A circularly polarized room temperature phosphorescent material based on marine polysaccharides and its preparation and application

Abstract

The invention belongs to the technical field of phosphorescent materials and specifically relates to a circularly polarized room temperature phosphorescent material based on marine polysaccharides and preparation and application thereof. 4-(4-bromophenyl)-pyridine and iodomethane are first dissolved in anhydrous ethanol and subjected to a reflux reaction to prepare bromophenylpyridinium. Then, a chiral marine polysaccharide λ-carrageenan containing a negatively charged sulfate group and an achiral phosphorescent chromophore bromophenylpyridinium containing a positively charged pyridine group are dissolved in deionized water, ultrasonically heated until clarified, and then gradually cooled to self-assemble to form a λ-carrageenan@bromophenylpyridinium suspension. Finally, the λ-carrageenan@bromophenylpyridinium suspension is vacuum-dried to obtain a circularly polarized room temperature phosphorescent thin film material based on marine polysaccharides. The material has stable properties and is suitable for applications such as phosphorescent digital encryption and optical anti-counterfeiting. The preparation method is simple and novel, the raw materials are widely available, and the cost is low. The invention is of great significance for the design and preparation of CP-RTP materials based on natural macromolecules.

Description

Technical field:

[0001] The present invention belongs to the technical field of phosphorescent materials, and in particular relates to a circularly polarized room temperature phosphorescent material based on marine polysaccharides, and a preparation and application thereof. Background technology:

[0002] Circularly polarized luminescence (CPL) is a phenomenon in which a chiral luminescent substance emits left-handed and right-handed circularly polarized light of different intensities under the excitation of monochromatic excitation light. It has potential application prospects in 3D display, bioimaging, anti-counterfeiting and encryption.

[0003] Currently, research on CPL-active materials mainly focuses on circularly polarized fluorescence and circularly polarized phosphorescence, involving singlet excited states and triplet excited states, respectively. Circularly polarized room temperature phosphorescent (CP-RTP) materials combine the advantages of room temperature phosphorescence and efficient circularly polarized luminescence, with properties such as large Stokes shift and long-lived emission. Chiral components, rigid microenvironments, and phosphors are prerequisites for achieving CP-RTP. However, the design and preparation of CP-RTP materials remain challenging due to the inherent instability of the triplet excited state and the complex chirality transfer between the chiral center and the phosphorescent unit.

[0004] Polysaccharides are widely present in living organisms. They are natural polymers composed of aldoses or ketoses linked by glycosidic bonds. They are important biomacromolecules and essential for the normal functioning of life. Polysaccharides are abundant, renewable, and readily available. They can be used to prepare room-temperature phosphorescent (RTP) materials. Their abundant hydroxyl groups provide a rigid microenvironment, stabilizing achiral organic phosphors through non-covalent interactions, thereby achieving RTP emission.

[0005] However, there are currently no reports on the use of marine polysaccharides to prepare circularly polarized room temperature phosphorescent materials. Summary of the invention:

[0006] The present invention aims to address technical issues in the prior art, such as the inherent instability of the triplet excited state, the complex chirality transfer between the chiral center and the phosphorescent unit, and the complex synthesis process of chiral phosphors or copolymers. The present invention provides a circularly polarized room temperature phosphorescent material based on marine polysaccharides, its preparation method, and application. Through supramolecular co-assembly technology, the chiral polysaccharide λ-carrageenan (λ-Car) is co-assembled with the achiral phosphorescent chromophore bromophenylpyridinium (PYI) to form a right-handed λ-carrageenan@bromophenylpyridinium (λ-Car@PYI) helical assembly. This prevents RTP quenching in the solid state, thereby constructing a luminescent material that emits left-handed circularly polarized phosphorescent light under stimulated emission at room temperature. This circularly polarized room temperature phosphorescent material does not require a complex synthesis process, effectively addresses the inherent instability of the triplet excited state and the complex chirality transfer between the chiral center and the phosphorescent unit, and has stable material properties, making it suitable for applications such as phosphorescent digital encryption and optical anti-counterfeiting.

