2D perovskite compound, preparation method thereof and polychromatic long afterglow luminescence application

Abstract

A 2D perovskite compound, a preparation method thereof and a multicolor long afterglow luminescence application, adopt HOF type organic ligand, can inhibit the non-radiative transition of triplet state, so that a long afterglow compound with good performance, high phosphorescence quantum yield and stability is obtained. The halide perovskite has the characteristics of excitation-dependent fluorescence and phosphorescence, and the fluorescence and phosphorescence luminescence color can be from blue to green and from cyan to yellow. Interestingly, the sample can emit blue and yellow long afterglow after the different excitation light sources are turned off, so that multicolor visual afterglow adjustment can be realized, and applied to multicolor anti-counterfeiting. At the same time, the potential application of the material in the fields of anti-counterfeiting and encryption is shown.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of multicolor anti-counterfeiting technology, and particularly relates to a 2D perovskite compound, a preparation method thereof and a multicolor long afterglow luminescence application. BACKGROUND

[0002] Long afterglow luminescence (LAL) materials have attracted much attention due to their wide application prospects in optoelectronic devices, biological imaging, afterglow lighting, etc. So far, most of the high-efficiency inorganic LAL materials contain expensive rare metals and lanthanide elements, which hinder their further commercial applications. In order to overcome these shortcomings, low-cost and easy-to-synthesize organic materials have been further developed. However, the spin-orbit coupling (SOC) in organic molecules is usually too weak to effectively break the spin barrier of triplet-singlet transition, resulting in poor quantum yield of phosphorescent emission. Recently, organic-inorganic hybrid perovskites have become one of the most promising luminescent materials due to their environmental friendliness, superior optoelectronic performance, easy availability, etc.

[0003] Here, a typical intraligand charge transfer (ILCT) ligand is designed and synthesized. This electrically neutral ligand, on the one hand, contains abundant carbonyl groups that can be protonated and provide hydrogen bonding sites, thus co-crystallizing with metal halide polyhedrons to produce abundant intermolecular interactions. On the other hand, the sufficient N-heteroatoms and carbonyl groups in the ligand are conducive to n-p transition, realizing effective LAL. By using ILCT ligand and CdCl2 self-assembly, a two-dimensional organic-metal halide perovskite (SL-1) is carefully constructed, in which the organic part forms a HOF network through hydrogen bonding, and the inorganic metal halide forms an infinite inorganic layer. This further protects the triplet excitons, thus significantly improving the room-temperature phosphorescent efficiency of the perovskite hybrid material. Therefore, the study of HOF-type organic-inorganic hybrid perovskites has very important significance. SUMMARY

[0004] The application aims to provide a 2D perovskite compound, a preparation method thereof and a multi-color long afterglow luminescence application, SL-1 has excitation-dependent fluorescence and phosphorescence characteristics, and the fluorescence and phosphorescence colors can be from blue to green and from cyan to yellow. More interestingly, the 2D perovskite compound (hereinafter referred to as compound SL-1) can emit long afterglow with color adjustable from cyan to yellow after different excitation light sources are removed. Meanwhile, the nanoscale particles of the material prepared by grinding, ultrasonic and other methods can be uniformly compounded with polymers such as polymethyl methacrylate to prepare a stable luminescent anti-counterfeiting film to achieve the anti-counterfeiting purpose, and the technical problem of overcoming the low stability and short service life of the two-dimensional organic-inorganic hybrid perovskite is solved.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is:

[0006] An organic ligand L has a molecular formula of C30H26N4O4, belongs to a monoclinic system, and has a P21 / c space group, and has a structure as follows:

[0007]

[0008] The preparation method of the ligand L includes the following steps:

[0009] 4-hydroxypyridine and K2CO3 are added into ethanol. After stirring at 80 DEG C for 4h, 1,2,4,5-tetrakis(bromomethyl)benzene is added into the mixture. After stirring at 80 DEG C overnight, yellow precipitate is formed. The solvent is removed to obtain a light yellow ligand mixture, and the light yellow ligand mixture is washed with ether for 3 times. The mixture of the obtained light yellow ligand mixture, DMF, distilled water and CH3CN is added into a glass bottle. The mixture is sealed and placed in an oven and heated at 90 DEG C for 2 days, and then gradually cooled to room temperature at a rate of 5 DEG C / h. Finally, colorless block crystals are collected by filtration to obtain the ligand L.

