Pyrazine coordination ruthenium complex, preparation method thereof and application of pyrazine coordination ruthenium complex as ratio type molecular photoswitch

Abstract

The invention belongs to the technical field of molecular photoswitch materials, and provides a pyrazine coordination ruthenium complex, a preparation method thereof and application of the pyrazine coordination ruthenium complex as a ratio type molecular photoswitch, the pyrazine coordination ruthenium complex is composed of positive ions and negative ions, the structural formula of the positive ions is shown in the formula (I), and the negative ions are shown in the specification. The preparation method comprises the following steps: firstly, reacting 2-acetylpyrazine with benzimidazole-2-formaldehyde to prepare a ligand L; and filtering after the reaction, adding a ligand L into the filtrate for heating reflux reaction, and purifying the product to obtain the pyrazine coordination ruthenium complex. The complex provided by the invention has unique dual emission and ratio type response, can realize high-precision and anti-interference ratio type pH sensing, and eliminates the influence of factors such as probe concentration, instrument efficiency and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biomedical detection and imaging materials, and particularly relates to a pyrazine-coordinated ruthenium complex, a preparation method thereof and application thereof as a ratio-type molecular optical switch. BACKGROUND

[0002] Organic molecules are widely used in the field of near-infrared luminescent materials due to their flexible structure and adjustable performance. However, these organic chromophores often face challenges such as sensitivity to photobleaching and limited Stokes shift. Molecules with ratio sensing function have significant advantages compared to single signal mode because they work by monitoring the intensity ratio of dual fluorescence signals. This self-calibration method can effectively improve the dynamic response range and detection accuracy, and greatly reduce the interference of factors such as temperature, humidity, pH value, probe concentration and instruments on detection accuracy. In terms of visual detection, ratio fluorescence sensing mode shows a change in color tone, bringing a more distinct visual contrast compared to the single color change in single signal fluorescence sensing mode, which can improve the sensitivity of visual detection. Therefore, ratio sensing technology overcomes the challenge of photobleaching sensitivity of ordinary near-infrared luminescent materials by reducing the dependence on the absolute intensity of single signal, and has become a research hotspot in this field.

[0003] Ru(II) complexes derived from multi-heterocyclic ligands have been found to be promising building blocks for constructing effective molecular optical switches due to their fascinating and tunable photophysical properties. The ability to reversibly modulate the luminescent properties of such chromophores by changing their peripheral structure (e.g. by protonation / deprotonation or coordination of metal ions) is of great significance for the possible development of switching mechanisms in future photochemical molecular devices. Based on this design concept and in response to the key challenges of organic near-infrared ratio probes, a new type of pyrazine-coordinated ruthenium complex with high-performance ratio sensing function has been successfully developed. SUMMARY

[0004] The present application aims to provide a pyrazine-coordinated ruthenium complex, a preparation method thereof and application thereof as a ratio-type molecular optical switch, which has unique dual-emission and ratio-type response, can realize high-precision and anti-interference ratio-type pH sensing, and eliminates the influence of factors such as probe concentration and instrument efficiency.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A pyrazine-coordinated ruthenium complex, which is composed of a cation and an anion, wherein the structure of the cation is shown as formula (I):

[0006] The anion is an inorganic anion, and preferably the anion is .

[0007] The present application also provides a preparation method of the pyrazine-coordinated ruthenium complex, comprising the following steps: (1) Preparation of ligand 2-(2,6-di(pyrazin-2-yl)pyridin-4-yl)-1H-benzimidazole: add benzimidazole-2-carboxaldehyde to a solution of 2-acetylpyrazine in anhydrous ethanol, stir uniformly, then add strong base in sequence, stir to obtain a reaction solution, add concentrated ammonia water to the reaction solution, continue to stir at room temperature until a precipitate is obtained, collect and wash the precipitate to obtain a crude product, dry and recrystallize the crude product, and then dry again to obtain the ligand L; (2) Preparation of the complex : disperse and in , heat to reflux under protection of , after cooling to room temperature, remove precipitate by filtration under normal pressure, collect the filtrate, remove acetonitrile by rotary evaporation, then add the ligand L into the reaction bottle, add ethylene glycol, heat to reflux under protection of nitrogen in dark, the reaction solution turns into deep red, after cooling to room temperature, add saturated sodium perchlorate solution to the reaction solution to induce precipitation, collect the precipitate by filtration, and dry under vacuum to obtain a crude product; purify the crude product to obtain the pyrazine-coordinated ruthenium complex.

