Photomagnetic Properties Research Articles

Achievements in the Photomagnetic Effect of Cobalt‐Iron Prussian Blue Analogues

AbstractHarnessing light for magnetization control presents a promising approach with compelling merits such as non‐contact operation, ultrafast response, reversibility, high spatial resolution, tunability, and energy efficiency. Photoinduced metal‐to‐metal charge transfer (MMCT) is one key mechanism in achieving photo‐controlled magnetic properties, making relevant materials prime candidates for versatile switchable devices. Cobalt iron Prussian blue analogues (CoFePBA) are trailblazers in showcasing photomagnetic properties via MMCT and the numerous related studies on CoFePBA have significantly enhanced the understanding of photoinduced MMCT processes. Thus, this review embarks on a thorough examination of three decades of research on the photomagnetic of CoFePBA to deep into the art of the photocontrol of spin. In addition to an introduction to the structure and preparation of CoFePBA, the focus is on elucidating the underlying mechanisms and introducing strategies for its manipulation and control. Finally, the challenges and prospects at this moment are summarized and discussed.

Influence of chelating ligands on photomagnetic properties of two erbium(III) coordination polymers

The magnetization dynamics of lanthanide coordination compounds are fundamentals governing their potential applications such as information storage or molecular switches. Herein, two two-dimensional coordination polymers [Er(CA)1.5(bpy) (DMF)]n (1) and [Er(CA)1.5(phen) (DMF)]n (2) (H2CA = 2,5-dichloro-3,6-dihydroxy-p-quinone, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) were synthesized and fully characterized. By the irradiation of ultraviolet light, 1 and 2 were converted to 1a and 2a which contain light-generated radicals, inducing an increase of χMT at room temperature. A detailed study of the dynamic magnetic property shows that the magnetization dynamics observed for 1 and 1a are dominated by Raman process, but Orbach and Raman processes are observed in 2 and 2a. The structural factors influencing the magnetic properties of this photomagnetic system are discussed.

Multifunctional Crystalline Coordination Polymers Constructed from 4,4'-Bipyridine-N,N'-dioxide: Photochromism, White-Light Emission, and Photomagnetism.

Multifunctional photochromic coordination polymers (CPs) have shown great potential in many areas, like molecular switches, anticounterfeiting, magnetics, and optoelectronics. Although multifunctional photochromic CPs can be obtained by introducing photoresponsive functional units or by exploiting the synergy effect of each component, relatively limited photochromic ligands hinder the development of various multifunctional photochromic CPs. In this work, we reported two multifunctional coordination polymers {[Zn(bpdo)(fum)(H2O)2]}n (1) and {[Mn(bpdo)(fum)(H2O)2]}n (2) based on an easily accessible but underestimated photoactive molecule 4,4'-bipyridine-N,N'-dioxide (bpdo). Compound 1 exhibits photochromism and white-light emission with an ultra-high color rendering index (CRI) of 92.1. Interestingly, compound 1 could emit intrinsic white light in the crystalline state upon UV irradiation both before and after photochromism. Meanwhile, compound 2 displays photochromic and photomagnetic properties, induced by the photogenerated radicals via a photoinduced electron transfer mechanism.

Alginate doped graphene oxide – TiO2 – Fe3O4 nanocomposite: preparation, characterization, and application of sonophotocatalyst for efficient decomposition of an organic dye

ABSTRACT In this research, the alginate doped graphene oxide (GO)-Fe3O4-TiO2 photomagnetic nanocomposite was synthesised through a three-step method. For comparison, alginate-GO was also prepared. The synthesised materials were characterised through FTIR, XRD, TGA, SEM, EDX, and TEM techniques. The photomagnetic properties of the resultant nanocomposite were evaluated by VSM. Degradation of Malachite green as a dye pollutant was studied in the presence of alginate (Alg), Alg-GO, and Alg-GO-Fe3O4-TiO2 nanocomposite using a sonophotocatalysis technique. The results showed, that, Alg-GO-Fe3O4-TiO2 nanocomposite has high efficiency in the removal of Malachite green. Recycling experiments displayed that the degradation efficiency dropped only by 12%, after five successive runs. and makes it a promising catalyst for efficient degradation of dye pollutants in the practical applications.

