An organic luminescent material and a corresponding solid hydrogel capable of emitting light upon water exposure, paper for inkjet printing

Abstract

The application belongs to the field of intelligent light-emitting materials, discloses an organic light-emitting material and corresponding solid hydrogel capable of emitting light when meeting water and paper for inkjet printing, wherein the organic light-emitting material has a chemical structure as shown in formula I; the aqueous solution of the organic light-emitting material can emit fluorescence under the participation of free radicals. The application uses the organic light-emitting material with a molecular structure as shown in formula I as a novel high polymer material capable of emitting light when meeting water, which can be mixed into a hydrogel network or paper as a light-emitting core, and a hydrogel capable of emitting light when meeting water and paper for inkjet printing can be prepared. The prepared hydrogel can have special response to pH and gamma-CD.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent luminescent materials, and more specifically, relates to an organic luminescent material and a corresponding solid hydrogel and inkjet printing paper that can emit light when exposed to water. The organic luminescent material can sense water, γ-cyclodextrin (γ-CD) and pH value and thus produce a fluorescent effect. Background Art

[0002] Smart luminescent materials, which emit luminescent signals that can be visually detected in response to stimuli, have attracted widespread attention. Dynamically tunable luminescent systems often exhibit sensitive modulation of luminescence properties in response to various external stimuli, such as light, temperature, magnetism, mechanical force, chemistry, electric fields, and pH. Consequently, these systems have attracted considerable attention and wide-ranging applications in fields such as information encryption, bioimaging, detection, sensing, diagnosis, and therapy. Over the past decade, scientists have reported numerous stimuli-responsive luminescent materials that exhibit multicolor luminescence and luminescence switching effects in response to external stimuli.

[0003] Supramolecular assemblies are defined as multimolecular groups formed by non-covalent bonds, and can be as simple as two molecules. They can be spherical, rod-shaped, or sheet-like. Their sizes range from nanometers to micrometers. Two or more molecules are bound together to form complex, organized aggregates that maintain a certain degree of integrity, resulting in well-defined microstructures and macroscopic properties. The relationship between molecules and supramolecular structures and intermolecular interactions is similar to the relationship between atoms and molecules and covalent bonds.

[0004] Pyrene-based π-conjugated materials are considered to be ideal organic electroluminescent materials for applications in semiconductor devices such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic photovoltaics (OPVs). Aggregation-induced quenching (AlQ) is a physical phenomenon that describes the quenching of fluorescence or luminescence signals by the formation of molecular or macroscopic aggregates in solutions or solid-state materials. This is because the formation of aggregates leads to close contact between molecules, which changes the internal electronic energy levels of the molecules, disrupting the luminescence pathway of the fluorescent marker, thereby reducing the amount of luminescence or completely extinguishing it. The biggest disadvantage of using pyrene as an organic luminescent material is the formation of quasi-molecular emission, which quenches efficiency at high concentrations or in the solid state. Therefore, in order to obtain efficient optical devices, scientists have invested a lot of effort in adjusting the structure of pyrene derivatives to achieve exploitable properties by adopting two strategies: 1) introducing various moieties into the pyrene core, and 2) exploring effective and convenient synthetic strategies to functionalize the pyrene core.

[0005] Water-responsive materials have garnered widespread attention due to their unique properties, with significant applications in erasable paper and sweat pore mapping. Conventional printing inks are relatively expensive due to their high material and R&D costs. However, using water as ink, the cheapest and most readily available liquid in our daily lives, can significantly reduce printing costs. Summary of the Invention

[0006] To address the aforementioned deficiencies and improvements in the prior art, the present invention aims to provide an organic luminescent material and the resulting solid hydrogel that luminesces upon exposure to water, as well as inkjet printing paper. By using an organic luminescent material with a molecular structure such as Formula I as a novel hydroluminescent polymer material, this organic luminescent material can be incorporated into a hydrogel network or incorporated into paper as a luminescent core, resulting in a hydroluminescent hydrogel and inkjet printing paper. The resulting hydrogel exhibits specific responses to pH and γ-CD. The resulting paper also exhibits hydroluminescence and γ-CD luminescence, with patterns generated only under fluorescent conditions, making it suitable for inkjet printing, information transmission, and decryption applications.

