Halogen-modified schiff base zinc complex and preparation method and application thereof

Abstract

The application belongs to the technical field of optoelectronic materials, and particularly relates to a halogen-modified Schiff base zinc complex and a preparation method and application thereof. The Schiff base zinc complex is obtained by coordination of a halogen-substituted thiohemisemicarbazone Schiff base as a ligand with zinc ions; the chemical expression of the Schiff base zinc complex is C 11 H 13 RN4OSZn, wherein R is any one of Cl, Br and I. The Schiff base zinc complex has enhanced thermal stability and adjustable luminescence performance, and the luminescence wavelength can be adjusted by a halogen substituent, and the Schiff base zinc complex has application potential in optoelectronic devices such as light-emitting diodes. The application further provides a solvothermal synthesis method of the complex, which is simple to operate and has a high yield.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic materials technology, specifically to a halogen-modified Schiff base zinc complex, its preparation method, and its application. Background Technology

[0002] Coordination chemistry, as an important bridge connecting inorganic and organic chemistry, has shown wide applications in materials science, catalysis, and optoelectronics in recent years. Among these, Schiff base ligands have attracted considerable attention due to their ease of synthesis, diverse functionalizations, and strong coordination abilities. Schiff base metal complexes, through their tunable electronic structures and coordination modes, show potential in luminescent materials. Zinc(II) ions, in particular, due to their d... 10 The electronic configuration has no dd electron transition quenching effect, which can effectively preserve the luminescence properties of the ligands, and the emission wavelength can be regulated through ligand modification.

[0003] While some progress has been made in the study of zinc complexes in the current technology, several key challenges remain in achieving systematic performance regulation through simple halogen substituents. These challenges mainly lie in the unclear structure-performance relationship, the lack of strategies for regulating thermal stability, and insufficient exploration of the tunability of luminescence performance and its deviceization. Firstly, although studies have confirmed that halogen substituents (such as Cl, Br, and I) can significantly affect the molecular structure of Schiff base zinc complexes, for example, by altering the C-R bond length to regulate molecular packing and hydrogen bond networks, thereby affecting thermal stability and luminescence behavior, the quantitative laws and microscopic mechanisms of this effect are still unclear. There is a lack of systematic correlation between halogen atomic radii, electronegativity, and polarizability, which limits the molecular design for specific applications such as wavelength-tunable LEDs. Furthermore, a systematic strategy for regulating thermal stability is lacking. Existing studies are mostly limited to reporting decomposition data of individual complexes, failing to develop a universal strategy for regulating thermal behavior through halogen engineering. There is also a lack of in-depth exploration of thermal decomposition, such as how halogens affect the stability of the complex framework and intermolecular interactions. Finally, the exploration of tunability and device-level application of luminescence properties is insufficient. Although halogen substitution can adjust the emission wavelength, such as achieving control from blue to green light, this is attributed to charge transfer processes within or between ligands. However, research on the fineness of control and the luminescence properties of the complexes in solid-state or device environments remains inadequate. It can be seen that existing Schiff base zinc complexes obtained using halogen substituents suffer from insufficient thermal stability and poor luminescence tunability. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a halogen-modified Schiff base zinc complex, its preparation method, and its application. The halogen-modified Schiff base zinc complex of this invention exhibits enhanced thermal stability and tunable luminescence properties, and the emission wavelength can be controlled by halogen substituents.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] A halogen-modified Schiff base zinc complex, wherein the Schiff base zinc complex is obtained by coordinating a halogen-substituted thiohexacarbazone Schiff base with zinc ions. The halogen-substituted thio-semicarbazone Schiff base is any one of 5-chloro-2-hydroxybenzaldehyde 4-ethylaminothiourea, 5-bromo-2-hydroxybenzaldehyde 4-ethylaminothiourea, and 5-iodo-2-hydroxybenzaldehyde 4-ethylaminothiourea. The chemical formula for the Schiff base zinc complex is C. 11 H 13 RN4OSZn, the structural formula is shown in formula (1), where R is a halogen; Equation (1).

[0007] This invention introduces halogens directly into the functional groups of ligands as an inherent part of the ligand skeleton. In the prior art, halogens are usually located on the periphery of ligands. In comparison, the halogens of this invention regulate the electron cloud density of ligands through strong electron-withdrawing inductive effects and conjugation effects, thereby affecting the microenvironment of the coordination center. As part of the ligand skeleton, halogens can regulate the molecular structure of ligands, thereby improving the thermal stability of Schiff base zinc complexes and achieving tunable luminescence.

[0008] In another preferred embodiment, the halogen is any one of Cl, Br, and I.

