Phosphorescent polymer microsphere and application thereof

Abstract

The invention discloses a phosphorescent polymer microsphere and application thereof, the phosphorescent polymer microsphere comprises a subject and a guest, the subject is a cross-linked polymer microsphere PAM, the guest is an organic room temperature phosphorescent (RTP) molecule, the subject is added into a guest solution for swelling to form the afterglow cross-linked polymer microsphere, and the afterglow cross-linked polymer microsphere is marked as PAM-RTP. Hydrophilic polymer microspheres are introduced as a multifunctional carrier, and organic room temperature phosphorescence (RTP) with adjustable color and service life is realized through dynamic rearrangement of intermolecular hydrogen bonds between a polymer matrix and a phosphor. According to the invention, the application field of the doped cross-linked polymer microspheres is widened, and a new solution is provided for the fields of information security and decoration in the aspects of information encryption, colorful display and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano material preparation, and in particular relates to phosphorescent polymer microspheres and applications thereof. Background Art

[0002] In recent years, organic photoluminescent materials with tunable luminescence color have attracted increasing attention due to their unique optical phenomena, with applications in flexible displays, optoelectronic devices, sensing, and imaging. The preparation of tunable luminescent materials offers interesting insights into the fundamental theories and mechanisms of luminescence, and has gradually become a hot topic in basic materials science research. Generally speaking, the main strategies for achieving tunable luminescence color in organic materials are to adjust the material composition, construct dual fluorescence-phosphorescence emission, control the crystal stacking pattern, and modulate energy and charge transfer processes and excited-state intramolecular proton transfer. Based on these approaches, a variety of organic luminescent materials with tunable luminescence color have been developed, including carbon dots and polymer dots, and exhibit color tunability under external stimuli such as pH, mechanical force, temperature, and light irradiation.

[0003] Due to the sensitivity of triplet excitons in organic materials, the triplet emission levels of organic compounds are difficult to manipulate, making achieving tunable afterglow color in organic materials a significant challenge. Host-guest doping plays a key role in activating room-temperature organic phosphorescence (RTP) in pure organic materials due to the simplicity of the method and the rigid host microenvironment that restricts the molecular motion of the guest luminescent material. Unlike covalent interactions in crystal engineering and polymerization, host-guest doping primarily involves non-covalent interactions such as hydrogen bonding, electrostatic interactions, and other weak intermolecular interactions, which can avoid complex synthetic routes for RTP materials. Furthermore, multifunctional RTPs have been developed by replacing functionalized guest phosphorescent molecules. The weak interactions between the host and guest also enable tunable emission colors in host-guest RTP materials. However, current research on polymer materials with tunable afterglow color has primarily focused on polymer films. For polymer nanoparticles or microspheres, only a few studies have achieved single-color afterglow, and reports on polymer microspheres with tunable afterglow color are rare. Our previous work has achieved tunable afterglow color in polymer microspheres, but this control is limited to a single direction. The dynamic and reversible control of the afterglow color of polymer microspheres remains an unresolved problem. Achieving this dynamic and reversible control is crucial for a deeper understanding of the photophysical properties of polymer microspheres and opens up new possibilities for their application in areas such as colorful displays and anti-counterfeiting technologies. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention discloses a phosphorescent polymer microsphere and its application. By introducing hydrophilic polymer microspheres as multifunctional carriers, organic room-temperature phosphorescence (RTP) with adjustable color and lifetime is achieved through the dynamic rearrangement of intermolecular hydrogen bonds between the polymer matrix and the phosphor. Such adjustable RTP polymer microspheres have great application potential in printable optical multiplexing and anti-counterfeiting detection.

[0005] In order to solve the problems of the prior art, the technical solution adopted by the present invention is: A phosphorescent polymer microsphere comprises a host and a guest, wherein the host is a cross-linked polymer microsphere PAM, and the guest is an organic room temperature phosphorescent (RTP) molecule. The cross-linked polymer microsphere with afterglow formed by swelling the host in a guest solution is denoted as PAM-RTP.

[0006] Furthermore, the cross-linked polymer microspheres PAM are prepared by an inverse emulsion polymerization method.

[0007] Furthermore, the guest is a mixture of one or more of 2-(9H-carbazole-9-yl)acetic acid (CzA), biphenyl-4,4'-dicarboxylic acid (BPA), 1-pyrenecarboxylic acid (PyA), 7-benzocarbazole (7-BCz) or naphthaleneimine (NI).

[0008] In a further improvement, the doping ratio of the 2-(9H-carbazol-9-yl)acetic acid (CzA), biphenyl-4,4'-dicarboxylic acid (BPA), and 1-pyrenecarboxylic acid (PyA) is 1 wt%.

