CN113024752B - Preparation method and application of pure organic undoped polymer room temperature phosphorescent material - Google Patents
Preparation method and application of pure organic undoped polymer room temperature phosphorescent material Download PDFInfo
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Abstract
The invention relates to a preparation method and application of a pure organic undoped polymer room temperature phosphorescent material. The method effectively overcomes the defects of complex synthesis, limited variety, high price, poor stability, high biotoxicity, difficult adjustment of phosphorescence performance and the like of the conventional room temperature phosphorescence material, has the characteristics of low cost, high yield, batch production, simple operation and simple and convenient processing and film forming, can obtain linear condensation polymers with different polymerization degrees by adjusting the feeding proportion of the copolymer monomer and the copolycondensation reaction time, and simultaneously realizes the adjustment of room temperature phosphorescence emission life and wavelength. The polycondensate prepared by the invention has adjustable room-temperature phosphorescence emission life and wavelength, shows good stability and excitation wavelength dependence, and has huge application potential in the fields of anti-counterfeiting and information encryption.
Description
Technical Field
The invention relates to the technical field of organic luminescent materials, in particular to a preparation method and application of a pure organic non-doped polymer room-temperature phosphorescent material.
Background
In recent years, room temperature phosphorescent materials with ultra-long emission life are successfully applied to a plurality of fields such as information storage, optical anti-counterfeiting, biological imaging and chemical sensing, and have attracted extensive research interest. The traditional inorganic room temperature phosphorescent material mainly relies on the charge trapping effect of impurities, crystal defects or doped ions and the like to realize long afterglow, and is prepared by high temperature methods such as a high temperature solid phase method, a sol-gel method, combustion and the like. Compared with inorganic materials, the pure organic room temperature phosphorescent material without heavy metal elements has obvious development advantages due to the advantages of simple synthesis, easily obtained raw materials, lower cost, easy modification and regulation, good biocompatibility and the like.
Pure organic room temperature phosphorescent materials can be generally divided into organic micromolecules and organic polymer room temperature phosphorescent materials according to the difference of the molecular weight of the materials. Although the development of pure organic small molecule room temperature phosphorescent materials is very rapid, there are still some problems which hinder the development of their applications. Specifically, the organic small molecule materials reported at present mainly realize long-life room-temperature phosphorescence through crystal engineering, hydrogen bonding self-assembly, heavy atom effect and other strategies. Crystal engineering, hydrogen bonding and self-assembly effectively inhibit a non-radiative transition process by forming a rigid environment, and further promote phosphorescence emission; the heavy atom effect is to effectively enhance the intersystem crossing effect through the action of high nuclear charge of halogen atoms and obtain a large amount of triplet excitons so as to improve the phosphorescence efficiency. However, the conditions for the preparation or formation of crystals, hydrogen bonds and self-assemblies are harsh, especially for some molecules with complex structures. Furthermore, organic crystalline materials suffer from disadvantages such as poor processability, poor flexibility, susceptibility to damage during use, and the like. Secondly, heavy atoms are extremely harmful to human bodies, and the application of the room temperature phosphorescent material in the biological field is limited. In contrast, polymer materials are popular because of their advantages of excellent mechanical properties, good processability, easy chemical modification, and low cost.
Depending on the material composition, polymer-based room temperature phosphorescent materials can be subdivided into doped and undoped systems. The key of the two methods for realizing long-life room-temperature phosphorescent emission lies in that a rigid network environment is constructed by utilizing covalent bonds, hydrogen bonds and other Van der Waals forces, the molecular motion is limited, and the non-radiative transition of a chromophore is reduced. For example, in 2013, the Kim jin dang team obtained a series of room temperature phosphorescent materials with high phosphorescence quantum yield by suppressing non-radiative transitions by introducing organic small molecule phosphors into a rigid polymer matrix (d.lee, o.bolton, b.c.kim, j.h.youk, s.takayama, j.kim, journal of the american Chemical Society 2013,135, 6325). In 2015, a research team professor Kwon conveniently prepared a series of monomolecular room temperature phosphorescent materials by modifying the phosphorescent molecules onto the polymer molecular backbone (m.s.kwon, y.yu, c.coburn, a.w.phillips, k.chung, a.shanker, j.jung, g.kim, k.pipe, s.r.forrest, j.h.youk, j.giershner, j.kim, nature Communications 20156). However, in actual operation, the preparation process of the doped system room temperature phosphorescent material is slightly complicated, and the doped host has higher requirements on the type and concentration, so that the development and application of the pure organic room temperature phosphorescent material are restricted. In addition, although a guest polymer involved in host-guest doping, such as polyvinyl alcohol, polymethyl methacrylate and the like, has good transparency and flexibility, an organic small-molecule phosphorescent crystal material is often separated from the polymer in an unavoidable manner, so that the stability of the room-temperature phosphorescent material is poor and the transparency is reduced.