[0007] In order to achieve the above object, the present invention provides a method for preparing a circularly polarized room temperature phosphorescent material based on marine polysaccharides, the specific steps of which are as follows:

[0008] S1: Preparation of phosphorescent chromophore bromophenylpyridinium:

[0009] Dissolve 4-(4-bromophenyl)-pyridine and iodomethane in anhydrous ethanol and heat under reflux for 12-36 hours; after cooling to room temperature, concentrate the reaction mixture by rotary evaporation to obtain a light golden precipitate, wash with dichloromethane, and vacuum dry to obtain a light golden solid, which is the phosphorescent color body bromophenylpyridinium;

[0010] S2: Preparation of circularly polarized room temperature phosphorescent thin film materials:

[0011] S2.1: Dissolving λ-carrageenan and the phosphorescent chromophore bromophenylpyridinium prepared in step S1 in deionized water to obtain an aqueous solution; sonicating the aqueous solution, heating it until clear, and then gradually cooling it to allow it to self-assemble into a λ-Car@PYI suspension containing helical microfibers exhibiting circularly polarized room temperature phosphorescence;

[0012] S2.2: Take the λ-Car@PYI suspension prepared in step S2.1 on a cleaned substrate, and evenly spin-coat the suspension on the substrate using a spin coater. After vacuum drying in a vacuum drying oven at 25°C, a λ-Car@PYI film with circularly polarized room temperature phosphorescent properties is obtained, which is a circularly polarized room temperature phosphorescent material based on marine polysaccharides.

[0013] When preparing the phosphor chromophore bromophenylpyridinium in step S1 of the present invention, the mass volume ratio of 4-(4-bromophenyl)-pyridine and iodomethane dissolved in anhydrous ethanol is (0.25-1g): (2-5mL): (50-100mL); the reflux temperature is 85-90°C.

[0014] In step S2 of the present invention, the diameter of the spiral micron fibers in the λ-Car@PYI suspension is 2.5 μm.

[0015] When preparing the circularly polarized room temperature phosphorescent thin film material in step S2 of the present invention, the concentration of the phosphorescent color body bromophenylpyridinium in the aqueous solution is 6-25 mM / L, and the concentration of λ carrageenan is 15-25 mM / L.

[0016] In step S2.1 of the present invention, the ultrasonic frequency is 40-60 Hz and the ultrasonication is performed for 5-15 minutes.

[0017] In step S2.1 of the present invention, the heating temperature is 95-105° C. and the heating time is 5-10 minutes.

[0018] In step S2.2 of the present invention, the acceleration of the spin coater is 1000-2000 rpm, the speed is 300-400 rpm, and the time is 30-60 s.

[0019] In step S2.2 of the present invention, the drying time in a vacuum drying oven is at least 3 hours, and the temperature is controlled at 15-35°C.

[0020] The substrate of the present invention is a quartz glass sheet.

[0021] The present invention also provides a circularly polarized room temperature phosphorescent material based on marine polysaccharide prepared by the preparation method, the absolute value of the circularly polarized fluorescence asymmetry factor of which is 4.1×10 -3 .

[0022] The present invention provides application of the circularly polarized room temperature phosphorescent material based on marine polysaccharide in digital encryption.

[0023] The present invention provides application of the circularly polarized phosphorescent material based on marine polysaccharide in optical anti-counterfeiting, wherein the circularly polarized room temperature phosphorescent material is used as an optical label in optical anti-counterfeiting.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention adopts a chiral co-assembly strategy to hierarchically co-assemble the chiral anionic polysaccharide λ-Car and the achiral cationic phosphor PYI in water through electrostatic interaction to form helical micron fibers, and then spin-coats and dries the helical micron fibers to form λ-Car@PYI thin films. In the solid state, the RTP is prevented from being affected by quenchers such as H2O and O2, thereby constructing a luminescent material that emits left-handed circularly polarized phosphorescence under stimulated emission at room temperature. The inherent instability of the triplet excited state and the complex chirality transfer problem between the chiral center and the phosphorescent unit are effectively solved. The material has stable properties and can be used in applications such as phosphorescent digital encryption and optical anti-counterfeiting.

[0026] (2) Wide sources of raw materials: The marine polysaccharide λ-Car used in the present invention is extracted from red algae, which reduces costs.

[0027] (3) Simple preparation method: The present invention adopts a supramolecular co-assembly strategy and does not require a complicated synthesis process.

[0028] (4) High innovation: The present invention utilizes polysaccharides through non-covalent bonds, which expands new perspectives for the design and preparation of CP-RTP materials.

