Metal halide-based metal-organic framework (MOFs) materials with long-lasting luminescence and white light properties with multiple color tunability

Abstract

A class of metal halide-based metal-organic frameworks (MOFs) materials with multicolor tunable long-lasting emission and white light properties were synthesized by self-assembly of 15-crown ether-5 (CE) ligands and metal halide salts (CdX2), resulting in three complexes (15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2). In the solid state, the complexes (15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2) all exhibited near-standard white light emission under 340 nm ultraviolet radiation at room temperature, with CIE coordinates of (0.28, 0.32), (0.31, 0.39), and (0.30, 0.34), respectively. Simultaneously, they exhibit excitation-dependent room-temperature phosphorescence (RTP) ranging from blue / cyan to green / yellow, with 15-5-CdCl2 and 15-5-CdBr2 exhibiting multicolor tunable and visible light luminescence (LPL) with time-resolved luminescence lifetimes as high as 1-2 seconds. Single-crystal X-ray diffraction analysis and theoretical calculations indicate that the bright LPL of 15-5-CdCl2 and 15-5-CdBr2 originates from the aggregation state induced by the 15-crown ether-5 ligand and halogen bonds. The LPL obtained in this way can be widely used in lighting and display devices, optical recording devices, biological imaging, security systems, and other fields.

Description

Technical Field

[0001] Belonging to the field of crystalline materials technology, more specifically, this invention uses metal halides (MX) as a bridge to successfully construct metal halide MOFs materials with multi-color tunable long-lasting luminescence and white light characteristics. Background Technology

[0002] LPL-based RTP materials have attracted widespread attention due to their potential applications in chemical sensing, optical recording devices, bioimaging, and security systems. It is well known that most organic molecules cannot efficiently emit RTPs due to low intersystem crossing (ISC) efficiency and weak spin-orbit coupling (SOC). MOFs have addressed this challenge. However, conventional phosphorescent MOFs based on ligand-metal or metal-ligand charge transfer mechanisms typically have photoluminescence lifetimes ranging from hundreds of microseconds (μs) to milliseconds (ms) due to their rare-earth / noble metal content. Furthermore, high cost, complex fabrication methods, and relatively low photoluminescence decay times hinder their commercialization, leading to increasing interest in developing novel types of MOF materials with highly efficient LPLs.

[0003] Coordination interactions in MOFs typically enhance the rigidity of the luminescent molecule conformation, restricting molecular motion or vibration, thereby further reducing the loss of nonradiative transitions of triplet excitons and promoting phosphorescence emission at room temperature. Efficient LPL (Liquid Phosphorescence Optimization) is usually achieved through strategies such as introducing lone pairs of electrons; introducing atoms containing heavy halogens such as F, Cl, and Br into organic molecules; hyperfine coupling; and reducing the band gap energy. Among these, halogen atoms are widely used in the field of RTP (Liquid Phosphorescence Optimization) because they can form halogen bonds with ligands, such as CH...X, CX...N, XX and CX...π, thereby suppressing nonradiative transitions of triplet excitons.

[0004] Based on this, we first constructed a complex using organometallic halides as linkers, and then established MOFs by extending the halogen bridging of inorganic components. Considering factors such as multiple coordination sites and the principle of electroneutrality, we selected the fluorescent molecule CE as a ligand and successfully synthesized a series of multicolor tunable long-lasting emission and white light-emitting metal halide-based complexes by self-assembly with MX. Summary of the Invention

[0005] The purpose of this invention is to prepare MOF materials with multicolor tunable long-lasting emission and white light properties based on metal halides. Specifically, three complexes (15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2) were prepared by self-assembly of metal halides and organic ligands. All three complexes exhibit white light emission under ultraviolet irradiation, providing long lifetimes and excitation-dependent phosphorescence emission from blue / cyan to green / yellow. In particular, 15-5-CdCl2 has the longest RTP lifetime of 0.12 s. Furthermore, at room temperature, 15-5-CdCl2 and 15-5-CdBr2 achieved LPL emission color transitions from blue to green and from green to orange. These materials have great application potential in information storage, encryption, and anti-counterfeiting fields.

[0006] The purpose of this invention is to provide a method for preparing 15-5-CdX2.