[0009] Furthermore, the guest is a combination of 2-(9H-carbazol-9-yl)acetic acid (CzA), biphenyl-4,4'-dicarboxylic acid (BPA) and 1-pyrenecarboxylic acid (PyA), which then forms red, green and blue dynamically cross-linked polymer microspheres PAM-RGB with the host.

[0010] In a further improvement, the cross-linked polymer microspheres PAM-RTP are further doped with fluorescent molecules.

[0011] In a further improvement, the fluorescent molecule is fluorescein sodium (FL), rhodamine 6G (Rh6G) or rhodamine B (RhB).

[0012] Application of the above-mentioned phosphorescent polymer microspheres in the fields of colorful display or information encryption.

[0013] Furthermore, when the phosphorescent polymer microspheres are used in multi-color display, the main body of the phosphorescent polymer microspheres is cross-linked polymer microspheres polyacrylamide PAM, and the cross-linked polymer microspheres PAM are doped with at least one organic room temperature phosphorescent molecule to form multi-color dynamic cross-linked polymer microspheres, thereby realizing multi-color reversible afterglow display.

[0014] Furthermore, the cross-linked polymer microspheres PAM are co-doped with 2-(9H-carbazol-9-yl)acetic acid (CzA), biphenyl-4,4'-dicarboxylic acid (BPA), and 1-pyrenecarboxylic acid (PyA).

[0015] The present invention utilizes cross-linked polymer microspheres polyacrylamide (PAM) and phosphorescent molecules to form afterglow polymer microspheres (PAM-RTP). These microspheres emit phosphorescence of a specific color when excited by ultraviolet light of a specific wavelength. The PAM-RTP microspheres are redispersed in deionized water to cause the microspheres to swell. Because the hydrogen bonding between water molecules and the cross-linked polymer microspheres (PAM) is stronger than the hydrogen bonding between the phosphorescent molecules and the cross-linked polymer microspheres (PAM), the water molecules gradually replace the phosphorescent molecules within the microspheres. During this process, the phosphorescent molecules are gradually released into the deionized water, while the internal structure of the PAM-RTP microspheres changes. The phosphorescent molecules released into the water are then completely separated from the microspheres by centrifugation, resulting in cross-linked polymer microspheres that no longer contain phosphorescent molecules. Finally, the cross-linked polymer microspheres (PAM) are dried to remove the water molecules, restoring the microspheres to their original state. However, since the phosphorescent molecules within them have been removed, the microspheres no longer exhibit afterglow properties. Beneficial effects

[0016] Compared with the prior art, the phosphorescent polymer microspheres and their applications of the present invention have the following advantages: 1. Leveraging the specific structure of cross-linked polymer microspheres (PAMs), the team successfully doped guest organic room-temperature phosphorescent (RTP) molecules, including CzA, BPA, and PyA, into the host PAM microspheres. Hydrogen bonding enhances the rigid environment and effectively suppresses non-radiative transitions, resulting in blue, green, and red persistent emission from the microspheres. The blue phosphorescence lifetime reached 3.7 s, demonstrating excellent long-lasting properties.

[0017] 2. This application achieves a dynamic change in the afterglow color of the microspheres from red to white and finally to blue by co-doping three phosphorescent molecules, CzA, BPA and PyA, providing a novel and efficient technical means for the anti-counterfeiting field.

[0018] 3. This application makes full use of the reversibility of hydrogen bonds and realizes the dynamic reversible change of the microsphere afterglow color between blue, green, yellow and red by loading and releasing CzA, BPA, NI and PyA molecules respectively.

[0019] 4. This application successfully prepared polymer microspheres with tunable afterglow color by doping PAM-RTP microspheres with fluorescent molecules FL, Rh6G, and RhB in varying proportions. In particular, when PAM-CzA was used, the lifetime of the microspheres after doping with the fluorescent molecules was greater than 1.8 s. This broadens the application of doped cross-linked polymer microspheres, providing new solutions for information security and decorative applications in areas such as information encryption and colorful displays. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 a is a scanning electron microscope (SEM) photograph of the cross-linked polymer microspheres PAM prepared in the present invention; Figure 1 b is the Fourier transform infrared (FT-IR) spectrum of the cross-linked polymer microspheres PAM prepared in the present invention.

