Circularly polarized luminescent material and preparation method and application thereof

Abstract

The invention relates to the technical field of luminescent materials, in particular to a circular polarization luminescent material and a preparation method and application thereof. Raw materials of the circular polarization luminescent material comprise cellulose nanocrystals, glucose and organic luminescent small molecules, the mass ratio of the cellulose nanocrystals to the glucose is 1: (0-1.5), and the dosage of the glucose is not 0. According to the invention, organic light-emitting micromolecules, glucose and cellulose nanocrystals are combined, such that room temperature phosphorescence performance is successfully optimized. The RTP service life of the optimized material at room temperature reaches 2.04 seconds, and the RTP service life is obviously superior to that of a traditional pure organic RTP material. By accurately regulating and controlling the chiral nematic phase structure of CNC and PBG, the CPL film system disclosed by the invention can reach a luminescence asymmetry factor of-0.749 to the maximum extent.

Description

Technical Field

[0001] The present invention relates to the technical field of luminescent materials, and in particular to a circularly polarized luminescent material and a preparation method and application thereof. Background Art

[0002] Circularly polarized luminescent (CPL) materials have attracted increasing attention in recent years due to their wide application potential in optoelectronic devices, biosensors, information encryption and three-dimensional display. Existing technologies mainly focus on the development of two major types of CPL materials: inorganic and organic, but each has certain limitations. For example, inorganic nanomaterials, including chalcogenide semiconductor nanomaterials, metal nanoclusters, perovskites and lanthanide complexes, have been widely used to construct CPL materials. However, such materials usually face the problems of complex preparation process, high cost and unfriendly environment, which limits their promotion in large-scale applications. In contrast, pure organic CPL materials are gradually becoming a research hotspot due to their diverse structures, mild synthesis conditions, low cost and environmental friendliness. In particular, organic molecules based on aggregation-induced emission (AIE) properties have been shown to effectively improve CPL performance, but the circularly polarized luminescence intensity of such materials in the solid state still needs to be improved, and their synthesis process may still be relatively complicated.

[0003] It is worth noting that in recent years, a new method for constructing CPL materials by regulating the chiral physical environment of chromophores has gradually attracted widespread attention. This method is not only simple to prepare, but also has strong applicability. It can be compatible with a variety of chiral or non-chiral chromophores, and at the same time significantly improves the luminescence asymmetry factor (g lum ). However, this method still faces certain challenges in achieving material processability and flexibility, which limits its widespread promotion in practical applications.

[0004] At present, the main technical bottlenecks of CPL materials include: the luminescence asymmetry factor is low, which leads to limited performance in high-performance devices; the synthesis process of some materials is complicated and difficult to meet the needs of large-scale production; harmful elements may be involved in inorganic CPL materials and the preparation cost is high; some materials exhibit poor flexibility and processability in the solid state, which limits their application in flexible light-emitting devices.

[0005] In summary, although there has been some progress in the research of circularly polarized luminescent materials, there are still many challenges in improving luminescence performance, simplifying preparation processes, reducing production costs, enhancing environmental friendliness, and improving material flexibility and processability. lum CPL materials with high performance, simple preparation, low cost, environmental friendliness and good processability, especially those based on pure organic systems, will become an important research direction in the future, showing great research value and broad application prospects. Summary of the invention

[0006] The purpose of the present invention is to provide a circularly polarized luminescent material and a preparation method and application thereof, which has high g lum It has the characteristics of high value, simple preparation, low cost, environmental friendliness and good processability.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention: a circularly polarized luminescent material, the raw materials include cellulose nanocrystals, glucose and organic luminescent small molecules, wherein the mass ratio of the cellulose nanocrystals to the glucose is 1:(0-1.5), and the amount of glucose is not 0; the mass ratio of the cellulose nanocrystals to the organic luminescent small molecules is 100:(0-1), and the amount of the organic luminescent small molecules is not 0.

[0009] Optionally, the organic light-emitting small molecule is 1H-benz[g]indole, tetraphenylethylene or rhodamine 6G.

[0010] Optionally, the mass ratio of the cellulose nanocrystals to glucose is 1:0.2, 1:0.5, 1:0.9 or 1:1.5.

[0011] Optionally, the mass ratio of the cellulose nanocrystals to the organic luminescent small molecules is 100:0.5.

