Small-molecule fluorescent dye with emission wavelength exceeding 1300 nm and preparation method of small-molecule fluorescent dye

Abstract

The invention discloses a micromolecular fluorescent dye with emission wavelength exceeding 1300 nm and a preparation method thereof. Complex fluorescent molecules with the emission wavelength exceeding 1300 nm are constructed through nucleophilic substitution, electrophilic substitution, coupling reaction and oxidation reaction, the route steps are short, operation is easy and convenient, the total yield is high, the synthesis difficulty, time and cost are greatly reduced, and the method is suitable for industrial production. Multiple functional group modification and tedious pi-system expansion steps for adjusting the spectral performance in the prior art are avoided, and a traditional synthesis path needing more than six steps is compressed to four steps. The molecular weight of the prepared fluorescent dye is only 592.2383, and the traditional design difficulty that long wavelength is inevitably accompanied by large molecular weight (generally gt and 800 Da) in the prior art is fundamentally broken through.

Description

Technical Field

[0001] This invention relates to the field of organic fluorescent materials technology, specifically to a small molecule fluorescent dye with an emission wavelength exceeding 1300 nm and its preparation method. Background Technology

[0002] In the field of in vivo fluorescence imaging, fluorescent dyes with emission wavelengths in the near-infrared II region have attracted widespread attention due to their advantages such as strong tissue penetration and low autofluorescence interference. Generally speaking, in this spectral region, longer emission wavelengths usually mean lower tissue scattering and a better signal-to-noise ratio, thus potentially leading to higher resolution imaging results.

[0003] However, developing small organic molecule dyes with emission wavelengths exceeding 1300 nm faces significant challenges. Traditionally, to achieve such long emission wavelengths, molecular design typically requires the construction of large-sized π-conjugated systems or complex donor-acceptor structures, which directly leads to problems such as excessively large molecular weights (usually exceeding 800 Da), lengthy synthetic steps, low yields, and difficulties in purification.

[0004] First, the synthesis of existing long-wavelength dyes typically involves lengthy linear steps. For example, the total synthesis of a typical high-performance NIR-II dye molecule usually requires six or more reaction steps. This mainly includes: 1) multi-step preparation of complex electron-donating units (such as triphenylamine and indoline); 2) multi-step synthesis of complex electron-withdrawing units (such as benzobisthiadiazole and thienobisthiadiazole); 3) the first coupling reaction between the donor and acceptor units; 4) functional group transformation of the initial coupling product to introduce reaction sites; 5) a second coupling with a second donor or acceptor unit to further extend the conjugated, redshifted wavelength; and 6) finally introducing water-soluble or biocompatible groups and carrying out the necessary deprotection reactions.

[0005] Secondly, the multi-step synthesis leads to a significant decrease in overall yield and difficulties in purification. Since each chemical reaction results in yield loss, after six or more steps, the cumulative overall yield of the target product is usually extremely low (reported in the literature as even below 5%). This low yield significantly increases the cost of raw materials and time, making the preparation of this type of dye economically unfeasible and severely restricting its in-depth research and large-scale application.

[0006] Furthermore, each intermediate requires tedious separation and purification processes, which are time-consuming and labor-intensive. These factors severely restrict the practical application and clinical translation of such dyes. Therefore, there is an urgent need in this field to develop a novel fluorescent dye that can effectively balance "long wavelength," "small molecular weight," and "synthetic simplicity" to overcome the high cost and complexity bottlenecks of existing technologies. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a small molecule fluorescent dye with an emission wavelength exceeding 1300 nm and its preparation method.

[0008] A small-molecule fluorescent dye with an emission wavelength exceeding 1300 nm has the following structure:

[0009]

[0010] The molecular formula of the fluorescent dye is C 42 H 30 N3O + It has a molecular weight of 592.2383, a maximum absorption wavelength of 1180 nm, and a maximum emission wavelength of 1304 nm.

[0011] A method for preparing the above-mentioned fluorescent dye, the synthetic route is shown below:

[0012]

[0013] Includes the following steps:

[0014] (1) Dissolve phenoxazine and benzyl chloride in 1,2-dichloroethane, add triethylamine, reflux, concentrate, crystallize and recrystallize to obtain compound of formula 1.

[0015] (2) The compound of formula 1 was dissolved in dichloromethane, and liquid bromine was added dropwise under ice bath conditions. After the reaction was completed, the mixture was quenched, extracted, crystallized, and recrystallized to obtain the compound of formula 2.

[0016] (3) The compound of formula 2, 1-methyl-2-phenylindoleazine, potassium acetate and palladium acetate were dissolved in N,N-dimethylformamide and refluxed under nitrogen protection. The compound of formula 3 was obtained by extraction, drying and column chromatography.

