Preparation method of a light / heat dual-mode switchable single-molecule magnet material

Abstract

The present invention belongs to the technical field of magnetic materials, and specifically relates to a preparation method of a photo / thermal dual-mode switchable single-molecule magnet material. Dysprosium(III) chloride hexahydrate, 9-anthracene carboxylic acid, N,N-dimethylformamide and deionized water are mixed evenly. The mixture is placed in a 20 mL glass bottle. After hydrothermal reaction, it is naturally cooled to room temperature, filtered and washed to obtain the single-molecule magnet material. By utilizing the dual photoactive characteristics of the 9-anthracene carboxylic acid ligand, through the dual regulation mechanisms of photoinduced cycloaddition and electron transfer, while maintaining the integrity of the single crystal, the structural transformation of the single-molecule magnet from 0D to 1D is realized, and it is endowed with the dual magnetic switching functions of light control and thermal control, opening up a new way for the intelligent regulation and high-performance application of molecule-based magnetic materials. The preparation method has simple and efficient process, and the obtained substance has strong stability, is easy to scale up production, and has broad market prospects.

Description

Technical Field:

[0001] The present invention belongs to the technical field of magnetic materials, and particularly relates to a preparation method of a photo / thermal dual-mode switchable single-molecule magnet material. Background Art:

[0002] In the field of molecular-based magnetic materials, single-molecule magnets (SMMs) are considered potential key materials for future information storage, quantum computing, spintronics, etc. due to their unique magnetic properties, such as significant magnetic hysteresis effects, quantum tunneling effects, and high-spin state stability. However, the magnetic regulation of traditional single-molecule magnets mostly relies on macroscopic means such as external magnetic fields or temperatures, and their response speed and reversibility are difficult to meet the requirements of practical applications. Therefore, developing new, efficient, and reversible magnetic regulation methods has become an important direction in the current research of molecular-based magnetic materials.

[0003] In recent years, light-controlled and thermally controlled magnetic materials have attracted much attention because they can achieve remote and non-contact magnetic regulation. By introducing photosensitive or thermosensitive groups, these materials undergo changes in molecular structure or electron arrangement under light irradiation or temperature changes, thereby realizing reversible magnetic regulation. However, most existing light-controlled or thermally controlled magnetic materials often suffer from the destruction of crystal structure or phase transition during the magnetic regulation process, resulting in unstable or lost material properties.

[0004] Single-molecule magnets (SMMs), as an important branch of molecular nanomagnets, have attracted wide attention in the scientific community due to their unique magnetic properties and potential application values, such as high-density information storage, complex logic gates, and advanced device architectures. However, achieving reversible regulation of SMMs remains a highly challenging topic. Summary of the Invention:

[0005] The object of the present invention is to solve the problem in the existing technology that the dual-photoactivity response of photoinduced cycloaddition and photo-generated free radicals cannot be used to regulate the performance of single-molecule magnets, and to provide a preparation method of a photo / thermal dual-mode switchable single-molecule magnet material. Using 9-anthracene carboxylic acid as an organic ligand, a structural transformation from zero-dimensional to one-dimensional and from single crystal to single crystal (SC-SC) is achieved, and through a dual-regulation mechanism of photoinduced cycloaddition and electron transfer, the reversible on / off switching of SMMs behavior is successfully realized.

[0006] To achieve the above object, the present invention provides a preparation method of a photo / thermal dual-mode switchable single-molecule magnet material, a single-molecule magnet material that realizes photo / thermal switching on / off through cycloaddition and electron transfer, and the specific steps are as follows:

[0007] (1) Add dysprosium salt (0.035 - 0.040 g), organic acid (0.025 - 0.03 g), N,N-dimethylformamide (DMF) (1 mL), and deionized water (5 mL) into a reaction glass bottle;

[0008] (2) Ultrasonicate the mixture obtained in step (1) at room temperature for 20 - 30 minutes. After mixing evenly, carry out a solvothermal reaction, heat it to 90 °C and react for 12 - 14 h. Take it out, cool it naturally to room temperature, filter, wash, and dry to obtain yellow block crystals, which are the photo / thermal dual-mode switchable single-molecule magnet materials.

