Double-channel long-lasting luminescent material of secondary structure unit and organic ligand in metal-organic framework

Abstract

The invention relates to a dual-channel long-lasting luminescent material of a secondary structural unit and an organic ligand in a metal-organic framework, which is characterized in that the TPP organic ligand with a characteristic of charge transfer between ligands and PbX2 (X = Cl, Br) are self-assembled to obtain PJJ-1 of pure Cl and PJJ-2 of doped Br. In a solid state, the two MOFs both display broadband emission, and after the excitation wavelength is changed, adjustable fluorescence and phosphorescence from blue to green and from cyan to orange are generated. Wherein the PJJ-1 obtains cold white light emission under excitation of 380 nm. And after the excitation light source is removed, a toned LPL from cyan to yellow / orange is observed. Monocrystal X-ray diffraction, spectral analysis and theoretical calculation show that multicolor phosphorescence of the two MOFs and LPL are caused by aggregation of ligands, charge transfer between the ligands and halogen and a self-trapping exciton (STE) channel of distorted SBUs. A basic design strategy is provided for realizing the dual-channel multi-color adjustable LPL in the MOF, and an effective way is provided for developing new platforms of multi-color display, ink-jet printers and other potential applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystalline materials, and relates to a dual-channel long persistent luminescence material of secondary structure units and organic ligands in metal-organic frameworks. More specifically, the present invention studies a novel organic ligand with ILCT characteristics, and self-assembles it with PbX2 (X = Cl, Br), successfully realizing multicolor tunable LPL caused by aggregated ligands, charge transfer between ligands and halogens, and STE channels of distorted SBUs. Background Art

[0002] Due to their large Stokes shift and long exciton migration distance, LPL MOFs show great potential applications in fields such as anti-counterfeiting, data encryption, and bioimaging. However, the LPL of existing MOFs mainly originates from the triplet excited state of the organic ligand center, even in the case of multiple triplets. SBUs only participate in the heavy atom effect and coordination interaction, while SBUs themselves have weak or no luminescence performance. Therefore, combining the luminescence of SBUs is an important strategy to achieve color-tunable LPL.

[0003] STE is an effective way to achieve the luminescence of SBUs. STE emission usually occurs in a strong electron-phonon coupling system, in which the excited electrons and holes cause elastic distortion of the lattice in their surrounding environment. In this case, the excited state electrons and holes with energy lower than free carriers are rapidly captured by the self-trapped states caused by lattice distortion, and finally STE emission is generated through the transition process. In recent years, organic-inorganic hybrid 0D metal halide optoelectronic materials with STE emission have been widely used due to their advantages such as broadband emission, large Stokes shift, and high quantum yield (QY).

[0004] Based on this, a typical ILCT-type organic ligand TPP was preliminarily designed and synthesized. On the one hand, this compound lacks active hydrogen protons in the organic crystal state and has multiple coordination sites, which is beneficial for metal halides to be incorporated into MOFs as SBUs. On the other hand, it contains heteroatoms and 4-hydroxypyridine phosphorescent groups, which is beneficial for generating LPL. Using this organic ligand and PbX2 (X = Cl, Br) for self-assembly, two MOFs, PJJ-1 containing pure Cl anions and PJJ-2 doped with Br anions, were constructed. Summary of the Invention

[0005] To overcome the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a dual-channel long persistent luminescence material of secondary building units and organic ligands in metal-organic frameworks, incorporating metal halides as SBUs into MOFs to achieve dual-channel LPL of organic ligands and inorganic SBUs in MOFs. Specifically, two kinds of MOFs, namely PJJ-1 containing pure Cl anions and PJJ-2 doped with Br anions, are constructed. Under 380 nm excitation, both kinds of MOFs exhibit broadband emission characteristics. PJJ-1 shows blue luminescence, while PJJ-2 shows unique cold white luminescence. Due to the SBUs of metal halides in the two kinds of MOFs, they exhibit dual-channel luminescence of TPP molecules and SBUs. By changing the excited state, various phosphorescent colors from cyan to orange can be achieved. In addition, due to their long lifetimes, they exhibit LPL from cyan to orange after removing the light source. These materials have great application potential in the fields of multicolor display, anti-counterfeiting encryption, etc.