[0029] (5) Excellent optical properties: The present invention forms a material with circularly polarized room temperature phosphorescence properties by co-assembling the anionic polysaccharide λ-Car and the non-chiral cationic phosphor PYI, which gives non-polarized light circular polarization properties, and has the advantages of excellent optical properties and room temperature emission.

[0030] In summary, the present invention co-assembles the chiral polysaccharide λ-Car with the achiral phosphorescent chromophore PYI through supramolecular co-assembly technology to form a λ-Car@PYI helical assembly with right-handed chirality, preventing room-temperature phosphorescence quenching in the solid state, thereby constructing a luminescent material that emits left-handed circularly polarized phosphorescence under stimulated emission at room temperature; it solves the inherent instability of the triplet excited state and the complex chirality transfer problem between the chiral center and the phosphorescent unit, and the material properties are stable, which can be suitable for applications such as phosphorescent digital encryption and optical anti-counterfeiting; its preparation method is simple and novel, the raw materials are widely available, and the cost is low, which is of great significance for the design and preparation of CP-RTP materials based on natural macromolecules. Description of the drawings:

[0031] Figure 1 (a) UV-visible absorption spectrum, (b) fluorescence spectrum of the PYI solution described in Example 1 of the present invention, and (c) phosphorescence spectrum of the PYI powder.

[0032] Figure 2 Circular dichroism (CD) spectrum of the λ-Car@PYI suspension described in Example 1 of the present invention and its photograph under sunlight.

[0033] Figure 3 This is a high-resolution scanning electron microscope image of the λ-Car@PYI spiral microfiber obtained in Example 1 of the present invention.

[0034] Figure 4 (a) Fluorescence spectrum and photograph at 365 nm excitation wavelength, and (b) laser confocal image of the λ-Car@PYI suspension described in Example 1 of the present invention.

[0035] Figure 5 This is the circularly polarized fluorescence spectrum of the λ-Car@PYI suspension described in Example 1 of the present invention.

[0036] Figure 6 Schematic diagram of the principle of circularly polarized fluorescence emission by the λ-Car@PYI suspension described in Example 1 of the present invention.

[0037] Figure 7 This is a circular dichroism spectrum of the λ-Car@PYI film described in Example 1 of the present invention and a photograph thereof under sunlight and 365nm excitation.

[0038] Figure 8 (a) Phosphorescence spectrum and (b) laser confocal image of the λ-Car@PYI film described in Example 1 of the present invention.

[0039] Figure 9 This is the phosphorescence lifetime test result of the λ-Car@PYI film described in Example 1 of the present invention.

[0040] Figure 10 This is the circularly polarized phosphorescence spectrum of the λ-Car@PYI film described in Example 1 of the present invention.

[0041] Figure 11 Schematic diagram of the principle of circularly polarized room temperature phosphorescence emitted by the λ-Car@PYI film described in Example 1 of the present invention.

[0042] Figure 12 This is a picture of the λ-Car@PYI circularly polarized room temperature phosphorescent thin film material described in Example 1 of the present invention being used for digital encryption display. Specific implementation method:

[0043] The technical solution of the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0044] Example 1:

[0045] (1) Preparation of phosphorescent chromophore bromophenylpyridinium (PYI):

[0046] 4-(4-Bromophenyl)-pyridine (1 g) and iodomethane (2 mL) were dissolved in 50 mL of anhydrous ethanol and heated under reflux for 24 h at 85°C. After cooling to room temperature, the reaction mixture was concentrated by rotary evaporation to obtain a pale golden precipitate, which was washed with dichloromethane and dried under vacuum to obtain a pale golden solid, namely, the phosphorescent colorant bromophenylpyridinium (PYI), in a yield of 50%.

[0047] PYI was dissolved in a certain amount of DMSO to obtain a PYI-DMSO solution, and its UV-visible absorption spectrum and fluorescence spectrum were tested. The phosphorescence spectrum of the synthesized PYI solid powder was also tested. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the UV-visible absorption spectrum of PYI-DMSO solution shows a strong absorption peak at 302 nm ( Figure 1 a), emits blue fluorescence at 380 nm ( Figure 1 b), while PYI solid powder shows orange phosphorescence at 580 nm under 302 nm ultraviolet light ( Figure 1 c);

[0048] (2) Preparation of circularly polarized room temperature phosphorescent thin film materials:

[0049] (a) Solid powders of the chiral marine polysaccharide λ carrageenan and the achiral phosphorescent chromophore PYI were weighed at a molar ratio of 1:0.4 and dissolved in deionized water to a concentration of 20 mM / L λ carrageenan and 8 mM / L PYI. The solution was sonicated for 10 min, heated at 100°C for 10 min until clear, and then gradually cooled to self-assemble into a λ carrageenan@bromophenylpyridinium (λ-Car@PYI) milky white suspension containing helical microfibers exhibiting circularly polarized room temperature phosphorescence.