[0012] The second technical solution of the present invention is a method for preparing the circularly polarized luminescent material, which uses cellulose nanocrystals, glucose and organic luminescent small molecules as raw materials and prepares the circularly polarized luminescent material by inducing self-assembly through solvent evaporation.

[0013] Furthermore, the method specifically includes the following steps:

[0014] Dissolving the organic luminescent small molecule in an organic solvent, and adding glucose to form a mixed solution;

[0015] adding the mixed solution into the cellulose nanocrystal water suspension to obtain a uniform mixed suspension;

[0016] The mixed suspension is cast into a mold, and the circularly polarized luminescent material is formed by evaporation-induced self-assembly.

[0017] Furthermore, the organic solvent is N,N-dimethylformamide (DMF); DMF is miscible with water and can dissolve small molecules, and has a moderate volatilization rate, which is helpful for the preparation of circularly polarized luminescent materials.

[0018] Furthermore, the concentration of the organic light-emitting small molecules in the mixed solution is 1-10 mM.

[0019] Furthermore, the concentration of the organic light-emitting small molecules in the mixed solution is 5 mM.

[0020] Furthermore, the mass fraction of the cellulose nanocrystal water suspension is 2-5%.

[0021] Furthermore, the mass fraction of the cellulose nanocrystal water suspension is 2.74%.

[0022] The third technical solution of the present invention is the application of the above circularly polarized luminescent material in optoelectronic devices, biosensors, information encryption or three-dimensional display.

[0023] A fourth technical solution of the present invention is application of the circularly polarized luminescent material in solvent detection.

[0024] Optionally, the solvent detection is to detect the water content in the ethanol solvent;

[0025] Optionally, the circularly polarized luminescent material provided by the present invention can be used to detect mixed solvents in which the volume content of water in the ethanol solvent is 10%, 30%, 50%, 70%, or 90%.

[0026] The present invention solves the following technical problems:

[0027] 1. Improve the luminescence performance of pure organic CPL materials in the solid state, thereby enhancing their practicality and application value: The present invention utilizes the chiral photonic crystal properties of cellulose nanocrystals (CNCs) to prepare CPL composite materials with photonic bandgap effects, wherein the matrix material is cellulose nanocrystals, and the additive is glucose. A hydrogen bond network is formed between glucose and organic luminescent small molecules, giving the material ultra-long phosphorescence performance and improving the luminescence performance of the material. Compared with other technical solutions using polyols as additives, glucose has excellent water solubility and can be evenly distributed when mixed with the CNCs aqueous phase system. Polyols have low water solubility and dispersibility, especially high molecular weight polyols, and uneven distribution in water may affect the regulation effect. In addition, as a natural biological molecule, the use of glucose is more environmentally friendly and has excellent biocompatibility, which helps to develop green and sustainable materials.

[0028] 2. Improve the luminescence asymmetry factor (g lum ) to meet the application requirements of high-chiral luminescent materials: The present invention adjusts the ratio of CNC to glucose, regulates the CNC self-assembly pitch, thereby adjusting the photonic band gap, and uses the reflection spectrum (300-800nm ​​range) to monitor the photonic band gap position to match it with the emission wavelength of organic luminescent small molecules, optimizes the overlap between the photonic band gap (PBG) and the emission spectrum, and improves g lum value.

[0029] 3. Develop a green and environmentally friendly CPL material system, avoid the use of inorganic elements that are harmful to the environment or high in cost, and improve the sustainability of the materials: The present invention uses pure natural bio-based materials (such as CNC and glucose), avoids the use of toxic elements, and the solvent used in the preparation process is water, which is safe and environmentally friendly, and achieves green sustainability by simplifying the preparation process.

[0030] 4. Design CPL materials with good flexibility and processability to expand their application range: The introduction of glucose can achieve the flexibility of the material and prepare CPL film materials with good flexibility and processability, thereby expanding its application (solvent detection).

[0031] The present invention achieves the following technical effects:

[0032] 1. Significantly improved the luminescence performance.

[0033] The present invention successfully optimizes the room temperature phosphorescence (RTP) performance by combining organic luminescent small molecules, glucose (Glu), and cellulose nanocrystals (CNC). The RTP lifetime of the optimized material at room temperature reaches 2.04 seconds, which is significantly better than traditional pure organic RTP materials (usually less than 1 second).

[0034] Meanwhile, existing RTP systems usually require complex ligand design or additional inorganic components to extend the phosphorescence lifetime, while the present invention achieves significant extension of the phosphorescence lifetime by forming hydrogen bonds and oxygen barrier means without the involvement of heavy metals.