[0006] The object of the present invention is to provide a preparation method of PJJ-1 and PJJ-2.

[0007] Another object of the present invention is to provide applications based on PJJ-1 and PJJ-2, specifically in the development of advanced encryption applications, as well as applications in display and anti-counterfeiting.

[0008] The above object of the present invention is achieved by the following technical solution: Using TPP as a ligand and PbX2 (X = Cl, Br) for self-assembly reaction, an MOF material composed of a composite of an organic ligand and a metal halide is successfully synthesized.

[0009] Specifically, the preparation method of PJJ-1 and PJJ-2 is characterized in that: the preparation method of PJJ-1 and PJJ-2 includes the following steps:

[0010] Step 1: Put the ligand TPP and PbCl2 into a mixed solution of DMF and CH3OH, heat and raise the temperature in a sealed pressure-resistant reaction kettle for 1 to 3 hours from room temperature to 90 to 110 °C, keep this temperature and heat for 24 to 30 h, and then cool to room temperature in 8 to 12 h; after filtration, wash with a DMF solution and dry to obtain pure PJJ-1 crystals.

[0011] Furthermore, the molar ratio of TPP to PbCl2 in Step 1 is 1:3 to 1:4. Among them, preferably, the molar ratio of TPP to PbCl2 in Step 1 is 1:3.

[0012] Furthermore, the dosage ratio of CH3OH to DMF in Step 1 is 1:1 to 2:1.

[0013] Among them, preferably, the molar ratio of CH3OH to DMF in Step 1 is 2:1.

[0014] Step 2: Put the ligand TPP and PbX2 (X = Cl, Br) into the mixed solution of DMF and CH3OH, heat and raise the temperature in a sealed pressure-resistant reactor for 1 - 3 hours from room temperature to 90 - 110 °C, keep this temperature and heat for 24 - 30 h, then cool to room temperature in 8 - 12 h; after filtration, wash with DMF solution and dry to obtain pure PJJ-2 crystals.

[0015] Furthermore, the molar ratio of TPP, PbCl2 and PbBr2 in Step 2 is 1:2:2 - 1:3:3.

[0016] Among them, preferably, the molar ratio of TPP, PbCl2 and PbBr2 in Step 2 is 1:2:2.

[0017] Furthermore, the dosage ratio of DMF to CH3OH in Step 2 is 1:1 - 2:1.

[0018] Among them, preferably, the molar ratio of DMF to CH3OH in Step 2 is 2:1.

[0019] Specific applications of the PJJ-1 and PJJ-2:

[0020] A special printing ink, by obtaining its excellent photophysical properties through the following method, prompts us to further develop its applications in different scenarios. The first step is to combine PJJ-1 with a polymer to make a printable ink, and then load it into an ink cartridge for easy printing of various anti-counterfeiting patterns such as flowers. Under ultraviolet excitation, due to the interference of the blue background fluorescence of the printed paper, the pattern cannot be recognized. However, after removing the ultraviolet light at 365 nm and 385 nm, the green or cyan LPL pattern can be clearly displayed.

[0021] Color anti-counterfeiting inkjet printer.

[0022] Meanwhile, the multi-color LPL characteristics of PJJ-1 and PJJ-2 are combined to encrypt the information in Morse code. When observed under daylight and 385 nm ultraviolet light, the Morse code shows the error code "ERROR-a". However, after removing the 385 nm ultraviolet light, the cyan LPL of PJJ-1 and the green LPL of PJJ-2 can decrypt the code into "SUST". Subsequently, since PJJ-2 shows slightly stronger performance than PJJ-1, PJJ-1 gradually disappears after 2 seconds, allowing further decoding of the letter into the final code "T" (True), thus enabling multi-step encryption.