[0010] Further, the molar ratio of the 4-hydroxypyridine, potassium carbonate and 1,2,4,5-tetrakis(bromomethyl)benzene is 4:2.5:1 to 4:3:1.

[0011] Preferably, the molar ratio of the 4-hydroxypyridine, potassium carbonate and 1,2,4,5-tetrakis(bromomethyl)benzene is 4:2.5:1.

[0012] Further, the use amount ratio of the ethanol and 4-hydroxypyridine is 15ml:2mmol to 20ml:2mmol.

[0013] Preferably, the use amount ratio of the ethanol and 4-hydroxypyridine is 15ml:2mmol.

[0014] Further, the use amount ratio of the DMF and the ligand L mixture is 2ml:1mmol to 4ml:1mmol.

[0015] Preferably, the mixture of DMF and ligand L is in a ratio of 4ml:1mmol.

[0016] Further, the mixture of DMF, distilled water and CH3CN is in a ratio of 1:1:1 to 1:2:2.

[0017] Preferably, the mixture of DMF, distilled water and CH3CN is in a ratio of 1:1:1.

[0018] As an alternative embodiment, the method for preparing the ligand L comprises the following steps: 4-hydroxypyridine (4mmol, 0.6g) and potassium carbonate (2.5mmol, 0.9g) are added to ethanol (30mL), after stirring at 80℃ for 4h, 1,2,4,5-tetrabromomethylbenzene (1mmol, 0.5g) is added. After stirring at 80℃ overnight, a yellow precipitate is formed. The solvent is removed to obtain a light yellow solid, which is washed with diethyl ether for 3 times. The obtained mixture of light yellow ligand, DMF (1ml), distilled water (1ml) and CH3CN (1ml) is added to a glass bottle. The mixture is sealed and placed in an oven and heated at 90℃ for 2 days, and then gradually cooled to room temperature at a rate of 5℃ / h. Finally, colorless block crystals are collected by filtration to obtain the ligand L.

[0019] A compound SL-1 with a molecular weight of 1604.06, which belongs to monoclinic system, space group P21 / c, and has a molecular formula of C30H40Cd5Cl12N4O10.

[0020] The compound SL-1 is prepared from L and cadmium chloride.

[0021] The method for preparing the compound SL-1 comprises the following steps:

[0022] S1. The cadmium chloride and the organic L are mixed in a molar ratio of 1-5:1 and put into a reaction bottle, and methanol, acetonitrile and hydrochloric acid are added to the reaction kettle in a volume ratio of 1-2:1-3:1;

[0023] S2. The sealed pressure-resistant reaction kettle is placed in an oven, and the program is set to heat for 1-2 hours, so that the temperature rises from room temperature to 100-120℃, and then the temperature is kept at this temperature for 40-60 hours, and then the temperature is cooled down for 8-12 hours;

[0024] S3. After cooling to room temperature, white block crystals are obtained, which are filtered and washed with methanol to obtain pure crystals.

[0025] Further, the molar ratio of the cadmium chloride and the L in step S1 is 5:1.

[0026] Further, the volume ratio of methanol, acetonitrile and (0.1 mol / L) hydrochloric acid in step S1 is 1:1:1.

[0027] Further, the oven program in step S2 is set to heat for 2 hours to raise the temperature from room temperature to 90℃, keep this temperature for 48 hours, and then cool down to room temperature in 10 hours.

