Organic luminescent material, correspondingly obtained solid hydrogel capable of emitting light when meeting water and ink-jet printing paper

Abstract

The invention belongs to the field of intelligent luminescent materials, and discloses an organic luminescent material, a correspondingly obtained solid hydrogel capable of emitting light when encountering water, and ink-jet printing paper, the organic luminescent material has a chemical structure as shown in a formula I; an aqueous solution of the organic light-emitting material can emit fluorescence under the participation of free radicals. The organic light-emitting material with the molecular structure shown in the formula I is used as a novel polymer material capable of emitting light when encountering water, can be used as a light-emitting core to be mixed into a hydrogel network or brew paper, and can be prepared into hydrogel capable of emitting light when encountering water and paper for ink-jet printing. And the prepared hydrogel can have special response to pH (Potential of Hydrogen) and gamma-CD (Compact Disc). # imgabs0 #

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 in contact with water, and can sense water, γ-cyclodextrin (γ-CD) and pH value to produce a fluorescent effect. Background Art

[0002] Smart luminescent materials have attracted widespread attention because their luminescent signals can be recognized by the naked eye when they sense stimuli. Dynamically adjustable luminescent systems usually show sensitive modulation of luminescent properties under various external stimuli such as light, temperature, magnetism, mechanical force, chemistry, electric field, pH, etc., and therefore have attracted considerable attention and wide application in the fields of information encryption, bioimaging, detection, sensing, diagnosis and treatment. In the past decade, scientists have reported many stimuli-responsive luminescent materials that show multicolor luminescence and luminescent switching effects in response to external stimuli.

[0003] Supramolecular assembly is defined as a multi-molecule group composed of non-covalent bonds, which can be as simple as two molecules. They can be spherical, rod-shaped, or sheet-like samples. Their size ranges from nanometers to micrometers. It is composed of two or more molecules that rely on binding together to form a complex organized aggregate and maintain a certain integrity, so that it has a clear microstructure and macroscopic characteristics. The relationship from molecules to supramolecular and the interaction between molecules is just like the relationship from atoms to molecules and covalent bonds.

[0004] Pyrene-based π-conjugated materials are considered to be ideal organic electroluminescent materials for semiconductor devices, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic photovoltaics (OPVs). Aggregation-induced quenching (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 materials. This is because the formation of aggregates leads to close contact between molecules, which changes the internal electronic energy levels of the molecules, destroys the luminescence path of the fluorescent marker, and reduces or completely extinguishes the luminescence. The biggest disadvantage of using pyrene as an organic luminescent material is the formation of quasi-molecular emission, which quenches the 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 in order to achieve exploitable properties by adopting two strategies, 1) introducing various parts into the pyrene core, and 2) exploring effective and convenient synthetic strategies to functionalize the pyrene core.

[0005] Water-responsive materials have received extensive attention due to their special properties, and have important applications in erasable paper and sweat pore mapping. Ordinary printing inks are relatively expensive because of their expensive materials and high R&D costs. Water is the cheapest and most easily available liquid in people's lives. Using it as ink will greatly save printing costs. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide an organic luminescent material and a corresponding solid hydrogel and inkjet printing paper that can emit light when in contact with water. By using an organic luminescent material with a molecular structure as shown in Formula I as a new type of new polymer material that emits light when in contact with water, the organic luminescent material can be mixed into the hydrogel network or soaked in paper as a luminescent core, and a hydrogel and inkjet printing paper can be made. The prepared hydrogel can have a special response to pH and γ-CD. The prepared paper will also have the effect of emitting light when in contact with water and γ-CD, and only produces patterns under fluorescent conditions, which can be used for inkjet printing, information transmission and decryption applications.

[0007] To achieve the above object, 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 amount of attachment 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 the second aspect of the present invention, the present invention provides a solid hydrogel that can emit light when in contact with water. The solid hydrogel is firstly prepared by uniformly dispersing the above-mentioned organic light-emitting material and a thermal free radical initiator that can be dissolved in water 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 to obtain the same.

[0012] According to the third aspect of the present invention, the present invention provides a solid hydrogel that can emit light when in contact with water. The solid hydrogel is prepared by first uniformly dispersing the above-mentioned organic light-emitting material with 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 to obtain the same.