[0009] A second aspect of the present invention provides a method for preparing the halogen-modified Schiff base zinc complex, comprising the following steps: Using a halogen-substituted thio-semicarbazone Schiff base as a ligand, the ligand, piperazine, and zinc salt were mixed in an equimolar ratio in a solvent system, and an aqueous dimethylamine solution was added as a base to obtain a mixture. The mixture was then placed at 80℃~90℃ to undergo a coordination reaction, yielding a halogen-modified Schiff base zinc complex.

[0010] In another preferred embodiment, the volume ratio of the dimethylamine aqueous solution to the solvent is 1:1000~2000; the mass percentage concentration of the dimethylamine aqueous solution is 33%~40%, preferably, the molar concentration of dimethylamine in the reaction system is 3.3 mmol / L.

[0011] In another preferred embodiment, the coordination reaction takes 48h to 72h.

[0012] In another preferred embodiment, the solvent system uses a mixture of isopropanol and methanol in a volume ratio of 3~4:2~3.

[0013] In another preferred embodiment, the zinc salt is zinc sulfate.

[0014] The third aspect of this invention provides the application of the halogen-modified Schiff base zinc complex in the preparation of optoelectronic devices.

[0015] In another preferred embodiment, the emission peak of the optoelectronic device is located at 488nm~498nm.

[0016] In another preferred embodiment, the light-emitting device includes a light-emitting diode.

[0017] Compared with the prior art, the present invention has the following beneficial effects: In the halogen-substituted thiohexacarbazone Schiff base ligands of this invention, the halogen is located on the ligand backbone. Through strong electron-withdrawing inductive effects and conjugation effects, the electron cloud density of the ligand is modulated, thereby affecting the microenvironment of the coordination center and controlling the molecular structure of the ligand. This results in improved thermal stability and tunable luminescence properties. Furthermore, the Schiff base zinc complexes of this invention all crystallize in the triclinic crystal system. P-1 The space group is [space group], and the zinc center has a five-coordinate geometry. Thermogravimetric analysis shows that the thermal stability of the Schiff base zinc complex is related to the C-R bond length; the longer the bond length, the lower the thermal stability. Regarding luminescence properties, the Schiff base zinc complex exhibits tunable luminescence in the solid state, with the emission peak redshifting with increasing halogen atomic number, attributed to charge transfer transitions within and between ligands.

[0018] The Schiff base zinc complex of this invention exhibits high thermal stability, a decomposition temperature above 260°C, and tunable luminescence properties, with the emission wavelength precisely controlled by halogen substituents. The preparation method of this invention is simple, operates under mild conditions, and achieves a high yield of 67%–76%, making it suitable for large-scale production. This Schiff base zinc complex shows potential application in optoelectronic devices such as LEDs, providing a new approach for developing novel luminescent materials. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a halogen-modified Schiff base zinc complex.

[0020] Figure 2 The diagrams show the single-crystal structure, supramolecular chain, and hydrogen bond interactions of the complex. In the diagrams, a) is the single-crystal structure of the complex, b) is a schematic diagram of the supramolecular chain, and c) and d) are both hydrogen bond interaction diagrams. The diagrams also show the multidimensional framework of the crystal.

[0021] Figure 3 Thermogravimetric analysis curves of the complexes 1Cl, 2Br, and 3I show the trend of thermal stability with respect to halogens.

[0022] Figure 4 The fluorescence emission spectrum of the complex demonstrates the tunability of its luminescence properties. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] Synthesis of 5-chloro-2-hydroxybenzaldehyde 4-ethylaminothiourea: The synthesis was carried out according to the methods reported in the literature [Lo,KM,&Ng,SW(2011).Structure Reports,67(6),o1453-o1453; Hussein,MA et al.(2015).Polyhedron,85,93-103; Li,Zhao-Yang,et al.(2023).CCS Chemistry,5(2),412-422.]. 5-chloro-2-hydroxybenzaldehyde (156.0 mg, 1.0 mmol) was reacted with 4-ethyl-3-thioaminourea (119.0 mg, 1.0 mmol) under reflux in anhydrous ethanol (10.0 mL) for 3 hours to obtain 5-chloro-2-hydroxybenzaldehyde 4-ethylaminothiourea.

[0025] Synthesis of 5-bromo-2-hydroxybenzaldehyde 4-ethylaminothiourea: The same method as above was used, except that 5-chloro-2-hydroxybenzaldehyde was replaced with 5-bromo-2-hydroxybenzaldehyde (201.0 mg, 1.0 mmol) to obtain 5-bromo-2-hydroxybenzaldehyde 4-ethylaminothiourea.