[0008] In the present application, preferably, the washing in step (1) is to wash the precipitate with distilled water and ethanol in sequence.

[0009] In the present application, preferably, the recrystallization in step (1) is to recrystallize the crude product in DMF.

[0010] In the present application, preferably, the temperature of heating to reflux in step (2) is 90°C.

[0011] In the present application, preferably, the purification method of the crude product in step (2) is to dissolve the crude product in acetonitrile, separate and purify the dissolved crude product by column chromatography, collect the target component, remove most of the solvent by rotary evaporation, then add a few drops of saturated sodium perchlorate aqueous solution, collect the precipitate by filtration, and recrystallize the precipitate by diffusion with acetonitrile / ethyl ether to obtain the target product.

[0012] In the present application, preferably, the eluent is a mixed solution composed of acetonitrile, water and saturated potassium nitrate aqueous solution in a volume ratio of 80:4:1.

[0013] In the present application, preferably, the diffusion recrystallization is to dissolve the precipitate in acetonitrile, diffuse the acetonitrile solution into acetonitrile solution through ethyl ether to realize recrystallization, and then dry the crystals under vacuum to obtain the target pyrazine-coordinated ruthenium complex.

[0014] The application also provides the use of the pyrazine-coordinated ruthenium complex as a ratiometric molecular photoswitch.

[0015] In summary, due to the adoption of the technical solutions described above, the present application has the following beneficial effects: 1. The present application successfully prepares a novel 2,6-dipyrazinyl-4-pyridine ruthenium complex The complex innovatively realizes step-by-step and reversible double deprotonation response through two independent imidazole protonation sites in the structure = 2.16 ± 0.03; = 9.62 ± 0.02), which can cover extreme pH environments and trigger reversible signal switching within an ultra-wide dynamic range (pH 0.25~11.96), and is compatible with the application environment requirements from strong acid to strong base.

[0016] 2. The ruthenium complex of the present application exhibits a unique absorption-fluorescence dual-mode ratiometric response, and the responses of the 665 nm and 755 nm near-infrared emission peaks to pH are different, which constitutes a perfect built-in reference system. By calculating the intensity ratio of the two peaks , high-precision and anti-interference ratiometric pH sensing can be realized, and the effects of probe concentration, instrument efficiency, temperature / humidity changes, etc. are eliminated, and the problem of light bleaching sensitivity of traditional near-infrared materials is solved. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the protonation / deprotonation process of the complex .

[0018] Figure 2 is the effect of pH on the ultraviolet-visible spectrum of the complex ([Ru] = 4.0 μM). (a) pH = 0.25 ~ 4.04, (b) pH = 6.16 ~ 11.96, and the interpolation diagram is the change of the absorption value at 522 nm with pH.

[0019] Figure 3 is the effect of pH on the emission spectrum of the complex ([Ru] = 4.0 μM). (a) pH = 1.76 ~ 5.56, (b) pH = 7.36 ~ 10.57, and the interpolation diagram is the change of the emission peak intensity at 665 nm with pH.

[0020] Figure 4 is a linear relationship diagram of the luminescence intensity of the complex solution at 755 nm and 665 nm and the luminescence intensity ratio of the complex solution at different pH. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field, and all reagents and materials used are commercially available. Among them, ethylene glycol, diethyl ether and acetonitrile are all commercially available analytical grade, and concentrated ammonia water is commercially available concentrated ammonia water with a concentration of 25%-28%. The reaction for preparing ligands in the present invention does not require a strictly anhydrous environment, but to reduce interference, commercially available analytical grade anhydrous ethanol is preferred. Those skilled in the art can also choose 95 vol% conventional ethanol aqueous solution according to actual needs, all of which are within the scope of commercially available conventional reagents.

[0022] The pyrazine-coordinated ruthenium complex developed in this invention is composed of a cation and an anion, and the structural formula of the cation is shown in formula (I): (I) The anion of the Ru(II) complex is .