[0007] To achieve the above objectives, according to a first aspect of the present invention, an organic light-emitting material is provided, having a chemical structure as shown in Formula I:

[0008]

[0009] In formula I, X and Y represent the attachment amount of the corresponding monomer, and X:Y does not exceed 0.5;

[0010] The aqueous solution of the organic light-emitting material can emit fluorescence under the participation of free radicals.

[0011] According to a second aspect of the present invention, a solid hydrogel capable of luminescence in contact with water is provided. The solid hydrogel is obtained by first uniformly dispersing the above-mentioned organic luminescent material and a water-soluble thermal free radical initiator in water to form a hydrogel solution. Then, the hydrogel solution is heated to generate free radicals to obtain a synthetic hydrogel, and finally, the synthetic hydrogel is dehydrated.

[0012] According to a third aspect of the present invention, a solid hydrogel capable of luminescence in contact with water is provided. The solid hydrogel is obtained by first uniformly dispersing the above-mentioned organic luminescent material with acrylamide, sodium acrylate, ammonium persulfate (APS), N,N'-methylenebisacrylamide (MBAA), and tetramethylethylenediamine (TEMED) in water to form a hydrogel solution. Subsequently, the hydrogel solution is heated to generate free radicals to obtain a synthetic hydrogel, and finally the synthetic hydrogel is dehydrated.

[0013] As a further preferred embodiment of the present invention, in the hydrogel solution, the mass ratio of the acrylamide to the sodium acrylate is 5:1;

[0014] The concentration of the organic light-emitting material in the hydrogel solution does not exceed 0.1 mg / mL;

[0015] The concentration of acrylamide in the hydrogel solution does not exceed 0.2 g / mL;

[0016] The concentration of ammonium persulfate (APS) in the hydrogel solution does not exceed 1 mg / mL;

[0017] The concentration of N,N'-methylenebisacrylamide (MBAA) in the hydrogel solution does not exceed 1 mg / mL;

[0018] The concentration of tetramethylethylenediamine (TEMED) in the hydrogel solution does not exceed 5 μL / mL.

[0019] As a further preferred embodiment of the present invention, the heating is performed at a temperature above 40°C, preferably at a temperature of 80°C.

[0020] According to a fourth aspect of the present invention, there is provided a paper for inkjet printing, which is obtained by impregnating a paper body with a hydrogel solution and then heating and drying it;

[0021] The hydrogel solution is formed by uniformly dispersing the organic light-emitting material and a water-soluble thermal free radical initiator in water.

[0022] According to a fifth aspect of the present invention, there is provided a paper for inkjet printing, which is obtained by impregnating a paper body with a hydrogel solution and then heating and drying it;

[0023] The hydrogel solution is formed by uniformly dispersing the above organic light-emitting material, acrylamide, sodium acrylate, ammonium persulfate (APS), tetramethylethylenediamine (TEMED), and N,N'-methylenebisacrylamide (MBAA) in water.

[0024] As a further preferred embodiment of the present invention, in the hydrogel solution, the mass ratio of the acrylamide to the sodium acrylate is 5:1;

[0025] The concentration of the organic light-emitting material in the hydrogel solution does not exceed 0.1 mg / mL;

[0026] The concentration of acrylamide in the hydrogel solution does not exceed 0.2 g / mL;

[0027] The concentration of ammonium persulfate (APS) in the hydrogel solution does not exceed 1 mg / mL;

[0028] The concentration of N,N'-methylenebisacrylamide (MBAA) in the hydrogel solution does not exceed 1 mg / mL;

[0029] The concentration of tetramethylethylenediamine (TEMED) in the hydrogel solution does not exceed 5 μL / mL.

[0030] As a further preferred embodiment of the present invention, the heat drying is performed at a temperature of 40° C. or higher until the moisture is completely eliminated; preferably, the heat drying is performed at a temperature of 80° C. until the moisture is completely eliminated.

[0031] According to a sixth aspect of the present invention, the present invention provides the use of the above-mentioned organic light-emitting material, the above-mentioned solid hydrogel capable of luminescence in contact with water, or the above-mentioned paper for inkjet printing in fluorescent color change in response to water.