[0028] As an alternative embodiment, the preparation method of the compound SL-1 comprises the following steps: putting 10 mg, 0.02 mmol of L and 18 mg, 0.1 mmol of cadmium chloride into a reaction bottle, then adding 1 mL of methanol, 1 mL of acetonitrile and 1 mL (0.1 mol / L) of hydrochloric acid, and slightly shaking the reaction kettle to make the mixture uniform; then putting the reaction kettle into an oven, and setting the oven program to heat for 2 hours to raise the temperature from room temperature to 90℃, keep this temperature for 48 hours, and then cool down to room temperature in 10 hours; finally filtering the obtained mixture, and washing with methanol to obtain white coordination compound SL-1 single crystal.

[0029] The present application has the following beneficial effects:

[0030] (1) The present application provides a stable spatial structure formed by using HOF type organic ligand, which inhibits non-radiative transition, thereby obtaining a long afterglow coordination compound with good performance and stability;

[0031] (3) The compound SL-1 has stable luminescent performance; has excitation-dependent fluorescence and phosphorescence characteristics, the luminescent color can be from blue to green, is easy to recycle, and has environmental friendliness;

[0032] (4) The anti-counterfeiting, encryption and other materials prepared based on the compound SL-1 have wide application range and can be reused. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The crystal structure of SL-1. a) asymmetric unit and coordination environment of metal ions; b, c) 2D structure formed by self-assembly of metal and L; d) 2D layered structure formed by hydrogen bond interaction.

[0034] Figure 2 The infrared spectrum of SL-1.

[0035] Figure 3 The PXRD spectrum of simulated and synthesized SL-1.

[0036] Figure 4 The instantaneous and delayed emission spectra of L and SL-1 at room temperature.

[0037] Figure 5 The fluorescence and phosphorescence lifetime decay curves of L and SL-1.

[0038] Figure 6 Time-resolved emission spectra of SL-1.

[0039] Figure 7 Excitation-related instantaneous and delayed emission spectra and corresponding CIE coordinates of SL-1 under ambient conditions.

[0040] Figure 8 Excitation spectra of SL-1 at 450, 490, 520 and 620 nm, respectively.

[0041] Figure 9 Instantaneous (a, b) and delayed (c, d) emission spectra of SL-1 before and after grinding of the crystal.

[0042] Figure 10 Temperature-dependent emission spectra and lifetime decay curves in the range from 300 to 77 K.

[0043] Figure 11 LAL spectra of SL-1 under removal of UV irradiation of different excitation wavelengths.

[0044] Figure 12 CIE coordinates of SL-1 under removal of UV irradiation of different excitation wavelengths.

[0045] Figure 13 LAL photographs of SL-1 under removal of UV irradiation of different excitation wavelengths.

[0046] Figure 14 Anti-counterfeiting schematic diagram of the material. DETAILED DESCRIPTION

[0047] The present application will be further described by the following description of the drawings and specific examples, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0048] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0049] Example 1 Preparation of ligand L

[0050] To a reaction flask was charged with 4-hydroxypyridine (4 mmol, 0.6 g) and potassium carbonate (2.5 mmol, 0.9 g) in ethanol (30 mL) and stirred at 80 °C for 4 h, then 1,2,4,5-tetrabromomethylbenzene (1 mmol, 0.5 g) was added. After stirring at 80 °C overnight, a yellow precipitate was formed. The solvent was removed to give a light yellow solid, which was washed with diethyl ether for 3 times. The resulting light yellow ligand mixture, DMF (1 ml), distilled water (1 ml) and CH3CN (1 ml) were added into a glass bottle. The mixture was sealed and put into an oven and heated at 90 °C for 2 days, then gradually cooled to room temperature at a rate of 5 °C / h. Finally, colorless block crystals were collected by filtration to give the ligand L.