[0017] (4) Dissolve the compound of formula 3 in dichloromethane, add perchloric acid solution dropwise, and after the reaction is completed, neutralize, extract, dry and column chromatography to obtain the target fluorescent dye of formula 4.

[0018] The beneficial effects of this invention are:

[0019] This invention is the first to realize the construction of complex fluorescent molecules with emission wavelengths exceeding 1300 nm through only four chemical reactions. This route is short, easy to operate, and has a high overall yield, which greatly reduces the difficulty, time and cost of synthesis.

[0020] This invention utilizes precise molecular design, a modular construction strategy, and commercially available raw materials to construct the target molecule via a streamlined linear synthetic route (four steps): nucleophilic substitution, electrophilic substitution, coupling reaction, and oxidation reaction. Specifically, this route avoids the multiple functional group modifications and lengthy π-system expansion steps required in existing technologies to adjust spectral performance. Instead, it directly forms a core chromophore with long-wavelength emission characteristics through a single, crucial, and efficient coupling reaction, thus compressing the traditional six-step or more synthetic path into four steps.

[0021] Existing synthetic routes for long-wavelength dyes involving six or more steps often result in overall yields below 5%. This invention, through the simplified route design and optimized reaction conditions described above, achieves a competitive overall yield. The yields for each step are approximately: step one, step two, step three, and step four, respectively. Calculations show that the cumulative overall yield of this invention across four steps is significantly higher than that of similar long-wavelength dyes requiring six or more steps as reported in many publications. This yield level, while ensuring the optical performance of the product, greatly improves synthesis efficiency and atom economy, and significantly reduces raw material costs and waste disposal burden per batch.

[0022] This invention, through ingenious molecular framework design, successfully achieved an emission wavelength exceeding 1300 nm with a small molecular weight of only 592.2383. This characteristic fundamentally overcomes the traditional design dilemma in existing technologies where "long wavelengths inevitably come with large molecular weights (typically >800 Da)." Small molecular weight not only means lower synthetic molecular complexity but is also expected to bring superior pharmacokinetic properties, such as faster in vivo distribution and clearance rates, thereby helping to reduce background signal during in vivo imaging. Simultaneously, the small molecular weight also makes the purification and quality control of the final product simpler and more precise. Attached Figure Description

[0023] Figure 1 The absorption and emission spectra of the fluorescent dye of this invention in dichloromethane are shown.

[0024] Figure 2 The 1H NMR spectrum of the compound shown in Formula 1 is shown below.

[0025] Figure 3 The image shows the carbon NMR spectrum of the compound represented by Formula 1.

[0026] Figure 4 The high-resolution mass spectrum of the compound shown in Formula 1 is shown below.

[0027] Figure 5 The image shows the proton NMR spectrum of the compound represented by Equation 2.

[0028] Figure 6The image shows the carbon NMR spectrum of the compound represented by Equation 2.

[0029] Figure 7 The high-resolution mass spectrum of the compound shown in Formula 2 is shown below.

[0030] Figure 8 The 1H NMR spectrum of the compound shown in Formula 3 is shown below.

[0031] Figure 9 The image shows the carbon NMR spectrum of the compound represented by Equation 3.

[0032] Figure 10 The high-resolution mass spectrum of the compound shown in Formula 3 is shown below.

[0033] Figure 11 The following is the proton NMR spectrum of the compound shown in Formula 4.

[0034] Figure 12 The image shows the high-resolution mass spectrum of the compound represented by Equation 4. Detailed Implementation

[0035] To further understand the present invention, the embodiments of the present invention will be described in more detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0036] This invention discloses a novel small-molecule fluorescent dye with an emission wavelength exceeding 1300 nm, the structure of which is shown below:

[0037]

[0038] The molecular formula of the fluorescent dye is C 42 H 30 N3O + It has a molecular weight of 592.2383, a maximum absorption wavelength of 1180 nm, and a maximum emission wavelength of 1304 nm.

[0039] This invention also discloses a method for preparing the aforementioned fluorescent dye, the synthetic route of which is shown below:

[0040]

[0041] Includes the following steps:

[0042] (1) Weigh phenoxazine and benzyl chloride into a container, add 1,2-dichloroethane to dissolve them completely, then add triethylamine, heat the system to reflux (usually in an oil bath), and stir at this temperature (the temperature at which the mixture is heated to reflux) until the reaction is complete, to obtain a mixed solution. Concentrate the mixed solution under reduced pressure to remove the solvent and residual reactants. After standing, a white solid precipitates out. Collect the white solid and wash it with petroleum ether. After recrystallization, the compound shown in Formula 1 is obtained.