In comparison, the development of the undoped polymer room temperature phosphorescent material can effectively solve the problems of phase separation, difficult processing, instability caused by spontaneous crystallization and the like in the doping of the organic small molecule host and guest, and has obvious advantages in the aspect of self-supporting transparency. Meanwhile, the research in the field of pure organic polymer room temperature phosphorescence is still in the beginning stage, and the types of non-doped polymer room temperature phosphorescence candidate materials are very limited. Meanwhile, the existing pure organic room temperature phosphorescent material has complex synthetic route, high cost of raw material monomers (mainly comprising carbazole, pyrene, tetraphenyl ethylene, triphenylamine, benzophenone and derivatives thereof and the like), complicated post-treatment and low yield, so that the preparation cost is high and the material is not suitable for large-scale production.
Therefore, the development of the undoped polymer room temperature phosphorescent material which has the advantages of low cost, adjustable phosphorescence, no need of compounding and simple application has important research value.
Disclosure of Invention
The invention aims to provide a preparation method and application of a pure organic non-doped ultra-long room temperature phosphorescent multi-component polymer aiming at the technical analysis and problems. The polymer is conveniently prepared from melamine monomer, paraformaldehyde and optional thiourea through condensation polymerization.
The invention combines the condensation polymerization and stepwise polymerization principles, adopts a solution polymerization implementation strategy to obtain a melamine formaldehyde random prepolymer with a certain molecular weight, then removes other impurities through centrifugation, filtration and dialysis, and further obtains a linear copolymer solid with room temperature phosphorescence emission in high yield through freeze drying. The polymers all show obvious excitation wavelength dependence in a solid state, and the phosphorescence wavelength can be flexibly regulated and controlled by the excitation wavelength. The method effectively overcomes the defects of complex synthesis, limited variety, high price, poor stability, high biotoxicity, difficult adjustment of phosphorescence performance and the like of the existing room temperature phosphorescence materials, has the characteristics of low cost, high yield, batch production, simple operation and simple and convenient processing and film forming, can obtain linear condensation polymers with different polymerization degrees by adjusting the feeding proportion of copolymer monomers and the copolycondensation reaction time, and simultaneously realizes the adjustment of room temperature phosphorescence emission life and wavelength. The polycondensate prepared by the invention has adjustable room-temperature phosphorescence emission life and wavelength, shows good stability and excitation wavelength dependence, and has huge application potential in the fields of anti-counterfeiting and information encryption.
Therefore, an object of the present invention is to provide a method for preparing a pure organic undoped polymer room temperature phosphorescent material, which comprises the following steps:
1) Polymerizing formaldehyde with melamine monomers and optionally a third component in water under alkaline conditions;
2) Separating the polymerization product obtained in the step 1), washing the obtained solid with water, then freeze-drying to remove the water solvent, and grinding to obtain the pure organic non-doped polymer room temperature phosphorescent material.
In one embodiment, the melamine to formaldehyde molar ratio is 1.5 to 1. Preferably, the molar ratio of melamine to formaldehyde is 1.8 to 1, preferably 1 to 2 to 1.
In another embodiment, the molar ratio of melamine to formaldehyde is from 1.4 to 1. Preferably, the molar ratio of melamine to formaldehyde is 1.7 to 1; the molar ratio of melamine to the third component is 1.
In a preferred embodiment of the invention, the formaldehyde is selected from paraformaldehyde.
In a preferred embodiment of the present invention, the third component is at least one selected from thiourea, benzoguanamine, and urea, but is not limited thereto.