[0021] Figure 2 a is a fluorescence microscope photograph of the cross-linked polymer microspheres PAM prepared in the present invention; Figure 2 b is the photoluminescence (blue line) and phosphorescence spectra (green line) of the cross-linked polymer microspheres PAM prepared in the present invention; Figure 2 c is the excitation spectrum of the phosphorescence peak (445 nm) of the cross-linked polymer microspheres PAM prepared in the present invention; Figure 2 d is the phosphorescence lifetime decay curve of the cross-linked polymer microspheres PAM prepared in the present invention under different excitations.

[0022] Figure 3 PAM microspheres doped with different organic room-temperature phosphorescent (RTP) molecules, where a is CzA; b is BPA; c is the fluorescence microscope photo (left) and afterglow photo (right) of PyA; df is the photoluminescence and phosphorescence spectra corresponding to ac.

[0023] Figure 4 PAM microspheres doped with different organic room-temperature phosphorescent (RTP) molecules, where a is 7-benzocarbazole (7-BCz); b is the fluorescence microscope photo (left) and afterglow photo (right) of naphthaleneimine (NI); cd are the photoluminescence and phosphorescence spectra corresponding to ab.

[0024] Figure 5 a is the afterglow time dependence mapping diagram of PAM microspheres doped with RGB, b is the phosphorescence lifetime decay curve at 365 nm corresponding to PAM-RGB, c is the trajectory of the afterglow color in the CIE coordinate diagram of PAM-RGB; d is BG; e is BR; f is the trajectory of the afterglow color in the CIE coordinate diagram of GR.

[0025] Figure 6a is the phosphorescence spectrum and afterglow photograph of PAM microspheres doped with BPA before and after washing, and b is the phosphorescence lifetime decay curve; c is the Fourier transform infrared spectrum; d is the change in phosphorescence intensity after multiple reversible cycles of PAM washing and loading with BPA; e is the change in phosphorescence intensity and afterglow color after PAM washing and loading with different molecules, respectively. f is the trajectory of the afterglow color in the corresponding CIE coordinate diagram.

[0026] Figure 7 Fluorescence microscope photographs and photoluminescence (dashed line) and phosphorescence (solid line) spectra of PAM-CzA microspheres doped with different proportions of a for FL, b for Rh6G, and c for RhB, and df are the corresponding CIE coordinate trajectories and afterglow photographs.

[0027] Figure 8 Polymer microspheres are used for a: colorful reversible display; b: dynamic afterglow anti-counterfeiting.

[0028] Figure 9 This is a colorful long-lasting display of polymer microspheres PAM-CzA doped with fluorescent molecules. DETAILED DESCRIPTION

[0029] The following examples are provided to help those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way. The main reagents and drugs used in the present invention are shown in Table 1, all of which are commercially available products.

[0030] Table 1 Main reagents and drugs

[0031] The steady-state photoluminescence (PL) and phosphorescence spectra of dilute solutions and solids were measured by a F-7100 at room temperature or 77 K in low-temperature atmospheric conditions.

[0032] Phosphorescence lifetimes are measured and characterized using the FLSP920 and FLS1000 steady-state / transient fluorescence spectrometers at room temperature or at low temperatures (77 K). The Edinburgh FLSP920 transient fluorescence spectrometer uses a Xe900 xenon lamp for characterizing short-lived luminescence (nanosecond timescale), while the Edinburgh FLS1000 transient fluorescence spectrometer is used for characterizing long-lived luminescence (from milliseconds to seconds).

[0033] The UV-visible absorption spectra of the samples were measured by a UV-1780 UV spectrophotometer from Shimadzu Corporation of Japan.

[0034] Scanning electron micrographs were taken using a field emission scanning electron microscope (SEM) JSM-7800F.

[0035] Fluorescence micrographs of all crystals were taken with a Nikon DS-Ri2 fluorescence microscope camera equipped with a Nikon INTENSILIGHT C-HGFI mercury lamp excitation device.

[0036] Example 1 Synthesis of host polymer microspheres The synthesis path is as follows:

[0037] Oil phase: 500 mg of Span 80 emulsifier was added to a three-necked round-bottom flask equipped with a mechanical stirrer, and then 30 mL of cyclohexane was added. The mixture was stirred at 500 rpm for 10 min to completely dissolve the emulsifier in the cyclohexane. Nitrogen was introduced into the three-necked round-bottom flask for protection.

[0038] Aqueous phase: Acrylamide (AM) (4 g, 56 mmol), acrylic acid (AA) (0.8 g, 0.00111 mmol), and cross-linker N,N'-methylenebisacrylamide (MBA) (200 mg, 1.29 mmol) were added to 4 mL of deionized water and dissolved by ultrasonication. The dissolved aqueous phase was protected by nitrogen.

