Circularly polarized luminescent material, preparation method and application thereof

Abstract

The present application relates to the technical field of luminescent material, in particular to a circularly polarized luminescent material and a preparation method and application thereof.The raw materials of the circularly polarized luminescent material include cellulose nanocrystal, glucose and an organic luminescent small molecule, wherein the mass ratio of the cellulose nanocrystal and the glucose is 1:(0-1.5), and the amount of the glucose is not 0.The present application successfully optimizes the room-temperature phosphorescence performance by combining the organic luminescent small molecule, the glucose and the cellulose nanocrystal.The optimized material has a room-temperature RTP lifetime of 2.04 seconds, which is significantly better than that of a conventional pure organic RTP material.Through precise regulation of the chiral nematic structure and the PBG of the CNC, the CPL film system of the present application can reach a maximum luminescence asymmetry factor of-0.749.

Description

TECHNICAL FIELD

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

[0002] Circularly polarized luminescent (CPL) materials have attracted increasing attention in recent years due to their potential applications in optoelectronic devices, biosensing, information encryption and three-dimensional display. The existing technologies mainly focus on the development of inorganic and organic CPL materials, 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 problems such as complex preparation process, high cost and environmental unfriendliness, which limit their promotion in large-scale applications. In contrast, pure organic CPL materials, with their diverse structures, mild synthesis conditions, low cost and environmental friendliness, are gradually becoming a research hotspot. In particular, organic molecules based on the aggregation-induced emission (AIE) property have been proven to effectively improve the CPL performance, but the circularly polarized luminescent intensity of such materials in the solid state still has room for improvement, and their synthesis process may still be relatively complex.

[0003] Notably, in recent years, a new method of constructing CPL materials by regulating the chiral physical environment of chromophores has gradually attracted widespread attention. This method not only has a simple preparation process, but also has strong applicability, can be compatible with a variety of chiral or achiral chromophores, and significantly improves the luminescence asymmetry factor (g lum ) of the material. However, this method still faces certain challenges in realizing the processability and flexibility of the material, limiting its widespread promotion in practical applications.

[0004] Currently, the main technical bottlenecks of CPL materials include: a low luminescence asymmetry factor, which limits their performance in high-performance devices; a complex synthesis process of some materials, which is difficult to meet the demand of large-scale production; the use of harmful elements in inorganic CPL materials and high preparation cost; and poor flexibility and processability of some materials in the solid state, which limits their application in flexible light-emitting devices.

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

[0006] The present application aims to provide a circularly polarized luminescent material and its preparation method and application, which has high g lum value, simple preparation, low cost, environmental friendliness and good processability.

[0007] To achieve the above-mentioned purpose, the present application provides the following solutions.

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

[0009] Optionally, the organic luminescent small molecule is 1H-benzo[g]indole, tetraphenyl ethylene or rhodamine 6G.

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

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

[0012] The second technical solution of the present application is the preparation method of the above-mentioned circularly polarized luminescent material, using cellulose nanocrystals, glucose and organic luminescent small molecules as raw materials, and preparing the circularly polarized luminescent material by solvent evaporation induced self-assembly.

[0013] Further, it specifically includes the following steps:

[0014] Dissolve the organic luminescent small molecule in the organic solvent, add glucose to form a mixed solution;

[0015] Add the mixed solution to the cellulose nanocrystal aqueous suspension to obtain a uniform mixed suspension;

[0016] Pour the mixed suspension into a mold, and form the circularly polarized luminescent material by evaporation induced self-assembly.

[0017] Further, the organic solvent is N,N-dimethylformamide (DMF); DMF is miscible with water and can dissolve small molecules, and has moderate evaporation speed, which is helpful for the preparation of the circularly polarized luminescent material.

[0018] Further, the concentration of the organic luminescent small molecule in the mixed solution is 1-10mM.

[0019] Further, the concentration of the organic luminescent small molecule in the mixed solution is 5 mM.

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

[0021] Further, the mass fraction of the cellulose nanocrystal aqueous suspension is 2.74%.

[0022] Three, the application of the above-mentioned circularly polarized luminescent material in optoelectronic devices, biosensing, information encryption or three-dimensional display.

[0023] Four, the application of the above-mentioned circularly polarized luminescent material in solvent detection.

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

[0025] Optionally, the circularly polarized luminescent material provided by the application can be used to detect a mixed solvent with a water volume content of 10%, 30%, 50%, 70%, or 90% in an ethanol solvent.