[0026] Synthesis of 5-iodo-2-hydroxybenzaldehyde 4-ethylaminothiourea: The same method as above was used, except that 5-chloro-2-hydroxybenzaldehyde was replaced with 5-iodo-2-hydroxybenzaldehyde (248.0 mg, 1.0 mmol) to obtain 5-iodo-2-hydroxybenzaldehyde 4-ethylaminothiourea.

[0027] The following is a detailed description of a zinc complex modified with Schiff base, its preparation method, and its application.

[0028] Example 1: A halogen-modified Schiff base zinc complex, the preparation method of which is as follows: S1. Dissolve 0.02 mmol of 5-chloro-2-hydroxybenzaldehyde 4-ethylaminothiourea, 0.02 mmol of piperazine, and 0.02 mmol of zinc sulfate in 5 mL of a mixed solvent, which is obtained by mixing 3 mL of isopropanol and 2 mL of methanol. Add 2.5 μL of dimethylamine aqueous solution as a base to obtain a reaction system, wherein the concentration of dimethylamine in the reaction system is 3.3 mmol / L, and a mixture is obtained.

[0029] S2. The mixture was ultrasonically treated for 15 min using an ultrasonic cleaner at 200 W and 40 kHz. It was then transferred to a reaction vessel and reacted at 85 °C for 48 hours. After cooling, a yellow crystalline product was obtained, which is the halogen-modified Schiff base zinc complex, denoted as 1Cl, with a yield of 67%. The structure was confirmed by single-crystal X-ray diffraction, showing that the complex crystallizes in a triclinic crystal system. P-1 Space group.

[0030] Example 2: A halogen-modified Schiff base zinc complex, the preparation method of which is as follows: S1. Dissolve 0.02 mmol of 5-bromo-2-hydroxybenzaldehyde 4-ethylaminothiourea, 0.02 mmol of piperazine, and 0.02 mmol of zinc sulfate in 5 mL of a mixed solvent, which is obtained by mixing 3 mL of isopropanol and 2 mL of methanol. Add 2.5 μL of dimethylamine aqueous solution as a base to obtain the reaction system. The concentration of dimethylamine in the reaction system is 3.3 mmol / L, and a mixture is obtained.

[0031] S2. The mixture was ultrasonically treated for 15 minutes at 200W and 40kHz using an ultrasonic cleaner. It was then transferred to a reaction vessel and reacted at 85℃ for 48 hours. After cooling, a yellow crystalline product was obtained, which is the halogen-modified Schiff base zinc complex, denoted as 2Br, with a yield of 71%. The structure was confirmed by single-crystal X-ray diffraction, showing that the complex crystallized in a triclinic crystal system. P-1 Space group.

[0032] Example 3: A halogen-modified Schiff base zinc complex, the preparation method of which is as follows: S1. Dissolve 0.02 mmol of 5-iodo-2-hydroxybenzaldehyde 4-ethylaminothiourea, 0.02 mmol of piperazine, and 0.02 mmol of zinc sulfate in 5 mL of a mixed solvent, which is obtained by mixing 3 mL of isopropanol and 2 mL of methanol. Add 2.5 μL of dimethylamine aqueous solution as a base to obtain the reaction system. The concentration of dimethylamine in the reaction system is 3.3 mmol / L, and a mixture is obtained.

[0033] S2. The mixture was ultrasonically treated for 15 min at 200 W and 40 kHz using an ultrasonic cleaner. It was then transferred to a reaction vessel and reacted at 85 °C for 48 hours. After cooling, a yellow crystalline product was obtained, which is the halogen-modified Schiff base zinc complex, denoted as 3I, with a yield of 76%. The structure was confirmed by single-crystal X-ray diffraction, showing that the complex crystallized in a triclinic crystal system. P -1 space group.

[0034] Structural characterization X-ray single-crystal diffraction analysis showed that the structure of the Schiff base zinc complexes prepared in Examples 1-3 was characterized as follows: Figure 1 and Figure 2 As shown, all three complexes form five-coordinated zinc centers, and their crystal parameters are shown in Table 1. The complexes form one-dimensional chains via piperazine bridging and extend into three-dimensional supramolecular structures through NH···N hydrogen bonds. Bond length comparisons show that the CR bond length increases significantly with increasing halogen atomic number, with Cl: 1.742 Å, Br: 1.904 Å, and I: 2.099 Å, while the Zn coordination bond length changes only slightly, indicating the localization of the halogen effect.

