Preparation and application of ionic organic crystals with photoinduced blue shift and fluorescence enhancement

Abstract

The present invention discloses an ionic organic crystal with photoinduced blue shift and fluorescence enhancement, which is obtained by ion self-assembly in a methanol-water solution using a tetraphenylethylene polydentate imidazole ionic liquid and a polydentate sulfonic acid as substrates. The ionic organic crystal of the present invention has high crystallinity, regular morphology, and very high thermal stability. The crystal structure contains TPE molecules, which maintain the AIE characteristics of the TPE molecules and have specific photoinduced blue shift and fluorescence enhancement properties. Optical studies have shown that the ionic organic crystal material of the present invention exhibits a significant response to light. In a dilute solution, it is observed that under the irradiation of an ultraviolet lamp, the fluorescence undergoes a blue shift and an enhanced abnormal phenomenon, so it can be used as a material for optical devices. In addition, in a water-methanol mixed solution, the ionic organic crystal has a highly selective fluorescence quenching performance for 2,4,6-trinitrophenol, and can therefore be used as a highly sensitive and highly selective fluorescent probe for 2,4,6-trinitrophenol.

Description

Technical Field

[0001] The present invention relates to the preparation and application of an ionic organic crystal, and in particular to a method for preparing an ionic organic crystal with photoinduced blue shift and fluorescence enhancement. The present invention also relates to the application of the ionic organic crystal as a fluorescent probe for 2,4,6-trinitrophenol. Background Art

[0002] Ionic bonds are a very special class of non-covalent bonds formed by electrostatics. They are widely used to construct physically and / or chemically cross-linked supramolecular ionic nanomaterials. Due to their advantages such as simple synthesis and strong functional modification specificity, they have attracted widespread attention from scientists. Ionic self-assembly is the process of preparing ionic supramolecules by combining oppositely charged units through electrostatic interactions. It is a powerful tool for manufacturing ionic nanomaterials and has experienced rapid development in the past two decades. It is well known that ionic materials composed of polyvalent cations and polyvalent anions include ionic networks, ionic polymers, and crystalline porous organic salts. However, the challenges of self-assembly have limited the application of crystalline ionic materials.

[0003] Light is one of the most ubiquitous stimuli in nature, and photoresponsive materials have attracted widespread attention due to their wide applications in smart windows, information storage, energy conversion, and ink-free printing. However, the simultaneous occurrence of photoinduced blue shift and emission enhancement in π-π stacked ionic nanomaterials has not been reported. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing ionic organic crystals with photoinduced blue shift and fluorescence enhancement;

[0005] Another object of the present invention is to study the photoluminescence properties and fluorescence responsiveness of the prepared ionic organic crystals with good aggregation-induced emission effect to nitro compounds, and to use them as fluorescent probes for 2,4,6-trinitrophenol.

[0006] 1. Synthesis of ionic organic crystals

[0007] The present invention uses a tetraphenylethylene polydentate imidazolium ionic liquid and a polydentate sulfonic acid as substrates to synthesize two ionic organic crystals through ionic self-assembly in a methanol-water solution. The specific method is as follows: the polydentate sulfonic acid is completely dissolved in methanol to form solution A, and the tetraphenylethylene polydentate imidazolium ionic liquid is dissolved in water to form solution B; solution A is then slowly added dropwise to solution B and allowed to stand at room temperature for 3 to 10 days; single crystals are slowly crystallized, filtered, and washed multiple times with methanol / water to obtain crystals. The crystals are then dried at 60 to 120°C for 2 to 10 hours to obtain a white powder, which is the ionic organic crystal.

[0008] The tetraphenylethylene polydentate imidazolium ionic liquid is a tetraphenylethylene polydentate imidazolium ionic liquid, and its structural formula is as follows:

[0009] .

[0010] The multidentate sulfonic acid is tetraphenylethylene tetrasulfonate, and the ionic organic crystal synthesized by ionic self-assembly of the multidentate sulfonic acid and tetraphenylethylene tetradentate imidazolium ionic liquid is named single crystal-1 (IOC-1). The molar ratio of the tetraphenylethylene tetradentate imidazolium ionic liquid to the tetraphenylethylene tetrasulfonate is 1:1 to 1:3. The synthesis formula is as follows:

[0011]

[0012] The multidentate sulfonic acid may also be tetrasulfonic tetraphenylethylene, and the ionic organic crystal synthesized by ionic self-assembly of the tetraphenylethylene tetradentate imidazolium ionic liquid is single crystal-2 (IOC-2), wherein the molar ratio of the tetraphenylethylene tetradentate imidazolium ionic liquid to 4,4-biphenyldisulfonic acid is 1:2 to 1:4, and the synthesis formula is as follows:

[0013]

[0014] In the methanol-water solution, the volume ratio of methanol to water is 3:1 to 2:1.

