A reactive zero-valent palladium fluorescent probe compound and a synthesis method thereof

Abstract

This invention discloses a reactive zero-valent palladium fluorescent probe based on BDP dye molecules, as shown in Formula I, and its synthesis method: wherein R = H or NH2. This probe is the first reactive zero-valent palladium fluorescent probe based on BDP dye molecules. The preparation method is simple and efficient, with significant and rapid fluorescence response, completing the change in fluorescence intensity from "on" to "off" within 8 minutes. The probe has extremely high sensitivity, with a detection limit as low as 0.3 ppb. It exhibits high selectivity for zero-valent palladium and shows no significant response to divalent palladium ions and 18 other interfering metal cations.

Description

Technical fields:

[0001] This invention relates to the field of organic small molecule fluorescent probe technology, specifically to a reactive zero-valent palladium fluorescent probe compound and its synthesis method. Background technology:

[0002] Palladium (Pd) is a platinum group element in Group VIII of the fifth period. Palladium metal and related materials play an irreplaceable role in industries such as automotive, catalytic synthesis, electronic materials, dental appliances, and jewelry manufacturing. Palladium can be emitted into the environment through vehicle exhaust, accumulating in roadside dust, soil, and vegetation, and subsequently being dispersed and washed into nearby waters and oceans, impacting surrounding ecosystems and human health. Palladium can have lethal or sublethal effects on aquatic organisms; in vitro toxicity tests have shown that palladium is also biotoxic to human cell lines. Palladium can also amplify the human immune response to allergens, leading to allergies and allergic contact dermatitis. As a critical environmental and health issue, the detection of palladium in industrial, environmental, and biological samples has attracted considerable attention in recent years.

[0003] Currently, common methods for palladium content detection include atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). However, these techniques can only determine the total palladium content and cannot distinguish between palladium in different valence states (0, +2, +4). Sample preparation also typically requires destructive methods. Fluorescent probes, on the other hand, offer advantages such as simple operation, rapid response, high sensitivity, high selectivity, and real-time in-situ detection, making them a highly promising detection method. In recent years, various fluorescent probes for palladium detection have been reported in the literature. Based on their different response mechanisms, they can be broadly classified into two categories: coordination probes and reactive probes. Coordination probes are mostly based on the complexation of palladium ions with acceptor molecules. These probes typically exhibit rapid fluorescence response, high selectivity, and reversibility. Reactive probes, however, are based on various chemical reactions between palladium ions and acceptor molecules under different reaction conditions (solvent, pH, temperature, and oxidation state), leading to chemical modification of the acceptor molecules and the generation of a new acceptor derivative, exhibiting a fluorescence change from "on→off" or "off→on". Due to their catalytic properties, reactive probes have high selectivity and sensitivity, but their response time is usually slower compared to coordination probes (Balamurugan, R.; Liu, J.-H.; Liu, B.-T. Coord. Chem. Rev. 2018, 376, 196-224).

[0004] The Tsuji-Trost reaction is a nucleophilic substitution reaction catalyzed by zero-valent palladium. Allyl ethers in the substrate react with zero-valent palladium to generate an electrophilic (π-allyl)Pd intermediate, followed by allyl departure. Using the Tsuji-Trost reaction as the palladium detection response mechanism, several examples of palladium detection fluorescent probes based on dyes such as fluorescein, coumarin, naphthalenedicarboximide, anthocyanin, and perylenediimide have been reported in recent years (①Wang, X.;Guo, Z.;Zhu, S.;Tian, ​​H.;Zhu, W. Chem. Commun. 2014, 50, 13525-13528;②Luo, W.;Liu, WJ Mater. Chem. B 2016,4,3911-3915; ③Ding, Y.; Zhao, S.; Wang, Q.; Yu, X.; Zhang, W. SensorsActuat.B:Chem.2018, 256, 1107-1113; ④ Jiang, L.; Mak, HN; Walter, ERH; W ong,WT;Wong,KL;Long,NJChem.Sci.2021,12,9977-9982;⑤Xie,Z.;Zhou,Y.;Fu,M.;Ni,L.;Tong,Y.;Yu,Y.;Li,N.;Yang,Z.;Zhu,Q.;Wang,J.Talanta 2021,231,122365.). The probes mentioned above have high sensitivity, with detection limits ranging from nanomolar (nM) to micromolar (μM); however, some probes are not highly selective for other platinum group elements (such as Pt, Ru, Rh, etc.) and different valence states of palladium ions, and their response times are generally long (most require a reaction time of more than 1 hour).