[0039] The aqueous phase was added dropwise to the oil phase under mechanical stirring at 500 rpm. After complete addition, stirring was continued for 30 minutes to obtain a reaction solution. Next, the initiator, ammonium persulfate (APS, 40 mg, 0.175 mmol), was dissolved in 0.5 mL of deionized water. After removing oxygen, the solution was added to the reaction solution, which was heated to 70°C for 3 hours. The reaction was then allowed to cool to room temperature with stirring. The resulting solution was poured into a beaker, and a large amount of anhydrous ethanol was added and centrifuged to precipitate the polymer microspheres. This step was repeated three times to completely remove the emulsifier. The collected product was then placed in a beaker, swollen with deionized water, and centrifuged. This was repeated three times to remove all unreacted monomers. Finally, anhydrous ethanol was added to precipitate the product, which was collected by centrifugation and dried in vacuo at 40°C for 48 hours to obtain the final cross-linked polymer microspheres (PAM).

[0040] The particle size of the polymer microspheres prepared above was 15.1±5.5 μm ( Figure 1 a). From the measured Fourier infrared spectrum showing 3000-3500 cm −1 The stretching vibrations of hydroxyl (OH) and amino (NH) groups are shown at 1650–1750 cm −1 The stretching vibration of 1110 cm −1 The stretching vibration peak indicates the presence of CN bonds ( Figure 1 b).

[0041] Under a fluorescence microscope, the main cross-linked polymer microspheres PAM were observed. Figure 2 As can be seen in a, the cross-linked polymer microspheres PAM exhibit blue photoluminescence characteristics, which is consistent with the test results of the steady-state photoluminescence (PL) spectrum ( Figure 2 b) is consistent with the above results, and its spectral peak is located at 445 nm, further confirming the blue luminescence characteristics of the cross-linked polymer microspheres PAM.

[0042] After analyzing the retardation spectrum of cross-linked polymer microspheres PAM, the results are as follows Figure 2 As shown in Figure c. As can be seen from the figure, the cross-linked polymer microspheres PAM exhibit a clear delayed luminescence peak at 445 nm, which intuitively indicates that the microspheres have the characteristics of phosphorescent emission. The excitation spectrum of the delayed luminescence peak at 445 nm was further tested. The test data clearly shows that the PAM microspheres exhibit the best excitation effect at a wavelength of 254 nm, and also show a weaker excitation peak at 365 nm, as shown in Figure 4. Figure 2 c. It further proves that the cross-linked polymer microspheres PAM can stimulate phosphorescence under different wavelengths of excitation, but the excitation efficiency is different. Subsequently, the delayed luminescence lifetime of the cross-linked polymer microspheres PAM under 254 nm and 365 nm excitation was tested, and the results are shown in Figure 2 As shown in Figure d, the delayed luminescence lifetime of the cross-linked polymer microspheres PAM is 1.8 ms under 254 nm excitation and 1.5 ms under 365 nm excitation.

[0043] Example 2

[0044] Doped polymer microspheres were prepared by dissolving small molecules in deionized water and allowing the microspheres to swell in the aqueous solution, thereby absorbing the small molecules into the microspheres. Specifically, the polymer microspheres were doped with CzA (PAM-CzA) and the CzA doping concentration was 1 wt%. The photoluminescence at 380 nm was consistent with the blue microspheres observed under a fluorescence microscope. The phosphorescence spectrum is shown in Figure 2. Figure 3 a and Figure 3 As shown in Figure d, the PAM-CzA microspheres exhibit a phosphorescence peak at 450 nm, accompanied by a shoulder at 400 nm, consistent with the blue afterglow observed after turning off the UV lamp. Further comparison revealed that the phosphorescence spectrum of the PAM-CzA microspheres overlaps well with that of a dilute CzA solution at low temperature (77 K), further confirming that the phosphorescence emission originates from the luminescence of a single CzA molecule.

[0045] According to the above method, the small molecule doping substance is replaced.

[0046] When the cross-linked polymer microspheres are doped with BPA (PAM-BPA), their photoluminescence also appears at 380 nm, accompanied by shoulder peaks at 470 nm and 500 nm, which is consistent with the cyan microspheres observed under a fluorescence microscope. Figure 3 b and Figure 3 As shown in Figure e, the phosphorescence peak of the PAM-BPA microspheres is located at 500 nm, with a shoulder at 470 nm, consistent with the green afterglow observed after turning off the UV light. Compared to the phosphorescence properties of dilute BPA solutions at low temperatures, the phosphorescence emission of the PAM-BPA microspheres is also attributed to luminescence from single BPA molecules.