New photomagnetic ionic salts based on [MoIV(CN)8]4− and [WIV(CN)8]4− anions

Three new ionic salts containing [M(CN)8]4− (M = MoIV and WIV) were prepared using large complex cations based on a non-conventional motif built with the tris(2-aminoethyl)amine (noted hereafter tren) ligand, [{M’(tren)}3(μ-tren)]6+ (M’ = CuII and ZnII). The crystal structures of the three compounds show that the atomic arrangement is formed by relatively isolated anionic and cationic entities. The three compounds were irradiated with a blue light at low temperature, and show a significant photomagnetic effect. The remarkable properties of these compounds are (i) the long-lived photomagnetic metastable states for the [Mo(CN)8]4−-based compounds well above 200 K and (ii) the rare efficient photomagnetic properties of the [W(CN)8]4−-based compound. These photomagnetic properties are compared with the singlet-triplet conversion recently reported for the K4[Mo(CN)8]·2H2O compound

New Photomagnetic Ionic Salts Based on [MoIV(CN)8]4− and [WIV(CN)8]4− Anions

Three new ionic salts containing [M(CN)8]4− (M = MoIV and WIV) were prepared using large complex cations based on a non-conventional motif built with the tris(2-aminoethyl)amine (noted hereafter tren) ligand, [{M’(tren)}3(μ-tren)]6+ (M’ = CuII and ZnII). The crystal structures of the three compounds show that the atomic arrangement is formed by relatively isolated anionic and cationic entities. The three compounds were irradiated with a blue light at low temperature, and show a significant photomagnetic effect. The remarkable properties of these compounds are (i) the long-lived photomagnetic metastable states for the [Mo(CN)8]4−-based compounds well above 200 K and (ii) the rare efficient photomagnetic properties of the [W(CN)8]4−-based compound. These photomagnetic properties are compared with the singlet-triplet conversion recently reported for the K4[Mo(CN)8]·2H2O compound.

Functional Capabilities of Silicon with Nanoclusters of Manganese Atoms

The paper reports that silicon with nanoclusters of manganese atoms has unique electrical, photoelectric, magnetic, and photomagnetic properties that are absent in ordinary doped semiconductor materials. The samples revealed an anomalously high impurity photosensitivity in the region of λ = 1–3 μm, a large negative magnetoresistance at room temperature, and new thermomagnetic and photomagnetic effects, which were observed in the same sample. The optimal electrophysical parameters of the samples were found. A unique set of the observed physical effects allows the creation of fundamentally new multifunction sensors of physical quantities based on these materials.

Heterotrimetallic Cyanide-Bridged 3d-4d-5d Frameworks Based on a Photomagnetic Secondary Building Unit.

The rational design of coordination frameworks combining more than two different metal ions using a self-assembly approach is challenging because it rarely offers sufficient control over the building blocks at the actual self-assembly stage. In this work, we present a successful two-step strategy toward heterotrimetallic coordination frameworks by employing a new bimetallic [(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]4– secondary building unit (SBU). This anionic moiety has been isolated and characterized as a simple salt with an organic dppipH22+ cation (dppipH2)2[(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]·15H2O (1) (dppip = 1,4-di(4-pyridinyl)piperazine). The salt presents a second-order phase transition related to cation conformational change around 250 K and a photomagnetic effect after irradiation with 450 nm light at 10 K. When combined with aqueous solutions of MnII or CuII complexes, it forms either a one-dimensional chain [MnII(dpop)][MnII(dpop)(H2O)][(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]·36H2O (2) (dpop = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) or a photomagnetic two-dimensional honeycomb network [CuII(cyclam)]2[(NC)7MoIV-CN-PtIV(NH3)4-NC-MoIV(CN)7]·40.89H2O (3) (cyclam = 1,4,8,11-tetraazacyclotetradecane), both characterized by very large cavities in their structure filled with solvent molecules. Both 2 and 3 incorporate three different transition-metal ions and constitute a new family of 3d-4d-5d coordination frameworks. Moreover, compound 3 inherits the photomagnetic properties of the MoPtMo SBU.