[0050] The circular dichroism spectrum of the λ-Car@PYI milky white suspension was tested at room temperature and photographed under sunlight. The results are as follows: Figure 2 As shown, the results show that at the corresponding absorption wavelength of 302nm, CD presents a right-handed chiral signal that is first positive and then negative, and the λ-Car@PYI suspension appears milky white under sunlight; at the same time, according to the above method, the suspensions prepared with different molar ratios of λ carrageenan and PYI (1:0, 1:0.2, 1:0.6, 1:0.8, 1:1.0) were tested by circular dichroism spectroscopy, and the results are shown as follows Figure 2 As shown, there is no chiral signal when the molar concentration ratio of λ carrageenan to PYI is 1:0 and 1:0.2.

[0051] The milky white suspension of λ-Car@PYI was dried and then tested by high-resolution scanning electron microscopy. Figure 3 Scanning electron microscopy images show that λ-Car and PYI co-assemble to form helical microfibers with a diameter of approximately 2.5 μm.

[0052] The samples were taken for fluorescence spectrum of λ-Car@PYI suspension at room temperature, laser confocal imaging and photo shooting at 365nm excitation wavelength. The results are as follows: Figure 4 As shown, the results show that the fluorescence position is at 380nm ( Figure 4 a), λ-Car@PYI suspension emits blue fluorescence at 365 nm excitation wavelength ( Figure 4 a), Laser confocal micrometer fiber that emits blue fluorescence but no yellow phosphorescence ( Figure 4 b);

[0053] The circular polarization fluorescence spectrum of λ-Car@PYI suspension was tested and the principle diagram was speculated. The results are shown in the figure. Figure 5 and Figure 6 The results show that CPL presents a positive signal at the fluorescence position of 380 nm, and the absolute value of its luminescence asymmetry factor is 4.1×10 -3 , no CPL signal was detected at the phosphorescence position of 580nm; this is because the quenchers such as H2O and O2 present in the suspension quench the triplet excitons, causing them to return to the ground state in a non-radiative relaxation state and unable to emit phosphorescence.

[0054] (b) 30 μL of the λ-Car@PYI suspension was applied to a cleaned quartz glass slide and evenly spin-coated using a spin coater. After vacuum drying in a vacuum drying oven at 25°C for at least 3 h, a λ-Car@PYI film with circularly polarized room temperature phosphorescence (CPRP) properties was obtained, which is a CPRP material based on marine polysaccharides.

[0055] The λ-Car@PYI film was tested for circular dichroism spectrum at room temperature and photographed under sunlight and 365nm excitation. The results are as follows: Figure 7 As shown, the results show that at the corresponding absorption wavelength of 302nm, the CD presents a right-handed chiral signal that is first positive and then negative, which is consistent with the CD measured by the λ-Car@PYI suspension; compared with sunlight, the λ-Car@PYI film emits yellow phosphorescence under 365nm excitation.

[0056] The λ-Car@PYI film was taken for phosphorescence spectrum, laser confocal imaging and phosphorescence lifetime test. The results are as follows: Figure 8 and 9 As shown, the results show that its phosphorescence characteristic emission is at 580nm ( Figure 8 a), phosphorescence lifetime is 7.88ms ( Figure 9), laser confocal micrometer fiber with yellow phosphorescence ( Figure 8 b).

[0057] The circularly polarized phosphorescence spectrum of the λ-Car@PYI film was tested and its principle diagram was inferred. The results are shown in the figure. Figure 10 and Figure 11 As shown. Figure 10 As can be seen, the CPL exhibits a positive signal at the phosphorescence position of 580 nm. The solid-state circularly polarized room-temperature phosphorescence of the λ-Car@PYI film is achieved by preventing quenching of triplet (T1) excitons by quenchers such as H2O and O2, promoting intersystem crossing (S1→T1), suppressing nonradiative relaxation, and returning to the ground state (T1→S0) to emit phosphorescence in the form of light.