[0005] There are currently no reports of reactive zero-valent palladium fluorescent probes based on boron dipyrrole (BDP) fluorescent dyes. Summary of the Invention:

[0006] The purpose of this invention is to provide a reactive zero-valent palladium fluorescent probe compound, its synthesis method, and its application.

[0007] This invention is achieved through the following technical solutions:

[0008] A reactive zero-valent palladium fluorescent probe based on BDP dye molecules, with the structural formula shown in Formula I:

[0009]

[0010] Where R = H or NH2.

[0011] When R = H, the probe compound is denoted as NA-BDP-NPIH; when R = NH2, the probe compound is denoted as NA-BDP-NPINH.

[0012] When R = H, the preparation method of the above reactive zero-valent palladium fluorescent probe is expressed by the following equation:

[0013]

[0014] Includes the following steps:

[0015] (1) Under nitrogen protection, ethanol solutions of compounds 1 and 2 were heated to reflux, and after the reaction was completed, compounds 3 were obtained by separation and purification.

[0016] (2) Under nitrogen protection, sodium bicarbonate and compound 4 were added sequentially to the tetrahydrofuran solution of compound 3. After the reaction was completed, the probe compound NA-BDP-NPIH was obtained by separation and purification.

[0017] Compound 1 is aminoBDP, compound 2 is 1,8-naphthalenedicarboxylic anhydride, and compound 4 is allyl chloroformate.

[0018] Preferably, the reaction time in step (1) is 4 to 12 hours, and the molar ratio of compound 1 to compound 2 is 1:1 to 1:1.2.

[0019] Preferably, the reaction temperature in step (2) is room temperature, the reaction time is 8 to 16 hours, and the molar ratio of compound 3, sodium bicarbonate and compound 4 is 1:2.5:2.5 to 1:10:10.

[0020] When R = NH2, the preparation method of the above reactive zero-valent palladium fluorescent probe is expressed by the following equation:

[0021]

[0022] Includes the following steps:

[0023] (1) Under nitrogen protection, ethanol solutions of compounds 1 and 5 were heated to reflux, and after the reaction was completed, compounds 6 were obtained by separation and purification.

[0024] (2) Under nitrogen protection, hydrazine hydrate and palladium on carbon were added to the ethanol solution of compound 6. After the reaction was completed, the mixture was separated and purified to obtain compound 7.

[0025] (3) Under nitrogen protection, sodium bicarbonate and compound 4 were added to the tetrahydrofuran solution of compound 7. After the reaction was completed, the probe compound NA-BDP-NPINH was obtained by separation and purification.

[0026] In step (1), compound 1 is amino BDP and compound 5 is 4-nitro-1,8-naphthalenedicarboxylic anhydride.

[0027] Preferably, the reaction time in step (1) is 4 to 12 hours, and the molar ratio of compound 1 to compound 5 is 1:1 to 1:1.5.

[0028] Preferably, the reaction temperature in step (2) is reflux of ethanol, and the reaction time is 1.5 to 3 hours.

[0029] Preferably, the reaction temperature in step (3) is room temperature, the reaction time is 8 to 16 hours, and the molar ratio of compound 7, sodium bicarbonate and compound 4 is 1:2.5:2.5 to 1:10:10.

[0030] Another object of the present invention is to protect the application of the above-mentioned reactive zero-valent palladium fluorescent probe compound based on BDP dye molecules in the detection of zero-valent palladium.

[0031] The beneficial effects of this invention are:

[0032] (1) The fluorescent probe compound proposed in this invention is the first reactive zero-valent palladium fluorescent probe based on BDP dye molecules.

[0033] (2) The fluorescent probe compound proposed in this invention responds rapidly to zero-valent palladium and can complete the change of fluorescence intensity from "on→off" within 8 minutes. The response time is significantly better than other reactive zero-valent palladium fluorescent probes reported in the literature. The change in probe fluorescence intensity is very significant and can be observed with the naked eye under handheld ultraviolet light irradiation (365nm).

[0034] (3) The fluorescent probe proposed in this invention has extremely high sensitivity and a detection limit as low as 0.3 ppb, which is among the top zero-valent palladium fluorescent probes reported to date. The probe has high selectivity for zero-valent palladium and no obvious response to divalent palladium ions and 18 other interfering metal cations.