[0023] The preparation method of pyrazine-coordinated ruthenium complexes is illustrated below through specific examples: Example 1: Preparation of ligand 2-(2,6-bis(pyrazin-2-yl)pyridin-4-yl)-1H-benzimidazole (L) The ligand synthesis pathway is shown below:

[0024] To 100 mL of anhydrous ethanol solution containing 4.84 g (40 mmol) of 2-acetylpyrazine, benzimidazole-2-carboxaldehyde (2.29 g, 20 mmol) was added. After stirring until homogeneous, KOH (3.08 g, 55 mmol) and concentrated ammonia (58 mL) were added sequentially. The resulting solution was stirred at room temperature for one week to obtain a yellow precipitate. The precipitate was collected by suction filtration and washed sequentially with 25 mL of distilled water and 25 mL of ethanol to obtain the crude product. After vacuum drying, the crude product was recrystallized in DMF, and after vacuum drying, 6.02 g of yellow powder was obtained, with a yield of 85.8%.

[0025] 1H NMR spectrum: 1 H NMR (500 MHz, DMSO- d6) δ 13.64 (s, 1H), 9.91 (s, 2H), 9.22 (s, 2H), 8.84 (d, J = 12.5 Hz, 4H), 7.79 (d, J = 7.8 Hz, 1H), 7.62 (d, J = 7.8 Hz, 1H), 7.31 (dt, J = 23.2, 7.0 Hz, 2H).

[0026] Example 2: Complex Preparation The synthesis route for the coordination compound is shown below:

[0027] Will (0.099 g, 0.38 mmol) and (0.24 g, 1.2 mmol) dispersed in 20 mL In Under protective conditions, the mixture was heated to 90°C and refluxed for 3 hours. After cooling to room temperature, the AgCl precipitate was removed by filtration under normal pressure. The filtrate was collected, and acetonitrile was removed by rotary evaporation. Ligand L (0.267 g, 0.76 mmol) was added to the reaction flask, followed by 15 mL of ethylene glycol. The mixture was heated to 90°C and refluxed for 12 hours under nitrogen protection, protected from light. The reaction solution turned dark red. After cooling to room temperature, 1 mL of saturated sodium perchlorate solution was added to the reaction solution to initiate precipitation. The precipitate was collected by filtration and vacuum drying to obtain the crude product. The crude product was dissolved in 10 mL of acetonitrile. The dissolved crude product was separated and purified by column chromatography using acetonitrile / water / saturated potassium nitrate aqueous solution (80:4:1, V / V / V). After collecting the target component, most of the solvent was removed by rotary evaporation, and a few drops of saturated sodium perchlorate aqueous solution were added. The complex precipitate was collected by filtration. The obtained complex precipitate was dissolved in a small amount of acetonitrile and placed in a 10 mL beaker. The beaker was sealed with plastic wrap and some small holes were punched in the top. 25 mL of diethyl ether was placed in a wide-mouth bottle with a ground glass stopper. The beaker containing the complex solution was placed into the wide-mouth bottle containing diethyl ether, the lid was closed, and the mixture was left to stand at room temperature for a few days. After the precipitate precipitated, it was filtered and collected. After vacuum drying, 145 mg of powder was obtained, with a yield of 38.1%.

[0028] 1H NMR spectrum: NMR (500 MHz, ) δ 13.63 (d, J = 6.6 Hz,2H), 10.02 – 10.02 (m, 4H), 9.91 (d,J = 3.0 Hz, 4H), 8.52 (d, J = 3.3 Hz, 4H), 7.96 (d, J = 8.1 Hz, 2H), 7.88 (d, J = 8.0 Hz, 2H), 7.80 (d, J = 3.2 Hz, 4H), 7.52– 7.39 (m, 4H).

[0029] Carbon-13 NMR spectrum: NMR (101 MHz, ) δ 192.63, 186.12, 188.18, 131.06, 127.41, 100.05, 71.38, 66.56, 11.59, 8.33.

[0030] Mass spectrometry: (MALDI-TOF MS in) Calculated value: m / z: 803.8 Measured value: 803.88 (100%).

[0031] Elemental analysis: (FW=1056.75), calculated values: C: 45.46%; H: 3.05%; N: 18.56%, measured values: C: 45.26%; H: 3.11%; N: 18.43%.