[0032] As a further preferred embodiment of the present invention, the fluorescent color change is reversible fluorescent color change, and the organic light-emitting material, the solid hydrogel, or the inkjet printing paper can be restored by drying and dehydrating, and can be used again in the fluorescent color change in response to water.

[0033] According to the seventh aspect of the present invention, the present invention provides the use of the above-mentioned organic luminescent material, the above-mentioned solid hydrogel capable of luminescence in contact with water, or the above-mentioned paper for inkjet printing in fluorescence color change in response to pH value, which can undergo fluorescence quenching under acidic conditions and restore fluorescence under alkaline conditions.

[0034] As a further preference of the present invention, the fluorescent color change is reversible fluorescent color change.

[0035] According to the eighth aspect of the present invention, the present invention provides the use of the above-mentioned organic luminescent material, the above-mentioned solid hydrogel capable of luminescence in contact with water, or the above-mentioned inkjet printing paper in fluorescent color change in response to a γ-cyclodextrin aqueous solution.

[0036] Compared with the prior art, the above technical solutions proposed by the present invention can achieve the following:

[0037] Beneficial effects:

[0038] (1) The organic light-emitting material of Formula I obtained in the present invention is a high-molecular-weight functional molecule that has a special response to water. The compound of Formula I will reassemble upon contact with water with the participation of free radicals, thereby generating fluorescence.

[0039]

[0040] The organic light-emitting material of Formula I obtained by the present invention can be formed by attaching Compound 3 (structural formula shown in the table below) and 1-bromobutane (structural formula shown in the table below) to P4VP (polyvinylpyridine, structural formula shown in the table below, where n is the number of pyridines in P4VP). In Formula I, X and Y represent the amounts of Compound 3 and 1-bromobutane attached to P4VP, respectively, and the ratio of X / n:Y / n does not exceed 0.5 (i.e., X:Y ≤ 0.5).

[0041]

[0042] (2) The organic light-emitting material shown in Formula I obtained by the present invention can generate fluorescence by adding water-soluble free radicals to its aqueous solution (the solvent is H2O) and heating to generate free radicals. The light-emitting molecule obtained by the present invention is a new type of light-emitting molecule, the light-emitting excitation mode of which is free radical initiation, and the light-emitting state requires water as a medium to be maintained. In particular, the present invention can uniformly disperse the organic light-emitting material shown in Formula I together with acrylamide, sodium acrylate, APS, TEMED, and MBAA in water to form a hydrogel solution (in the hydrogel solution, the mass ratio of acrylamide to sodium acrylate is 5:1, the concentration of the organic light-emitting material in the hydrogel solution does not exceed 0.1 mg / mL, the concentration of acrylamide in the hydrogel solution does not exceed 0.2 g / mL, the concentration of APS in the hydrogel solution does not exceed 1 mg / mL, the concentration of MBAA in the hydrogel solution does not exceed 1 mg / mL, and the concentration of TEMED in the hydrogel solution does not exceed 5 μL / mL). The hydrogel solution can be used to form a solid hydrogel or to form paper for inkjet printing.

[0043] (3) The solid hydrogel obtained by the present invention has the characteristics of intelligent response. The solid hydrogel obtained by the present invention produces blue-green fluorescence when it comes into contact with water, and the color will fade after it is dried. It is a reusable color-changing hydrogel. In addition, the solid hydrogel obtained by the present invention has pH response. It will quench the fluorescence under acidic conditions and restore the fluorescence under alkaline conditions. The quenching and appearance of fluorescence are reversible with the change of acid and base. The γ-CD aqueous solution can make the hydrogel produce light yellow fluorescence. In this process, γ-CD and the organic light-emitting material (i.e., the compound of formula I) produce a host-guest interaction, so the fluorescence color change is irreversible.

[0044] (4) The hydrogel solution formed based on the compound of formula I can be used to form paper for inkjet printing. In particular, the luminescent effect of water can be utilized to realize inkjet printing using water as ink, thereby greatly reducing the cost of ink. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is the characteristic ultraviolet absorption spectrum of the compound of structural formula I.

[0046] Figure 2 1 is the fluorescence emission spectrum of the hydrogel solution before and after heating in Example 2. In the figure, the black curve corresponds to before heating, and the red curve corresponds to after heating.