[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 of 40°C or above, preferably at a temperature of 80°C.

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

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

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

[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 heating and drying is performed at a temperature of 40° C. or above until the moisture is completely eliminated; preferably, the heating and drying is performed at a temperature of 80° C. until the moisture is completely eliminated.

[0031] According to the 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 emitting light 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 a reversible fluorescent color change, and the organic light-emitting material, the solid hydrogel, or the inkjet printing paper can be restored by drying and dehydration, 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 a 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 paper for inkjet printing in fluorescent color change in response to a γ-cyclodextrin aqueous solution.

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

[0037] Beneficial effects:

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

[0039]

[0040] The organic light-emitting material shown in Formula I obtained by the present invention can be formed by compound 3 (structural formula as shown in the following table) and 1-bromobutane (structural formula as shown in the following table) on P4VP (polyvinyl pyridine, structural formula as shown in the following table, wherein n is the number of pyridines in P4VP). In Formula I, X and Y respectively represent the amount of compound 3 and 1-bromobutane on P4VP, and the numerical range of 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, and its light-emitting excitation mode 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 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 meets water, and the color will fade when it is dried by water. It is a reusable color-changing hydrogel. In addition, the solid hydrogel obtained by the present invention has pH response, which 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 effect, 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 used 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 physical picture of the solid hydrogel obtained in Example 2 luminescing when exposed to water and undergoing five water-drying cycles.

[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 prepared in Example 1. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can be combined with each other as long as they do not conflict with each other.

[0054] Taking compound 2 as an example, the synthesis 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 are all commercially available; compound 3 is prepared according to prior art reports (for example, relevant prior art can be found in: 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] The various 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 and cool to room temperature, precipitate with anhydrous ether, and centrifuge to obtain a solid product, which is then dissolved in methanol solution and centrifuged 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. The mixture was heated under reflux for 48 h, cooled to room temperature, and precipitated with anhydrous ether. The solid product was obtained by centrifugation. The solid product was dissolved in methanol solution and then centrifuged with ether solution for three times to wash away DMF to obtain solid compound 2.

[0062] The compound 2 was subjected to hydrogen spectrum detection (the 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. It can be seen 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 of the aqueous solution of compound 2, 0.5 g of acrylamide, 0.1 g of sodium acrylate (acrylamide / sodium acrylate mass ratio is 5:1), 1 mg of APS, 1 mg of MBAA, and 10 μL of TEMED were added and mixed evenly to obtain a hydrogel solution.

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

[0069] (4) Continue heating at 80° C. to evaporate all the water in the synthesized hydrogel to obtain a solid hydrogel.

[0070] Fluorescence emission spectra of the hydrogel solution before and after heating, such as Figure 2 As shown, it can be seen that the hydrogel solution has no fluorescence before heating (that is, the hydrogel solution sample obtained in step (2) has no fluorescence; it is not difficult to see that no free radicals are generated in the system at this time); the hydrogel solution has fluorescence after heating (that is, the synthetic hydrogel sample obtained in step (3) has fluorescence; heating generates free radicals in the system), and its emission peak is at 475nm.

[0071] The solid hydrogel prepared in Example 2 was tested for its perception and response to water. The results are as follows: Figure 3 As shown, the solid hydrogel will produce a cyan-blue fluorescence response after contacting water (the contact in the present invention is to immerse the solid hydrogel in the corresponding solution and take it out after contacting for 5 seconds). When dried, the cyan-blue fluorescence fades. This process is repeatable. It can be seen that the response of the solid hydrogel to water obtained based on the present invention can be reused.

[0072] The selective response of the solid hydrogel prepared in Example 2 to different solvents was tested. Figure 4 As shown, only samples in contact with water will produce a cyan-blue fluorescence response; other solvents similar to water (i.e., ethanol, methanol, DMSO, DMF) cannot cause it to change color; it can be seen that the solid hydrogel obtained based on the present invention has a special response only to water and no response to other solvents, and has the characteristic of selective response.

[0073] The solid hydrogel prepared in Example 2 was tested for its response to pH value by using OH - (Specifically, a 1 mol / L NaOH aqueous solution was used) and H + (Specifically, a 1 mol / L HCl aqueous solution was used) to contact the same solid hydrogel sample. The results are as follows Figure 5 As shown, it can be seen that the solid hydrogel obtained based on the present invention responds to the pH of the aqueous solution. When the solution is acidic, the fluorescence will be quenched, and when it returns to alkalinity, the fluorescence will be restored.