[0026] The application solves the following technical problems:

[0027] 1. Improve the luminescent performance of pure organic CPL materials in solid state, thereby enhancing their practicality and application value: The application utilizes the chiral photonic crystal properties of cellulose nanocrystals (CNC) to prepare CPL composite materials with photonic bandgap effect, 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, which endows the material with super-long phosphorescent performance and improves the luminescent performance of the material. Compared with other technical solutions using polyols as additives, glucose has excellent water solubility and can be uniformly distributed when mixed with the CNCs aqueous system. The water solubility and dispersibility of polyols are relatively low, especially for high molecular weight polyols. Uneven distribution in water may affect the control effect. In addition, as a natural biomolecule, the use of glucose is more environmentally friendly and has excellent biocompatibility, which helps to develop green and sustainable materials.

[0028] 2. Improve the luminescent asymmetry factor (g lum ) of the CPL material to meet the application requirements of high chiral luminescent materials: By adjusting the ratio of CNC to glucose, the application regulates the self-assembly pitch of CNC, thereby adjusting the photonic bandgap. The position of the photonic bandgap is monitored using reflectance spectroscopy (300-800 nm range) to match the emission wavelength of the organic luminescent small molecule. The degree of overlap between the photonic bandgap (PBG) and the emission spectrum is optimized to improve the g lum value.

[0029] 3. Develop green and environmentally friendly CPL material system, avoid using inorganic elements harmful to the environment or high cost, improve the sustainability of the material: the invention uses pure natural bio-based materials (such as CNC and glucose), avoids the use of toxic elements, and uses water as the solvent in the preparation process, which is safe and environmentally friendly, and realizes 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 realize the flexibility of the material, and prepare CPL film materials with good flexibility and processability, so as to expand the application (solvent detection).

[0031] The invention achieves the following technical effects:

[0032] 1. Significantly improve the luminescence performance.

[0033] The invention successfully optimizes the room temperature phosphorescence (RTP) performance by combining organic luminescent small molecules, glucose (Glu), and cellulose nanocrystals (CNC).

[0034] At the same time, the existing RTP system usually needs complex ligand design or additional inorganic components to prolong the phosphorescence lifetime, while the invention realizes the prolongation of the phosphorescence lifetime by forming hydrogen bonds and oxygen barrier means without the participation of heavy metals.

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

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

[0037] Comparison: the g lum value of existing pure organic CPL materials is generally between 0.01 and 0.1, while the g lum of the material of the invention is significantly higher than this range, which has the potential to be applied to high-performance chiral luminescent materials.

[0038] 3. Green and environmentally friendly advantage.

[0039] The invention uses pure natural bio-based materials (such as CNC and glucose) to avoid the use of traditional toxic elements, and realizes green sustainability by simplifying the preparation (solvent evaporation self-assembly) process.

[0040] 4. Application breakthrough.

[0041] When the material is exposed to ethanol-water mixed solvent, the solvent molecules can cause the micro-reconstruction of the CNC-glucose network structure, resulting in significant changes in chiral luminescent properties, providing the feasibility of high-sensitivity solvent detection, and realizing the preparation of solvent-responsive chiral performance change materials for the first time. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

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

[0044] Figure 2 The fluorescence and phosphorescence spectra of CNC / Glux-BI prepared in Example 1 of the present application; 0.2

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

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

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

[0048] Figure 6 The g lum curve of CNC / Glux-BI mixed photonic film prepared in Example 1 of the present application;

[0049] Figure 7 The fluorescence and phosphorescence spectra of CNC / Glu 0.2 -TPE in Example 2 of the present application under different ethanol-water mixing ratios; 0.2 -TPE and CNC / Glu 0.2 -R6G in Example 2 of the present application;

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

[0051] Figure 9 CNC / Glu for Example 2 of the present application 0.2 g of R6G at different ethanol-water mixing ratios lum curve;

[0052] Figure 10 Flow chart for preparing circularly polarized luminescent material in Example 1 of the present application. DETAILED DESCRIPTION

[0053] The various illustrative embodiments of the present application will now be described in detail in connection with the accompanying drawings. This description is made for the purpose of demonstrating various aspects of the present application and is not intended to limit the present application in any manner. Features, attributes and embodiments of the present application described in the context of one illustrative embodiment are applicable to other illustrative embodiments as well, unless the context clearly indicates otherwise.