[0035] (4) The method for preparing the fluorescent probe compound described in this invention is simple and efficient, and the fluorescence detection is easy to operate. It has practical application prospects in the rapid detection of zero-valent palladium. Attached image description:

[0036] Figure 1 The fluorescent probe compound NA-BDP-NPIH obtained in Example 2 1 HNMR spectrum (solvent is deuterated chloroform);

[0037] Figure 2 The fluorescent probe compound NA-BDP-NPIH obtained in Example 2 13 C10 NMR spectrum (solvent is deuterated chloroform);

[0038] Figure 3The fluorescent probe compound NA-BDP-NPINH obtained in Example 5 1 1H NMR spectrum (solvent is deuterated dimethyl sulfoxide);

[0039] Figure 4 The fluorescent probe compound NA-BDP-NPINH obtained in Example 5 13 C10 NMR spectrum (solvent is deuterated dimethyl sulfoxide);

[0040] Figure 5 The high-resolution mass spectrum of the fluorescent probe compound NA-BDP-NPIH obtained in Example 2 is shown below.

[0041] Figure 6 The high-resolution mass spectrum of the fluorescent probe compound NA-BDP-NPINH obtained in Example 5 is shown below.

[0042] Figure 7 The UV-Vis absorption spectra of the fluorescent probe compounds NA-BDP-NPIH and NA-BDP-NPINH in Example 6 are shown, where the concentration of NA-BDP-NPIH and NA-BDP-NPINH is 5 μM and the test solvent is methanol.

[0043] Figure 8 The fluorescence emission spectra of the fluorescent probe compounds NA-BDP-NPIH and NA-BDP-NPINH in Example 7 are shown. The concentrations of NA-BDP-NPIH and NA-BDP-NPINH are both 5 μM. The test solvent is methanol. The excitation wavelengths of NA-BDP-NPIH are 345 nm and 475 nm, and the excitation wavelengths of NA-BDP-NPINH are 420 nm and 475 nm.

[0044] Figure 9 In Example 8, after the addition of zero-valent palladium, the fluorescence intensity of the fluorescent probe compound NA-BDP-NPIH at 513 nm was plotted against time. The test solvent was methanol, the probe concentration was 5 μM, the zero-valent palladium concentration was 10 μM, and the excitation wavelength was 475 nm.

[0045] Figure 10 In Example 8, after the addition of zero-valent palladium, the fluorescence intensity of the fluorescent probe compound NA-BDP-NPINH at 513 nm was plotted against time. The test solvent was methanol, the probe concentration was 5 μM, the zero-valent palladium concentration was 10 μM, and the excitation wavelength was 475 nm.

[0046] Figure 11 The images show the fluorescence emission spectra of the fluorescent probe NA-BDP-NPIH in Example 9 in the presence of different concentrations of zero-valent palladium. The concentration of the fluorescent probe was 5 μM and the concentration of zero-valent palladium was 0–10 μM.

[0047] Figure 12 This is a graph showing the fluorescence intensity variation of the fluorescent probe NA-BDP-NPIH at 513 nm in the presence of different concentrations of zero-valent palladium in Example 9.

[0048] Figure 13 The images show the fluorescence emission spectra of the fluorescent probe NA-BDP-NPINH in Example 9 in the presence of different concentrations of zero-valent palladium. The concentration of the fluorescent probe was 5 μM and the concentration of zero-valent palladium was 0–10 μM.

[0049] Figure 14 This is a graph showing the fluorescence intensity variation of the fluorescent probe NA-BDP-NPINH at 513 nm in the presence of different concentrations of zero-valent palladium in Example 9.

[0050] Figure 15 This is a bar chart comparing the fluorescence emission intensity at 513 nm of the fluorescent probe NA-BDP-NPIH mixed with different metal cations in Example 10.

[0051] Figure 16 This is a bar chart comparing the fluorescence emission intensity at 513 nm of the fluorescent probe NA-BDP-NPINH mixed with different metal cations in Example 10.

[0052] Figure 17 These are comparative photographs showing the response of the probe solution to zero-valent palladium under handheld ultraviolet light irradiation (365nm) in Example 10.

[0053] Figure 18 This is a graph showing the change in fluorescence emission intensity at 513 nm over time after the fluorescent probe NA-BDP-NPIH is mixed with different types of palladium salts in Example 11.

[0054] Figure 19 This is a graph showing the change in fluorescence emission intensity at 513 nm over time after the fluorescent probe NA-BDP-NPINH was mixed with different types of palladium salts in Example 11.

[0055] Figure 20 This is a schematic diagram of the response mechanism of the probe to zero-valent palladium. Detailed implementation method:

[0056] The following is a further description of the invention, but not a limitation thereof.

[0057] Unless otherwise specified, the equipment and reagents used in this invention are commercially available products conventional in this technical field, wherein aminoBDP was prepared and synthesized according to the method we previously reported (Chen, X.-F.;Ma, Q.;Wang, Z.;Xie, Z.;Song, Y.;Ma, Y.;Yang, Z.;Zhao, X.Chem.Asian J.2020,15,4104-4112).