[0007] Another object of the present invention is to provide applications based on 15-5-CdCl2 and 15-5-CdBr2, specifically in the development of advanced encryption applications, and applications in display and anti-counterfeiting.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution: using CE as a ligand and CdX2 (X = Cl, Br, I) for self-assembly reaction, a MOF material composed of organic ligand and metal halide was successfully synthesized.

[0009] (1) Specifically, the preparation method of 15-5-CdX2 is characterized in that: the preparation method of 15-5-CdX2 includes the following steps:

[0010] Step 1: Add ligand CE and CdX2 (X = Cl, Br, I) to a mixed solution of CH3CN and DMF. Heat the mixture in a sealed, pressure-resistant reactor for 1–3 hours from room temperature to 90–110°C. Maintain this temperature for 24–30 hours, then cool it to room temperature for 8–12 hours. Filter the mixture and wash it with DMF solution, then dry it to obtain pure 15-5-CdX2 crystals.

[0011] Furthermore, the molar ratio of CE to CdX2 in step one is 1:1 to 3:1.

[0012] Preferably, the molar ratio of CE to CdX2 in step one is 1:1.

[0013] Furthermore, the ratio of CH3CN to DMF in step one is 1:1 to 2:1.

[0014] Preferably, the molar ratio of CH3CN to DMF in step one is 2:1.

[0015] Specifically, as an alternative implementation, the 15-5-CdX2 is prepared as follows: CE (22.1 mg, 0.1 mmol) and CdCl2 (22.8 mg, 0.1 mmol) are added to a mixed solution of CH3CN (10 mL) and DMF (5 mL), and heated in a sealed pressure-resistant reactor for 2 hours from room temperature to 100°C. This temperature is maintained for 24 hours, and then cooled to room temperature for 8 hours. The mixture is filtered and washed with DMF solution, and then dried to obtain pure 15-5-CdCl2.

[0016] (2) Specific applications of 15-5-CdCl2 and 15-5-CdBr2:

[0017] Utilizing tunable multicolor emission and excitation / time-dependent LPL may offer a promising approach for advanced data encryption and anti-counterfeiting applications in these MOF materials. Figure 5 As shown, we can define a logic gate using 15-5-CdCl2 and 15-5-CdBr2 to prepare a uniform pattern (4*8 dots). Under ultraviolet light (275 / 311 / 365nm), 15-5-CdCl2 emits cool white light, while 15-5-CdBr2 emits warm white light. After the ultraviolet light is turned off (275 / 311nm), all the dots turn cyan or green, giving a misleading "NUL" code by converting the binary code to ASCII (American Standard Code for Information Interchange). However, by directly converting the binary code to ASCII and interpreting it within a 1s (365nm flashlight) delay, it is interpreted as "LEHN" (LEHN Functional Materials Institute, School of Chemistry, Sun Yat-sen University).

[0018] Meanwhile, 15-5-CdCl2 and 15-5-CdBr2 are used as inks in handcrafted anti-counterfeiting and display applications. For example... Figure 5 As shown, "Sanchuang Liangqian" (a type of Chinese character) and Chinese knots were prepared using 15-5-CdCl2 and 15-5-CdBr2, respectively. Both materials are beige in sunlight. Under ultraviolet light irradiation at 311 or 365 nm (311 or 405 nm), the Chinese characters (Chinese knots) emit white light. When the ultraviolet light source at 311 or 365 nm (311 or 405 nm) is removed, the Chinese characters (Chinese knots) emit cyan or green (green or orange) LPL (light pulse). Therefore, by combining these materials, a clever multi-layered anti-counterfeiting / encryption process can be achieved. Figure 13 ).

[0019] Furthermore, the above-mentioned compound preparation strategies and their applications in developing encrypted applications and luminescent inks are all within the scope of protection of this invention.

[0020] The present invention has the following beneficial effects:

[0021] 1. The introduction of halide anions awakens phosphorescence in the aggregated state, realizing multicolor tunable LPL.

[0022] 2. The CE is locked in the halide layer, which provides a more rigid microenvironment that hinders molecular rotation and vibration, stabilizes the triplet exciton, and thus prolongs phosphorescence emission.

