Elagic acid-based fluorescent compound constructed through C-N coupling reaction as well as synthesis method and application of ellagic acid-based fluorescent compound

Abstract

The invention discloses an ellagic acid-based fluorescent compound constructed through C-N coupling reaction and a synthesis method and application thereof.Natural D-A fluorophore-ellagic acid serves as a core, nitrogen-containing aromatic molecules NHR2 are introduced into EA molecules through C-N coupling, pi-p-pi coupling is formed while four hydroxyl groups of the nitrogen-containing aromatic molecules NHR2 are reserved, and the ellagic acid-based fluorescent compound is obtained. Thus, an EA derivative is obtained, and red shift of EA fluorescence emission is realized. The EA-based fluorescent material provided by the invention has specific binding affinity with metal ions, so that the EA-based fluorescent material is used as a fluorescent sensor for detecting the metal ions, and the EA-based fluorescent material has important application prospects in the fields of organic fluorescent molecules, photoelectrons, photo-thermal technologies, fluorescent sensing material technologies and the like.

Description

Technical Field

[0001] The present invention belongs to the field of organic fluorescent molecules and relates to the technical field of fluorescent sensing materials, and specifically relates to an ellagic acid-based fluorescent compound constructed by a CN coupling reaction and a synthesis method and application thereof. Background Art

[0002] Ellagic acid (EA) is an edible polyphenol found in berries, grapes, and some nuts, and has a wide range of biological activities, including anti-inflammatory, antioxidant, free radical scavenging, and antioxidant and free radical scavenging activities. In addition, EA has a unique molecular structure consisting of a planar biphenyl moiety connected by two lactone rings, resulting in a wide range of sp 2 The highly ordered planar structure of the carbon conjugated system allows EA to absorb photons, enter an excited state, and subsequently relax to a lower energy state by emitting photons, thereby generating fluorescence. The emission peak of EA in different solvents ranges from 400 to 520 nm, producing blue-green fluorescence. This natural polyphenol has great application potential in fluorescent probes, bioimaging, and biosensors. However, its emission peak in the range of 400-520 nm may overlap with the emission peaks of certain biomacromolecules, causing interference. In order to avoid this conflict, it is necessary to induce a red shift in the emission peak of EA. More specifically, EA has structural similarities with coumarin, with two lactones and four hydroxyl groups, which can act as electron donors (D) and acceptors (A). This suggests that EA can function as a natural DA-type fluorophore.

[0003] The fluorescence mechanism of DA-type fluorophores is attributed to intramolecular charge transfer (ICT), in which molecules with a push-pull electron structure undergo intramolecular electron transitions in the excited state, followed by electron transfer from the electron-donating group to the electron-accepting group. Various strategies are commonly used to achieve the red shift of fluorescence emission of DA-type molecules. For example, increasing the sp 2 The carbon conjugated area makes the molecule more likely to be excited and emit higher wavelength fluorescence. In addition, the introduction of -NH 2 、-NR 2 Electron-donating groups such as -OH and -OR are direct methods to induce red shifts because these groups enhance p-π conjugation within the fluorophore. In addition, the incorporation of nitrogen-containing aromatic molecules can significantly improve the planarity of the molecule and reduce the lowest unoccupied molecular orbital (LUMO) energy level, thereby affecting the optical band gap by changing the localized electronic state. This method has been successfully applied to the fields of luminescence, optoelectronics, and photothermal technology. Summary of the invention

[0004] The present invention provides an ellagic acid-based fluorescent compound constructed by a CN coupling reaction, a synthesis method and an application thereof. A nitrogen-containing aromatic group is introduced into an EA molecule by CN coupling, thereby forming a π-p-π coupling while retaining its four hydroxyl groups. The obtained EA derivative can significantly improve the planarity of the molecule and reduce the lowest unoccupied molecular orbital (LUMO) energy level due to the incorporation of the nitrogen-containing aromatic molecule, thereby achieving a red shift in the fluorescence emission of EA.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] An ellagic acid-based fluorescent compound constructed by CN coupling reaction has the following structural formula:

[0007]

[0008] R=H or CH 3 or CH 2 CH 3 or:

[0009]

[0010] The two symmetrical R cannot be H or CH at the same time. 3 , CH 2 CH 3 , that is, at least one of the two Rs must contain a benzene ring.