[0047] Figure 3 This is a photo of the solid hydrogel obtained in Example 2 luminescing upon contact with water and undergoing five cycles of water contact and drying.

[0048] Figure 4 This is a physical diagram of the selective response of the solid hydrogel obtained in Example 2 to different solvents.

[0049] Figure 5 This is a physical picture of the solid hydrogel obtained in Example 2 responding to acid and base.

[0050] Figure 6 This is a physical picture of the response of the solid hydrogel obtained in Example 2 to γ-CD.

[0051] Figure 7 This is the special paper prepared in Example 3 that responds to water.

[0052] Figure 8 This is the hydrogen spectrum of compound 2 obtained in Example 1. DETAILED DESCRIPTION

[0053] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0054] Taking compound 2 as an example, the synthetic route of the compound of formula I of the present invention is as follows:

[0055]

[0056] The raw materials P4VP (polyvinylpyridine), 1-n-bromobutane, and DMF used in the following examples were all commercially available; compound 3 was prepared independently according to prior art reports (for relevant prior art, see: Yuan, Y.-C., et al. (2021). "Enantiopure isothiourea@carbon-based support: stacking interactions for recycling a lewis base in asymmetric catalysis." Organic Chemistry Frontiers 8(17): 4693-4699.).

[0057] All reagents used in the detection operations in the following examples were also purchased from commercial sources.

[0058] Example 1: Synthesis of Compounds of Formula I

[0059] The following steps are involved:

[0060] (1) Weigh 107 mg of P4VP (polyvinyl pyridine) and 73.4 mg of compound 3 and dissolve them in 5 mL of DMF. Then, heat and reflux for 48 h, cool to room temperature, precipitate with anhydrous ether, and centrifuge to obtain a solid product. Dissolve it in methanol solution and centrifuge it with ether solution three times to wash away DMF to obtain solid compound 1.

[0061] (2) The synthesized compound 1 was dissolved in 15 mL of DMF, and then 1.5 mL of 1-n-bromobutane was added. After heating and reflux for 48 h, the mixture was cooled to room temperature and precipitated with anhydrous ether. The solid product was then centrifuged to obtain a solid product. The solid product was then dissolved in methanol solution and centrifuged three times with ether solution to wash away DMF to obtain a solid compound 2.

[0062] Compound 2 was subjected to hydrogen spectrum detection (solvent was deuterated DMSO), and the results were as follows Figure 8 As shown, 5.23, 8.18, 8.29 and 9.03 are characteristic peaks, which shows that compound 2 belongs to one of the compounds of formula I (corresponding to X:Y=1:9 in formula I).

[0063] The UV absorption spectrum of the aqueous solution of compound 2 is shown in Figure 1 As shown, the peak at 345 nm is the characteristic peak of pyrene.

[0064] Example 2: Preparation of hydrogel

[0065] The following steps are involved:

[0066] (1) Compound 2 obtained in Example 1 was used as a raw material to prepare an aqueous solution of Compound 2 with a concentration of 0.1 mg / mL.

[0067] (2) To 5 mL aqueous solution of compound 2, 0.5 g of acrylamide, 0.1 g of sodium acrylate (mass ratio of acrylamide / sodium acrylate is 5:1), 1 mg of APS, 1 mg of MAA, 10 μL of TEMED were added, and mixed uniformly to obtain a hydrogel solution.

[0068] (3) The hydrogel solution was heated at 80℃ for 10 min to obtain a synthetic hydrogel.

[0069] (4) The synthetic hydrogel was continuously heated at 80℃ until the water in the synthetic hydrogel was completely evaporated to obtain a solid hydrogel.

[0070] The fluorescence emission spectra of the hydrogel solution before and after heating are shown in FIG. 1. Figure 2 As shown in FIG. 1, the hydrogel solution before heating has no fluorescence (that is, the hydrogel solution sample obtained in step (2) has no fluorescence; it can be seen that no free radicals are generated in the system at this time); the hydrogel solution after heating has fluorescence (that is, the synthetic hydrogel sample obtained in step (3) has fluorescence; heating generates free radicals in the system), and the light emission peak is at 475 nm.