In a preferred embodiment of the present invention, the basic conditions include a weakly basic condition at a pH of 8.0 to 9.0. The basic conditions are adjusted by adding a base selected from at least one of inorganic bases including alkali metal hydroxides or alkaline earth metal hydroxides, alkali metal salts or alkaline earth metal salts, including, for example, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, and the like; the organic base comprises triethylamine, pyridine, diethanolamine, triethanolamine and the like.
In a preferred embodiment of the invention, the separation is performed by centrifugation, filtration, dialysis or the like. Preferably, the separation is performed by centrifugation, in particular high speed centrifugation.
Preferably, the preparation method of the pure organic undoped polymer room temperature phosphorescent material comprises the following steps:
dissolving formaldehyde in water, adjusting the pH value of the formaldehyde to be alkaline by using alkali, then heating to 40-70 ℃, adding a melamine monomer and an optional third component into the solution, and stirring and dispersing; then heating to 80-95 ℃, optionally adding a certain amount of third component after the solution system is clear and transparent, and continuously reacting for 0.5-3 hours to obtain a transparent or milky mixed solution; and cooling, separating, washing the obtained solid with water, freezing, performing vacuum freeze-drying to remove the water solvent, and grinding to obtain the pure organic non-doped polymer room-temperature phosphorescent material.
In a preferred embodiment of the present invention, the first temperature rise is preferably to 45 to 60 ℃, more preferably to 50 to 55 ℃.
In a preferred embodiment of the invention, the rate of the second temperature rise is 3 to 7 deg.C/min, preferably 4 to 6 deg.C/min, more preferably 5 deg.C/min.
In a preferred embodiment of the invention, the second temperature increase is preferably to 85 to 90 ℃.
In a preferred embodiment of the invention, the additional moles of the third component are between 0.01 and 0.2%, preferably between 0.03 and 0.1%, more preferably between 0.05 and 0.07% of the moles of melamine.
In a preferred embodiment of the invention, the time for continuing the reaction after the second temperature rise is from 0.5 to 2 hours, preferably from 0.5 to 1 hour.
In a preferred embodiment of the invention, the temperature of the freeze-drying is-78 ℃.
Another object of the present invention is to provide a pure organic undoped polymer room temperature phosphorescent material prepared by the above preparation method of the present invention.
The invention also aims to provide the application of the pure organic non-doped polymer room temperature phosphorescent material in anti-counterfeiting and information encryption.
In a preferred embodiment of the invention, the anti-counterfeiting comprises a time-resolved multi-level anti-counterfeiting.
The invention also aims to provide a room temperature phosphorescent polymer film which is prepared from the pure organic undoped polymer room temperature phosphorescent material.
It is a further object of the present invention to provide a method for preparing a room temperature phosphor photopolymer film, the method comprising:
the pure organic undoped polymer room temperature phosphorescent material is prepared into 10-100 mg/mL polymer aqueous solution, and the polymer aqueous solution is heated and cured to form a film in an oven after being coated on the surface of a base material.
In a preferred embodiment of the present invention, the concentration of the aqueous polymer solution is preferably 20 to 80mg/mL, more preferably 40 to 60mg/mL, and still more preferably 50mg/mL.
In a preferred embodiment of the present invention, the temperature for the heat curing is 120 to 160 ℃, preferably 130 to 150 ℃, more preferably 140 ℃.
It is still another object of the present invention to provide a room temperature phosphorescent polymer film prepared by the above preparation method of the present invention.
The technical scheme of the invention has the following beneficial effects:
1. the raw materials used in the invention are all pure organic micromolecular compounds, the source is wide, the synthesis is simple and convenient, and the raw materials are easy to obtain. The whole process of the synthetic route does not need additional protective gas (such as nitrogen, argon and the like), and the content of adjuvant materials (pH regulators: sodium hydroxide, triethanolamine and the like) is low, so that the method is economical and contributes to the reduction of cost.
2. The pure organic non-doped polymer room temperature phosphorescent material designed by the invention can flexibly adjust the phosphorescent performance by regulating the feeding proportion, controlling the reaction time and introducing other comonomers (thiourea, benzoguanamine, urea and the like). Due to the existence of multiple aggregation states of the prepared copolymer, the phosphorescence emission has obvious excitation wavelength dependence. The copolymer can be dissolved in common organic solvents such as N, N-dimethylformamide and the like, has good film forming property, can be processed into a film on the surfaces of various materials such as glass, ceramics, thermosetting plastics and the like, and has good transparency.