[0011] The present invention also provides a method for synthesizing the ellagic acid-based fluorescent compound constructed by the CN coupling reaction, comprising the following steps:

[0012] Ellagic acid (EA) is dissolved in dimethyl sulfoxide (DMSO), and then nitrogen-containing aromatic molecules and organic bases are added to carry out CN coupling reaction under oxygen atmosphere and high temperature. After purification, a fluorescent compound based on the CN coupling reaction of ellagic acid is obtained.

[0013] The nitrogen-containing aromatic molecule is aniline, diphenylamine, chloroaniline, dimethylaniline, N-methylaniline, N-ethylaniline, etc.; the organic base is selected from pyridine, 1,8-diazabicycloundec-7-ene (DBU), etc.

[0014] The molar ratio of ellagic acid, nitrogen-containing aromatic molecules and organic base is 1:1-100:1-100.

[0015] The temperature for the CN coupling reaction at high temperature is 80-120° C., and the reaction time is 24-72 hours.

[0016] The present invention also provides the ellagic acid-based fluorescent compound constructed by the CN coupling reaction as a fluorescent sensor for detecting metal ions.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The ellagic acid-based fluorescent compound constructed by CN coupling reaction of the present invention takes the natural DA type fluorophore-ellagic acid as the core, and introduces the nitrogen-containing aromatic molecule NHR into the EA molecule by CN coupling. 2 , with a symmetrical structure, thus forming π-p-π coupling while retaining its four hydroxyl groups. The obtained EA derivatives can significantly improve the planarity of the molecule and reduce the lowest unoccupied molecular orbital (LUMO) energy level due to the incorporation of nitrogen-containing aromatic molecules, thereby achieving the red shift of EA fluorescence emission; the addition of power-donating groups can effectively alleviate the strong regular stacking between molecules and slow down the interaction between molecules, so that the fluorescence intensity and the concentration of aggregation quenching are greatly improved.

[0019] The present invention discloses a method for synthesizing an ellagic acid-based fluorescent compound constructed by a CN coupling reaction, wherein natural polyphenol ellagic acid is selected as a substrate, and under the condition of adding a base, a stepwise nucleophilic substitution strategy is used to realize aromatic ring CN coupling to prepare a target product with a symmetrically substituted structure, and the method has the characteristics of a one-pot reaction, simple operation, high product yield, and convenient post-processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Compound EAAn 2 High-resolution mass spectra of

[0021] Figure 2 For compounds EA and EAAn 2 Fluorescence in different organic solvents;

[0022] Figure 3 Compound EAAn 2 The fluorescence lifetime fitting diagram of

[0023] Figure 4 Compound EAAn 2 Fluorescence emission spectra at different concentrations in different solvents;

[0024] Figure 5 Compound EAAn 2 Its effect as a fluorescent sensor for the detection of alkali metal and alkaline earth metal ions;

[0025] Figure 6 Compound EAAn 2 Its effect as a fluorescent sensor for detecting transition metal ions;

[0026] Figure 7 Compound EAAn 2 As a fluorescent sensor for the detection of late transition metal ions. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0028] Example 1

[0029] An ellagic acid-based fluorescent compound EAAn constructed via CN coupling reaction 2 And its synthesis method, the structural formula of the fluorescent compound is as follows:

[0030]

[0031] The ellagic acid-based fluorescent compound EAAn constructed by CN coupling reaction 2 The synthetic reaction formula is as follows:

[0032]