[0071] The solid hydrogel prepared in Example 2 was detected for sensing and responding to water, and the results are shown in FIG. 2. Figure 3 As shown in FIG. 2, the solid hydrogel produces a cyan blue fluorescence response after contacting water (in the present application, contacting is immersing the solid hydrogel in the corresponding solution, and taking it out after 5 s of contact); the cyan blue fluorescence disappears after drying, and the process is repeatable. It can be seen that the response of the solid hydrogel based on the present application to water is reusable.

[0072] The solid hydrogel prepared in Example 2 was detected for selective response to different solvents, and the results are shown in FIG. 3. Figure 4 As shown in FIG. 3, only the sample contacting with water produces a cyan blue fluorescence response; other solvents similar to water (i.e., ethanol, methanol, DMSO, DMF) cannot make it discolor; it can be seen that the solid hydrogel based on the present application only has a special response to water and does not respond to other solvents, and has the characteristic of selective response.

[0073] The solid hydrogel prepared in Example 2 was detected for response to pH value, and OH - (concentration of 1 mol / L NaOH aqueous solution) and H + (concentration of 1 mol / L HCl aqueous solution) were used to contact with the same solid hydrogel sample, and the results are shown in FIG. 4. Figure 5 As shown in FIG. 4, the solid hydrogel based on the present application has a response to the pH of the aqueous solution, and the fluorescence is quenched when the solution is acidic, and the fluorescence is recovered when it returns to alkaline.

[0074] The solid hydrogel prepared in Example 2 was detected for response to γ-CD, a 0.01 mol / L γ-CD aqueous solution was prepared, and the solid hydrogel prepared in Example 2 was contacted with the γ-CD aqueous solution, and the result is shown in FIG. 2. Figure 6 As shown in FIG. 2, the hydrogel produced a light yellow fluorescence (and the process was irreversible, and would not disappear with the disappearance of water), and it can be seen that the solid hydrogel obtained in the application has response to the γ-CD aqueous solution.

[0075] Example 3: Preparation of a printing paper

[0076] The preparation includes the following steps:

[0077] (1) Compound 2 prepared in Example 1 was used as a raw material, and a 0.1 mg / mL compound 2 aqueous solution was prepared.

[0078] (2) 0.5 g of acrylamide, 0.1 g of sodium acrylate (mass ratio of acrylamide / sodium acrylate is 5:1), 1 mg of APS, 1 mg of M BAA, and 10 μL of TEMED were added to 5 mL of the compound 2 aqueous solution, and mixed uniformly to obtain a hydrogel solution.

[0079] (3) The obtained hydrogel solution was used to soak filter paper, and then the filter paper was taken out and placed in an 80℃ environment to dry the filter paper, thereby obtaining a printing paper.

[0080] The paper obtained in this example has a water-emitting luminescence effect, and can be used for inkjet printing with H2O as ink, as shown in FIG. 3. The printed pattern will disappear with the disappearance of water, and can only be kept for a short time, for example, it can be applied to the storage of short-term secret information (after the water disappears with time, the printing paper is also decrypted). Figure 7

[0081] Of course, a γ-CD aqueous solution can also be used as printing ink; at this time, since the response of the solid hydrogel to the γ-CD aqueous solution is irreversible, the printing effect can be kept for a long time.

[0082] The above examples are only examples, for example, other fluorescent groups can also be mixed in the hydrogel by physical mixing, so that multiple color fluorescence regulation can be produced after water; for another example, in addition to APS and TEMED, other water-soluble thermal free radical initiators can also be used as free radical initiators, and the concentration of the thermal free radical initiator in the hydrogel solution can also be flexibly adjusted. In addition, heating can also be performed at other temperatures (such as 40℃ or above).

[0083] ​Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An organic light-emitting material, characterized in that: It has the chemical structure shown in Formula I: Formula I In formula I, X and Y represent the attachment amount of the corresponding monomer, and X:Y does not exceed 0.5; The aqueous solution of the organic light-emitting material can emit fluorescence under the participation of free radicals.

2. A solid hydrogel that can emit light when exposed to water, characterized in that: The solid hydrogel is obtained by first uniformly dispersing the organic light-emitting material as claimed in claim 1 and a water-soluble thermal free radical initiator in water to form a hydrogel solution, then heating the hydrogel solution to generate free radicals to obtain a synthetic hydrogel, and finally dehydrating the synthetic hydrogel.