[0074] The solid hydrogel prepared in Example 2 was tested for its response to γ-CD. A γ-cyclodextrin aqueous solution with a concentration of 0.01 mol / L was prepared and the solid hydrogel prepared in Example 2 was contacted with the γ-CD aqueous solution. The results were as follows: Figure 6 As shown, the hydrogel produces light yellow fluorescence (and this process is irreversible and will not disappear with the disappearance of water). It can be seen that the solid hydrogel obtained by the present invention responds to the γ-CD aqueous solution.

[0075] Example 3: Preparation of printing paper

[0076] The following steps are involved:

[0077] (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.

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

[0079] (3) Soak filter paper in the obtained hydrogel solution, then take out the filter paper and place it in an environment of 80° C. to dry the filter paper, thereby obtaining printing paper.

[0080] The paper obtained in this embodiment has a water-luminescent effect, and can be used as ink for inkjet printing. Figure 7 As shown. The printed pattern will disappear with the disappearance of water and can only be retained for a short time. For example, it can be used for storing short-term confidential information (after the water disappears over time, the printed paper will also be decrypted).

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

[0082] The above embodiments are only examples. For example, other fluorescent groups can be mixed into the hydrogel by physical mixing, so that multi-color fluorescence regulation can be produced after contact with water; for another example, in addition to APS and TEMED, other water-soluble thermal free radical initiators can 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 (e.g., other temperatures above 40°C).

[0083] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An organic light-emitting material, characterized in that: It has a chemical structure as shown in Formula I: In formula I, X and Y represent the amount of attachment 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 in contact with water, characterized in that: The solid hydrogel is obtained by first uniformly dispersing the organic luminescent 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 in contact with water, characterized in that: The solid hydrogel is prepared 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 to obtain the solid hydrogel. Preferably, 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.

4. The solid hydrogel capable of emitting light in water as claimed in claim 3, characterized in that: The heating is performed at a temperature of 40°C or higher, preferably 80°C.

5. A paper for inkjet printing, characterized in that: The paper body is soaked with a hydrogel solution and then heated and dried; The hydrogel solution is formed by uniformly dispersing the organic light-emitting material as claimed in claim 1 and a thermal free radical initiator soluble in water in water.

6. A paper for inkjet printing, characterized in that: The paper body is soaked with a hydrogel solution and then heated and dried; The hydrogel solution is formed by uniformly dispersing the organic light-emitting material as claimed in claim 1, acrylamide, sodium acrylate, ammonium persulfate (APS), tetramethylethylenediamine (TEMED), and N,N'-methylenebisacrylamide (MBAA) in water; Preferably, 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.

7. The inkjet printing paper according to claim 5 or 6, characterized in that: The heating and drying is performed by heating at a temperature of 40° C. or above until the moisture is completely eliminated; preferably, the heating and drying is performed by heating at a temperature of 80° C. until the moisture is completely eliminated.

8. Use of the organic luminescent material according to claim 1, the solid hydrogel capable of luminescence in water according to any one of claims 2 to 4, or the inkjet printing paper according to any one of claims 5 to 7 in fluorescence color change in response to water; Preferably, the fluorescent color change is a reversible fluorescent color change, and the organic light-emitting material, the solid hydrogel, or the inkjet printing paper can be restored by drying and dehydration, and then used again in the fluorescent color change in response to water.

9. The organic light-emitting material according to claim 1, the solid hydrogel capable of luminescence in water according to any one of claims 2 to 4, or the inkjet printing paper according to any one of claims 5 to 7, for use in fluorescence color change in response to pH value, wherein fluorescence quenching occurs under acidic conditions and fluorescence is restored under alkaline conditions; Preferably, the fluorescent color change is a reversible fluorescent color change.

10. Use of the organic luminescent material according to claim 1, the solid hydrogel capable of luminescence in water according to any one of claims 2 to 4, or the inkjet printing paper according to any one of claims 5 to 7 in fluorescence color change in response to a γ-cyclodextrin aqueous solution.

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