[0051] Preparation of SL-1

[0052] Preparation of compound SL-1:

[0053] To a reaction flask was charged with L (10 mg, 0.02 mmol), cadmium chloride (18 mg, 0.1 mmol), then 1 mL of methanol and 1 mL of acetonitrile and 1 mL of 0.1 mol / L hydrochloric acid solution were added, and the reaction flask was shaken slightly to make the mixture uniform; then the reaction flask was put into an oven, and the oven program was set to heat for 2 hours to raise the temperature to 100 °C, and keep this temperature for 48 hours, then reduce to room temperature for 10 hours; finally, the resulting mixture was filtered, and washed with methanol to obtain white compound single crystals.

[0054] Crystal structure determination of SL-1

[0055] The single crystal X-ray diffraction data of SL-1 were collected on a Rigaku-Oxford SuperNova X-ray diffractometer system equipped with a Mo target at 50 kV and 0.80 mA.

[0056] The structure was solved by direct methods and refined by full-matrix least squares using the SHELXL-2014 program package. All hydrogen atoms were obtained by theoretical hydrogen addition and refined along the anisotropic direction; the relevant crystallographic data of SL-1 are shown in Table 1 below.

[0057] Table 1 Crystallographic data of compound SL-1

[0058]

[0059]

[0060]

[0061] The present application is prepared through a large number of research and exploration, and a 2D perovskite compound is prepared. The present application uses ligand L and cadmium chloride to synthesize compound SL-1 by adopting a solvothermal reaction method, and the molecular formula is: C30H40Cd5Cl12N4O10. The crystal of a suitable size is selected to carry out single crystal diffraction, and the result shows that SL-1 is crystallized in a monoclinic crystal system and belongs to a P21 / c space group. An asymmetric unit is formed by 1 / 2 protonated L, 5 / 2 Cd ions, 6 Cl ions, 2 coordinated water molecules and 1 free water molecule. In SL-1, there are three different types of Cd2+ ions, and all of them are six-coordinated, wherein Cd1 is coordinated with 1 oxygen atom and 5 chlorine ions, Cd2 is directly coordinated with six chlorine atoms, and Cd3 is coordinated with two oxygen atoms and four chlorine ions. Among them, the organic cations form a stable rigid HOF structure through intermolecular hydrogen bonding and pi-pi stacking. This stacking mode can effectively improve the rigidity of the molecule, inhibit the rotational vibration of the molecule, and further improve the luminescent performance. Further, the organic HOF layer and the inorganic halide layer are arranged in a close-packed three-dimensional framework structure. This structure significantly improves the afterglow performance of SL-1.

[0062] The infrared spectrum of SL-1 is shown as Figure 2 The phase purity is verified by powder x-ray diffraction (PXRD), and the result shows that the synthesis and simulation results are completely matched, further proving that the phase purity is good Figure 3 )。

[0063] Example 4: Photophysical properties of SL-1

[0064] In order to better understand the luminescent characteristics at room temperature, the steady-state and transient spectra of L and SL-1 are studied in the solid state Figure 4 ). The results show that the transient emission of SL-1 has a single emission peak at 450 nm, while the main emission peak of L is at 500 nm, and there is a shoulder peak emission at 470 nm, and the decay curve lifetimes are 1.20 and 4.26 ns, respectively. The delayed spectrum result shows that the emission peak at short wavelength of ligand L (1 ms) disappears, and a new emission peak appears at 500 nm. In contrast, the delayed 1 ms gating spectrum of SL-1 appears double emission peaks (490 nm and 520 nm). The decay curves give their lifetimes at different peak values as 14.83 (L: 500 nm), 35.40 (SL-1: 490 nm) and 37.10 ms (SL-1: 520 nm), respectively. The former belongs to fluorescence, and the latter can be attributed to phosphorescence. In addition, the time-resolved emission spectrum further confirms the existence of long-lifetime phosphorescence of SL-1 Figure 6 )。