3. The pure organic non-doped polymer room temperature phosphorescent material described by the invention has long-life afterglow luminescence (> 400 milliseconds), is different from a fluorescent material, and can still display clear characters or patterns after an excitation light source is removed. The characteristics that the polymer film is transparent in sunlight, blue-green fluorescence is displayed under an ultraviolet lamp, and phosphorescence is slowly annihilated after the ultraviolet lamp is turned off are utilized, so that a multistage anti-counterfeiting strategy can be conveniently constructed, and the method is suitable for the fields of information encryption and advanced anti-counterfeiting.
4. The pure organic undoped polymer room temperature phosphorescent material prepared by the invention is free from culturing a specific crystal or eutectic structure, the prepared polymer material has stable luminescent property, can still effectively avoid quenching of oxygen or moisture to phosphorescence after being processed into a film, and can be used in air without inert gas protection or vacuum environment. Moreover, the prepared material still has certain phosphorescence emission performance in a high-temperature environment below the melting point of the material. The room temperature phosphorescent material prepared by the invention has good heat resistance, oxygen resistance and moisture resistance.
Drawings
FIG. 1 is a fluorescence spectrum of a room temperature phosphorescent polymer material prepared in example 1;
FIG. 2 shows phosphorescence spectra (a) and phosphorescence spectra (b) measured at different retardation times of the room temperature phosphorescent polymer material prepared in example 1;
FIG. 3 shows phosphorescence spectra measured at different excitation wavelengths for the room temperature phosphorescent polymer material prepared in example 1;
FIG. 4 is the CIE color coordinates of the room temperature phosphorescent polymer material prepared in example 1;
FIG. 5 is a life curve of a room temperature phosphorescent polymer material prepared in example 1;
FIG. 6 is a fluorescence spectrum of a room temperature phosphorescent polymer material prepared in example 8;
FIG. 7 shows phosphorescence spectra (a) and phosphorescence spectra (b) measured at different retardation times of the room temperature phosphorescent polymer material prepared in example 8;
FIG. 8 shows phosphorescence spectra measured at different excitation wavelengths of the room temperature phosphorescent polymer material prepared in example 8;
FIG. 9 is the CIE color coordinates of the room temperature phosphorescent polymer material prepared in example 8;
FIG. 10 is a life curve of the room temperature phosphorescent polymer material prepared in example 8;
fig. 11 is a demonstration of the effect of the room temperature phosphorescent polymer material prepared in example 1 for multi-level anti-counterfeiting.
Detailed Description
The present invention is described in more detail below to facilitate an understanding of the present invention.
It should be understood that the terms or words used in the specification and claims should not be construed as having a meaning defined in dictionary, but should be construed as having a meaning consistent with their meaning in the context of the present invention on the basis of the following principles: the concept of terms may be defined appropriately by the inventors for the best explanation of the invention.
Example 1: preparation of melamine-formaldehyde bipolymer
8.14g of paraformaldehyde is weighed, stirred and dissolved in 20mL of deionized water, the pH value of the solution is adjusted to be alkalescent (8.0-9.0) by using 2mol/L sodium hydroxide solution, and then the temperature is gradually increased. When the temperature of the solution reaches 50 ℃, weighed melamine monomer (the molar ratio of melamine to formaldehyde is about 1: 2.5) is quickly added into the solution, fully stirred and dispersed, and mixed uniformly. Heating to about 90 ℃ at the heating rate of 5 ℃/min under reflux, and continuously reacting for 0.5-1 hour after a solution system is clear and transparent to obtain a transparent or milky mixed solution. After natural cooling, the obtained mixed solution was transferred to a 50mL centrifuge tube, and a milky white precipitate was obtained after high-speed centrifugation. After the precipitate was further filtered, it was washed 3 times with deionized water to remove residual impurities. Freezing the obtained solid, carrying out vacuum freeze-drying (-78 ℃) for 48 hours, completely removing the water solvent, and grinding to obtain the melamine-formaldehyde copolymer solid powder with room-temperature phosphorescence.