[0058] Example 1: Preparation of compound 3:

[0059] Under nitrogen protection, 1,8-naphthalenedicarboxylic anhydride (compound 2, 60 mg, 0.28 mmol) was added to an ethanol solution (30 mL) of amino BDP (compound 1, 104 mg, 0.26 mmol). The reaction was heated under reflux for 4 h. After the solvent was suspended to dryness, the crude product was eluent with dichloromethane and purified by silica gel chromatography to obtain compound 3 as an orange needle-like solid (118 mg, 81%).

[0060] 1 H NMR (CDCl3): δ=8.64 (d, J=7.3Hz, 2H, ArH), 8.24 (d, J=8.3Hz, 2H, ArH), 7.78 (t, J=7.8Hz, 2H, ArH), 6. 97(d,J=8.3Hz,2H,ArH),6.74(d,J=8.3Hz,2H,ArH),5.92(s,2H,pyrrole-H),4.54(t,J=6.3Hz,3H,NH and CH2),3.59(t,J=6.3Hz,2H,CH2),2.52(s,6H,CH3),1.40(s,6H,CH3). 13 C{ 1 H}NMR (CDCl3): δ=165.0,154.9,148.6,143.4,143.2,134.5,132.3,131.8,131.7,129.0, 128.4,127.2,123.3,122.5,120.9,112.9,42.9,39.8,14.8,14.7ppm.HRMS(HR-ESI):m / z calcd for C 33 H 30 BF2N4O2[M+H] + :563.2430,found:563.2431.

[0061] Example 2: Preparation of the fluorescent probe compound NA-BDP-NPIH:

[0062] Under nitrogen protection, compound 3 (101 mg, 0.18 mmol) obtained in Example 1 was dissolved in 30 mL of tetrahydrofuran. Sodium bicarbonate (37.8 mg, 0.45 mmol) and allyl chloroformate (compound 4, 54 mg, 0.45 mmol) were added sequentially in an ice-water bath. The mixture was stirred at 0 °C for 15 min and then stirred at room temperature for 12 h. After the solvent was suspended to dryness, the crude product was eluent with dichloromethane / tetrahydrofuran (v / v = 100:1) and then purified by silica gel chromatography to obtain compound NA-BDP-NPIH as an orange solid powder (102 mg, 88%).

[0063] 1 H NMR (CDCl3): δ=8.59 (d, J=7.3Hz, 2H, ArH), 8.21 (d, J=8.2Hz, 2H, ArH), 7.76 (t, J=7.8Hz ,2H,ArH),7.48(d,J=7.9Hz,2H,ArH),7.16(d,J=8.4Hz,2H,ArH),5.91(s,2H,pyrrole- H),5.69-5.86(m,1H,CH),5.11(d,J=17.1Hz,1H,CH),5.03(dd,J=10.6,1.6Hz,1H,CH), 4.51-4,54(m,4H,CH2),4.17(t,J=5.8Hz,2H,CH2),2.52(s,6H,CH3),1.18(s,6H,CH3). 13 C{ 1 H}NMR(CDCl3): δ=164.4,155.5,155.1,143.3,143.1,141.0,134.1,132.8,132.3,131.6,131.31 28.5,128.2,127.4,127.0,122.5,121.2,117.2,66.5,48.9,39.2,14.6,14.2.HRMS(HR-ESI):m / z calcd for C37H34BF2N4O4[M+H] + :647.2642,found:647.2641.

[0064] Example 3: Preparation of compound 6:

[0065] Under nitrogen protection, 4-nitro-1,8-naphthalenedicarboxylic anhydride (compound 5, 68 mg, 0.28 mmol) was added to an ethanol solution (30 mL) of amino BDP (compound 1, 104 mg, 0.26 mmol). The reaction was heated under reflux for 6 h. After the solvent was suspended to dryness, the crude product was eluent with dichloromethane and purified by silica gel chromatography to obtain compound 6 as an orange solid powder (85.3 mg, 54%).

[0066] 1 H NMR (CDCl3): δ=8.86 (d, J=8.8Hz, 1H, ArH), 8.77 (d, J=7.4Hz, 1H, ArH), 8.73 (d, J=8. 0Hz,1H,ArH),8.42(d,J=8.0Hz,1H,ArH),7.97-8.06(m,1H,ArH),6.99(d,J=8.5Hz,2 H, ArH), 6.75 (d, J = 8.5Hz, 2H, ArH), 5.93 (s, 2H, pyrrole-H), 4.54 (t, J = 6.2Hz, 2H, C H2),4.36(s,1H,NH),3.60(t,J=6.2Hz,2H,CH2),2.52(s,6H,CH3),1.40(s,6H,CH3). 13 C{ 1 H}NMR (CDCl3): δ=164.0,163.1,154.8,149.8,148.3,143.1,142.8,132.8,132.1,130.2,130.0 ,129.7,129.2,129.0,126.6,123.9,123.8,123.5,122.7,120.9,112.8,42.5,40.0,14.6(some signals are overlapped).HRMS(HR-ESI):m / z calcd for C 33 H 29 BF2N5O4[M+H] + :608.2281,found:608.2282.