[0054] It should be understood that the terms used herein are merely descriptive, but that the application should not be construed as being limited thereto. In addition, with respect to numerical ranges in the present application, it should be understood that each numerical value between the upper and lower limits of the range is specifically disclosed. Each intermediate value between any stated value or stated range, as well as any other stated value or intermediate value in the stated range, is also included in the application. The upper and lower limits of these smaller ranges can be independently included or excluded from the ranges.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All publications mentioned in this specification are herein incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference in this specification is not intended as an admission that the reference is prior art, but rather that the reference is part of the technical literature that is relevant to A person of ordinary skill in the art.

[0056] Many modifications and variations of this application specification can be made in the light of the above teachings without departing from the spirit or ambit of the application. Other implementations of this application will be apparent to those skilled in the art from consideration of the specification and practice of the application. The specification and examples are illustrative only.

[0057] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional, unrecited elements or method steps.

[0058] The raw materials used in the following examples of the present application are commercially available, and the source thereof does not affect the technical effects of the present application.

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

[0060] In the following examples of the present application, a feasible CNC preparation method is provided and used to prepare circularly polarized luminescent materials. CNCs prepared by other methods can also be used in the present application, and the source of CNCs does not affect the technical effects of the present application.

[0061] Example 1

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

[0063] Step 1: Microcrystalline cellulose is stirred at high speed with a 64wt% sulfuric acid solution at 45°C for hydrolysis. After 60 minutes of hydrolysis, the resulting light yellow suspension is diluted with ice water at least 20 times to terminate the reaction, and is left to stand for 24 hours. The upper clear phase of the layered suspension is slowly decanted, and the lower turbid phase is treated by centrifugation (8000 rpm, 5 minutes). After centrifugation, the supernatant is decanted, and the separated thick white phase is washed multiple times with ultrapure water to remove unwanted soluble cellulose material. The suspension is further centrifuged under the same conditions until the upper layer becomes turbid. Subsequently, the upper turbid liquid is poured into a dialysis bag (with a 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 is soaked in a high proportion of ultrapure water, and slight stirring is applied to accelerate the dialysis process. When the pH value of the ultrapure water outside the dialysis bag reaches 7, the suspension is added to a mixed bed resin and gently shaken for 1 day to remove residual soluble electrolytes. After the mixed suspension is filtered through filter paper (Whatman 541), the resulting light blue CNC suspension is treated with ultrasonic waves (power 1200W, 40% output) for 10 minutes. Finally, the CNC water suspension is concentrated by evaporation of water, and is stored in a refrigerator (2-8°C). The prepared cellulose nanocrystals are added to water to prepare a cellulose nanocrystal water suspension with a mass fraction of 2.74%.

[0064] Step 2: A 5 mM solution of 1H-benzo[g]indole small molecules in DMF was prepared using 1H-benzo[g]indole (BI) and DMF as raw materials, followed by the addition of different amounts of anhydrous glucose, which was stirred uniformly to form a mixed solution of organic light-emitting small molecules and anhydrous glucose. The mixed solution was slowly added to the cellulose nanocrystal aqueous suspension prepared in step 1 (the mass ratio of cellulose nanocrystals to organic light-emitting small molecules was 100:0.5) while maintaining strong stirring to ensure thorough mixing, resulting in a uniform mixed suspension. The prepared mixed suspension was cast in a plastic petri dish with a diameter of 35 mm, and the evaporation-induced self-assembly process was completed spontaneously at room temperature. After evaporation, a free-standing solid-state mixed photonic film (circularly polarized luminescent material) was obtained, which was named CNC / Glux-BI mixed photonic film, where "x" represents the mass ratio of anhydrous glucose to CNC. Based on the CNC to glucose ratio, the corresponding mixed photonic films obtained were named CNC / Glu0-BI, CNC / Glu0.2-BI, CNC / Glu0.5-BI, CNC / Glu0.9-BI, CNC / Glu1.5-BI, respectively. 0.2 CNC / Glu 0.5 CNC / Glu 0.9 CNC / Glu 1.5 CNC / Glu

[0065] Figure 1 Photographs of the luminescence of CNC / Glux-BI mixed photonic films prepared in Example 1 of the present application and CNC before and after excitation by 365 nm ultraviolet light; the luminescence of Figure 1 It can be seen that the photonic film obtained after co-assembly of BI molecules with CNC and glucose exhibits a significant green afterglow with a duration of more than 4 seconds, which is significantly longer than that of pure CNC and CNC / Glu0-BI films.