[0043] (2) Weigh the compound shown in Formula 1 obtained in step (1) into a container, add dichloromethane to dissolve it completely, and slowly add liquid bromine dropwise while stirring under ice bath conditions. After the addition is complete, continue stirring until the reaction is finished. Then add saturated sodium thiosulfate aqueous solution to quench excess liquid bromine and obtain a mixed solution. Extract the mixed solution with saturated sodium chloride aqueous solution, collect the organic phase after standing and separation, dry it with anhydrous sodium sulfate and concentrate it under reduced pressure to remove the solvent. After standing, a green solid precipitates out. Collect the green solid and wash it with petroleum ether. After recrystallization, obtain the compound shown in Formula 2.

[0044] (3) Weigh the compound shown in Formula 2 obtained in step (2), 1-methyl-2-phenylindoleazine, potassium acetate and palladium acetate into a container (potassium acetate and palladium acetate are used as catalysts), replace with nitrogen several times, add N,N-dimethylformamide to completely dissolve it, heat the system to reflux in an oil bath, and stir at this temperature (the temperature when heated to reflux) until the reaction is complete to obtain a mixed solution. Add saturated sodium chloride aqueous solution and dichloromethane to the mixed solution in sequence, let stand to separate, collect the organic phase, dry with anhydrous sodium sulfate, concentrate under reduced pressure to remove the solvent, and purify by silica gel column chromatography to obtain the compound shown in Formula 3.

[0045] (4) Weigh the compound shown in Formula 3 obtained in step (3) into a container, add dichloromethane to dissolve it completely, and add perchloric acid solution dropwise under stirring. After the addition is complete, continue stirring until the reaction is finished to obtain a mixed solution. Adjust the pH of the mixed solution to neutral with saturated sodium bicarbonate aqueous solution, and then extract the mixed solution with saturated sodium chloride aqueous solution. After standing separation, collect the organic phase, dry it with anhydrous sodium sulfate, concentrate it under reduced pressure to remove the solvent, and purify it by silica gel chromatography to obtain the compound shown in Formula 4. When the amount of the compound shown in Formula 3 is less than or equal to 0.6 g, the amount of perchloric acid solution is fixed at 15 mL; when the amount of the compound shown in Formula 3 is greater than 0.6 g and less than or equal to 2 g, the amount of perchloric acid solution is fixed at 25 mL; when the amount of the compound shown in Formula 3 is greater than 2 g, for every 1 g increase, the amount of perchloric acid solution is increased by about 5 mL from 25 mL.

[0046] Furthermore, in step (1), the molar ratio of phenoxazine to benzyl chloride and triethylamine is 1:3 to 7:3 to 7. The reflux temperature is 75 to 85°C, and the reaction time is monitored by TLC until the phenoxazine disappears.

[0047] Furthermore, in step (2), the molar ratio of the compound shown in Formula 1 to liquid bromine is 1:1.8-3. The bromination temperature is -5 to 5°C, and stirring continues for 0.5 to 3 h after the bromine is added.

[0048] Furthermore, in step (3), the molar ratio of the compound shown in Formula 2 to 1-methyl-2-phenylindoleazine, potassium acetate, and palladium acetate is 1:1.9–4:4–7:0.05–0.25. The reflux temperature is 105–115 °C, and the reaction time is monitored by TLC until the compound of Formula 2 disappears.

[0049] Furthermore, in step (4), the mass fraction of the perchloric acid solution is 70% to 72%.

[0050] Example 1

[0051] like Figure 1 As shown, the fluorescent dye (the compound shown in Formula 4) prepared in this embodiment has a maximum absorption wavelength of 1180 nm and a maximum emission wavelength of 1304 nm in dichloromethane.

[0052] (1) Synthesis of the compound shown in Formula 1:

[0053] 5 g (27.29 mmol) of phenoxazine and 10.36 g (81.87 mmol) of benzyl chloride were weighed into a 250 mL round-bottom flask. A suitable amount of 1,2-dichloroethane was added to completely dissolve them. Then, approximately 11 mL of triethylamine was added as a catalyst. The round-bottom flask was placed in an oil bath and heated. When the system temperature reached 80 °C, reflux was initiated. The mixture was stirred continuously at this temperature until the reaction was complete (the reaction progress was monitored by TLC; the entire reaction process took approximately 72 hours), yielding a mixed solution. The mixed solution was concentrated under reduced pressure to remove the solvent and residual reactants. After standing, a large amount of white solid precipitated. This white solid was collected and washed with petroleum ether. Recrystallization yielded 6.7 g of white solid, which is the compound shown in Formula 1 (yield approximately 90%).