[0047] When the cross-linked polymer microspheres are doped with PyA (PAM-PyA), their photoluminescence appears at 400 nm, which is consistent with the blue microspheres observed under a fluorescence microscope. Figure 3 c and Figure 3 As shown in Figure 5, the PAM-PyA microspheres exhibit phosphorescence peaks at 613 nm and 670 nm, which is consistent with the red afterglow observed after turning off the UV lamp. Comparison with the phosphorescence properties of a low-temperature dilute PyA solution confirms that the phosphorescence emission of the PAM-PyA microspheres originates from the luminescence of PyA.

[0048] Therefore, the present invention successfully prepares cross-linked phosphorescent polymer microspheres capable of emitting red, green and blue colors.

[0049] Example 3

[0050] Referring to the doping method described in Example 2, two oil-soluble molecules—7-benzocarbazole (7-BCz) and naphthaleneimine (NI)—were selected to verify the universality of cross-linked polymer microspheres (PAMs). Since both molecules are insoluble in water, they were first dissolved in a small amount of DMF, followed by the addition of deionized water to ensure complete and uniform dispersion. Subsequently, the cross-linked polymer microspheres were introduced into this mixed solution, leveraging their swelling properties to effectively adsorb these small molecules.

[0051] After testing, it was found that when the cross-linked polymer microspheres were successfully doped with 7-BCz, the photoluminescence spectrum showed a luminescence peak at 390 nm, which was consistent with the blue microspheres observed under a fluorescence microscope. Further observation of the phosphorescence spectrum revealed a phosphorescence peak at 520 nm for the PAM-7-BCz microspheres, accompanied by a shoulder peak at 500 nm. After turning off the UV light, a green afterglow was observed, which was completely consistent with the observation results of the phosphorescence spectrum ( Figure 4 a, Figure 4 c).

[0052] When cross-linked polymer microspheres are doped with NI, the photoluminescence spectrum shows a luminescence peak at 420 nm, which is consistent with the blue microspheres observed under a fluorescence microscope. The phosphorescence spectrum reveals that the PAM-NI microspheres have a phosphorescence peak at 550 nm, accompanied by a shoulder peak at 590 nm. After turning off the UV light, a yellow afterglow is clearly visible, which is consistent with the observation results of the phosphorescence spectrum ( Figure 4 b, d).

[0053] These experimental results demonstrate that as long as the molecules can be uniformly dispersed in water and are smaller than the microspheres, they have the potential to form cross-linked phosphorescent polymer microspheres through doping. This further demonstrates the universal applicability of the cross-linked phosphorescent polymer microspheres presented herein, providing a solid foundation for further exploration and application of cross-linked phosphorescent polymer microspheres in a wider range of molecular fields.

[0054] Example 4

[0055] CzA, BPA, and PyA were co-doped into cross-linked polymer microspheres at a ratio of 1 wt% to form multi-color red, green, and blue cross-linked polymer microspheres (PAM-RGB). This multi-component doping strategy aims to achieve dynamic control of afterglow color. The specific doping method is shown in Example 2. The afterglow time dependence mapping of PAM-RGB clearly shows three unique luminescence centers, which correspond to the characteristic luminescence of the three different doping molecules ( Figure 5 a). It was further confirmed that the three molecules were successfully co-doped into the microspheres while retaining their unique luminescence properties.

[0056] Given the significant differences in phosphorescence lifetimes after doping with the three molecules, namely 3689.69 ms, 585.10 ms, and 149.29 ms, this lays a solid foundation for the realization of tunable afterglow color ( Figure 5 b). Because different phosphorescent molecules decay at different rates after the UV lamp is turned off, the afterglow color changes over time. At the moment the UV lamp is turned off, the afterglow is primarily red. Subsequently, the red afterglow gradually fades, while blue and green afterglow begin to appear. At 240 ms, the three colors of afterglow overlap, resulting in a white afterglow. Then, the red afterglow disappears completely, and the afterglow color shifts to cyan. Finally, at 1000 ms, only blue emission remains ( Figure 5 c).

[0057] This study doped CzA, BPA, and PyA molecules into microspheres in pairs and carefully observed the changes in the afterglow color. The experimental results showed that different combinations can achieve flexible control of the afterglow color. When doped with CzA and BPA, the afterglow color gradually changed from the initial cyan to cyan and finally stabilized to blue ( Figure 5d); The combination of CzA and PyA shows a persistent glow from red to white and finally to blue ( Figure 5 e); When doped with BPA and PyA, the afterglow color transitions from red to yellow-green and finally stabilizes to green ( Figure 5 f). Further confirmation was obtained that a multi-component doping method could achieve multicolor, dynamic, and tunable afterglow in polymer microspheres. This invention addresses the problem of existing microsphere phosphorescent systems often emitting a single color of light after formation. By utilizing the breaking and forming of hydrogen bonds, the dynamic, reversible process of microsphere phosphorescence is achieved, thereby changing the microsphere's luminescent color.