[0015] 2. Structure and Property Characterization of Ionic Organic Crystals

[0016] The crystal structure was determined using single crystal analysis, and then powder diffraction was used to characterize the crystal forms of the two ionic organic crystals obtained.

[0017] 1. X-ray diffraction

[0018] Figure 1 Figure 1 shows the powder X-ray diffraction patterns of single crystals (a: single crystal-1, b: single crystal-2). Comparison of the data simulated using VESTA with the experimental data shows a good match between the experimental and simulated data, with no extraneous peaks, indicating that both crystals have good crystallinity and the expected structure has been achieved.

[0019] 2. Fourier transform infrared spectroscopy

[0020] Figure 2 The infrared analysis spectra of ionic organic crystals (a: single crystal-1, b: single crystal-2) show that the wave number at 3400 cm -1 ~ 3050 cm -1 The range can be attributed to the presence of water molecules, hydroxyl groups and hydrogen bonds in the single crystal. -1 ~1030 cm -1The wavenumbers between the two can be attributed to the symmetric stretching vibration of the sulfonate anion. Infrared spectra show that the ionic organic crystals were successfully synthesized.

[0021] 3. Thermogravimetric analysis

[0022] Thermogravimetric analysis of two ionic organic crystals was performed. Figure 3 Thermogravimetric analysis spectra of ionic organic crystals (a: single crystal-1, b: single crystal-2). It can be seen that both crystals have good thermal stability, reaching a maximum of 400 o C on (100 o The weight loss before C is due to the departure of solvent molecules from the crystal).

[0023] 4. Microscopic analysis

[0024] The morphology of the single crystals was studied by optical microscopy. Figure 4 Single crystal images (a: IOC-1, b: IOC-2) under an optical microscope. IOC-1 and IOC-2-2 appear as blue rhombic tetrahedrons under an optical microscope.

[0025] 5. Variable temperature powder X-ray diffraction

[0026] In order to characterize the thermal stability of the two ionic organic crystals, they were placed at 120 o C for several hours and then conduct powder X-ray diffraction experiments. The experiment found that the single crystal -1 o C for two hours, it changed from crystal to white powder, while under the same conditions, the morphology of single crystal-2 did not change. Figure 5 Figure 2 shows the powder diffraction patterns of crystals treated at 120°C (a: single crystal-1, b: single crystal-2). The peaks observed for single crystal-1 differ from those observed in the simulation, while those for single crystal-2 remain unchanged. This further demonstrates that single crystal-1 is unstable at high temperatures after losing guest molecules.

[0027] 3. Analysis of Photoinduced Blue Shift and Fluorescence Enhancement in Ionic Organic Crystals

[0028] 1. Comparison before and after UV light irradiation

[0029] Because the crystal contains tetraphenylethylene molecules, it has a good aggregation-induced emission effect. We dissolved single crystal-1 and single crystal-2 in a water / methanol (5:1~2:1) solution to prepare c=13.5×10 -6 The emission spectra of the solution of M under UV light irradiation for different times were tested on a fluorescence spectrometer. Figure 6 The photochromic image (a: single crystal-1, b: single crystal-2) and fluorescence change image (c: single crystal-1; d: single crystal-2) of the crystal in solution. Figure 6As can be seen, when single crystal-1 solutions were irradiated at an excitation wavelength of 350 nm, and when single crystal-2 solutions were irradiated at an excitation wavelength of 340 nm, the fluorescence emission spectra of both solutions underwent a blue shift, changing from light green to blue, accompanied by enhanced fluorescence. Calculated fluorescence quantum yields increased from 5.6% and 7.0% to 54.6% and 41.3%, respectively. This demonstrates that these two ionic organic crystals exhibit both blue-shifting and fluorescence enhancement properties, and therefore hold promise for use as materials for optical devices.

[0030] 2. Powder X-ray diffraction

[0031] In order to understand the mechanism of blue shift and enhancement of light, powder X-ray diffraction was performed on the solid before and after illumination. Figure 7 Powder X-ray diffraction patterns of crystals before and after irradiation (a: single crystal-1, b: single crystal-2). Figure 7 It can be seen that the powder X-ray diffraction does not change before and after solid irradiation, which indicates that the blue shift of light and fluorescence enhancement are not related to the morphology of the crystal.