[0023] 3. The ink prepared based on the complex is safe and stable, and the encryption and decryption of information can be achieved accurately and conveniently by switching the ultraviolet irradiation. Attached Figure Description

[0024] Figure 1 This represents the crystal structure of Cl-MOFs. (Cd) 2+ a) Asymmetric units and coordination environment. b) Two-dimensional plane assembled from metal 15-crown ether-5 and metal salt. c) One-dimensional metal halide chain. d) Intramolecular halogen bonds. e) Three-dimensional framework maintained by intermolecular CH…Cl interactions.

[0025] Figure 2 The zero-dimensional crystal structure of 15-5-CdI2: Cd 2+ Coordination environment with ligands.

[0026] Figure 3 The infrared spectra of 15-5-CdCl2, 15-5-CdBr2 and 15-5-CdI2 are shown.

[0027] Figure 4 PXRD patterns of the synthesis and simulation of 15-5-CdCl2, 15-5-CdBr2 and 15-5-CdI2.

[0028] Figure 5 TGA curves for 15-5-CdCl2, 15-5-CdBr2 and 15-5-CdI2.

[0029] Figure 6 Solid-state UV-Vis absorption spectra and experimental optical band gaps of 15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2.

[0030] Figure 7 The photoluminescence (PL) characteristics of halides under solid-state conditions are shown in a, b, and c) as instantaneous and delayed excitation spectra of 15-5-CdCl₂, 15-5-CdBr₂, and 15-5-CdI₂. d) CIE coordinates of instantaneous emission at 340 nm excitation. e and f) Integration of delayed spectra and corresponding time-resolved phosphorescence decay curves (λ). ex =340nm).

[0031] Figure 8 The solid-state room temperature / low temperature decay curves of 15-5-CdCl2, 15-5-CdBr2 and 15-5-CdI2 at 440 nm (a, c, e) are shown.

[0032] Figure 9 The 15-5-CdCl2(a), 15-5-CdBr2(b), and 15-5-CdI2(c) at varying temperatures (λ) ex Solid-state emission spectrum and corresponding CIE coordinate diagram at 340 nm.

[0033] Figure 10 a) Temperature-dependent emission and temperature-dependent decay curves of 15-5-CdCl2. c) Delayed spectra of excitation from 270 to 410 nm at RT (1 ms delay). e) LPL spectra after removing different excited states at room temperature (collected after 8 ms).

[0034] Figure 11 LPL spectra of 15-5-CdCl2 after various excitation flashlights were turned off under environmental conditions.

[0035] Figure 12 LPL spectra of 15-5-CdBr2 after various excitation flashlights were turned off under environmental conditions.

[0036] Figure 13 a) A theoretical model for understanding the RTP performance of three halide complexes in the solid state based on Jablonski diagrams. b) Tiltable LPL photographs of 15-5-CdCl2 and 15-5-5-CdBr2. c) Application of logic gates. d) Anti-counterfeiting application of 15-5-CdCl2 and 15-5-CdBr2 (SL represents sunlight). Detailed implementation method:

[0037] The following examples will help to understand the present invention, but the examples do not limit the invention in any way. Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0038] Example 1: Synthesis of products at each stage

[0039] C 10 H 20 Synthesis of Cd3Cl6O5(15-5-CdCl2).

[0040] CE (22.1 mg, 0.1 mmol) and CdCl2 (68.4 mg, 0.3 mmol) were added to a mixed solution of CH3CN (10 mL) and DMF (5 mL). The mixture was heated in a sealed, pressure-resistant reactor for 2 hours, from room temperature to 100 °C, and maintained at this temperature for 24 hours. After heating, the mixture was cooled to room temperature for 8 hours. The solution was filtered, washed with DMF solution, and then dried to obtain pure 15-5-CdCl2. For 15-5-CdCl2(( Figure 4 ), IR:3481(br),2882(w),1596(w),1545(w),1462(w),1349(w),1273(w),124 2(w),1110(s),1084(s),1072(s),1035(w),939(m),857(w),814(w),543(w).

[0041] C 20 H 40 Br 12 Cd6O 10 Synthesis of (15-5-CdBr2).