[0065] Interestingly, SL-1 exhibits excitation-dependent characteristics under ambient conditions, as shown inFigure 7 As shown, SL-1 achieved tunable fluorescence from blue to cyan to green when the excitation wavelength was increased in 20 nm increments from 270 nm to 450 nm. Similarly, excitation-dependent time-gated spectra with a delay of 1 ms were collected to investigate the phosphorescence properties of the material. With decreasing excitation energy, the emission peak of SL-1 showed a redshift. Specifically, the emission peak shifted from 470 nm to 530 nm, and the CIE plot showed that SL-1 emitted cyan to yellowish-green phosphorescence under different excitations. Figure 7 Notably, when the excitation wavelength was 450 nm, the spectral shape changed significantly, with a new phosphorescence peak appearing at 620 nm. The excitation spectrum confirmed that these emission peaks originated from two triplet states. Figure 8 We hypothesize that the phosphorescence at 490 nm and 520 nm can be attributed to ligand L-induced room-temperature phosphorescence, while the emission peak at 620 nm may be due to self-trapped exciton (STE) emission resulting from the distortion of inorganic layer metal halides under ultraviolet light irradiation. This can be supported by the following photophysical properties. Figure 9 As shown, the emission spectrum shape and wavelength of the microcrystalline powder are very similar to those of the bulk crystal, except that the intensity is slightly lower, which rules out the possibility that the emission near 620 nm is related to permanent defects.

[0066] As is well known, temperature is one of the factors affecting the luminescence of MOFs. Therefore, emission spectra and time-resolved decay tests were performed between 300 and 77 K. The intensity of SL-1 decreased with increasing temperature, as shown in the figure. Figure 10 As shown, the lifetime decay curves exhibit similar changes at different temperatures. The increase in phosphorescence lifetime and luminescence intensity at lower temperatures is likely due to the suppression of triplet nonradiative transitions at low temperatures, thereby enhancing phosphorescence emission.

[0067] Benefiting from the material's long phosphorescence lifetime, SL-1 exhibits bright LAL emission after the excitation source is removed. Six representative wavelengths of 275, 311, 365, 385, 405, and 450 nm were selected as excitation sources. Figure 11 As shown in Figures 12 and 13, the changes in the LAL emission spectrum are similar to those in the phosphorescence emission spectrum. As the excitation energy decreases, the LAL color of SL-1 changes from cyan to yellow. Furthermore, the LAL can be captured using a camera when these different excitation sources are removed, demonstrating excitation-dependent color tuning of the LAL.

[0068] Example 5: Application of SL-1 Complex

[0069] like Figure 14As shown in a, the fingerprint pattern printed on A4 paper using SL-1 ink presents multicolor LAL (cyan and green) under 275 nm and 405 nm light irradiation. Impressively, the dynamic LAL color change is observed by naked eye after removing the 365 nm UV light. This also means that the password is successfully unlocked and the encrypted information is obtained. In addition, CdCL2, L and SL-1 are selectively filled into the grooves. By converting the binary code into ASCII (American Standard Code for Information Interchange) code, a dot matrix pattern (4x8) for information encryption and decryption is formed. It can be imagined that this pattern will present dynamic evolution in different delay times. As shown in Figure 14 b, if the dot is excited, the output is "1", otherwise the output is "0". Under the excitation of ultraviolet light (365 nm), all dots are blue and the output is invalid binary code. When the time is prolonged to 0.1 seconds, the new binary code can be decoded as "SUST" according to ASCII. In addition, the code appearing at 1 second is decoded as "3534" according to the decimal number. Therefore, according to ASCII and decimal, these codes should finally be decoded as "SUST 3534". At the same time, the three materials are selected to design a multi-level dynamic three-dimensional anti-counterfeiting code Figure 14 c). The anti-counterfeiting code will display "error" information under the irradiation of daylight and 365 nm ultraviolet light. When the 365 nm ultraviolet light is removed, the first level of encrypted information (EI) begins to appear. After 1 second, EI-1 continues to change to "EI-2". However, the color change ability of SL-1 as an additional variable can excite EI-3, thereby enhancing the complexity of its anti-counterfeiting. Compared with traditional anti-counterfeiting and encryption materials, SL-1 has higher flexibility and complexity, which can meet the needs of high security anti-counterfeiting field.