[0032] 4. Sensing performance test of single crystal-1 to 2,4,6-trinitrophenol

[0033] After vacuuming the single crystal-1 crystal, the crystal collapsed into a white powder. The powder was dispersed in a mixture of water and methanol (volume ratio 5:1) to prepare a solution with c = 13.5%. Different concentrations of 2,4,6-trinitrophenol (TNP) were added to the solution, and the changes in the solution fluorescence were observed. The results showed that with the addition of 2,4,6-trinitrophenol, the fluorescence of the single crystal-1 solution gradually weakened until it was quenched. The fluorescence quenching diagram of single crystal-1 on 2,4,6-trinitrophenol is shown in Figure 2. Figure 8 As shown in Figure 2, the fluorescence intensity of the single crystal-1 solution gradually decreases with the addition of 2,4,6-trinitrophenol. The Stern-Volmer plot of the fluorescence intensity of the single crystal-1 and the concentration of TNP (2,4,6-trinitrophenol) was fitted ( Figure 9 ), the concentration of 2,4,6-trinitrophenol and log(I o / I) is linear ( Figure 10 ), R 2 =0.999. This property makes it a fluorescent probe for 2,4,6-trinitrophenol.

[0034] In summary, the present invention constructs ionic organic crystals with photoinduced blue shift and fluorescence enhancement properties by self-assembly using a tetraphenylethylene-based multidentate ionic liquid and multidentate sulfonic acid. These ionic organic crystals exhibit high crystallinity, regular morphology, and very high thermal stability. Furthermore, the crystal structure contains tetraphenylethylene (TPE) molecules, maintaining the AIE properties of TPE molecules and exhibiting specific photoinduced blue shift and fluorescence enhancement properties. Under ultraviolet light, a solution prepared by dispersing the ionic organic crystals changes from green to blue, exhibits a blue shift in the fluorescence emission spectrum, and enhances fluorescence intensity. The quantum yield increases from 5.6% and 7.0% to 54.6% and 41.3%, respectively, making them suitable for use as materials in optical devices. Furthermore, in a water-methanol mixture, the ionic organic crystals exhibit highly selective fluorescence quenching for 2,4,6-trinitrophenol, making them suitable as highly sensitive and selective fluorescent probes for 2,4,6-trinitrophenol. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the powder X-ray diffraction pattern of a single crystal;

[0036] Figure 2 This is the infrared analysis spectrum of ionic organic crystals;

[0037] Figure 3 This is the thermogravimetric analysis spectrum of ionic organic crystals;

[0038] Figure 4 This is a picture of a single crystal under an optical microscope;

[0039] Figure 5 This is the powder diffraction pattern of the crystal after being treated at 120℃;

[0040] Figure 6 This is the photochromic image of the crystal in solution;

[0041] Figure 7 Powder X-ray diffraction patterns of the crystal before and after irradiation;

[0042] Figure 8 Single crystal-1 quenching diagram of 2,4,6-trinitrophenol;

[0043] Figure 9 Single crystal-1 selectivity experiment of nitrobenzene compounds;

[0044] Figure 10 Single crystal-1 linear relationship of selectivity experiments for nitrobenzene compounds. DETAILED DESCRIPTION

[0045] The synthesis and application of the ionic organic crystals of the present invention are further described below through specific examples.

[0046] Example 1: Preparation of Single Crystal-1

[0047] Tetrasulfonic acid tetraphenylethylene (0.1 mmol) was added to 10 mL of methanol and completely dissolved to form solution A. Tetradentate imidazole tetraphenylethylene ionic liquid (0.1 mmol) was dissolved in 10 mL of water to form solution B. Solution A was slowly added dropwise to solution B and then allowed to stand at room temperature for 10 days. After slow crystallization at room temperature, it was filtered and washed with methanol / water several times to obtain crystals. The crystals were then heated at 120 o C for 10 h to obtain a white powder, which was then subjected to powder X-ray diffraction. The structure and properties of single crystal-1 are shown in Figures 1 to 7 .

[0048] Single crystal-1 exhibits blue-shifted light and enhanced fluorescence, making it a promising material for optical devices. It can be used as a fluorescent probe for detecting the explosive nitro compound 2,4,6-trinitrophenol. The specific procedure is as follows: After evacuating the single crystal-1, it collapses into a white powder. This powder is then dispersed in a mixture of water and methanol (5:1 by volume) to create a 13.5% c solution. To this solution are added 200 μM solutions of nitrobenzene (NB), 1,3-dinitrobenzene, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-methylnitrobenzene, 3-methylnitrobenzene, 4-methylnitrobenzene, 4-ethylnitrobenzene, 4-boronitrobenzene, 4-nitrobenzoic acid, 2,4-dinitrobenzaldehyde, 4-nitrobenzonitrile, 4-chloronitrobenzene, 4-bromonitrobenzene, and 2,4,6-trinitrophenol. Observe the fluorescence changes of the single crystal-1 crystal solution. Figure 9 This is a selectivity experiment of single crystal-1 for nitrobenzene compounds. The results show that in the crystal-1 solution, only the addition of 2,4,6-trinitrophenol can quench the fluorescence of the single crystal-1 solution.