[0067] Example 4: Preparation of compound 7:

[0068] Under nitrogen protection, hydrazine hydrate (0.25 mL) and palladium on carbon (5 mg) were added to an ethanol solution (15 mL) of compound 6 (51 mg, 0.08 mmol) obtained in Example 3. The reaction was heated under reflux for 3 h. After the solvent was suspended to dryness, the crude product was eluent with dichloromethane / tetrahydrofuran (v / v = 40:1) and passed through a silica gel column to obtain compound 7 as an orange-yellow solid powder (25.9 mg, 56%).

[0069] 1 H NMR(DMSO-d6)δ=8.62(d,J=7.9Hz,1H,ArH),8.45(d,J=8.4Hz,1H,ArH),8.22(d,J=8.4Hz,1H,ArH ),7.61-7.70(m,1H,ArH),7.47(s,2H,NH2),6.99(d,J=8.2Hz,2H,ArH),6.85(d,J=8.4Hz,3H,ArH and NH),6.32(t,J=6.2Hz,1H,ArH),6.13(s,2H,pyrrole-H),4.21(t,J=7.4Hz,2H,CH2),3.31(pseudo-s,2H,CH2),2.43(s,6H,CH3),1.45(s,6H,CH3). 13 C{ 1 H}NMR (DMSO-d6): δ=164.0,163.1,154.0,152.9,149.4,143.7,142.8,134.1,131.5,131.1,129.8,129.4, 128.5,124.0,121.8,121.0,120.6,119.4,112.1,108.2,107.5,40.3,38.3,14.3,14.2.HRMS(HR-ESI):m / z calcd for:C 33 H 31 BF2N5O2[M+H] + :578.2539,found:578.2534.

[0070] Example 5: Preparation of the fluorescent probe compound NA-BDP-NPINH:

[0071] Under nitrogen protection, compound 7 (23 mg, 0.04 mmol) obtained in Example 4 was dissolved in 10 mL of tetrahydrofuran. Sodium bicarbonate (33.6 mg, 0.4 mmol) and allyl chloroformate (compound 4, 48 mg, 0.4 mmol) were added sequentially in an ice-water bath. The mixture was stirred at 0 °C for 15 min and then stirred at room temperature for 12 h. After the solvent was suspended to dryness, the crude product was eluent with dichloromethane / tetrahydrofuran (v / v = 40:1) and then purified by silica gel chromatography to obtain compound NA-BDP-NPINH as a bright orange solid powder (20.6 mg, 78%).

[0072] 1H NMR(DMSO-d6)δ=8.59(d,J=8.4Hz,1H,ArH),8.41(d,J=8.4Hz,1H,ArH),8.18(d,J=8.4Hz,1H,ArH),7.60-7.67(m ,1H,ArH),7.50(d,J=8.5Hz,2H,ArH),7.43(s,2H,NH2),7.23(d,J=8.5Hz,2H,ArH),6.83(d,J=8.4Hz,1H,ArH),6 .09(s,2H,pyrrole-H),5.76-5.81(m,1H,CH),5.11(d,J=17.2Hz,1H,CH),5.03(dd,J=10.6,1.7Hz,1H,CH),4.47 (d,J=4.9Hz,2H,CH2),4.31(t,J=5.8Hz,2H,CH2),4.04(t,J=5.6Hz,2H,CH2),2.42(s,6H,CH3),1.11(s,6H,CH3). 13 C{ 1 H}NMR (DMSO-d6): δ=164.6,163.6,155.3,154.6,153.2,143.5,143.2,141.9,134.5,133.2,132.0,131.5,131.1,130.3,12 9.8,128.5,127.9,124.4,122.1,121.8,119.8,116.8,108.6,107.9,66.0,49.0,38.6,14.6,14.1.HRMS(HR-ESI):m / zcalcd for:C 37 H 35 BF2N5O4[M+H] + :662.2751,found:662.2755.