3. A solid hydrogel that can emit light when exposed to water, characterized in that: The solid hydrogel is obtained by uniformly dispersing the organic light-emitting material as claimed in claim 1, acrylamide, sodium acrylate, ammonium persulfate (APS), N,N'-methylenebisacrylamide (MBAA), and tetramethylethylenediamine (TEMED) in water to form a hydrogel solution, then heating the hydrogel solution to generate free radicals to obtain a synthetic hydrogel, and finally dehydrating the synthetic hydrogel.

4. The solid hydrogel capable of luminescence in contact with water as claimed in claim 3, characterized in that: In the hydrogel solution, the mass ratio of the acrylamide to the sodium acrylate is 5:1; The concentration of the organic light-emitting material in the hydrogel solution does not exceed 0.1 mg / mL; The concentration of acrylamide in the hydrogel solution does not exceed 0.2 g / mL; The concentration of ammonium persulfate (APS) in the hydrogel solution does not exceed 1 mg / mL; The concentration of N,N'-methylenebisacrylamide (MBAA) in the hydrogel solution does not exceed 1 mg / mL; The concentration of tetramethylethylenediamine (TEMED) in the hydrogel solution does not exceed 5 μL / mL.

5. The solid hydrogel capable of luminescence in contact with water as claimed in claim 3, characterized in that: The heating is heating at a temperature above 40°C.

6. The solid hydrogel capable of luminescence in contact with water as claimed in claim 5, characterized in that: The heating is carried out at a temperature of 80°C.

7. A paper for inkjet printing, characterized in that: It is obtained by soaking the paper body with a hydrogel solution and then heating and drying it; The hydrogel solution is formed by uniformly dispersing the organic light-emitting material according to claim 1 and a water-soluble thermal free radical initiator in water.

8. A paper for inkjet printing, characterized in that: It is obtained by soaking the paper body with a hydrogel solution and then heating and drying it; The hydrogel solution is formed by uniformly dispersing the organic light-emitting material according to claim 1, acrylamide, sodium acrylate, ammonium persulfate (APS), tetramethylethylenediamine (TEMED), and N,N'-methylenebisacrylamide (MBAA) in water.

9. The inkjet printing paper according to claim 8, wherein: In the hydrogel solution, the mass ratio of the acrylamide to the sodium acrylate is 5:1; The concentration of the organic light-emitting material in the hydrogel solution does not exceed 0.1 mg / mL; The concentration of acrylamide in the hydrogel solution does not exceed 0.2 g / mL; The concentration of ammonium persulfate (APS) in the hydrogel solution does not exceed 1 mg / mL; The concentration of N,N'-methylenebisacrylamide (MBAA) in the hydrogel solution does not exceed 1 mg / mL; The concentration of tetramethylethylenediamine (TEMED) in the hydrogel solution does not exceed 5 μL / mL.

10. The inkjet printing paper according to any one of claims 7 to 9, wherein: The heat drying is performed by heating at a temperature above 40° C. until the moisture is completely eliminated.

11. The inkjet printing paper according to claim 10, wherein: The heat drying is performed by heating at 80° C. until the moisture is completely eliminated.

12. Use of the organic luminescent material according to claim 1, the solid hydrogel capable of luminescence in contact with water according to any one of claims 2 to 6, or the inkjet printing paper according to any one of claims 7 to 11 in fluorescence color change in response to water.

13. The use according to claim 12, characterized in that The fluorescent color change is reversible, and the organic light-emitting material, the solid hydrogel, or the inkjet printing paper can be restored by drying and dehydrating, and can be used again in the fluorescent color change in response to water.

14. Use of the organic luminescent material according to claim 1, the solid hydrogel capable of luminescing in water according to any one of claims 2 to 6, or the inkjet printing paper according to any one of claims 7 to 11 in fluorescence color change in response to pH value, wherein fluorescence quenching occurs under acidic conditions and fluorescence is restored under alkaline conditions.

15. The use according to claim 14, characterized in that The fluorescent color change is reversible.

16. Use of the organic luminescent material according to claim 1, the solid hydrogel capable of luminescence in contact with water according to any one of claims 2 to 6, or the inkjet printing paper according to any one of claims 7 to 11 in fluorescence color change in response to a γ-cyclodextrin aqueous solution.

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