The photoluminescence properties of the prepared binary polycondensate were first characterized, with an optimum excitation wavelength of 270nm and an optimum emission wavelength of 380nm, and the solid powder showed blue fluorescence (fig. 1). Meanwhile, when the excitation wavelength was 270nm, the phosphorescence emission peak was measured to be around 440nm (FIG. 2). The phosphorescence emission spectrum (fig. 3) shows that it has an excitation-dependent characteristic, with the phosphorescence emission peak red-shifted to a greater extent as the excitation wavelength increases. After 365nm uv excitation was turned off, the polymer emitted blue-green afterglow (fig. 4). The transient test results prove that the solid powder has longer phosphorescence lifetime, and the phosphorescence lifetime at room temperature can reach 520.57ms (figure 5).
Example 2: similar to example 1, except that the molar ratio of melamine to formaldehyde was about 1.5, a solid melamine-formaldehyde copolymer powder having room temperature phosphorescent properties was obtained.
Example 3: similar to example 1, except that the molar ratio of melamine to formaldehyde was about 1.8, a solid melamine-formaldehyde copolymer powder having room temperature phosphorescent properties was obtained.
Example 4: similar to example 1, except for a molar ratio of melamine to formaldehyde of about 1.
Example 5: similar to example 1, except that the molar ratio of melamine to formaldehyde was about 1.
Example 6: similar to example 1, except that the molar ratio of melamine to formaldehyde was about 1.2, a solid melamine-formaldehyde copolymer powder having room temperature phosphorescent properties was obtained.
Example 7: similar to example 1, except that the molar ratio of melamine to formaldehyde was about 1.
Example 8: preparation of melamine-formaldehyde-thiourea multi-component copolymer
7.5g of paraformaldehyde is weighed, stirred and dissolved in 20mL of deionized water, the pH value of the solution is adjusted to be alkalescent (8.0-9.0) by using 2mol/L sodium hydroxide solution, and then the temperature is gradually increased. When the temperature of the solution reaches 50 ℃, the weighed melamine monomer and thiourea (the molar ratio of melamine to formaldehyde is about 1, and the molar ratio of melamine to thiourea is about 1.1) are quickly added into the solution, fully stirred and dispersed, and mixed uniformly. Heating to about 90 ℃ at a heating rate of 5 ℃/min under reflux, adding thiourea with the mole number of 0.05 percent of that of melamine after a solution system is clear and transparent, and continuously reacting for 0.5-1 hour to obtain a transparent or milky mixed solution. After natural cooling, the obtained mixed solution is transferred to a 50mL centrifuge tube, and a precipitate is obtained after high-speed centrifugation. After the precipitate was filtered with a buchner funnel, it was washed 3 times with deionized water to remove residual impurities. Freezing the obtained solid, carrying out vacuum freeze-drying (-78 ℃) for 48 hours, completely removing the water solvent, and grinding to obtain the melamine-formaldehyde-thiourea copolymer solid powder with room-temperature phosphorescence.
After the third component is introduced, the copolymer solid powder still has excellent photoluminescence characteristics and stronger phosphorescence (fig. 6 and 7). When the excitation wavelength is 310nm, the phosphorescence emission peak is around 500nm (FIG. 8). In addition, it has a more significant excitation wavelength dependence, and when the excitation wavelength is increased from 260nm to 310nm, the corresponding chromaticity coordinates gradually transit from the blue region to the green region (fig. 9). The phosphorescence lifetime of the multipolymer at room temperature is further improved and can reach 640.22ms (figure 10).
Example 9: similar to example 8, except that the molar ratio of melamine to formaldehyde was about 1.4, a solid powder of melamine-formaldehyde-thiourea copolymer was obtained having room temperature phosphorescent properties.
Example 10: similar to example 8, except that the molar ratio of melamine to formaldehyde was about 1.7, a solid powder of melamine-formaldehyde-thiourea copolymer was obtained having room temperature phosphorescent properties.
Example 11: similar to example 8, except that the molar ratio of melamine to formaldehyde was about 1.9, a solid powder of melamine-formaldehyde-thiourea copolymer was obtained having room temperature phosphorescent properties.