[0023] Dynamic message encryption display based on Morse code is as Figure 17 shown.

[0024] In addition, the change of LPL at low temperature provides an idea for a color LPL display. Thus, we designed a display unit mainly composed of a cooling plate, ultraviolet lamp beads, a controller, and a sample layer, which is integrated with a control switch to form a color LPL display that displays in a 3×3 matrix. As Figure 18 shown, by controlling the temperature, the display can show specific LPL colors from yellow to blue at the corresponding temperature. Colorful LPL patterns with different visual effects are presented dynamically over time, including time-, temperature-, and excitation-related. This opens up the possibility of manufacturing display and recording devices with high spatial resolution and data capacity.

[0025] The color afterglow display unit is as Figure 19 shown.

[0026] The present invention has the following advantages:

[0027] 1. It demonstrates dual-channel luminescence characteristics from organic ligand molecules and SBUs. This dual-channel luminescence characteristic generates multiple excited states, and various phosphorescent colors from cyan to orange can be obtained by changing the excitation wavelength.

[0028] 2. It has the characteristic of long lifetime and still shows LPL from cyan to orange after removing the light source. The realization of this luminescence characteristic is the result of the synergistic effect of the TPP ligand, halogen-bond-induced aggregation state, and self-trapped excitons caused by the structural distortion of SBUs under ultraviolet light.

[0029] 3. The design and synthesis of this kind of MOFs provide a new way to achieve long persistent luminescence and have potential application prospects.

[0030] 4. Using the organic ligand {[1,1',1'',1'''-(benzene-1,2,4,5-tetramethylene)tetrakis(pyridin-4(1H)-one)], TPP} with ligand-to-ligand charge transfer (ILCT) properties, and further self-assembling it with PbX2 (X = Cl, Br), pure Cl-containing PJJ-1 and Br-doped PJJ-2 are obtained respectively. In the solid state, both of these two MOFs show broadband emission, and after changing the excitation wavelength, tunable fluorescence and phosphorescence from blue to green and from cyan to orange are generated. Among them, PJJ-1 obtains cold white light emission under 380 nm excitation. And after removing the excitation light source, color-tuned LPL from cyan to yellow / orange is observed. Single-crystal X-ray diffraction, spectral analysis and theoretical calculations show that the multicolor phosphorescence and LPL of the two MOFs are caused by ligand aggregation, charge transfer between the ligand and the halogen, and self-trapped exciton (STE) channels of distorted SBUs. This study not only provides a basic design strategy for realizing dual-channel multicolor tunable LPL in MOFs, but also provides an effective way for developing new platforms for multicolor displays, inkjet printers and other potential applications. Description of the Drawings

[0031] Figure 1 IR spectra of TPP, PJJ-1 and PJJ-2.

[0032] Figure 2 PXRD of PJJ-1 and PJJ-2.

[0033] Figure 3 TG diagrams of PJJ-1 and PJJ-2.

[0034] Figure 4 Asymmetric unit of PJJ-2.

[0035] Figure 5 3D framework formed by PJJ-1 through assembling 2D HOF and 2D CP

[0036] Figure 6 Intermolecular halogen bond interactions of PJJ-1.

[0037] Figure 7 Emission spectra and decay curves of TPP in 1.0 × 10 -5 mol / L solution and solid.

[0038] Figure 8 Concentration-dependent photoluminescence of TPP in THF-H2O mixtures with different water contents (0% - 100%).

[0039] Figure 9 Transient and delayed (1 ms) emission spectra of TPP and PJJ-1-2.

[0040] Figure 10 CIE coordinates for the transient and delayed spectra of TPP and PJJ-1-2.

[0041] Figure 11 Time-resolved emission spectra of PJJ-1 at different delay times (excitation wavelengths are 320, 380, and 450 nm respectively).

[0042] Figure 12 Time-resolved emission spectra of PJJ-2 at different delay times (excitation wavelengths are 320, 380, and 450 nm respectively).