[0042] CE (22.1 mg, 0.1 mmol) and CdBr2 (81.6 mg, 0.3 mmol) were added to a mixed solution of CH3CN (10 mL) and DMF (5 mL). The mixture was heated in a sealed, pressure-resistant reactor for 2 hours, from room temperature to 100 °C, and maintained at this temperature for 24 hours. After heating, the mixture was cooled to room temperature for 8 hours. The solution was filtered, washed with DMF solution, and then dried to obtain pure 15-5-CdBr2. For 15-5-CdBr2 ( Figure 4 ), IR:3493(br),2876(w),1582(w),1482(w),1462(w),1349(w),1280(w),125 5(w),1117(s),1091(s),1072(s),1046(w),933(m),852(w),814(w),529(w).

[0043] C 12 H 23 Synthesis of Cd2I4NO5(15-5-CdI2).

[0044] CE (22.1 mg, 0.1 mmol) and CdI2 (109.8 mg, 0.3 mmol) were added to a mixed solution of CH3CN (10 mL) and DMF (5 mL). The mixture was heated in a sealed, pressure-resistant reactor for 2 hours, from room temperature to 100 °C, and maintained at this temperature for 24 hours. After heating, the mixture was cooled to room temperature for 8 hours. The solution was filtered, washed with DMF solution, and then dried to obtain pure 15-5-CdI2. For 15-5-CdI2 (… Figure 4 ), IR:3563(br),2882(w),1607(w),1531(w),1451(w),1349(w),1300(w),124 2(w),1128(s),1117(s),1084(s),1035(w),946(m),857(m),814(w),523(w).

[0045] Crystallographic data related to 15-5-CdCl2, 15-5-CdBr2 and 15-5-CdI2 in Example 2.

[0046] Crystal data and structural refinement parameters for 15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2 are shown in Table 1.

[0047]

[0048]

[0049] Table 1

[0050] Structural analysis of 15-5-CdCl2, 15-5-CdBr2 and 15-5-CdI2 in Example 3

[0051] like Figure 1 As shown in figure a, 15-5-CdCl2 crystallizes in a monomeric clinoclinic system, belonging to space group P21. It consists of three crystallographically independent Cd(II) ions, one CE molecule, and six Cl... - The ions reside in the asymmetric unit of 15-5-CdCl2. Simultaneously, we can observe that the three Cd(II) ions exhibit two coordination configurations, with Cd2 and Cd3 giving a distorted trigonal-bipyramidal geometry of CdCl5, where all coordinating atoms originate from Cl. - The ion, Cd1, exhibits a pentagonal-bipyramidal CdO5Cl2 geometry, with coordinating atoms derived from the five O atoms of the CE atom located in the central plane and the two Cl atoms occupying the vertices. - Ions. It is well known that atoms containing lone pairs of electrons can form non-covalent interactions between molecules and within molecules. In particular, halogen atoms can act as halogen bridges to connect metal ions, forming multifunctional structures, and can also form halogen bonds to stabilize structures. Figure 1 (b, 1c) At the same time, halogen bonds harden the CE molecule, further stabilizing its structure. Figure 1 d). The structure of 15-5-CdBr2 is similar to that of 15-5-CdCl2, also exhibiting a two-dimensional framework structure. However, due to the increased radius of the halogen atoms and the disorder of the CE molecules, it crystallizes in the monoclinic crystal system in space group P21 / n. The asymmetric unit consists of 1 / 2 CE molecules, 3 / 2 Cd(II) ions, and 3 Cl atoms. - ion( Figure 2 The structure consists of 15-5-CdI₂, which exhibits only an 0D structure due to its large atomic radius. Furthermore, intramolecular and intermolecular halogen bonds connect these 0D structures, resulting in a three-dimensional framework. Figure 2 The infrared spectra of all coordination compounds are as follows: Figure 3 As shown. The phase purity of all complexes was verified by PXRD, and the results showed that the synthesis and simulation results were in perfect agreement, further demonstrating their good phase purity. Figure 4 TGA results showed that all complexes were stable up to 220°C. Above this temperature, CE gradually dissolved, accompanied by framework collapse. Figure 5 The spatial configurations of all coordination compounds were determined by X-ray single-crystal diffraction.