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

[0067] Figure 3 Fluorescence and phosphorescence spectra (room temperature) of BI;

[0068] Figure 2 It can be seen that even at a low glucose concentration (x = 0.2 in CNC / Glux-BI films), detectable phosphorescence can be observed. This is attributed to the rigidification of the co-assembly matrix by the formation of hydrogen bonds between glucose and BI molecules, which limits molecular motion, reduces the rate of non-radiative transitions, and stabilizes the excited state. These effects effectively reduce triplet quenching, promote the stabilization of triplets, and enhance room-temperature phosphorescence (RTP). Taking CNC / Glu 0.2 -BI as an example, Figure 2Its fluorescence spectrum showed a fluorescence peak of approximately 365 nm, consistent with the maximum fluorescence value of pure BI in solution. Figure 3 Its phosphorescence spectrum also corresponds to this.

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

[0070] Time-resolved decay curves indicate that these films have extremely long phosphorescence lifetimes, among which CNC / Glu0-BI and CNC / Glu 0.2 -BI, CNC / Glu 0.5 -BI, CNC / Glu 0.9 -BI and CNC / Glu 1.5 The lifetimes of -BI were 0.14s, 2.04s, 1.91s, 1.99s and 1.98s, respectively.

[0071] Building upon the above, this study further explores the modulating effect of the photonic bandgap (PBG) on chiral luminescence properties, and analyzes the relationship between the reflection spectrum of the photonic crystal thin film (hybrid photonic thin film) and the emission band of the guest molecules. The results are shown in […]. Figures 5-6 ;analyze Figures 5-6 It was discovered 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 -BI's PBG exhibits optimal overlap with the fluorescence and phosphorescence spectra of dispersed BI molecules, respectively, corresponding to g lum The values ​​reached -0.749 and -0.373 respectively. Figure 6 ).

[0072] Example 2

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

[0074] 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, respectively, to analyze CNC / Glu. 0.2 -TPE reflectance spectra under different ethanol-water mixing ratios and CNC / Glu 0.2TPE and CNC / Glu 0.2 Fluorescence spectra of R6G, results shown in Figure 7 CNC / Glu 0.2 g-factor of TPE photonic film under different ethanol-water mixing ratios lum Curves, shown in Figure 8 .

[0075] CNC / Glu 0.2 g-factor of R6G photonic film under different ethanol-water mixing ratios lum Curves, shown in Figure 9 .

[0076] As shown in Figures 7-9 , water can cause the pitch of chiral CNC photonic film to increase, thus making its photonic band gap (PBG) red-shift to longer wavelength. When the red-shifted PBG matches the emission wavelength of the luminophore, the g lum factor will change significantly. Taking CNC / Glu 0.2 -TPE as an example, when the mixing ratio of ethanol and water (7:3) can make the photonic band gap (PBG) match the emission wavelength of TPE Figure 7 , the g lum factor can reach the maximum (-0.331). Taking CNC / Glu 0.2 -R6G 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 , the g lum factor can reach the maximum (-0.345).

[0077] The above-described embodiments are merely preferred modes of the present application, and are not intended to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art shall fall within the scope of protection of the present application as defined by the claims.

Claims

1. Use of a circularly polarized luminescent material in solvent detection, characterized in that, The solvent detection is used for detecting the water content in the ethanol solvent; The circularly polarized luminescent material raw material comprises cellulose nanocrystals, glucose and an organic luminescent small molecule, wherein the mass ratio of the cellulose nanocrystals and the glucose is 1:(0-1.5), and the amount of the glucose is not 0; the mass ratio of the cellulose nanocrystals and the organic luminescent small molecule is 100:(0-1), and the amount of the organic luminescent small molecule is not 0; The organic luminescent small molecule is 1H-benzo[g]indole; The mass ratio of the cellulose nanocrystals and the glucose is 1:0.2, 1:0.5, 1:0.9 or 1:1.5; The preparation method of the circularly polarized luminescent material, wherein cellulose nanocrystals, glucose and an organic luminescent small molecule are used as raw materials, and the circularly polarized luminescent material is prepared through solvent evaporation induced self-assembly; specifically comprising the following steps: The organic luminescent small molecule is dissolved in an organic solvent, glucose is added, and a mixed solution is formed; The mixed solution is added to a cellulose nanocrystal water suspension to obtain a uniform mixed suspension; The mixed suspension is cast in a mold, and the circularly polarized luminescent material is formed through evaporation induced self-assembly; 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 molecule in the mixed solution is 1-10 mM; By adjusting the co-assembly ratio of the cellulose nanocrystals and the glucose, a mixed photonic film circularly polarized luminescent material with different PBGs is prepared.

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