[0009] The dysprosium salt used in the present invention is dysprosium chloride hexahydrate, the organic acid is 9-anthracene carboxylic acid, and the volume of the reaction glass bottle is 20 mL.

[0010] The present invention also provides a photo / thermal dual-mode switchable single-molecule magnet material prepared by the above method. The molecular formula of this material is C 126 H 88 Dy2N2O 18 , and it is yellow block crystals.

[0011] The photo / thermal dual-mode switchable single-molecule magnet material described in the present invention has a dual magnetic switch function of light control and heat control. Illumination makes the material exhibit magnet behavior, and heating makes the magnet behavior disappear.

[0012] The parameters of the illumination described in the present invention are: irradiate under a room temperature xenon lamp (320 - 780 nm, 300 W) for 120 - 150 min.

[0013] The parameters of the heating described in the present invention are: heat at 120 °C for 48 - 50 h.

[0014] The chemical formula of the photo / thermal dual-mode switchable single-molecule magnet material prepared by the present invention is [Dy2(DMF)2(HAC)2(AC)6]. This magnet material exhibits photo / thermal reversible switching magnet behavior, specifically: after irradiation with a xenon lamp (320 - 780 nm, 300 W), the magnet material undergoes dual structural changes in molecular and electronic structures. Under the stacking effect and hydrogen bond interaction, anthracene formate radicals are generated in the irradiated sample through the ligand internal metal ion-assisted electron transfer process. Due to the unique π-conjugated structure of 9-anthracene formic acid, a [4+4] cycloaddition reaction occurs under the π-π stacking interaction between anthracene rings, realizing the single crystal to single crystal (SC-SC) transformation, forming a one-dimensional chain-like complex, and exhibiting room-temperature radical-induced photochromism and fluorescence quenching phenomena; at the same time, through the synergistic regulation of photochemical cycloaddition and photogenerated radicals, significant single-molecule magnet behavior is exhibited after the structural transformation; heating the irradiated sample restores the sample structure to the original state, that is, heating causes the cycloaddition induced by light to undergo ring opening and return to the original monomer structure. The single-molecule magnet material of the present invention can realize the reversible regulation of the magnet through light irradiation and heating.

[0015] The present invention realizes the SC-SC structural transformation of the magnet material from 0D to 1D through a cycloaddition reaction. Without destroying the crystal structure, isolated molecular units are connected into a one-dimensional chain-like structure, thereby changing the intermolecular interaction and magnetic behavior. At the same time, combined with the electron transfer mechanism, the electronic arrangement and spin coupling state of the magnetic center can be further regulated to achieve fine regulation of magnetism.

[0016] Compared with the prior art, the present invention uses 9-anthracene formic acid as a ligand to prepare a photo / thermal dual-mode switchable single-molecule magnet material through self-assembly technology. Utilizing the dual photoactive characteristics of the 9-anthracene formic acid ligand, through the dual regulation mechanisms of photoinduced cycloaddition and electron transfer, while maintaining the integrity of the single crystal, the structural transformation of the single-molecule magnet from 0D to 1D is realized, and it is endowed with the dual magnetic switch functions of light control and heat control, opening up a new way for the intelligent regulation and high-performance application of molecular-based magnetic materials, and providing a new idea for designing functional molecules with complex light response behaviors; the preparation method has simple and efficient processes, and the obtained substance has strong stability, is easy to scale up production, and has broad market prospects. Brief Description of the Drawings:

[0017] Figure 1 It is a schematic diagram of the molecular structure principle of the single-molecule magnet material involved in the present invention.

[0018] Figure 2 It is a schematic diagram of the reversible [4+4] cycloaddition principle of the single-molecule magnet material involved in the present invention under the action of light and temperature.