[0033] The ellagic acid-based fluorescent compound EAAn constructed by CN coupling reaction 2 The synthetic method comprises the following specific steps:

[0034] (1) Dissolve 180 mg of EA in 300 mL of DMSO, then pour into a 500 mL single-necked bottle, add 3 mL of aniline and 3 mL of pyridine, add a stirrer, and seal with a glass three-way stopcock;

[0035] (2) Hang a balloon on the top of the tee, and use an oil pump and an oxygen bottle to oxygenate and remove impurities in the reaction device. Repeat this cycle three times to ensure that there is no interference from other impurities in the reaction device and that there is sufficient oxygen in the balloon;

[0036] (3) The reaction device was fixed in an oil bath, heated to 100°C, stirred and reacted at this temperature for 24 hours, cooled to room temperature, and the reaction solution was poured into 1 L of deionized water to terminate the reaction;

[0037] (4) Adjust the pH value to acidic with hydrochloric acid. At this time, a large amount of black solid will precipitate. Filter it with suction and wash the solid with cold water several times until the filtrate is clear. Then put the obtained black solid into a vacuum drying oven to dry to obtain a crude reaction product (0.2 g, yield 69.4%). The crude reaction product is subjected to silica gel column chromatography to obtain compound EAAn 2 (brown powder), HRMS (ESI-): C 26 H 15 N 2 O 8[MH], found (m / z): 483.0834, calculated (m / z): 483.0830 (e.g. Figure 1 ).

[0038] The crude reaction product was chromatographed on a silica gel column to obtain compound EAAn 2 (brown powder) The specific steps are as follows:

[0039] (1) Dry column packing: Take a clean and dry glass chromatography column with a diameter of 5 cm × 30 cm, insert a small amount of absorbent cotton from the column mouth and push it to the bottom of the column with a long glass rod to flatten it. Then use a funnel to carefully fill the column mouth with silica gel (300-40 mesh) to about half the height. While filling, tap the column with your fingers to ensure that the filling is tight and even. Fix the column on an iron stand. The column should be packed evenly without any fractures and the column bed surface should be level.

[0040] (2) Sampling: Weigh 0.2 g of the crude reaction product into a 25 mL beaker, dissolve it in 10 mL of tetrahydrofuran, and then use a graduated rubber-tipped pipette to draw the sample for analysis. Note that the sample should be loaded along the tube wall. Finally, add a small spoonful of anhydrous sodium sulfate to the column bed.

[0041] (3) Elution and separation: Slowly add about 200 mL of an eluent of petroleum ether: acetone = 1:1 (volume ratio) for elution. A yellow band can be seen on the column. Then continue to add about 350 mL of an eluent of dichloromethane: methanol: formic acid = 17:1:0.5 (volume ratio) for elution. A dark brown band can be seen on the column. During this process, a small test tube is used to collect the eluted solution, and the reaction product is confirmed by spot plate. The purified product is concentrated and dried to obtain a brown solid.

[0042] Referring to the method of Example 1, the nitrogen-containing aromatic molecule aniline is replaced by diphenylamine, chloroaniline, dimethylaniline, N-methylaniline, N-ethylaniline, etc., the organic base pyridine is replaced by 1,8-diazabicycloundec-7-ene (DBU), etc., the molar ratio of ellagic acid, nitrogen-containing aromatic molecule, and organic base fluctuates within the range of 1:1 to 100:1 to 100, the temperature of the CN coupling reaction in the high temperature of the oil bath in step (3) fluctuates within the range of 80 to 120° C., and the reaction time fluctuates within the range of 24 to 72 hours, and the compound EAAn can still be prepared. 2 .

[0043] Example 2

[0044] Example 1 Compound EAAn prepared 2 Performance Analysis

[0045] 1. Compound EAAn 2 Fluorescence in different organic solvents

[0046] Analysis method: 1,4-butanediol (BDO), polyethylene glycol (BDO), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) were selected as solvents to prepare EAAn 2 Solutions with a concentration of 10 ppm and EA concentration of 50 ppm were placed under a light source of 365 nm for fluorescence testing.