[0058] Cross-linked polymer microspheres serve as carriers. By remixing specific phosphorescent molecules with the microspheres and re-adsorbing them into the microspheres through hydrogen bonding, the microspheres regain their phosphorescent properties. The results of the phosphorescence spectrum test clearly show that when the microspheres are doped with CzA, BPA, PyA, and NI, they all exhibit obvious phosphorescent properties in their initial state. However, after washing, the phosphorescence spectra of these four doped microspheres almost completely disappear, the phosphorescence intensity is greatly reduced, and it is almost impossible to detect a clear phosphorescence signal. This result shows that the washing process effectively removes the phosphorescent molecules adsorbed in the microspheres. This method not only has the advantages of simple operation and reusability, but also provides new possibilities for the application of phosphorescent microspheres in information display, anti-counterfeiting labels and other fields.

[0059] Example 5

[0060] First, PAM-BPA was selected as the core object of the study. From the phosphorescence spectrum, it can be clearly observed that the loaded microspheres exhibit a significant phosphorescence peak at 500 nm. However, after washing, this phosphorescence peak almost completely disappears, and the afterglow photos also clearly show that the green afterglow of the microspheres is no longer there. This significant phenomenon indicates that the BPA molecules may have been successfully released from the microspheres ( Figure 6 a).

[0061] Next, the conventional phosphorescence lifetime decay curve was tested. The results showed that the phosphorescence lifetime of the loaded PAM-BPA at 500 nm was as long as 571.15 ms. However, after washing, the phosphorescence lifetime of the microspheres at the same wavelength dropped sharply to 0.07 ms, indicating that the phosphorescence had completely disappeared ( Figure 6 b). This result is highly consistent with the observations from the afterglow photograph, further confirming the release of BPA molecules from the microspheres. Fourier transform infrared spectroscopy can be used to analyze this process at the molecular level. The analysis results show that the washed microspheres have a wavelength of 3000-3500 cm -1 The peak area in the range is obviously reduced, which corresponds to the reduction of OH bonds ( Figure 6c). Given that OH bonds are usually closely related to hydrogen bonds, this directly demonstrates the weakening of hydrogen bonds, further confirming the release of BPA molecules from the microspheres.

[0062] In order to fully evaluate the stability and reusability of the microspheres during the phosphorescence reversible process, multiple loading and washing cycles were performed. Figure 6 As shown in Figure d, the phosphorescence intensity and afterglow effect of the microspheres remain relatively stable after each cycle and can withstand multiple cycles without significant performance degradation. This result fully demonstrates the excellent stability and reusability of the microspheres in the reversible phosphorescence process.

[0063] Example 6

[0064] First, PAM-CzA microspheres were prepared according to the method of Example 2. These microspheres exhibited a blue afterglow under specific excitation. Subsequently, the CzA molecules adsorbed in the microspheres were successfully removed through washing treatment, and the blue afterglow completely disappeared. This result preliminarily proves the reversibility of the microspheres in loading and releasing phosphorescent molecules. Next, this batch of microspheres was re-doped with BPA molecules to prepare microspheres that can emit a green afterglow. After washing again, the green afterglow also completely disappeared, further verifying the reversible conversion ability of the microspheres between phosphorescent molecules. Subsequently, naphthalene imine (NI) and pyrene carboxylic acid molecules (PyA) were doped into the microspheres in sequence, and the appearance and disappearance of yellow and red afterglow were observed in turn ( Figure 6 e). This series of experiments not only fully demonstrated the reversibility of the microspheres between different phosphorescent molecules, but also highlighted their great potential in achieving colorful reversible dynamic afterglow.

[0065] In order to more intuitively demonstrate the reversible cycle process of the microsphere phosphorescence from blue to green, then to yellow, and finally to red, it can also be seen from the CIE coordinate trajectory diagram that the phosphorescence color of the microsphere changes reversibly with the loading and release of phosphorescent molecules, forming a complete cycle process ( Figure 6 f). This achievement not only strongly proves that the microspheres can be loaded and washed with different phosphorescent molecules, but also demonstrates their potential for application in colorful reversible dynamic afterglow.