[0032] coordination compounds acid-base titration Test method: coordination compounds The acid-base titration experiment was conducted in Britton-Robinson (BR) buffer solution. The BR buffer solution consisted of 0.04 M glacial acetic acid, 0.04 M boric acid, and 0.1 M NaCl solution. 120 μL of ruthenium complex acetonitrile solution ([Ru] = 1 mM) was dissolved in 30 mL of BR buffer solution to obtain a 4 μM ruthenium complex test solution. This solution was divided into two portions. One portion was adjusted to pH 1.87–0.25 with concentrated sulfuric acid, and the other portion was adjusted to pH 1.87–11.96 with concentrated sodium hydroxide solution. Each pH adjustment was equilibrated for 5 min, and data was measured at 0.2 pH intervals to obtain the UV-Vis absorption and emission spectra of the ruthenium complex at different pH values. =503 nm).

[0033] Test results: such as Figure 1As shown, the complex underwent two consecutive deprotonation processes as the solution pH increased from 0.25 to 11.96.

[0034] Figure 2 The UV-Vis absorption spectrum of the complex is shown below. Figure 2 As can be seen, the first deprotonation process of the complex occurs at pH = 0.25 ~ 4.04, with a significant decrease in the absorption peaks at 349 nm and 498 nm, while the absorption peaks at 298 nm and 380 nm increase. Furthermore, three isoabsorption points appear at 316 nm, 361 nm, and 503 nm, and the absorption peak at 498 nm shows a 4 nm red shift. This process is due to the first deprotonation reaction of the nitrogen atom on the protonated imidazole ring. The second deprotonation process of the complex occurs at pH = 6.16 ~ 11.96 (the absorption peak at 522 nm hardly changes as pH increases from 4.04 to 7.36, so the part from pH 4.04 to 5.96 is omitted in the two spectra). The absorption peaks at 288 nm, 348 nm, and 502 nm decrease significantly, while the absorption peaks at 310 nm, 405 nm, and 522 nm increase significantly. Notably, the absorption peak at 502 nm undergoes a 20 nm redshift, and three isoabsorption points appear at 301 nm, 367 nm, and 510 nm. This process is due to the second deprotonation reaction of the nitrogen atom on the neutral imidazole ring of the ligand. Figure 2 The inner illustration is a coordination compound. The absorbance at 522 nm as a function of pH was plotted, and the complex was obtained by fitting with sigmoidal. The ground-state acid dissociation constants are respectively = 2.16 ± 0.03, = 9.62 ± 0.02.

[0035] Both the spectra and insets show that the absorbance at 522 nm is exceptionally sensitive to pH (especially in the alkaline region). Near 522 nm, the absorbance shows a sharp increase, and its UV-Vis spectrum, especially its color characteristics in the visible region (e.g., the significant color change caused by the decrease at 502 nm and the increase at 522 nm), is strongly dependent on the pH value of the solution, making it highly suitable for pH sensing. The presence of multiple isoabsorption points provides an ideal basis for ratiometric pH sensing. By comparing the absorbance ratio at two wavelengths, interferences from optical path length, probe concentration, and light source intensity can be eliminated, significantly improving the accuracy and reliability of the measurement. The decrease in the 498 / 502 nm peak and the increase in the 522 nm peak indicate that the solution color may change visibly under alkaline conditions (e.g., from one color to another), making it ideal for simple colorimetric pH test strips or reagents.

[0036] Figure 3 The graph shows the fluorescence spectrum of the complex as a function of pH. Figure 3 It can be seen that the changes are divided into two stages. The first stage is a pH change of 1.76 ~ 5.56, during which the fluorescence intensity at 665 nm decreased by 55.28%, and the emission peak shifted from 665 nm to 646 nm. This spectral change is due to the first deprotonation reaction of the nitrogen atom on the protonated imidazole ring. The second stage is a pH change of 7.36 ~ 10.57, during which the fluorescence intensity at 665 nm decreased by 60.89%. This spectral change is due to the second deprotonation reaction of the nitrogen atom on the neutral imidazole ring of the ligand. This complex is an on-off-off type pH-induced molecular fluorescence switch. According to formula (1) Formula (1) Where υ B - and υ HB The wavenumbers of the emission peaks of the complex, approximated by the wavenumbers of the complex in both deprotonated and protonated forms, can be used to calculate the wavenumbers of the complex. The two ionization constants of the excited state in these two stages = 3.11、 =9.77.