[0047] Analysis results: Compounds EA and EAAn 2 The fluorescence behavior in different organic solvents is as follows Figure 2 As shown, EAAn2 successfully achieved a red shift in fluorescence emission compared with EA in BDO, PEG400, NMP, DMF, and DMSO.

[0048] 2. Compound EAAn 2 Fluorescence lifetime analysis in different organic solvents

[0049] Analysis method: Place a sample with a concentration of 50 ppm in a sample cell, set the excitation and emission wavelength slits to 0.1 nm and 20 nm respectively, and use a 380 nm excitation lamp for fluorescence testing.

[0050] The calculation and fitting model of fluorescence lifetime are as follows:

[0051]

[0052] Y=B+A 1 *exp(-i / τ 1 )+…+A n *exp(-i / τ n )(n=1,2,3…)

[0053] Table 1 EAAn 2 Fluorescence lifetime fitting data in different organic solvents

[0054]

[0055]

[0056] Analysis results: Compound EAAn 2 The fluorescence lifetime fitting diagrams in different organic solvents are shown in Figure 3 The fitting data are listed in Table 2, and the second-order fitting coefficient R 2 The values ​​of are all greater than 0.998, the fitting effect is also good, the detection data is reliable, and the introduction of two power supply side chains prevents EAAn from 2 adhesion, avoiding self-quenching and leading to a higher fluorescence lifetime.

[0057] 3. Compound EAAn 2 Fluorescence emission spectra analysis in different organic solvents

[0058] Analysis method: 1,4-butanediol (BDO), polyethylene glycol (BDO), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) were used as solvents to prepare EAAn 2 A solution with a suitable concentration gradient is used to test its fluorescence emission properties.

[0059] Analysis results: Compound EAAn 2 The fluorescence spectra in different organic solvents are shown in Figure 4 , in compound EAAn 2 In the fluorescence spectra, except for BDO, the fluorescence intensity of EAAn2 in PEG400, NMP, DMF and DMSO ( Figure 4 b, 4c, 4d, and 4e) first increase and then decrease with increasing concentration, showing a typical aggregation quenching (ACQ) effect, and even causing a blue shift in the fluorescence emission of EAAn2. This phenomenon occurs because the stable planar structure of EAAn2 hinders its intramolecular motion in a dispersed state. Specifically, the absorbed energy is emitted in the form of fluorescence radiation at a lower concentration. However, with increasing concentration, EAAn2 molecules aggregate in the solution due to π-π stacking, which causes energy to be transferred between high-energy molecules in the excited state and low-energy molecules in the unexcited state. Therefore, energy is dissipated without the need for radiative leaps, resulting in a gradual decrease in luminescence until it eventually disappears. This phenomenon has greatly hindered the practical application of traditional luminescent groups.

[0060] 4. Compound EAAn 2 Analysis of fluorescence quantum yield in different organic solvents

[0061] Analysis method: The fluorescence quantum yield is determined by comparing the fluorescence intensity integral (i.e., the corrected area of ​​the fluorescence spectrum) and absorbance (to ensure the reliability of the measured value, the absorbance is controlled below 0.1) of the fluorescent substance to be tested and the reference substance with known quantum yield under the same excitation conditions. The QY value of EA in various solvents is calculated according to the following formula:

[0062]

[0063] The subscripts EA and R represent the analyte (EAAn 2 ) and the reference standard, QY is the fluorescence quantum yield, I is the fluorescence peak area, A is the absorbance, and η refers to the refractive index of the solvent (because the concentrations of the unknown substance to be measured and the reference standard in the experiment are extremely low, the influence of the solute can be ignored and they are considered to be consistent. 2 SO 4The quantum yield (QY) of quinine sulfate in was used as a reference substance, and the QY value of quinine sulfate was measured to be 0.54 at an excitation wavelength of 360 nm.