[0052] Example 4: Photophysical Analysis of 15-5-CdCl2, 15-5-CdBr2 and 15-5-CdI2

[0053] The PL properties of three complexes, 15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2, were analyzed. Solid-state UV-Vis absorption spectroscopy showed that the absorption wavelength range was 200–350 nm, exhibiting a redshift with increasing halogen atom concentration. Figure 6 Under room temperature excitation at 340 nm, the CIE coordinates of 15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2 are (0.28, 0.32), (0.31, 0.39), and (0.30, 0.34), respectively. Figure 7 d), which is very close to the CIE coordinates (0.33, 0.33) of ideal white light emission.

[0054] The room-temperature quantum efficiencies of 15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2 are 1.0%, 2.2%, and 1.7%, respectively. In transient PL measurements, both at room temperature and 77 K... Figure 8The decay lifetimes of a, c, and e at 400 nm are on the order of nanoseconds (2-3 ns), which is attributed to ligand-based fluorescence emission around 400 nm. For the lifetime at 540 nm, the values ​​of the three complexes differ significantly, illustrating the principle that phosphorescence lifetime decreases with increasing halogen atomic mass. Figure 7 f). However, at 300 K, the lifetimes of 15-5-CdCl2, 15-5-CdBr2, and 15-5-CdI2 were 117, 28, and 10 ms, respectively. With decreasing temperature, the phosphorescence lifetime and emission intensity of the three complexes gradually increased (f). Figure 8 and Figure 9 Because the triplet state is more sensitive to temperature, its non-radiative inactivation is significantly reduced at low temperatures. Taking 15-5-CdCl2 as an example, after cooling, the phosphorescence peak increases more rapidly, resulting in a slight redshift in the overall emission. Figure 10 a). The CIE coordinates between 300 and 77 K are essentially in the white light region. At 77 K, the lifetime of 15-5-CdCl2 reaches 267 ms. Figure 10 b).

[0055] We selected wavelengths of 275 nm, 311 nm, 365 nm, 385 nm, and 405 nm as excitation sources and collected LPL spectra. The trend of LPL spectrum variation is consistent with that of variable excitation time-gated spectrum, exhibiting a redshift with increasing excitation wavelength. Figure 10 e, 10f). Since the lifetime of 15-5-CdI2 is too short to be observed in RT, LPL was not collected. For 15-5-CdCl2, the color of LPL is cyan under 275 nm excitation; it is green when excited at 311 nm, and gradually stabilizes in the yellow region as the wavelength increases. Figure 11 ). When 15-5-CdBr2 is excited at 275 nm, the LPL color is green; when excited at 311 / 365 nm, it is yellowish-green, and gradually stabilizes in the orange region as the wavelength increases. Figure 12 Under 365nm excitation, the LPL times observed by the naked eye were 2s and 1s, respectively, indicating the best performance. Therefore, 15-5-CdCl2 exhibits the best LPL.

Claims

1. A metal halide-based metal-organic framework (MOF) material with multi-color tunable long-lasting luminescence and white light properties, characterized in that, The material is a coordination compound 15-crown-5-ether-cadmium halide, 15-5-CdX2, where X=Br. The molecular formula of the coordination compound is [insert molecular formula here]. The molecular weight is 2069.81, and the unit cell parameter is: a is b is c is α is ;β is γ is The method for preparing the coordination compound includes the following steps: The ligand 15-crown-5 ether and CdX2 were added to a mixed solution of CH3CN and DMF. The mixture was heated in a sealed pressure-resistant reactor for 1–3 hours from room temperature to 90–110 °C. This temperature was maintained for 24–30 hours, and then cooled to room temperature for 8–12 hours. After filtration, the mixture was washed with DMF solution and dried to obtain pure 15-5-CdX2 crystals.

2. The metal halide-based metal-organic framework (MOF) material with multi-color tunable long-lasting luminescence and white light characteristics according to claim 1, characterized in that, The molar ratio of the ligand 15-crown-5 ether to CdX2 is 1:1 to 3:

1.

3. The metal halide-based metal-organic framework (MOF) material with multi-color tunable long-lasting luminescence and white light characteristics according to claim 1, characterized in that, The volume ratio of CH3CN to DMF is 1:1 to 2:1.

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