[0019] Figure 3The UV-Vis spectra of the single-molecule magnet materials involved in the present invention under different conditions.

[0020] Figure 4 The EPR spectra of the single-molecule magnet materials involved in the present invention under different conditions.

[0021] Figure 5 The IR spectra of the single-molecule magnet materials involved in the present invention under different conditions.

[0022] Figure 6 The 1H NMR spectra of the single-molecule magnet materials involved in the present invention under different conditions in 0.6 mL DMSO-d6 and 0.5 μL DCI.

[0023] Figure 7 Schematic diagrams of the variable-temperature DC magnetic susceptibility of the single-molecule magnet materials involved in the present invention under the environment of 2 - 300 K under a 1000 Oe DC magnetic field before and after light irradiation.

[0024] Figure 8 Schematic diagrams of the change in field magnetization intensity of the single-molecule magnet materials involved in the present invention at 2 K before and after light irradiation.

[0025] Figure 9 Schematic diagrams of the AC magnetic susceptibility curves of the single-molecule magnet materials involved in the present invention with χ'(real part) and χ”(imaginary part) under a 0 Oe DC magnetic field, a 5 Oe AC magnetic field.

[0026] Figure 10 Schematic diagrams of the AC magnetic susceptibility curves of the single-molecule magnet materials involved in the present invention with χ'(real part) and χ”(imaginary part) under a 0 Oe DC magnetic field, a 5 Oe AC magnetic field after light irradiation.

[0027] Figure 11 Schematic diagrams of the AC magnetic susceptibility curves of the single-molecule magnet materials involved in the present invention with χ'(real part) and χ”(imaginary part) under a 0 Oe DC magnetic field, a 5 Oe AC magnetic field after the sample is heated. Detailed implementation methods:

[0028] The present invention will be further described below through examples in combination with the accompanying drawings.

[0029] Example 1:

[0030] This example relates to a preparation method of a photo / thermal dual-mode switchable single-molecule magnet material [Dy2(DMF)2(HAc)2(AC)6], and the specific steps are as follows:

[0031] (1) Mix 0.037 g of dysprosium(III) chloride hexahydrate, 0.03 g of 9-anthracene carboxylic acid, 1 mL of N,N-dimethylformamide (DMF), and 5 mL of deionized water, transfer the mixture to a 20 mL glass bottle, and ultrasonicate for 20 min;

[0032] (2) Seal the glass bottle containing the reactants in step (1), react in an oven at 90 °C for 12 h. After the reaction is completed, take out the glass bottle, cool it naturally at room temperature, filter, and rinse the obtained crystals with distilled water repeatedly 3 - 4 times to obtain yellow block crystals, which are the photo / thermal dual-mode switchable single-molecule magnet materials.

[0033] The structural formula of the 9-anthracene carboxylic acid is:

[0034]

[0035] In this example, single-crystal X-ray diffraction test was carried out on the prepared single-molecule magnet. The data shows that the single-molecule magnet crystallizes in the monoclinic system, space group P21 / c. The asymmetric unit consists of one Dy 3+ ion, three 9-anthracene carboxylic acid ions, one 9-anthracene carboxylic acid, and one DMF. The Dy atom adopts an eight-coordinate mode of [DyO8], presenting a square antiprism (D 4d ) shape (CShM = 1.418). Four 9-AC bridge two Dy atoms, connecting into a zero-dimensional binuclear structure ( Figure 1 ).