[0043] Figure 13 Peak-separated deconvolution time-gated spectra of PJJ-1 and PJJ-2.

[0044] Figure 14 Fluorescence and phosphorescence lifetime decay curves of different emission peaks of PJJ-1 and PJJ-2.

[0045] Figure 15 Time-gated spectrum of TPP in the solid state.

[0046] Figure 16 LPL maps of PJJ-1 and PJJ-2 at 311, 365, 385, 405, 450 nm after removing the ultraviolet light source (room temperature and 77 K).

[0047] Figure 17 Color anti-counterfeiting inkjet printer.

[0048] Figure 18 Dynamic information encryption display based on Morse code.

[0049] Figure 19 Color afterglow display unit. Detailed implementation manners

[0050] The following embodiments will help to understand the present invention, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents and materials used in the following embodiments are all commercially available.

[0051] Embodiment 1

[0052] Synthesis of products in each stage

[0053] Synthesis of C92H94Cl22N12O15Pb8 (PJJ-1):

[0054] The ligand TPP and PbCl2 were added into the mixed solution of DMF and CH3OH, and the temperature was raised from room temperature to 90-110 °C in a sealed pressure-resistant reaction kettle by heating for 1-3 hours. After maintaining this temperature for heating for 24-30 h, it was cooled to room temperature in 8-12 h; after filtration, it was washed with DMF solution and dried to obtain pure PJJ-1 crystals. For PJJ-1 ( Figure 1 ), IR: 3593 (w), 3126(w), 3043 (w), 2935 (w), 2827 (w), 2770 (w), 2712 (w), 2655 (w), 1926 (w),1714 (w), 1642 (s), 1517 (w), 1448 (w), 1365 (w), 1322 (w), 1197 (m), 1136(w), 1010 (w), 967 (w), 848 (m), 773 (w), 640 (w), 579 (w), 539 (w).

[0055] Synthesis of C92H94Br8Cl14N12O15Pb8 (PJJ-2):

[0056] The ligand TPP and PbX2 (X = Cl, Br) were added into the mixed solution of DMF and CH3OH, and the temperature was raised from room temperature to 90-110 °C in a sealed pressure-resistant reaction kettle by heating for 1-3 hours. After maintaining this temperature for heating for 24-30 h, it was cooled to room temperature in 8-12 h; after filtration, it was washed with DMF solution and dried to obtain pure PJJ-2 crystals. For PJJ-2 ( Figure 1 ), IR: 3442 (w),2820 (w), 2353 (w), 2020 (w), 1642 (s), 1599 (m), 1556 (w), 1448 (w), 1380(w),1348 (w), 1197 (m), 1147 (w), 1017 (w), 960 (w), 852 (m), 780 (w), 723(w), 658 (w), 568 (w), 532 (w).

[0057] Example 2 Crystallographic data of TPP, PJJ-1 and PJJ-2.

[0058] The crystal data and structure refinement parameters of TPP, PJJ-1 and PJJ-2 are shown in Table 1

[0059] Table 1 Crystal data and structure refinement for L, PJJ-1, PJJ-2.

[0060] Example 3 Structural Analysis of PJJ-1 and PJJ-2

[0061] The X-ray diffraction peaks of the synthesized samples were in good agreement with the simulated peaks of the single-crystal diffraction data, demonstrating good phase purity of the two MOFs ( Figure 2 ). The thermogravimetric analysis curves showed that these two MOFs remained stable at 300 °C ( Figure 3 ). The X-ray single diffraction results showed that TPP crystallized in the monoclinic space group P21 / c, while the two MOFs both crystallized in the triclinic system, belonging to the P-1 space group. These results are summarized in Table 1. The asymmetric unit of PJJ-1 consists of one semi-protonated H2TPP, 4 Pb(II) ions, 11 chloride ions, 1 methanol molecule and half a water molecule. It is worth noting that there are four metal centers in PJJ-1, all of which are six-coordinated, showing a distorted octahedral geometry. Among them, Pb2 is surrounded by 5 Cl ions and 1 O atom, and Pb1, Pb3 and Pb4 are coordinated by 6 Cl ions. As expected, PJJ-2 has the same structure as PJJ-1, except that four Cl ions are replaced by four Br ions in the asymmetric unit ( Figure 4 ). It is worth noting that the presence of metal halides can generate various halogen bonds. On the one hand, this enables the effective combination of 2D CP and 2D HOF to form an alternately arranged 3D framework structure ( Figure 5 ). On the other hand, they are beneficial to the luminescence of the material by restricting the vibration and rotation of the HOF layer, effectively protecting the triplet excitons ( Figure 6 ).