Photomagnetism in 5 nm nanocrystals of the alkali cation free-CoFe Prussian blue analogue embedded in a silica matrix

5 nm nanocrystals of CoFe Prussian blue analogue totally exempt from any alkali cation were prepared. Their photomagnetic properties were compared to those of the corresponding powder made of 150 nm particles as well as to those of 5 nm nanocrystals of CoFe PBAs embedded in comparable silica matrices, made of CoIIFeIII pairs and prepared under various conditions. The photomagnetic investigation of the nanoparticles exempt of any alkali cation clearly shows that they are transformed by light and the comparison of their photomagnetic properties to those of the powder made of particles of bigger size with the same chemical composition suggests that the species involved in the switching properties are surface species. Furthermore, the comparison of the magnetic properties of nanoparticles prepared under various conditions also suggests that the aggregation state of the nanoparticles in the porous channels of the silica matrix, by modulating inter-particle interactions, plays a predominant role in the magnetic properties of the nanoparticles assemblies.

Photoinduced Mo−CN Bond Breakage in Octacyanomolybdate Leading to Spin Triplet Trapping

AbstractThe photoinduced properties of the octacoordinated complex K4MoIV(CN)8⋅2 H2O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)7 species originating from the light‐induced cleavage of one Mo−CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt‐222)]3[MoIV(CN)7]⋅3 CH3CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution.

Photoinduced Mo-CN Bond Breakage in Octacyanomolybdate Leading to Spin Triplet Trapping.

The photoinduced properties of the octacoordinated complex K4 MoIV (CN)8 ⋅2 H2 O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)7 species originating from the light-induced cleavage of one Mo-CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt-222)]3 [MoIV (CN)7 ]⋅3 CH3 CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution.

Effect of alkali cations on the photomagnetic behavior of CoFe Prussian blue analogue nanoparticles embedded in ordered mesoporous silica

The size of CoFe Prussian blue analogue nanoparticles containing either rubidium or cesium cations was controlled by their formation through a nucleation process inside the calibrated pores of an ordered mesoporous silica matrix. The corresponding references were synthesized in powder form using the same ratio between the metal species in the reaction solution. The obtained samples were characterized via infrared (IR) spectroscopy, X-ray diffraction, and magnetometry to understand the differences arising from the size reduction and the nature of the inserted alkali cation. We were able to show that the nature of the cation has a significant influence on the photoswitching properties at the macroscale in the powders. However, on the nanoscale, the influence of the surface contribution becomes more prominent and cooperative effects disappear, resulting in a new role of the alkali cation in the photomagnetic properties.

Synthesis, Structure, and Photomagnetic Properties of a Hydrogen-Bonded Lattice of [Fe(bpp)2]2+ Spin-Crossover Complexes and Nicotinate Anions

In this paper, we report on the synthesis, crystal structure, and photomagnetic properties of the spin-crossover salt of formula [Fe(bpp)2](C6H4NO2)2·4H2O (1·4H2O) (bpp = 2,6-bis(pyrazol-3-yl)pyridine; C6H4NO2− = nicotinate anion). This compound exhibits a 3D supramolecular architecture built from hydrogen bonds between iron(II) complexes, nicotinate anions, and water molecules. As synthesized, the hydrated material is low-spin and desolvation triggers a low-spin (LS) to high-spin (HS) transformation. Anhydrous phase 1 undergoes a partial spin crossover (T1/2= 281 K) and a LS to HS photomagnetic conversion with a T(LIESST) value of 56 K.

Solvatomorphism-Induced 45 K Hysteresis Width in a Spin-Crossover Mononuclear Compound.

Spin-transition compounds are coordination complexes that can present two stable or metastable high-spin and low-spin states at a given temperature (thermal hysteresis). The width of the thermal hysteresis (difference between the maximum and minimum temperature between which the compound exhibits bi-stability) depends on the interactions between the coordination complexes within the compound, and which may be modulated by the absence or presence of solvent within the structure. The new compound [Fe(3-bpp)2 ][Au(CN)2 ]2 (1, 3-bpp=2,6-di-(1H-pyrazol-3-yl)pyridine) was synthesized and its properties were compared with those of the solvated compound [Fe(3-bpp)2 ][Au(CN)2 ]2 ⋅2 H2 O (1.H2 O) already described. 1 has a two-steps thermal hysteresis of 45 K, in contrast to the compound 1.H2 O which exhibits a gradual conversion without hysteresis. This hysteretic transition is accompanied by a reversible reconstructive structural transition and twinning. This stepped behaviour is also observed in the photomagnetic properties despite the low efficiency of photoswitching. Single-crystal photocrystallographic investigations confirm this low conversion, which we attributed to the high energy cost to form the high-spin structure, whose symmetry differs from that of the low-spin phase.