[0037] The above results indicate that the complex contains a coordination structure that sequentially responds to acidic and alkaline environments, causing secondary fluorescence changes (especially accompanied by a first spectral blue shift); the complex exhibits "on-off-off" fluorescence switching behavior and significant luminescence characteristics in the visible light region (646-665 nm); it has two distinct pH response thresholds with a relatively stable state in between (pH stable phase). Due to the biphasic decrease in luminescence intensity and the first response accompanied by a 19 nm red shift, the reliability and safety of detection are significantly improved. It can be used as a dual-channel pH indicator for scenarios requiring strong acid tolerance and specific recognition in strong alkaline ranges with high-penetration luminescence (medical detection, industrial pollution monitoring).

[0038] Figure 4 The luminescence intensity of the complex solution at different pH at 665 nm and 755 nm and the luminescence intensity ratio thereof are shown in Table 1. The complex has two emission peaks at 665 nm and 755 nm with an excitation wavelength of 503 nm, and in the pH = 1.76 ~ 4.36 and pH = 8.77 ~ 10.37 ranges, The complex has a good linear relationship with pH, is a dual-emission ratio type pH sensor, and can be used to detect the pH value of an unknown water sample.

[0039] The above description is a detailed description of the preferred embodiments of the present application, but the embodiments are not intended to limit the scope of the patent application of the present application. Any equivalent changes or modifications made under the technical spirit of the present application should be included in the patent scope of the present application.

Claims

1. A pyrazine-coordinated ruthenium complex, characterized by, The pyrazine-coordinated ruthenium complex is composed of a cation and an anion, and the structural formula of the cation is shown as formula (I): （Ⅰ） The anion is an inorganic anion.

2. The pyrazine coordinated ruthenium complex according to claim 1, characterized in that: The anion is .

3. The process for the preparation of a pyrazine coordinated ruthenium complex according to claim 1 or 2, characterized in that The method comprises the following steps: (1) Preparation of ligand 2-(2,6-di(pyrazin-2-yl)pyridin-4-yl)-1H-benzimidazole: 2-acetylpyrazine is dissolved in anhydrous ethanol, and benzimidazole-2-carboxaldehyde is added, and after stirring, a strong base is added, and the reaction solution is obtained by stirring, and concentrated ammonia is added to the reaction solution, and the mixture is continuously stirred at room temperature until a precipitate is obtained, and the precipitate is collected and washed to obtain a crude product; the crude product is dried and recrystallized, and then dried again to obtain the ligand L; (2) Preparation of the complex : disperse and into , heat to reflux under protection of , after cooling to room temperature, remove precipitate by normal pressure filtration, collect the filtrate, remove acetonitrile by rotary evaporation, then add ligand L into the reaction bottle, add ethylene glycol, heat to reflux under protection of nitrogen and away from light, the reaction solution turns to dark red, after cooling to room temperature, add saturated sodium perchlorate solution into the reaction solution to induce precipitation, collect the precipitate by filtration, and dry under vacuum to obtain the crude product; purify the crude product to obtain the pyrazine complex ruthenium complex.

4. The method of claim 3, wherein: The washing in step (1) is to sequentially wash the precipitate with distilled water and ethanol.

5. The preparation method according to claim 3, characterized in that, The recrystallization in step (1) is to recrystallize the crude product in DMF.

6. The preparation method according to claim 3, characterized in that, The temperature of the heating reflux in step (2) is 90°C.

7. The preparation method according to claim 3, characterized in that, The purification method of the crude product in step (2) is as follows: the crude product is dissolved in acetonitrile, the dissolved crude product is separated and purified by column chromatography, the target component is collected, most of the solvent is removed by rotary evaporation, a few drops of saturated sodium perchlorate aqueous solution are added, the precipitate is collected by filtration, and the precipitate is recrystallized by diffusion in acetonitrile / ethyl ether to obtain the target product.

8. The preparation method according to claim 7, characterized in that, The eluent is a mixture of acetonitrile, water and saturated potassium nitrate aqueous solution in a volume ratio of 80:4:

1.

9. The method of claim 7, wherein: The diffusion recrystallization is to dissolve the precipitate in acetonitrile, and then diffuse the acetonitrile solution into ethyl ether to realize recrystallization, and the crystal is dried in vacuum to obtain the target pyrazine-coordinated ruthenium complex.

10. Use of a pyrazine-coordinated ruthenium complex according to claim 1 or 2, characterized in that: The application is to use the pyrazine-coordinated ruthenium complex as a ratiometric molecular photoswitch.

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