[0064] Table 2

[0065]

[0066] Analysis results: As shown in Table 2, the addition of power-supplying N atoms is beneficial to the generation of fluorescence, because the electron cloud of this type of group is almost parallel to the electron cloud of the benzene ring orbital, making it very easy to share the conjugated electronic structure with the benzene ring, expanding the degree of conjugation of the fluorescent molecule, causing the ultraviolet-visible light absorption peak and fluorescence emission peak of the fluorescent organic matter to red-shift, while increasing the fluorescence quantum yield.

[0067] Example 3

[0068] Example 1 Compound EAAn prepared 2 Detection and analysis of metal ions as a fluorescent sensor

[0069] Analysis method: The metal ion solutions were prepared by dissolving the corresponding chloride and nitrate in deionized water, with a concentration of 20 mM, which mainly included the following types of metal ions: alkali metals and alkaline earth metals (Li + 、Na + , K + , Rb + , Cs + Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ ), transition metals (Sc 3+ 、Ti 4+ 、V 3+ Cr 2+ , Mn 2+ , Fe 3+ 、Co 2+ 、Ni 2+ , Cu 2+ 、Zn 2+ 、Cd 2+ ), post-transition metals (Al 3+ , Ga 3+ 、In 3+ Sn 4+ ), EAAn 2Dissolve it in DMSO solution to obtain a 100 ppm probe mother solution, and then mix the fluorescent compound in the probe mother solution with the metal ions in the metal ion stock solution at a molar ratio of 2:1. Use ultraviolet light irradiation colorimetry in a dark box ultraviolet analyzer to determine whether the mixed solution has specific detection performance, and then use a transient steady-state fluorescence spectrometer to analyze its fluorescence properties.

[0070] Analysis results: Figure 5-7 As shown, EAAn 2 The binding with these metal ions has a good fluorescence specific effect. Mg ions can be clearly distinguished from other alkali metal and alkaline earth metal ions by the difference in fluorescence emission, and Cr ions can also be clearly distinguished from transition metal ions by the difference in fluorescence emission.

[0071] The above-mentioned embodiments only express the preferred implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. An ellagic acid-based fluorescent compound constructed by CN coupling reaction, the structural formula of which is shown below: R=H or CH3 or CH2CH3 or: in, One or more of the two symmetrical R's contain a benzene ring.

2. The method for synthesizing the ellagic acid-based fluorescent compound constructed by CN coupling reaction according to claim 1, characterized in that: The steps include: The ellagic acid is dissolved in dimethyl sulfoxide, and then a nitrogen-containing aromatic molecule and an organic base are added to carry out a CN coupling reaction under an oxygen atmosphere and high temperature, and a fluorescent compound based on the CN coupling reaction of ellagic acid is obtained after purification.

3. The method for synthesizing the ellagic acid-based fluorescent compound constructed by CN coupling reaction according to claim 2, characterized in that: The nitrogen-containing aromatic molecule is aniline, diphenylamine, chloroaniline, dimethylaniline, N-methylaniline, and N-ethylaniline; and the organic base is pyridine or 1,8-diazabicycloundec-7-ene.

4. The method for synthesizing an ellagic acid-based fluorescent compound constructed by CN coupling reaction according to claim 2, characterized in that: The molar ratio of ellagic acid, nitrogen-containing aromatic molecules and organic base is 1:1-100:1-100.

5. The method for synthesizing the ellagic acid-based fluorescent compound constructed by CN coupling reaction according to claim 2, characterized in that: The temperature for the CN coupling reaction at high temperature is 80-120° C., and the reaction time is 24-72 hours.

6. The ellagic acid-based fluorescent compound constructed by CN coupling reaction according to claim 1 or 2 is used as a fluorescent sensor to detect metal ions.

Images