Switchable Heteroleptic Mononuclear Iron(II) Complexes as Versatile Molecular Building Block

A series of photoswitchable precursors based on [Fe(NCX)2L(L′)2], where X = S or Se, L is a bidentate ligand (phenanthroline or bipyrimidine), and L′ a monodentate ligand such as a pyridine or picoline derivative, were synthesized and their spin crossover (SCO) properties investigated in detail. The thermal and light‐induced magnetic properties of a family of [Fe(NCS)2L(py)2] [py = pyridine and L = bipyrimidine (1) or phenanthroline (phen) (2)] is reported. The [Fe(NCX)2(phen)(L′)2] compounds were further explored by changing the counteranion from NCS– to NCSe– (3) or by replacing pyridine with 4‐picoline (4) or 4‐ethylpyridine (5). Complexes 1–4 exhibit thermal and light‐induced SCO, while 5 remains in the high‐spin state. The kinetics governing the photoinduced back‐conversion was investigated for compounds 2 and 4. Complex 2 exhibits LIESST relaxation kinetics involving strongly cooperative (sigmoidal) behavior, whereas complex 4 displays a stretched exponential shape, typical for broad distributions of relaxation times. These results are discussed on the basis of the steric hindrance due to bulkiness and the electronic influence of the substituent effects on the magnetic and photomagnetic properties of mononuclear iron(II) complexes.

Synergistic photo optical and magnetic properties of a hybrid nanocomposite consisting of a zinc oxide nanorod array decorated with iron oxide nanoparticles

A ZnO/PBA/Fe3−δO4 nanocomposite displays enhanced magnetic and optical properties as a result of dual synergy.

Magnetism and Photomagnetism of Prussian Blue Analogue Nanoparticles Embedded in Porous Metal Oxide Ordered Nanostructures

Prussian blue analogues (PBAs) are key compounds in the field of molecular magnetism and photomagnetism. In parallel to the strong development of this class of compounds, many efforts have been devoted to produce PBAs in various shapes and sizes. In this microreview we focus on works reporting the use of porous metal oxide nanostructures as hard templates for controlling the size, shape and solid‐state organization of magnetic and photomagnetic PBA nanoparticles. The oxide matrices that have so far been developed and their characteristics are presented first. Then, the approaches that have been successfully used to control PBA formation within the pores of the matrices are described, as well as the morphology and environment of the functional nanoparticles. Lastly, the magnetic and photomagnetic properties of the nanocomposites are reviewed.

Graphene Nanoreactors: Photoreduction of Prussian Blue in Aqueous Solution

Prussian dyes are characterized by interesting photomagnetic properties due to the photoinduced electron transfer involved in the Fe oxidation and spin state changes. Ferromagnetic Prussian blue (PB) in contact with titanium dioxide (TiO2) can be reduced to paramagnetic Prussian white (PW) upon UV band gap excitation of TiO2. This process is promoted by the presence of a hole scavenger, such as water, fundamental to ensure the overall charge balance and the continuity of the process. In order to clarify the photoinduced reduction mechanism and the role of water, an innovative system of graphene nanobubbles (GNBs) filled with a PB aqueous solution was developed, enabling the application of electron spectroscopies to the liquid phase, up to now limited by the vacuum required to overcome the short electron inelastic mean free path in dense medium. In this work GNBs formed on the photocatalytic substrate are able to act as “nanoreactors”, and they can control and take part in the reaction. The evolution of Fe L2,3 edge X-ray absorption spectra measured in total electron yield through the graphene membrane revealed the electron reduction from PB (FeIII–CN–FeII) to PW (FeII–CN–FeII) upon UV irradiation, shedding light on the photoinduced electron transfer mechanism in liquid phase. The results, confirmed also by Raman spectroscopy, unequivocally demonstrate that the reaction occurs preferentially in aqueous solution, where water acts as hole scavenger.

On the Effect of the Internal Pressure on the Photoinduced Spin‐Crossover Behavior of [FexM1–x(1,10‐phenanthroline)2(NCS)2] Solid Solutions (M = NiII, ZnII, and CdII)

The thermal and light‐induced magnetic properties of a family of metal‐diluted spin‐crossover complexes, [FexM1–x(phen)2(NCS)2] (phen = 1,10‐phenantholine and M = NiII, CdII), are reported and compared to previous results obtained for the same series but with ZnII ions used to substitute FeII ions; the ultimate goal was to validate the influence of the size and nature of the inert metal ion on the light‐induced properties of spin‐crossover compounds. For all of the materials, we measured the thermally induced spin‐crossover temperature (T1/2) and T(LIESST) (LIESST = light‐induced excited spin‐state trapping) values systematically. We observed clearly that the dilution has a strong effect on the magnetic and photomagnetic properties. The magnitude of these effects depends strongly on the nature of the diluting metal. This comparison gives insights into the effect of the size of the diluting ion on T(LIESST) and T1/2 and completes the previous studies on the effect of internal pressure on the lifetime of the photoinduced state.

