(hfac)₃]⋅2H₂O led to the formation of a dinuclear coordination complex of formula [Yb₂(hfac)₆(H₂SQ)]⋅0.5CH₂Cl₂ (H₂SQ-Yb). After chemical oxidation of H₂SQ in 2,2’-cyclohexa-2,5-diene-1,4-diylidenebis(4,7-di-tert-butyl-1,3-benzodithiole-5,6-dione (Q), the latter triad reacted with the [Yb(hfac)₃]⋅2H₂O precursor to give the dinuclear complex of formula [Yb₂(hfac)₆(Q)] (Q-Yb). Both dinuclear compounds have been characterized by X-ray diffraction, DFT optimized structure and electronic absorption spectra. They behaved as field-induced Single-Molecule Magnets (SMMs) nevertheless the chemical oxidation of the semiquinone to quinone moieties accelerated by a factor of five the relaxation time of the magnetization of Q-Yb compared to the one for H₂SQ-Yb. The H₂SQ triad efficiently sensitized the Yb^III luminescence while the chemical oxidation of H₂SQ into Q induced strong modification of the absorption properties and thus a quenching of the Yb^III luminescence for Q-Yb. In other words, both magnetic modulation and luminescence quenching are reached by the oxidation of the protonated semiquinone into quinone.

Hysteresis Photomodulation via Single-Crystal-to-Single-Crystal Isomerization of a Photochromic Chain of Dysprosium Single-Molecule Magnets

A one-dimensional coordination solid 1_c is synthesized by reaction of a bispyridyl dithienylethene (DTE) photochromic unit with the highly anisotropic dysprosium-based single-molecule magnet [Dy(Tp^py)F(pyridine)₂]PF₆. Slow magnetic relaxation characteristics are retained in the chain compound 1_c, and photoisomerization of the bridging DTE ligand induces a single-crystal-to-single-crystal transformation that can be monitored using photocrystallography. Notably, the resulting chain compound 1_o exhibits faster low-temperature relaxation than that of 1_c, which is apparent in magnetic hysteresis data collected for both compounds as high as 4 K. Ab initio calculations suggest that this photomodulation of the magnetic relaxation behavior is due to crystal packing changes rather than changes to the crystal field splitting upon ligand isomerization.

A coloring tool for spiropyrans: solid state metal–organic complexation versus salification

Controlling the type of merocyanine metal interaction for broad solid-state coloration.

Electro-activity and magnetic switching in lanthanide-based single-molecule magnets

The present work reviews switching of single-molecule magnetic behaviour achieved through various stimuli such as temperature, light irradiation, redox processes, solvation/desolvation, and magnetic field.

An intense luminescent Dy(iii) single-ion magnet with the acylpyrazolonate ligand showing two slow magnetic relaxation processes

A new Dy(iii)-acylpyrazolonate complex displays both intense yellow-light emission and single-ion magnet behavior with two slow magnetic relaxation processes, acting as a potential bifunctional material.

trans to cis photo-isomerization in merocyanine dysprosium and yttrium complexes

A unique light-switching behavior is revealed in Yttrium(iii) and Dysprosium(iii) merocyanine complexes through NMR and AC magnetometry experiments. Its impact on slow relaxation of magnetization is described.