[0035] 2. Achieved high luminescence asymmetry factor (g lum ).

[0036] By precisely regulating the chiral nematic phase structure and PBG (photonic band gap) of CNC, the CPL film system of the present invention can achieve a maximum luminescence asymmetry factor of -0.749.

[0037] Comparison: g of existing pure organic CPL materials lum The value is generally between 0.01 and 0.1, and the g of the material of the present invention lum Significantly higher than this range, it has the advantage of potential application in high-performance chiral luminescent materials.

[0038] 3. Green and environmental protection advantages.

[0039] Pure natural bio-based materials (such as CNC and glucose) are used, avoiding the use of traditional toxic elements, and achieving green sustainability through a simplified preparation (solvent evaporation self-assembly) process.

[0040] 4. Application breakthrough.

[0041] When the material is exposed to a mixed solvent such as ethanol-water, the solvent molecules will cause microscopic reconstruction of the CNC-glucose network structure, resulting in a significant change in the chiral luminescence properties, which provides feasibility for high-sensitivity solvent detection and realizes the preparation of solvent-responsive chiral property change materials for the first time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 The luminescence photos of the CNC / Glux-BI hybrid photonic film and CNC prepared in Example 1 of the present invention before and after excitation by 365nm ultraviolet light;

[0044] Figure 2 CNC / Glu prepared in Example 1 of the present invention 0.2 - Fluorescence and phosphorescence spectra of BI;

[0045] Figure 3 is the fluorescence and phosphorescence spectra of BI;

[0046] Figure 4 The time-resolved phosphorescence decay curve of the CNC / Glux-BI hybrid photonic film prepared in Example 1 of the present invention;

[0047] Figure 5 The reflection spectrum of the CNC / Glux-BI hybrid photonic film prepared in Example 1 of the present invention and the luminescence spectrum of the BI solution;

[0048] Figure 6 g is the CNC / Glux-BI hybrid photonic film prepared in Example 1 of the present invention lum curve;

[0049] Figure 7 CNC / Glu in Example 2 of the present invention 0.2 -Reflectance spectra of TPE at different ethanol-water mixing ratios and CNC / Glu 0.2 -TPE and CNC / Glu 0.2 - Fluorescence spectrum of R6G;

[0050] Figure 8 CNC / Glu in Example 2 of the present invention 0.2 -TPE g under different ethanol-water mixing ratios lum curve;

[0051] Fig. 9 CNC / Glu in Example 2 of the present invention 0.2 -R6G g under different ethanol-water mixing ratios lum curve;

[0052] Fig.10 This is a flow chart for preparing circularly polarized luminescent material according to Example 1 of the present invention. DETAILED DESCRIPTION

[0053] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0054] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0055] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0056] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0057] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0058] The raw materials used in the following examples of the present invention are all purchased from the market, and their sources do not affect the technical effects of the present invention.

[0059] In the following embodiments of the present invention, the room temperature is specifically 26° C. and the relative humidity is 50±5%.

[0060] In the following embodiments of the present invention, a feasible CNC preparation method is provided and used for preparing circularly polarized luminescent materials. CNC prepared by other methods can also be used in the present invention, and the source of CNC does not affect the technical effect of the present invention.

[0061] Example 1

[0062] In this example, cellulose powder was used as raw material, and cellulose nanocrystals (CNC) were prepared by acid hydrolysis as the main structural component. Then, the membrane material was formed by evaporation-induced self-assembly. Glucose was added during the process to adjust the helical pitch to optimize the photonic band gap (PBG) and achieve high g lum value, and 1H-benzo[g]indole (BI) was selected as the main luminescent guest molecule to finally prepare a self-supporting photonic film. The specific process is as follows:

[0063] Step 1: Microcrystalline cellulose was hydrolyzed with 64 wt% sulfuric acid solution at 45 °C under high-speed stirring. After 60 minutes of hydrolysis, the resulting light yellow suspension was diluted at least 20 times with ice water to terminate the reaction and allowed to stand for 24 hours. The upper clear phase of the layered suspension was slowly decanted, while the lower turbid phase was centrifuged (8000 rpm, 5 minutes). After centrifugation, the supernatant was decanted and the separated thick white phase was washed several times with ultrapure water to remove unwanted soluble cellulose materials. The suspension was further centrifuged under the same conditions until the upper layer became turbid. Subsequently, the upper turbid liquid was poured into a dialysis bag (molecular weight cutoff range of 8000–14,000) and dialyzed in ultrapure water for 3–4 days. The CNC semi-finished product suspension in the dialysis bag was immersed in a high proportion of ultrapure water, and slight stirring was applied to accelerate the dialysis process. When the pH value of the ultrapure water outside the dialysis bag reached 7, the suspension was added to the mixed bed resin and gently shaken for 1 day to remove the residual soluble electrolyte. After the mixed suspension was filtered through filter paper (Whatman 541), the obtained light blue CNC suspension was ultrasonically treated for 10 minutes under an ultrasonic device (power 1200W, 40% output). Finally, the CNC water suspension was concentrated by water evaporation and stored in a refrigerator (2–8°C). The prepared cellulose nanocrystals were added to water to prepare a cellulose nanocrystal water suspension with a mass fraction of 2.74%.

[0064] Step 2: 1H-benzo[g]indole (BI) and DMF are used as raw materials to prepare a 5mM DMF solution of 1H-benzo[g]indole small molecules, and then different masses of anhydrous glucose are added and stirred evenly to form a mixed solution of organic luminescent small molecules and anhydrous glucose. The above mixed solution is slowly added to the cellulose nanocrystal water suspension prepared in step 1 (the mass ratio of cellulose nanocrystals to organic luminescent small molecules is 100:0.5), while maintaining strong stirring to ensure sufficient mixing to obtain a uniform mixed suspension. The prepared mixed suspension is cast in a plastic culture dish with a diameter of 35 mm and placed at room temperature to spontaneously complete the evaporation-induced self-assembly process. After evaporation, a free-standing solid-state hybrid photonic film (circularly polarized luminescent material) was obtained, which was named CNC / Glux-BI hybrid photonic film, where "x" represents the mass ratio of anhydrous glucose to CNC. The ratios of CNC to glucose were 1:0, 1:0.2, 1:0.5, 1:0.9, and 1:1.5, respectively. The corresponding hybrid photonic films were named CNC / Glu 0 -BI, CNC / Glu 0.2 -BI, CNC / Glu 0.5 -BI, CNC / Glu 0.9 -BI, CNC / Glu 1.5 -BI.

[0065] Figure 1 The luminescence photos of the CNC / Glux-BI hybrid photonic film and CNC prepared in Example 1 of the present invention before and after being excited by 365nm ultraviolet light; Figure 1 It can be seen that the photonic film obtained after co-assembling BI molecules with CNC and glucose exhibited a significant green afterglow, which lasted for more than 4 seconds, significantly longer than that of pure CNC and CNC / Glu. 0 -BI film.

[0066] Figure 2 For CNC / Glu 0.2 - Fluorescence and phosphorescence spectra of BI (room temperature);

[0067] Figure 3 is the fluorescence and phosphorescence spectra of BI (room temperature);

[0068] Figure 2 It can be seen that even at low glucose concentrations (x = 0.2 in CNC / Glu-BI films), detectable phosphorescence can be observed. This is attributed to the fact that glucose rigidifies the co-assembled matrix by forming hydrogen bonds with BI molecules, thereby restricting molecular motion, reducing the rate of non-radiative transitions, and stabilizing the excited state. These effects effectively reduce triplet quenching, promote triplet stabilization, and enhance room temperature phosphorescence (RTP). 0.2-BI as an example ( Figure 2 ), its fluorescence spectrum showed a fluorescence peak of about 365nm, which is consistent with the fluorescence maximum of pure BI in solution ( Figure 3 ), and its phosphorescence spectrum also corresponds to it.

[0069] Figure 4 The time-resolved phosphorescence decay curve of the CNC / Glux-BI hybrid photonic film prepared in Example 1 of the present invention;

[0070] The time-resolved decay curves show that these films have extremely long phosphorescence lifetimes, among which CNC / Glu 0 -BI, CNC / Glu 0.2 -BI, CNC / Glu 0.5 -BI, CNC / Glu 0.9 -BI and CNC / Glu 1.5 The lifetimes of -BI are 0.14s, 2.04s, 1.91s, 1.99s, and 1.98s, respectively.