[0036] Example 2:

[0037] This example involves the magnet test of the single-molecule magnet material prepared in Example 1 under light switching. The single-molecule magnetic material (original sample) obtained in Example 1 was irradiated under a room-temperature xenon lamp (320 - 780 nm, 300 W). After 120 min, the crystal changed from yellow to brown, and the obtained brown sample was denoted as the post-irradiation sample. Covalent bonds were formed between C2 and C9 atoms in adjacent molecules of the post-irradiation sample, and the C2–C9A / C9–C2A distance in the post-irradiation sample became 1.642(7). It shows that the binuclear structure of the original sample of the single-molecule magnet material undergoes a transformation from zero-dimensional to one-dimensional, from single crystal to single crystal, and becomes a one-dimensional chain structure with [4+4] cycloaddition occurring between adjacent anthryl groups. The interplanar π-π distance between adjacent anthracene rings is The intermolecular C2···C9A distance is The overlapping area is approximately 61.9%, indicating the existence of strong π–π interactions. The self-color-changing property of 9-anthracene carboxylic acid molecules is conducive to the occurrence of electron-transfer photochromism, and the intermolecular interactions between anthracene rings conform to the Schmidt's rule of [4+4] photocycloaddition reaction. Therefore, the single-molecule magnet material prepared in Example 1 can exhibit dual photoresponse behaviors after light irradiation.

[0038] At the same time, ultraviolet-visible spectroscopy, electron paramagnetic resonance spectroscopy (EPR), infrared spectroscopy (IR), and nuclear magnetic resonance hydrogen spectroscopy were performed on the original sample (before light irradiation) and the sample after light irradiation of the single-molecule magnet material, and the results are as Figures 3 - 6 shown. Figure 3 It can be seen from the ultraviolet-visible spectrum of [the sample] that a broad absorption peak appears at 450 - 550 nm. As the light irradiation time prolongs, the intensity of the absorption peak increases. This process is due to the continuous generation of free radicals and is accompanied by the gradual deepening of the color of the sample. In addition, new absorption appears at 325 nm, indicating that the AC component has undergone a photocycloaddition reaction to form a dimer product. From Figure 4 the EPR spectrum of [the sample], it can be known that a weak free radical signal is shown before light irradiation, and a sharp and strong free radical signal appears at around g = 2.0047 for the sample after light irradiation. The intensity changes of the signal peaks before and after light irradiation both confirm the generation of free radicals. From Figure 5 the infrared spectrum of [the sample], it can be known that three new peaks appear at 608.7, 686.7, and 812.1 cm, corresponding to the out-of-plane deformation vibration of C-H of dianthracene caused by photocycloaddition. From Figure 6 the analysis of the nuclear magnetic resonance hydrogen spectrum of [the sample], two new chemical shifts are observed at 5.63 ppm and 6.75 ppm, which can be attributed to the H atoms of the dianthracene unit. These spectral analyses provide strong support for the occurrence of photoinduced anthracene [4+4] cycloaddition and the generation of free radicals.

[0039] To deeply explore the regulation of the magnetic relaxation properties of the Dy 3+ complex by photoinduced free radicals and cycloaddition, the curve of the product of the molar susceptibility and temperature of the complex versus temperature from 2 - 300 K was measured under a 1000 Oe direct current magnetic field, as Figure 7 shown. The χT value of the single-molecule magnet material at 300 K is 13.92 cm 3 mol -1 K, which is lower than the theoretical value (14.17 cm 3+ mol 3 mol -1 K) of an uncoupled Dy 3 mol -1K indicates that there is a weak antiferromagnetic coupling between metal ions; the χT value of the sample after illumination at 300 K is 14.30 cm 3 mol -1 K. During the cooling process, it drops to the lowest value of 10.69 cm at 6 K 3 mol -1 K, and then increases slightly, reaching 10.97 cm at 2 K 3 mol -1 K, which proves that ferromagnetic coupling is generated at the metal ion center after illumination. The curve of the magnetic susceptibility varying with the magnetic field was studied at 2 K ( Figure 8 ) and it was found that as the magnetic field increases, the M value increases linearly in the low field and gradually reaches the maximum value of 5.5 Nβ at 50 kOe. After illumination, the M value increases to 5.6 Nβ. The temperature-dependent AC magnetic susceptibility of the original sample and the sample after illumination was measured at 0 DC field and 5 Oe AC field at frequencies of 100 Hz, 500 Hz, and 1000 Hz. The results are as Figure 9 and Figure 10 shown. Figure 9 No AC signal of the single-molecule magnet material was observed in Figure 10 , probably due to the existence of the magnetization quantum tunneling effect. However, significant changes occurred in the peaks of the real part (χ') and the imaginary part (χ”) of the sample after illumination at zero DC field and frequencies from 100 - 10000 Hz (