[0066] Example 7

[0067] Energy transfer is the process of transferring energy between molecules, typically involving an excited molecule transferring energy to another molecule, causing it to transition from the ground state to the excited state. PAM-CzA was chosen as the host phosphorescent material because it emits phosphorescence upon excitation. If the energy of this phosphorescence matches the absorption energy of the doped fluorescent molecule, energy transfer occurs, causing the fluorescent molecule to be excited and emit light. In this way, the long afterglow properties of PAM-CzA, combined with the emission characteristics of the fluorescent molecule, can be used to manipulate the luminescence properties of the entire system.

[0068] Three fluorescent molecules—fluorescein sodium (FL), rhodamine 6G (Rh6G), and rhodamine B (RhB)—were selected as guest dopants. The fluorescence emission characteristics of these fluorescent molecules overlap with the phosphorescence spectra of PAM-CzA, enabling efficient energy transfer between them. By doping these fluorescent molecules into PAM-CzA microspheres, it is hoped that the afterglow color and duration of the microspheres can be tuned.

[0069] In order to further control the color and lifetime of long afterglow, PAM-CzA was swelling-doped with three fluorescent molecules FL, Rh6G, and RhB at a ratio of 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, and 3 wt%, and the doping method was the same as before.

[0070] In the PAM-CzA-FL system, as the doping ratio of the fluorescent molecule increases, the photoluminescence shows that the fluorescence peak at 440 nm gradually decreases, and the peak at 540 nm gradually increases. This is due to the gradual increase of the fluorescent molecule FL. It can also be seen from the fluorescence microscope that as the doping ratio increases, the luminescence color of the microspheres changes from blue to green under ultraviolet light. The phosphorescence spectrum also shows that as the ratio increases, the phosphorescence peak at 450 nm gradually decreases, and the peak around 540 nm also gradually increases. It can be seen that the phosphorescence peak around 540 nm coincides with the fluorescence peak, and the peak around 540 nm belongs to the fluorescence emission of the fluorescent molecule FL, so it may be caused by energy transfer ( Figure 7 a). The red shift of the phosphorescence peak around 540 nm is due to FL aggregation. The CIE coordinate trajectory also shows the change of phosphorescence color from blue to green. After turning off the UV light, the color of the microsphere afterglow changes from blue to green, which is consistent with the change of the CIE coordinate trajectory ( Figure 7 d). The phosphorescence lifetime of the phosphorescence peak was tested, and the phosphorescence lifetime decay curve showed that the phosphorescence lifetime at 450 nm gradually decreased from 2830.92 ms to 2442.77 ms as the ratio increased ( Figure 7a), the phosphorescence lifetime at 540 nm gradually decreases from 2351.19 ms to 1954.87 ms ( Figure 7 d). This also proves that the color change of the microspheres is due to energy transfer, and the phosphorescence lifetime is greater than 1.9 s, achieving long afterglow of the microspheres and adjustable afterglow color.

[0071] By replacing the doped fluorescent molecules with Rh6G and RhB, two systems, PAM-CzA-Rh6G and PAM-CzA-RhB, were successfully constructed, further expanding the color tunability of the long afterglow of the microspheres.

[0072] In the PAM-CzA-Rh6G system, as the Rh6G doping ratio increases, the fluorescence peak at 440 nm in the photoluminescence spectrum gradually weakens, while the fluorescence peak at 570 nm gradually strengthens. This change was intuitively verified when observing the luminescence color of the microspheres under ultraviolet light under a fluorescence microscope. The luminescence color of the microspheres gradually changed from blue to yellow-green ( Figure 7 b). It is worth noting that due to the small overlap between the phosphorescence emission and absorption spectra and the relatively low energy transfer efficiency, the luminescent color of the microspheres did not completely change to yellow. The trend of the phosphorescence spectrum is consistent with the fluorescence spectrum, further confirming the occurrence of energy transfer. In addition, the CIE coordinate trajectory and the change in the afterglow color also coincide with the spectral data, showing a continuous change from blue to blue-violet ( Figure 7 e).

[0073] In the PAM-CzA-RhB system, a significant change in the color of photoluminescence and phosphorescence from blue to red was also observed. As the RhB doping ratio increased, the luminescence color of the microspheres gradually changed from blue to orange-red, and the afterglow color changed from blue to purple-red ( Figure 7 c, f). Phosphorescence lifetime tests show that the phosphorescence lifetime is greater than 1.8 s ( Figure 7 c, f), proving that the system also has long afterglow characteristics.