[0062] Example 4 Photophysical Analysis of PJJ-1 and PJJ-2

[0063] After purification, the photophysical properties of TPP were studied. As Figure 7 shown, upon excitation at 360 nm, TPP exhibited a blue instantaneous emission peak at 450 nm in CH3CN. A short lifetime of 3.35 ns was found at 450 nm, which can be attributed to molecule-based fluorescence. However, the fluorescence peak shifted from 450 nm to 485 nm, and the lifetime in the solid state was 3.79 ns. The results showed that TPP exhibited typical aggregation-induced emission characteristics, which were further confirmed by the concentration-dependent room-temperature luminescence signal intensity in solution. As Figure 8 shown, with the increase in the content of THF, the emission intensity also increased. When the ratio exceeded 30%, the emission intensity gradually decreased due to the solid precipitation of TPP. The results showed that TPP had aggregation-induced phosphorescence emission.

[0064] After being assembled into MOF, different emission peaks were observed in the steady-state photoluminescence spectrum. When the excitation wavelength was 380 nm, both PJJ-1 and PJJ-2 showed blue broadband double-peak excitation emission, with peaks around 450 and 500 nm up to 800 nm. Compared with TPP, the transient emission peaks of the two MOFs were blue-shifted, which can be attributed to the influence of metal halide coordination. After replacing part of the Cl ions with Br ions to obtain PJJ-2, the transient emission peak was further blue-shifted. The time-gated TG spectra (delay 1 ms) of the two MOFs were further measured to clarify the attribution of various emission peaks. As Figure 9 shown, the peak near 450 nm disappeared, while the emission peak near 508 nm still existed. New emission peaks appeared at 533 and 620 nm for PJJ-1, and a more obvious emission peak appeared at 615 nm for PJJ-2. And the delayed spectra of PJJ-1 and PJJ-2 both showed warm white emission, with CIE color coordinates of (0.35, 0.46) and (0.31, 0.46) ( Figure 10 ). The time-resolved emission spectrum (TRES) of PJJ-1 further confirmed the existence of multiple triplet excited states ( Figure 11 and Figure 12 ). Excitation wavelengths of 320, 380, and 450 nm were selected for optical matching respectively. The results showed that when irradiated at 320 and 380 nm wavelengths, the peak near 500 nm appeared significantly. However, when excited at 450 nm, two peaks appeared simultaneously at 530 and 615 nm before the delay time of 30 ms. After that, only the peak at 530 nm remained. The time-resolved PL decay curves were further measured to identify the attributes of each emission peak. First, the emission peaks of the spectra of PJJ-1 and PJJ-2 were deconvoluted ( Figure 13 ). Obviously, the lifetimes of the high-energy emission peaks near 450 nm for PJJ-1 and PJJ-2 were 2.2 and 2.5 ns respectively, which can be attributed to the fluorescence centered on TPP. However, the three emission peaks of PJJ-1 at 500, 533, and 620 nm showed longer luminescence lifetimes, with decay lifetimes of 28.25, 27.85, and 23.98 ms respectively ( Figure 14 ).