Example 12: similar to example 8, except that the molar ratio of melamine to formaldehyde was about 1.9, a solid powder of melamine-formaldehyde-thiourea copolymer was obtained having room temperature phosphorescent properties.
Example 13: similar to example 8, except that the molar ratio of melamine to formaldehyde was about 1.
Example 14: similar to example 8, except for a molar ratio of melamine to formaldehyde of about 1.9, a solid powder of melamine-formaldehyde-thiourea copolymer was obtained having room temperature phosphorescent properties.
Example 15: preparation of pure organic room temperature phosphorescent copolymer transparent film
200mg of the polymer powder obtained in example 1 was weighed and placed in a glass vial, and 4mL of deionized water was added thereto, followed by sufficient stirring to uniformly disperse the copolymer powder. Obtaining 50mg/mL polymer water solution, coating the water solution on a substrate, and curing the substrate in an oven at 130-150 ℃ (using the film prepared under the condition of 140 ℃ as application effect display) for 30min to form a film.
Example 16: pure organic room temperature phosphorescent copolymer used for time-resolved multi-stage anti-counterfeiting
The room temperature phosphorescent polymer obtained in example 1 was selected and prepared into an aqueous polymer solution according to the procedure of example 15. A polymer solution is used to draw a number or text pattern on a transparent quartz substrate as shown in fig. 11. After painting, the film is dried in an oven at 130-150 deg.C (using the film prepared at 140 deg.C as the effect display). The processed substrate is colorless and transparent under the sunlight, and emits bright blue light under the illumination of a 300nm ultraviolet lamp to serve as primary anti-counterfeiting. And after the ultraviolet lamp is just turned off, the whole pattern emits long-life phosphorescence to serve as secondary anti-counterfeiting.
The foregoing describes preferred embodiments of the present invention, but is not intended to limit the invention thereto. Modifications and variations of the embodiments disclosed herein may be made by those skilled in the art without departing from the scope and spirit of the invention.
Claims (7)
1. A method for preparing a pure organic undoped polymer room temperature phosphorescent material comprises the following steps:
1) Polymerizing formaldehyde with melamine monomers and optionally a third component in water under alkaline conditions;
2) Separating the polymerization product obtained in the step 1), washing the obtained solid with water, then freeze-drying to remove the hydrosolvent, and grinding to obtain the pure organic non-doped polymer room-temperature phosphorescent material;
wherein the method comprises the following steps:
dissolving formaldehyde in water, adjusting the pH value of the formaldehyde to be alkaline by using alkali to form a solution, then heating to 40-70 ℃, adding a melamine monomer and an optional third component into the solution, and stirring and dispersing; then heating to 80-95 ℃, optionally adding a certain amount of third component after the solution system is clear and transparent, and continuously reacting for 0.5-3 hours to obtain a transparent or milky mixed solution; cooling, separating, washing the obtained solid with water, freezing, vacuum freeze-drying to remove the water solvent, and grinding to obtain the pure organic non-doped polymer room-temperature phosphorescent material;
the third component is selected from thiourea;
the molar ratio of the melamine to the formaldehyde is 1.5-1 and the amount of the third component is 0; or the molar ratio of the melamine to the formaldehyde is 1.4-1.
2. The method according to claim 1, wherein the formaldehyde is selected from paraformaldehyde.
3. The method according to claim 1, wherein the temperature is raised to 45 to 60 ℃ at the first temperature raising; the rate of the second heating is 3-7 ℃/min; the temperature is raised to 85-90 ℃ during the second temperature rise.
4. The method according to claim 3, wherein the temperature is raised to 50 to 55 ℃ at the first temperature rise; the rate of the second temperature rise is 4-6 ℃/min.
5. The method according to claim 4, wherein the second temperature rise is performed at a rate of 5 ℃/min.
6. The production method according to claim 1, wherein the alkaline condition includes a weakly alkaline condition at a pH of 8.0 to 9.0; the alkaline condition is adjusted by adding a base selected from at least one of inorganic bases and organic bases, the inorganic bases including alkali metal hydroxides or alkaline earth metal hydroxides, alkali metal salts or alkaline earth metal salts; the organic base comprises triethylamine, pyridine, diethanolamine and triethanolamine.
7. The method of claim 6, wherein the inorganic base comprises sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate.
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