[0074] In summary, the above results demonstrate the successful realization of multi-color, tunable, and long-lasting emission from polymer microspheres via energy transfer. This approach not only enriches the application prospects of microspheres in fields such as information display and anti-counterfeiting labels, but also provides a new strategy for color control of phosphorescent materials.

[0075] Example 8

[0076] First, a simple template filling method was used to achieve reversible colorful display of microspheres. The initial polymer microspheres did not show afterglow after the UV lamp was turned off, but after being doped with phosphorescent molecules such as CzA, BPA, NI and PyA, the microspheres showed a rich and varied afterglow color. These microspheres were filled in the bear template and could show blue, green, yellow and red afterglow after the UV lamp was turned off. The afterglow can be removed by centrifugal washing to achieve reversible changes. This reversible colorful display not only enriches the display effect, but also saves resources and protects the environment ( Figure 8 a).

[0077] By doping CzA, BPA, and PyA together in microspheres, they produced microspheres whose afterglow color changes over time. When these microspheres were filled into a snowflake template, the afterglow color gradually changed from red to pink, white, and finally to blue. This time-varying afterglow color provides a new approach to anti-counterfeiting, effectively preventing forgery and tampering ( Figure 8 b).

[0078] The present invention can also realize high-precision information encryption application of polymer microspheres through inkjet printing technology, such as Figure 9 As shown, green PAM-BPA and yellow PAM-NI are used as encryption inks, respectively, and overlapping printing is performed to form an encrypted information image consisting of a QR code pattern and a "Fu" character pattern superimposed. After turning off the ultraviolet light of 365 nm wavelength, the "Fu" character pattern with a yellow afterglow can be observed by the naked eye under ambient conditions. When the ultraviolet light is changed to 310 nm, the QR code information with a green afterglow can be captured after turning off the ultraviolet light, which effectively improves the data storage capacity in the spatial dimension. In summary, the present invention has successfully developed a colorful amorphous polymer microsphere system with broad application prospects in the fields of colorful display, anti-counterfeiting and information encryption. In the future, we will continue to explore more functions and applications of microspheres to meet the needs of different fields and promote the development of related technologies.

Claims

1. A phosphorescent polymer microsphere, characterized in that: The invention comprises a host and a guest, wherein the host is a cross-linked polymer microsphere PAM, and the guest is an organic room temperature phosphorescent molecule. The cross-linked polymer microsphere with afterglow is formed by adding the host into the guest solution and swelling, and is recorded as PAM-RTP.

2. The phosphorescent polymer microsphere according to claim 1, characterized in that: The cross-linked polymer microspheres PAM are prepared by adopting an inverse emulsion polymerization method.

3. The phosphorescent polymer microsphere according to claim 1, characterized in that: The guest RTP molecule is a mixture of one or more of 2-(9H-carbazole-9-yl)acetic acid, biphenyl-4,4'-dicarboxylic acid, 1-pyrenecarboxylic acid, 7-benzocarbazole or naphthalene imine.

4. The phosphorescent polymer microsphere according to claim 3, characterized in that: The doping ratio of the 2-(9H-carbazol-9-yl)acetic acid, biphenyl-4,4'-dicarboxylic acid, and 1-pyrenecarboxylic acid is 1 wt %.

5. The phosphorescent polymer microsphere according to claim 3, characterized in that: The guest is a combination of 2-(9H-carbazole-9-yl)acetic acid, biphenyl-4,4'-dicarboxylic acid and 1-pyrenecarboxylic acid, which then forms red, green and blue dynamic cross-linked polymer microspheres PAM-RGB with the host.

6. The phosphorescent polymer microsphere according to claim 1, characterized in that: The cross-linked polymer microspheres PAM-RTP are also doped with fluorescent molecules.

7. The phosphorescent polymer microsphere according to claim 6, characterized in that: The fluorescent molecule is fluorescein sodium, rhodamine 6G or rhodamine B.

8. Application of the phosphorescent polymer microspheres according to claims 1 to 7 in the fields of colorful display or information encryption.

9. The use according to claim 8, characterized in that: When the phosphorescent polymer microspheres are used in multi-color display, the main body of the phosphorescent polymer microspheres is cross-linked polymer microspheres polyacrylamide PAM, and the cross-linked polymer microspheres PAM are doped with at least one organic room temperature phosphorescent molecule to form multi-color dynamic cross-linked polymer microspheres, thereby realizing multi-color reversible afterglow display.

10. The use according to claim 9, characterized in that: The cross-linked polymer microspheres PAM are co-doped with 2-(9H-carbazole-9-yl)acetic acid, biphenyl-4,4'-dicarboxylic acid and 1-pyrenecarboxylic acid.

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