[0071] On the basis of the above contents, the regulation effect of photonic band gap (PBG) on chiral luminescence properties is further explored, and the relationship between the reflection spectrum of photonic crystal film (hybrid photonic film) and the emission band of guest molecules is analyzed. The results are shown in Figure 5-6 ;analyze Figure 5-6 It was found that by adjusting the co-assembly ratio of CNC and glucose, CNC / Glux-BI hybrid photonic films with different PBGs were prepared. Figure 5 As shown, CNC / Glu 0.2 -BI and CNC / Glu 0.9 The PBG of -BI has the best overlap with the fluorescence and phosphorescence spectra of dispersed BI molecules, respectively. lum The values ​​are -0.749 and -0.373 ( Figure 6 ).

[0072] Example 2

[0073] The same as Example 1, except that the dye molecule 1H-benzo[g]indole (BI) was replaced by tetraphenylethylene (TPE) and rhodamine 6G (R6G) in equal mass to obtain CNC / Glux-TPE and CNC / Glux-R6G.

[0074] The prepared CNC / Glu 0.2 -TPE and CNC / Glu 0.2 -R6G was placed in ethanol-water mixed solvents with volume ratios of 9:1, 7:3, 5:5, 3:7, 1:9, and 0:10 to analyze the CNC / Glu 0.2-Reflectance spectra of TPE at different ethanol-water mixing ratios and CNC / Glu 0.2 -TPE and CNC / Glu 0.2 -R6G fluorescence spectrum, the results are shown in Figure 7 . Detection of CNC / Glu 0.2 -TPE photonic film g under different ethanol-water mixing ratios lum Curve, see Figure 8 .

[0075] Detection of CNC / Glu 0.2 g of R6G photonic film under different ethanol-water mixing ratios lum Curve, see Fig. 9 .

[0076] like Figure 7-9 As shown in Figure 2, moisture can cause the pitch of the chiral CNC photonic film to increase, thereby red-shifting its photonic band gap (PBG) to a longer wavelength. When the red-shifted PBG matches the emission wavelength of the luminescent body, g lum The value will change significantly. 0.2 -TPE is an example. When the mixing ratio of ethanol and water (7:3) can make the photonic band gap (PBG) match the TPE emission wavelength ( Figure 7 ), then we can reach g lum The value is the largest (-0.331). 0.2 -R6G is taken as an example. When the mixing ratio of ethanol and water (1:9) can make the photonic band gap (PBG) match the emission wavelength of R6G ( Figure 7 ), then we can reach g lum The value is the largest (-0.345).

[0077] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A circularly polarized luminescent material, characterized in that: The raw materials include cellulose nanocrystals, glucose and organic luminescent small molecules, wherein the mass ratio of the cellulose nanocrystals to glucose is 1:(0-1.5), and the amount of glucose is not 0; the mass ratio of the cellulose nanocrystals to the organic luminescent small molecules is 100:(0-1), and the amount of the organic luminescent small molecules is not 0.

2. The circularly polarized luminescent material according to claim 1, characterized in that: The organic light-emitting small molecule is 1H-benz[g]indole, tetraphenylethylene or rhodamine 6G.

3. The circularly polarized luminescent material according to claim 1, characterized in that: The mass ratio of the cellulose nanocrystals to glucose is 1:0.2, 1:0.5, 1:0.9 or 1:1.

5.

4. A method for preparing a circularly polarized luminescent material according to any one of claims 1 to 3, characterized in that: The circularly polarized luminescent material is prepared by using cellulose nanocrystals, glucose and organic luminescent small molecules as raw materials and inducing self-assembly through solvent evaporation.

5. The preparation method according to claim 4, characterized in that: The specific steps include: Dissolving the organic luminescent small molecule in an organic solvent, and adding glucose to form a mixed solution; adding the mixed solution into the cellulose nanocrystal water suspension to obtain a uniform mixed suspension; The mixed suspension is cast into a mold, and the circularly polarized luminescent material is formed by evaporation-induced self-assembly.

6. The preparation method according to claim 5, characterized in that: The organic solvent is N,N-dimethylformamide; the mass fraction of the cellulose nanocrystal water suspension is 2-5%; and the concentration of the organic luminescent small molecules in the mixed solution is 1-10 mM.

7. An application of the circularly polarized luminescent material according to any one of claims 1 to 3 in optoelectronic devices, biosensors, information encryption or three-dimensional displays.

8. Use of the circularly polarized luminescent material according to any one of claims 1 to 3 in solvent detection.

9. The use according to claim 8, characterized in that: The solvent detection is to detect the water content in the ethanol solvent.

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