[0049] Example 2: Preparation of Single Crystal IOC-2

[0050] 4,4-Biphenyldisulfonic acid (0.1 mmol) was added to 6 mL of methanol and completely dissolved to form Solution A. Tetradentate imidazole tetraphenylethylene ionic liquid (0.05 mmol) was dissolved in 6 mL of water to form Solution B. Solution A was slowly added to Solution B and then allowed to stand at room temperature for 10 days. Single crystals slowly crystallized at room temperature. The single crystals were filtered and washed with methanol and water multiple times to obtain orthorhombic crystals. The crystals were then dried at 120°C for 2 h and subjected to powder X-ray diffraction. The structure and properties of single crystal 2 are shown in [1]. Figures 1 to 7 .

[0051] Since Crystal-2 blue-shifts rapidly under illumination, it is not suitable for the detection of explosives, but can be used as a material for optical devices.

Claims

1. A method for preparing an ionic organic crystal with photoinduced blue shift and fluorescence enhancement, comprising: using a tetraphenylethylene polydentate imidazole ionic liquid and a polydentate sulfonic acid as substrates, and obtaining the crystal by ion self-assembly in a methanol-water solution; the tetraphenylethylene polydentate imidazole ionic liquid is a tetraphenylethylene tetradentate imidazole ionic liquid, and the polydentate sulfonic acid is tetrasulfonate tetraphenylethylene or 4,4-biphenyldisulfonic acid; The structural formula of the tetraphenylethylene tetradentate imidazolium ionic liquid is as follows: The structural formula of the tetrasulfonic acid tetraphenylethylene is as follows: The structural formula of the 4,4-biphenyldisulfonic acid is as follows: 。 2. The method for preparing an ionic organic crystal having photoinduced blue shift and fluorescence enhancement according to claim 1, wherein: The polydentate sulfonic acid is completely dissolved in methanol to form solution A, and the tetraphenylethylene polydentate imidazole ionic liquid is dissolved in water to form solution B. Solution A is then slowly added dropwise to solution B and allowed to stand at room temperature for 3 to 10 days. Single crystals are slowly crystallized, filtered, and washed multiple times with methanol / water to obtain crystals. The crystals are dried at 60 to 120°C for 2 to 10 hours to obtain white powder, which is the ionic organic crystal.

3. A method for preparing an ionic organic crystal having photoinduced blue shift and fluorescence enhancement according to claim 1 or 2, characterized in that: The molar ratio of the tetraphenylethylene tetradentate imidazolium ionic liquid to the tetrasulfonate tetraphenylethylene is 1:1-1:

3.

4. A method for preparing an ionic organic crystal having photoinduced blue shift and fluorescence enhancement according to claim 1 or 2, characterized in that: The molar ratio of the tetraphenylethylene tetradentate imidazolium ionic liquid to 4,4-biphenyldisulfonic acid is 1:2-1:

4.

5. Use of the ionic organic crystal with photoinduced blue shift and fluorescence enhancement prepared as claimed in claim 1 as a material for optical devices.

6. Use of an ionic organic crystal with photoinduced blue shift and fluorescence enhancement as prepared in claim 1 as a fluorescent probe for 2,4,6-trinitrophenol, characterized in that: The ionic organic crystal is a single crystal-1 prepared from tetraphenylethylene tetradentate imidazolium ionic liquid and tetrasulfonate tetraphenylethylene.

7. Use of the ionic organic crystal with photoinduced blue shift and fluorescence enhancement as claimed in claim 6 as a fluorescent probe for 2,4,6-trinitrophenol, characterized in that: In the water-methanol mixed solution of single crystal-1, solutions of nitrobenzene, 1,3-dinitrobenzene, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-methylnitrobenzene, 3-methylnitrobenzene, 4-methylnitrobenzene, 4-ethylnitrobenzene, 4-boronic acid nitrobenzene, 4-nitrobenzoic acid, 2,4-dinitrobenzaldehyde, 4-nitrobenzenenitrile, 4-chloronitrobenzene, 4-bromonitrobenzene, and 2,4,6-trinitrophenol were added respectively. Only the addition of 2,4,6-trinitrophenol could quench the fluorescence of the single crystal-1 solution.

Images