Claims

1. An organic ligand L, characterized in that, The ligand L is named 1,1',1'',1'''-(benzene-1,2,4,5-tetra(methylene))tetra(pyridin-4(1H)-one), and its molecular formula is: C 30 H 26 N4O4 belongs to the monoclinic crystal system, space group P21 / c, and its structure is as follows: 。 2. A compound SL-1, characterized in that, It has a molecular weight of 1604.06, belongs to the monoclinic crystal system, has a space group of P-1, and its molecular formula is C. 30 H 40 Cd5Cl 12 N4O 10 The cell parameters are: a = 10.3144 (7) Å, b = 11.4437 (8) Å, c = 12.3226 (9) Å, α = 62.626 (2)°; β = 72.073 (2)°; γ = 86.931 (2)°; The compound SL-1 is prepared using the organic ligand L and cadmium chloride as raw materials as described in claim 1, and its preparation method includes the following steps: S1. Mix cadmium chloride and organic ligand L in a molar ratio of 1 to 5:1 and add them to a reaction flask. Add methanol, acetonitrile and hydrochloric acid to the reaction vessel in a volume ratio of 1 to 2:1 to 3:

1. S2. Place the sealed pressure-resistant reactor into an oven, set the program, heat for 1 to 2 hours to raise the temperature from room temperature to 100 to 120°C, maintain this temperature for 40 to 60 hours, and then cool down for 8 to 12 hours. S3. After cooling to room temperature, white blocky crystals were obtained. The crystals were filtered and washed with methanol to obtain pure crystals.

3. The organic ligand L according to claim 1, characterized in that, The method for preparing the organic ligand L includes the following steps: Step 1: Add 4-hydroxypyridine and K2CO3 to ethanol, stir at 80°C for 4 h, then add 1,2,4,5-tetra(bromomethyl)benzene to the mixture, stir at 80°C overnight to form a pale yellow ligand mixture; Step 2: Remove the solvent to obtain a pale yellow ligand mixture, and wash it three times with ether. Add the obtained pale yellow ligand mixture, DMF, distilled water and CH3CN mixture into a glass bottle; seal the mixture and place it in an oven and heat it at 90 °C for 2 days, then gradually cool it to room temperature at a rate of 5 °C / h. Finally, collect the colorless blocky crystals by filtration to obtain ligand L.

4. An organic ligand L according to claim 3, characterized in that, The procedure includes the following steps: 4 mmol of 0.6 g of 4-hydroxypyridine and 2.5 mmol of 0.9 g of potassium carbonate were added to 30 mL of ethanol and stirred at 80 °C for 4 h. Then, 1 mmol of 0.5 g of 1,2,4,5-tetrabromomethylbenzene was added and stirred at 80 °C overnight to form a yellow precipitate. The solvent was removed to obtain a pale yellow solid, which was washed three times with diethyl ether. The resulting pale yellow ligand mixture, 1 mL of DMF, 1 mL of distilled water, and 1 mL of CH3CN were added to a glass bottle. The mixture was sealed and placed in an oven and heated at 90 °C for 2 days. Then, it was gradually cooled to room temperature at a rate of 5 °C / h. Finally, colorless blocky crystals were collected by filtration to obtain ligand L.

5. The compound SL-1 according to claim 2, characterized in that, Includes the following steps 10 mg, 0.02 mmol of L and 18 mg, 0.1 mmol of cadmium chloride were added to the reaction flask, followed by 1 mL of methanol, 1 mL of acetonitrile, and 1 mL of 0.1 mol / L hydrochloric acid. The reaction vessel was gently shaken to ensure uniform mixing. The reaction vessel was then placed in an oven and the oven program was set to heat from room temperature to 90°C for 2 hours. This temperature was maintained for 48 hours, followed by a 10-hour cooling to room temperature. Finally, the mixture was filtered and washed with methanol to obtain white single crystals of the coordination compound SL-1.

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