[0073] Example 6: UV-Vis absorption spectroscopy of fluorescent probe:

[0074] Stock solutions of the fluorescent probe compounds NA-BDP-NPIH and NA-BDP-NPINH obtained in Examples 2 and 5 were prepared using dimethyl sulfoxide (DMSO) at a concentration of 2 mM. 10 μL of each stock solution was diluted in 4 mL of methanol (concentration 5 μM), and the UV-Vis absorption spectra of the solutions were measured using a UV-Vis spectrophotometer.

[0075] Experimental results: The probe contains two chromophores, namely fluoroboron dipyrrole (BDP) and 1,8-naphthalenediamide (NPI). Therefore, the UV-Vis absorption spectrum shows the characteristic absorption of both chromophores. Figure 7It can be concluded that NA-BDP-NPIH (solid line) mainly has two absorption regions. The strong absorption peak at 500 nm (logε = 4.88) corresponds to the characteristic S0→S1 transition of the BDP structure, while the shoulder peaks at 331 nm (logε = 4.23) and 345 nm (logε = 4.21) are mainly the superposition of the characteristic NPI absorption and the S0→S2 transition of the BDP structure. Similarly, the strong absorption peak at 500 nm (logε = 4.91) of NA-BDP-NPINH (dashed line) also corresponds to the characteristic S0→S1 transition of the BDP structure, while the broad peak with the maximum value at 420 nm (logε = 4.14) corresponds to the charge transfer transition of the 4-amino-1,8-naphthalenedimide chromophore.

[0076] Example 7: Fluorescent probe fluorescence spectroscopy test:

[0077] The fluorescence spectra of the fluorescent probe compound solutions (5 μM concentration) prepared in Example 6 were measured using a fluorescence spectrophotometer. The excitation wavelengths for NA-BDP-NPIH were 345 nm and 475 nm, and for NA-BDP-NPINH, they were 420 nm and 475 nm. Specifically, 345 nm and 420 nm correspond to the excitation of NPI-dominant groups in the NA-BDP-NPIH and NA-BDP-NPINH compounds, respectively, while 475 nm corresponds to the excitation of BDP groups.

[0078] Experimental results: Figure 8 It can be concluded that, regardless of the choice of excitation wavelength, the probe compound only exhibits the characteristic fluorescence emission (λ) of the BDP group. max =513nm), no significant fluorescence emission attributable to the NPI group (λ) was observed. em <500nm), which proves that when the NPI group is selectively excited, an efficient excitation energy transfer (EET) occurs within the probe compound molecule from the excited-state NPI group to the BDP group. By comparing the fluorescence emission intensity of the compounds under NPI and BDP group excitation respectively, the EET efficiencies of NA-BDP-NPIH and NA-BDP-NPINH molecules are 76% and 67%, respectively. Using Rhodamine 6G as a reference compound (fluorescence quantum yield in ethanol is 0.95), the fluorescence quantum yield of NA-BDP-NPIH (Φ) was calculated. F ) is: λ em =345nm,Φ F =0.66; λ em =475nm,Φ F =0.87. The fluorescence quantum yield of NA-BDP-NPIH is: λem =345nm,Φ F =0.5; λ em =475nm,Φ F =0.74.

[0079] Example 8: Fluorescent probe response time test:

[0080] Pd(PPh3)4 (tetraphenylphosphine palladium) was selected as the source of zero-valent palladium in the experiment. The stock solution solvent was DMSO at a concentration of 2 mM. The test solvent was methanol, with the concentrations of the fluorescent probe compounds (NA-BDP-NPIH and NA-BDP-NPINH) at 5 μM and the zero-valent palladium concentration at 10 μM. After adding zero-valent palladium, the fluorescence emission spectrum (λ) of the mixture was recorded every 1–2 minutes. em =475nm). Plot the fluorescence intensity of the fluorescent probe compound at 513nm against time.

[0081] Experimental results: Figure 9 It can be concluded that the addition of zero-valent palladium to the NA-BDP-NPIH probe solution immediately induces a 0.7-fold fluorescence quenching, followed by a continued decrease in fluorescence intensity over time. Within 8 minutes, the fluorescence stabilizes, essentially achieving complete quenching, and the probe fluorescence completes a rapid transition from an "on" to an "off" state. Generally, the response time of reactive fluorescent probes is longer than that of coordination fluorescent probes (on the order of minutes). Literature review reveals that the response time of similar reactive zero-valent palladium probes is mostly greater than 1 hour. The reactive probe described in this invention responds rapidly to zero-valent palladium, with a response time comparable to coordination probes, demonstrating a significant advantage over previously reported cases. Similarly, from... Figure 10 It can be concluded that the NA-BDP-NPINH probe also exhibits a rapid fluorescence response to zero-valent palladium, and fluorescence quenching ("on→off") can be completed within 8 minutes. Based on literature review, the fluorescent probe compound proposed in this invention is the first reactive zero-valent palladium fluorescent probe based on BDP dye molecules.