[0035] Table 1 Crystal data and structural parameters of the complexes 1Cl, 2Br and 3I Thermogravimetric analysis (TGA) test Thermogravimetric analysis was performed to assess the thermal stability of the complex. The test was conducted under a nitrogen atmosphere at a heating rate of 10 °C / min. The results are as follows: Figure 3 As shown. From Figure 3 It can be seen that the Schiff base zinc complexes prepared in Examples 1-3 all exhibited high thermal stability, with no significant mass loss observed below 250℃, indicating that their frameworks are free of solvent molecules and have a dense structure. The decomposition initiation temperatures, based on the onset temperature of the first major decomposition step, showed a clear halogen-dependent trend: the decomposition initiation temperatures of complex 1Cl (C-Cl) were 283℃, 2Br (C-Br) were 276℃, and 3I (CI) were 262℃. This trend is highly correlated with the C-Cl bond lengths measured by single-crystal X-ray diffraction (C-Cl bond length 1.742 Å, C-Br bond length 1.904 Å, CI bond length 2.099 Å). Longer bond lengths indicate weaker bond strengths and lower thermal stability. Specifically, the weakening of the CI bond led to the earliest decomposition of 3I, while the strength of the C-Cl bond endowed 1Cl with optimal thermal stability. These results confirm that the thermal behavior of the complexes can be systematically controlled by halogen substituents, providing a basis for their application in high-temperature environments, such as optoelectronic device packaging. The TGA curves clearly demonstrate the decomposition process.

[0036] Fluorescence performance test Fluorescence performance tests were conducted at room temperature (25°C) in a solid state, with an excitation wavelength of 365 nm, to evaluate the luminescence properties and tunability of the complex. The results are as follows: Figure 4 As shown.

[0037] Zinc complexes exhibit single emission bands: 1Cl at 488 nm, 2Br at 498 nm, and 3I at 494 nm. This emission tunability is attributed to intraligand charge transfer (ILCT) and interligand charge transfer (LLCT) processes, rather than the involvement of the nonmetallic center, as Zn(II) is d... 10 Configuration, without MLCT or LMCT.

[0038] The non-monotonic variation in emission wavelength, such as the slight decrease in wavelength between 3I and 2Br, originates from the combined effects of electronic and steric halogens: the heavy atom iodine enhances spin-orbit coupling, shortening the Zn-S bond length from 2.3763 ​​Å in 1Cl to 2.3613 Å in 3I. Simultaneously, the large atomic radius introduces a slight spatial distortion, modulating the energy of the luminescent state. The hydrogen bond network of the complex, with a distance of approximately 3.10 Å between NH and N atoms, remains stable under halogen substitution, indicating that the luminescence modulation primarily stems from electronic perturbations rather than structural reconstruction.

[0039] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

Claims

1. A halogen-modified Schiff base zinc complex, characterized in that, It is obtained by coordinating zinc ions with halogen-substituted thiohexacarbazone Schiff base as a ligand. The halogen-substituted thio-semicarbazone Schiff base is any one of 5-chloro-2-hydroxybenzaldehyde 4-ethylaminothiourea, 5-bromo-2-hydroxybenzaldehyde 4-ethylaminothiourea, and 5-iodo-2-hydroxybenzaldehyde 4-ethylaminothiourea. The chemical formula for the halogen-modified Schiff base zinc complex is C. 11 H 13 RN4OSZn, the structural formula is shown in formula (1), where R is a halogen; Equation (1).

2. The halogen-modified Schiff base zinc complex according to claim 1, characterized in that, The halogen is any one of Cl, Br, and I.

3. A method for preparing the halogen-modified Schiff base zinc complex according to claim 2, characterized in that, Includes the following steps: Using a halogen-substituted thiohexacarbazone Schiff base as a ligand, the ligand, piperazine, and zinc salt were mixed in an equimolar ratio in a solvent system, and an aqueous dimethylamine solution was added as a base to obtain a mixture. The mixture was placed at 80℃~90℃ to undergo a coordination reaction, yielding a halogen-modified Schiff base zinc complex.

4. The preparation method according to claim 3, characterized in that, The volume ratio of the dimethylamine aqueous solution to the solvent is 1:1000~2000; the mass percentage concentration of the dimethylamine aqueous solution is 33%~40%.

5. The preparation method according to claim 3, characterized in that, The coordination reaction takes 48 to 72 hours.

6. The preparation method according to claim 3, characterized in that, The solvent system uses a mixture of isopropanol and methanol in a volume ratio of 3~4:2~3.

7. The preparation method according to claim 3, characterized in that, The zinc salt is zinc sulfate.

8. The application of the halogen-modified Schiff base zinc complex according to claim 2 in the preparation of optoelectronic devices.

9. The application according to claim 8, characterized in that, The emission peak of the optoelectronic device is located at 488nm~498nm.

10. The application according to claim 9, characterized in that, The light-emitting device includes a light-emitting diode.

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