[0040] Example 3:

[0041] This example involves the thermal switching magnet test of the single-molecule magnet material prepared in Example 1. The sample after illumination in Example 2 was heated at 120 °C for 48 h, and the obtained crystal was denoted as the sample after heating. Single-crystal X-ray diffraction test was performed on the sample after heating, and the obtained data was the same as that of the single-molecule magnet material in Example 1, proving the completion of the de-dimerization process ( Figure 2 ). It shows that the sample after illumination returns to its original structure after heating.

[0042] This example closely tracked this significant reversibility through 1 H NMR, IR, ultraviolet, and EPR spectra. The results are as Figures 3 - 6 shown. These results verify that the photoaddition product returns to its original monomer configuration after heating. However, the ultraviolet-visible spectrum and the EPR spectrum show that the photo-generated radicals of the sample after heating exhibit significant stability, indicating that the heat treatment selectively quenches the photodimerization reaction while the photo-induced electron transfer process is not affected.

[0043] In this embodiment, the magnetic susceptibility of the heated sample was also measured to further study its reversibility, and the results are as Figure 11 shown. From Figure 11 it can be seen that the frequency dependence of χ' and χ” almost disappeared and returned to the initial state shown by the original sample. This observation indicates that the SMMs behavior was effectively eliminated by heat treatment.

Claims

1. A method for preparing a light / thermal dual-mode switchable single-molecule magnetic material, characterized in that: The specific steps are as follows: Dysprosium trichloride hexahydrate, 9-anthracenecarboxylic acid, N,N-dimethylformamide and deionized water are mixed evenly, and then a solvent thermal reaction is carried out; filtering, washing and drying are performed to obtain yellow block crystals, which are light / thermal dual-mode switchable single-molecule magnet materials; The mass volume ratio of the dysprosium trichloride hexahydrate, 9-anthracenecarboxylic acid, N,N-dimethylformamide and deionized water is (0.035-0.040) g: (0.025-0.03) g: 1 mL: 5 mL; The mixing method is ultrasound, and the ultrasound time is 20-30 min; The temperature of the solvothermal reaction is 90 °C and the time is 12-14 hours.

2. The optical / thermal dual-mode switchable single-molecule magnetic material prepared by the preparation method according to claim 1 is characterized in that: The molecular formula of the material is C 126 H 88 Dy2N2O 18 , which is a yellow block crystal; the single-molecule magnet is crystallized in the monoclinic P21 / c space group, and the asymmetric unit consists of a Dy 3+ ions, three 9-anthracenecarboxylate ions, one 9-anthracenecarboxylic acid and one DMF. The Dy atom adopts the eight-coordination mode of [DyO8], presenting a square antiprism D composed of 7 O atoms from 9-AC and 1 O atom from DMF. 4d Shape: Four 9-ACs bridge two Dy atoms, connecting into a zero-dimensional binuclear structure.

3. The optical / thermal dual-mode switchable single-molecule magnetic material according to claim 2, characterized in that: The material has dual magnetic switch functions of light control and heat control. Light causes the material to produce magnetic behavior, and heating causes the magnetic behavior to disappear.

4. The optical / thermal dual-mode switchable single-molecule magnetic material according to claim 3, characterized in that: The illumination parameters are: irradiation under a xenon lamp at room temperature for 120-150 min.

5. The optical / thermal dual-mode switchable single-molecule magnetic material according to claim 3, characterized in that: The heating parameters are: heating at 120° C. for 48-50 h.

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