[0082] Example 9: Titration test of zero-valent palladium against fluorescent probe solution:

[0083] The test solvent was methanol, and the concentration of the fluorescent probe compounds (NA-BDP-NPIH and NA-BDP-NPINH) was 5 μM. Zero-valent palladium (0-10 μM) was added, and after waiting 8 minutes, the fluorescence emission spectrum of the mixed solution was recorded. The excitation wavelength was 475 nm. Figures 11-14 As shown.

[0084] Experimental results: With the addition of zero-valent palladium, the fluorescence emission of the fluorescent probe gradually weakened and decreased linearly, and the change tended to level off after 8 μM.

[0085] Detection limit of fluorescent probe:

[0086] Based on the results of the fluorescence titration test, a graph was plotted between the fluorescence intensity of the probe at 513 nm and the concentration of zero-valent palladium. It can be seen that the change in fluorescence intensity is linearly related to the added concentration of zero-valent palladium. The detection limit of the probe for palladium ions can be calculated using the formula: Detection limit = 3 x σ / K, where σ is the standard deviation of the blank sample and K is the slope of the line. Calculations show that the detection limits of the fluorescent probes NA-BDP-NPIH and NA-BDP-NPINH described in this invention for zero-valent palladium are both as low as 0.3 ppb, placing them among the top zero-valent palladium fluorescent probes reported to date, based on literature review.

[0087] Example 10: Selectivity of fluorescent probe for zero-valent palladium:

[0088] The experiment selected 18 metal cations that easily interfere with palladium ion detection, including Ag. + ,Ba 2+ Ca 2+ Cd 2+ Co 2+ Cu 2+ ,Fe 2+ ,Fe 3+ Hg 2+ ,K + Mg 2+ ,Mn 2+ Na + ,Pb 2+ ,Pt 2+ ,Rh 3+ ,Ru 3+ ,Zn 2+ The concentration of each metal cation was 10 μM. The test solvent was methanol, and the concentration of the probe compounds (NA-BDP-NPIH and NA-BDP-NPINH) was 5 μM. After adding the metal ions, the mixture was thoroughly mixed and allowed to stand for 8 minutes. The fluorescence emission spectrum of the solution was then measured, and the fluorescence intensity of the compounds at 513 nm was plotted against different metal ion species.

[0089] Experimental results: such as Figure 15 , 16 As shown in the fluorescence emission spectra, both the NA-BDP-NPIH and NA-BDP-NPINH probes exhibit a significant fluorescence signal quenching response only to zero-valent palladium, demonstrating high probe selectivity and strong anti-interference ability. Figure 17 It can be seen that the fluorescence change of the probe solution is significant before and after the addition of zero-valent palladium, and can be quickly determined by the naked eye under a handheld ultraviolet lamp at a wavelength of 365nm.

[0090] Example 11: Response of a fluorescent probe to divalent palladium ions:

[0091] Several common palladium salts were selected for the experiment: PdCl2 (palladium dichloride), PdBr2 (palladium dibromide), Pd(OAc)2 (palladium acetate), and Pd(dppf)Cl2 ([1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride) to test the selectivity of fluorescent probe compounds for divalent and zero-valent palladium ions. Pd(PPh3)4 (tetraphenylphosphine palladium) was used as the source of zero-valent palladium. The stock solution solvent was DMSO or DMSO / H2O (v / v = 1:9), and the stock concentration of palladium salts was 2 mM. The test solvent was methanol, in which the concentration of fluorescent probe compounds (NA-BDP-NPIH and NA-BDP-NPINH) was 5 μM, and the concentration of palladium salts was 10 μM. After adding the corresponding palladium salts, the fluorescence emission spectra (λ) of the mixtures at different time points were recorded. em =475nm). Plot the fluorescence intensity of the fluorescent probe compound at 513nm against different palladium salts.

[0092] Experimental results: such as Figure 18 , 19 As shown, while the addition of divalent palladium ions can reduce the fluorescence emission intensity of the probes (NA-BDP-NPIH and NA-BDP-NPINH) to some extent, the probes still maintain strong fluorescence; only with the addition of zero-valent palladium can the probe fluorescence be quenched from "on→off". The response changes of probe NA-BDP-NPIH show the following trends: Pd(PPh3)4 >> Pd(dppf)Cl2 ≈ Pd(OAc)2 > PdCl2 ≈ PdBr2; the response changes of probe NA-BDP-NPINH show the following trends: Pd(PPh3)4 >> Pd(dppf)Cl2 ≈ Pd(OAc)2 ≈ PdCl2 > PdBr2. It is evident that the probe compounds exhibit high selectivity for zero-valent palladium compared to divalent palladium ions.