Insertion of Cesium in Prussian Blue Films

Hexacyanometallate-like materials have raised intense interests because of their electrocatalytic, electrochromic, ion-exchange, ion-sensing or photomagnetic properties. Nano-electrogravimetric measures during the electrochemical stabilization process of Prussian Blue (PB) in CsCl aqueous solution yields interesting information about the insertion role of the Cs into the crystalline structure trough the interfacial regions [1]. In addition to the intrinsic scientific interest of this topic, many works have suggested that hexacyanoferrate compounds can be used as precipitants for cesium removal from aqueous radioactive wastes [2]. This work was carried out by means of simultaneous measurements of resonant frequency of quartz as well as the motional resistance of the Butterworth-Van Dyke equivalent circuit model measured by means of a an electrochemical quartz crystal microbalance (R-EQCM) during successive cyclic voltammograms. The simultaneous measure of current, mass and motional resistance magnitudes allows to explain the differences between the electrochemical cation insertion processes in a solution of CsCl salt with respect to the cation insertion observed in KCl aqueous solutions [3,4]. Accordingly, the main goal of this work was to study in depth the different redox processes which involve the PB electrochemistry during the PB«ES switch, where ES is the reduced form (Everitt’s salt). Derivative voltabsommetric scans together with nano-electrogravimetric results allow the different electrochemical processes to be distinguished during voltammetric scans. Cesium, proton and hydrated proton counter-ions involved in the PB electrochemistry are related here to the electrochemical reactions of specific Fe-sites. Cesium counterions show two different sites for their insertion: one located into the crystalline framework and other into ferrocyanide vacancies PB deposits were voltammetric cycled or only immersed in CsCl aqueous solutions. In both cases, their respective motional resistances R increase about of 300 ohm. Simultaneously, a decrease in the resonance frequency is also recorded, suggesting that in both cases a spontaneous entrance of Cs should be considered. Then, two different types of cesium exchange are postulated: one associated to the electrochemical reaction during the first scan, and another spontaneous non-stoichiometric entrance where the Cs is located inside the inner water cluster. This means that a part of the water molecules are expelled from the cluster and consequently the film losses electrical conductance as well as their mechanical rigidity increases. It is proposed that the Cs is retained into the interstitial water cluster placed between the framework formed by means Fe(II)low spin-CN-Fe(III)high spin structural units. Then, there are two different ways for entering the cesium to the structural zeolite-building of Prussian Blue: CsCl enters chemically by an spontaneous substitution of inner water molecules of the interstitial water cluster and, also its could enters as counter-ion Cs+ during the first reduction scan of the electrochemical stabilization process of the PB. REFERENCES [1] J.J. García-Jareño, D. Giménez-Romero, F. Vicente, C. Gabrielli, M. Keddam, H. Perrrot. EIS and ac-electrograimetry study of PB films in KCl , NaCl and CsCl solutions. J. Phys. Chem. B 107 (2003) 11321-11330. [2]C.Thammawong,P. Opaprakasit, P. Tangboribonrat,.P, Sreerunothai. PB-coated magnetic nanoparticles for removal of cesium from contaminated environment. Journal of Nanoparticles Research 15 (2013) 1689. [3] J. Garcia-Jareño, J. Navarro-Laboulais, A. Sanmatias, F. Vicente. The correlation between electrochemical CsCl aqueous solutionimpedance spectra and voltammograms of PB films in aqueous NH4Cl and CsCl., Electrochim. Acta, 43 (1998) 1045-1052. [4] J. Agrisuelas, J.J. García-Jareño, C. Moreno-Guerrero, A. Roig, F. Vicente, Identification of electroactive sites in Prussian Yellow films, Electrochimica Acta. 113 (2013) 825–833. ACKNOWLEDGEMENTS Part of this work was supported by FEDER-CICyT CTQ2015-71794-R