[0065] The phosphorescence peaks showed obvious decay attributes, indicating different sources of triplet excited states. The peak around 500 nm in PJJ-1 (referred to as P1) is the phosphorescence from TPP, which matches the phosphorescence position of pure TPP ( Figure 15). The peak around 530 nm (referred to as P2) is assigned to the aggregated phosphorescence involving halogens. However, another peak at 620 nm can be attributed to the self-trapped exciton emission caused by the distortion of the SBU of the MOF under ultraviolet irradiation (defined as P STE ). Subsequently, considering the sensitivity of the mid-gap states of surface defects in some semiconductor materials to the broadband emission intensity, the emission spectra between the crystals and microcrystals of these two MOFs were analyzed. As Figure 16 shown, the spectral shape and wavelength of the microcrystalline powder are very similar to those of the large single crystal, except that the emission intensity is slightly reduced, indicating that the low-energy band emission near 620 nm is not related to permanent defects.

[0066] Furthermore, LPL images and spectra were collected. The dual-channel phosphorescence adjusts its relative intensity by changing the excitation wavelength, thus providing a way to adjust the LPL color ( Figure 16 ). Five representative excitation light sources of 311, 365, 385, 405, and 450 nm were selected. At room temperature, after removing the ultraviolet light of 311, 365, 385, and 405 nm, both MOFs showed cyan and green LPLs at RT. Yellow-white LPL was obtained after turning off the 450 nm irradiation source. At 77 K, blue LPL was detected after turning off the 311 nm ultraviolet light. Cyan LPL was observed after removing the ultraviolet light of 365, 385, and 405 nm. While after turning off the 450 nm low-energy excitation source, the LPL showed yellow and orange.

Claims

1. A dual-channel long-lasting luminescent material of a secondary structural unit and an organic ligand in a metal-organic framework, characterized in that: It includes two compounds PJJ-1 and PJJ-2. The molecular formula of PJJ-1 is: C 92 H 94 Cl 22 N 12 O 15 The molecular formula of Pb8 and PJJ-2 is C 92 H 94 Br8Cl 14 N 12 O 15 Pb8, molecular weights are 4045.21 and 4400.89 respectively, PJJ-1 and PJJ-2 belong to the triclinic system, and the space group is P-1.

2. The dual-channel long-lasting luminescent material of a secondary structural unit and an organic ligand in a metal-organic framework according to claim 1, characterized in that: The preparation method of the two coordination compounds PJJ-1 and PJJ-2 uses TPP as a ligand and PbX2 (X=Cl, Br) for self-assembly, and successfully synthesizes a MOFs material composited with an organic ligand and a metal halide.

3. The method for preparing a dual-channel long-lasting luminescent material of a secondary structural unit and an organic ligand in a metal-organic framework according to claim 2, characterized in that: The preparation method comprises the following steps: ； Step 1: Put the ligand TPP and PbCl2 into a mixed solution of DMF and CH3OH, and heat it in a sealed pressure reactor from room temperature to 90-110°C for 1-3 hours. o C, keep this temperature for 24 to 30 hours, then cool to room temperature for 8 to 12 hours; filter, wash with DMF solution and dry to obtain pure PJJ-1 crystals; Step 2: Place the ligand TPP and PbX2 (X = Cl, Br) into a mixed solution of DMF and CH3OH, and heat in a sealed pressure reactor for 1 to 3 hours from room temperature to 90 to 110 o C, keep this temperature for 24 to 30 hours, then cool to room temperature for 8 to 12 hours; filter, wash with DMF solution and dry to obtain pure PJJ-2 crystals.

4. The method for preparing a dual-channel long-lasting luminescent material of a secondary structural unit and an organic ligand in a metal-organic framework according to claim 2, characterized in that: The molar ratio of TPP to PbCl2 in step 1 is 1:3 to 1:4, and the molar ratio of CH3CN to DMF in step 1 is 1:1 to 2:

1.

5. The method for preparing a dual-channel long-lasting luminescent material of a secondary structural unit and an organic ligand in a metal-organic framework according to claim 2, characterized in that: The molar ratio of TPP, PbCl2 and PbBr2 in step 2 is 1:2:2 to 1:3:3, and the molar ratio of DMF to CH3OH in step 1 is 1:1 to 2:1.

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