[0093] Example 12: Recognition mechanism of zero-valent palladium by fluorescent probe:

[0094] The reactive fluorescent probe compounds described in this invention respond to zero-valent palladium based on the Tsuji-Trost reaction. In the presence of zero-valent palladium, the allyl formamide group on the aniline N atom at the meso position of BDP in probe compounds NA-BDP-NPIH and NA-BDP-NPINH undergoes oxidative addition, reductive elimination, and decarboxylation to generate compound 3 in Example 1 and compound 6 in Example 3, respectively. Under photoexcitation, the N atom undergoes photo-induced electron transfer (PeT) to the excited-state BDP, causing quenching of the BDP's fluorescence. When the N atom is bonded to the allyl formamide group, this PeT process is significantly suppressed, and the compound exhibits the characteristic strong fluorescence of the BDP fluorophore. To verify this recognition mechanism, 10 μM methanol solutions of NA-BDP-NPIH or NA-BDP-NPINH were added to 20 μM Pd(PPh3)4, stirred at room temperature for 20 minutes, and the reaction solution was then analyzed by mass spectrometry and compared with compounds 3 and 6.

[0095] Experimental Results: After the reactions of NA-BDP-NPIH and NA-BDP-NPINH with Pd(PPh3)4, mass spectrometry analysis revealed high concentrations of compounds 3 and 6, respectively. This demonstrates that zero-valent palladium can indeed promote the removal of the allyl formamide group from the N atom of aniline, leading to the recovery of the PET process from the N atom to the excited state of BDP, resulting in BDP fluorescence quenching. Whether the NPI group is excited to generate excited-state BDP via EET, or the BDP group is directly excited, the above fluorescence quenching process can occur. The response mechanism of the probe to zero-valent palladium is as follows: Figure 20 As shown.

[0096] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included in the patent scope of this case.

Claims

1. A reactive zero-valent palladium fluorescent probe based on BDP dye molecules, with the structural formula shown in Formula I: in, R = H or NH2.

2. The method for preparing the reactive zero-valent palladium fluorescent probe according to claim 1, characterized in that, When R = H, the equation is: Includes the following steps: (1) Under nitrogen protection, ethanol solutions of compounds 1 and 2 were heated to reflux, and after the reaction was completed, compounds 3 were obtained by separation and purification. (2) Under nitrogen protection, sodium bicarbonate and compound 4 were added sequentially to the tetrahydrofuran solution of compound 3. After the reaction was completed, the probe compound was obtained by separation and purification, and it was denoted as NA-BDP-NPIH.

3. The preparation method according to claim 2, characterized in that, The reaction time for step (1) is 4 to 12 hours, and the molar ratio of compound 1 to compound 2 is 1:1 to 1:1.

2.

4. The preparation method according to claim 2, characterized in that, The reaction temperature in step (2) is room temperature, the reaction time is 8 to 16 hours, and the molar ratio of compound 3, sodium bicarbonate and compound 4 is 1:2.5:2.5 to 1:10:

10.

5. The method for preparing the reactive zero-valent palladium fluorescent probe according to claim 1, characterized in that, When R = NH2, the equation is: Includes the following steps: (1) Under nitrogen protection, ethanol solutions of compounds 1 and 5 were heated to reflux, and after the reaction was completed, compounds 6 were obtained by separation and purification. (2) Under nitrogen protection, hydrazine hydrate and palladium on carbon were added to the ethanol solution of compound 6. After the reaction was completed, the mixture was separated and purified to obtain compound 7. (3) Under nitrogen protection, sodium bicarbonate and compound 4 were added to the tetrahydrofuran solution of compound 7. After the reaction was completed, the probe compound was obtained by separation and purification, and it was denoted as NA-BDP-NPINH.

6. The preparation method according to claim 5, characterized in that, The reaction time in step (1) is 4 to 12 hours, and the molar ratio of compound 1 to compound 5 is 1:1 to 1:1.

5.

7. The preparation method according to claim 5, characterized in that, The reaction temperature in step (2) is reflux of ethanol, and the reaction time is 1.5 to 3 hours.

8. The preparation method according to claim 5, characterized in that, The reaction temperature in step (3) is room temperature, the reaction time is 8 to 16 hours, and the molar ratio of compound 7, sodium bicarbonate and compound 4 is 1:2.5:2.5 to 1:10:

10.

9. The application of the reactive zero-valent palladium fluorescent probe compound based on BDP dye molecules as described in claim 1 in the detection of zero-valent palladium.

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