[0058] A certain amount of λ-Car aqueous solution and λ-Car@PYI suspension with a concentration of 20 mM / L were injected into different parts of the 3D printed digital “8888” mold for digital encryption display, such as Figure 12 As shown, after the solution in the mold naturally dried into a thin film, it was irradiated under sunlight and found that the mold showed the number "8888". However, when excited by 365nm ultraviolet light, the mold showed the encrypted number "2024" of orange phosphorescence.

[0059] As described above, the circularly polarized room temperature phosphorescent material based on marine polysaccharides prepared in the present invention has circularly polarized room temperature phosphorescent properties, imparts circular polarization to non-polarized light, and has the advantages of excellent optical properties and room temperature emission.

Claims

1. A method for preparing a circularly polarized room temperature phosphorescent material based on marine polysaccharides, characterized in that: The specific steps are as follows: S1: Preparation of phosphorescent chromophore bromophenylpyridinium: 4-(4-bromophenyl)-pyridine and iodomethane are dissolved in anhydrous ethanol and heated under reflux; after cooling to room temperature, the reaction mixture is concentrated to obtain a light golden precipitate, which is washed and dried to obtain a light golden solid, which is the phosphorescent color body bromophenylpyridinium; S2: Preparation of circularly polarized room temperature phosphorescent thin film materials: S2.1: Dissolving λ carrageenan and the phosphorescent chromophore bromophenylpyridinium from step S1 in deionized water to obtain an aqueous solution; sonicating the aqueous solution, heating it until clarified, and then cooling it to allow it to self-assemble into a λ carrageenan@bromophenylpyridinium suspension containing helical microfibers exhibiting circularly polarized room temperature phosphorescence; S2.2: The λ-carrageenan@bromophenylpyridinium suspension prepared in step S2.1 is vacuum dried to obtain a circularly polarized room temperature phosphorescent material based on marine polysaccharides.

2. The method for preparing a circularly polarized room temperature phosphorescent material based on marine polysaccharides according to claim 1, characterized in that: In step S1, 4-(4-bromophenyl)-pyridine and iodomethane are dissolved in anhydrous ethanol in a mass volume ratio of 0.25-1 g: 2-5 mL: 50-100 mL; the reflux temperature is 85-90° C., and the reflux time is 12-36 h.

3. The method for preparing a circularly polarized room temperature phosphorescent material based on marine polysaccharides according to claim 1, characterized in that: The vacuum drying time in step S2 is at least 3 hours, and the temperature is controlled at 15-35°C.

4. The preparation method according to claim 1, characterized in that In step S2.1, the concentration of the phosphorescent chromophore bromophenylpyridinium in the aqueous solution is 6-25 mM / L, and the concentration of λ carrageenan is 15-25 mM / L; the ultrasonic frequency is 40-60 Hz, and the ultrasonication is performed for 5-15 min; and the heating temperature is 95-105° C. and the heating is performed for 5-10 min.

5. The method for preparing a circularly polarized room temperature phosphorescent material based on marine polysaccharides according to claim 1, characterized in that: Before vacuum drying in step S2.2, the λ-carrageenan@bromophenylpyridinium suspension is spin-coated on the substrate using a spin coater.

6. The method for preparing a circularly polarized room temperature phosphorescent material based on marine polysaccharides according to claim 5, characterized in that: The acceleration of the spin coater is 1000-2000 rpm, the speed is 300-400 rpm, and the time is 30-60 s.

7. A circularly polarized room temperature phosphorescent material based on marine polysaccharide prepared by the preparation method according to any one of claims 1 to 6.

8. The circularly polarized room temperature phosphorescent material based on marine polysaccharides according to claim 7, characterized in that: The absolute value of the circularly polarized fluorescence asymmetry factor of the circularly polarized room temperature phosphorescent material is 4.1×10 -3 .

9. Use of the circularly polarized room temperature phosphorescent material based on marine polysaccharides according to claim 7 in digital encryption.

10. Use of the circularly polarized phosphorescent material based on marine polysaccharides according to claim 7 in optical anti-counterfeiting, characterized in that: The circularly polarized room temperature phosphorescent material is used as an optical label in optical anti-counterfeiting.

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