[0054] like Figure 2 , Figure 3 and Figure 4 As shown, the 1H NMR spectrum of the compound represented by Formula 1 ( 1 H NMR, carbon nuclear magnetic resonance (NMR) 13 The specific data for CNMR and high-resolution mass spectrometry (HRMS) are as follows:

[0055]

[0056] (2) Synthesis of the compound shown in Formula 2:

[0057] Weigh 5 g (18.31 mmol) of the compound shown in Formula 1 obtained in step (1) into a 250 mL round-bottom flask, add an appropriate amount of dichloromethane to completely dissolve it, and add 5.85 g (36.62 mmol) of liquid bromine dropwise while stirring under ice bath conditions. After the addition is complete, continue stirring until the reaction is finished (the reaction progress is judged by TLC monitoring, and the entire reaction process takes about 2 hours). Then, add about 3 g of saturated sodium thiosulfate aqueous solution to quench the excess liquid bromine, and obtain a mixed solution. Add about 50 mL of saturated sodium chloride aqueous solution to the mixed solution, let it stand to separate, and collect the organic phase. The organic phase is dried with anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. After standing, a green solid precipitates out. Collect the green solid and wash it with petroleum ether. After recrystallization, 6.4 g of light green solid is obtained, which is the compound shown in Formula 2 (yield about 90%).

[0058] like Figure 5 , Figure 6 and Figure 7 As shown, the 1H NMR spectrum of the compound represented by Formula 2 ( 1 H NMR, carbon nuclear magnetic resonance (NMR) 13 The specific data for CNMR and high-resolution mass spectrometry (HRMS) are as follows:

[0059]

[0060] (3) Synthesis of the compound shown in Formula 3:

[0061] Weigh 2 g (4.62 mmol) of the compound shown in Formula 2 obtained in step (2), 2.01 g (9.70 mmol) of 1-methyl-2-phenylindoleazine (9.70 mmol), 1.81 g (18.47 mmol) of potassium acetate and 104.17 mg (0.464 mmol) of palladium acetate into a 250 mL three-necked flask. After purging with nitrogen three times, add an appropriate amount of N,N-dimethylformamide to completely dissolve it. Place the three-necked flask in an oil bath and heat it. When the system temperature rises to 110 °C, start reflux. Stir at this temperature until the reaction is complete (the reaction progress is judged by TLC monitoring, and the entire reaction process takes about 24 hours) to obtain a mixed solution. First, add 80 mL of saturated sodium chloride aqueous solution to the mixed solution, then add dichloromethane in three portions for extraction, each time using 50 mL. After standing and separation, collect the organic phase, dry the organic phase with anhydrous sodium sulfate, concentrate under reduced pressure to remove the solvent, and then purify by silica gel column chromatography to obtain 1.42 g of the compound shown in Formula 3 (yield of about 45%).

[0062] like Figure 8 , Figure 9 and Figure 10 As shown, the 1H NMR spectrum of the compound represented by Formula 3 ( 1 H NMR, carbon nuclear magnetic resonance (NMR)13 The specific data for CNMR and high-resolution mass spectrometry (HRMS) are as follows:

[0063]

[0064] (4) Synthesis of the compound shown in Formula 4:

[0065] Weigh 300 mg (0.437 mmol) of the compound shown in Formula 3 obtained in step (3) into a 250 mL round-bottom flask, add an appropriate amount of dichloromethane to completely dissolve it, and add 15 mL of perchloric acid solution dropwise under stirring. After the addition is complete, continue stirring until the reaction is finished (the reaction needs to be carried out overnight, and the reaction progress is judged by TLC monitoring. The entire reaction process takes about 14 hours). A mixed solution is obtained. Adjust the pH of the mixed solution to neutral with saturated sodium bicarbonate aqueous solution, and then add about 15 mL of saturated sodium chloride aqueous solution. After standing and separation, collect the organic phase. The organic phase is dried with anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. It is then purified by silica gel column chromatography to obtain 65 mg of the compound shown in Formula 4 (yield of about 25%).

[0066] like Figure 11 and Figure 12 As shown, the 1H NMR spectrum of the compound represented by Formula 4 ( 1 The specific data for H NMR and high-resolution mass spectrometry (HRMS) are as follows:

[0067]

[0068] The ease of operation of the synthesis route in this embodiment is mainly reflected in:

[0069] The separation and purification process of intermediates and final products is simple. The product yields of the first and second steps are high (approximately 90%), and the required purity can be achieved through simple recrystallization or extraction, avoiding the cumbersome process of time-consuming column chromatography purification required for each step in existing technologies.

[0070] Each reaction step is carried out under conventional organic synthesis conditions, without the need for harsh anhydrous, oxygen-free, or ultra-low temperature environments, thus reducing the equipment threshold and operational difficulty.

[0071] By optimizing the reaction sequence, the continuity of multiple bonding steps was achieved, avoiding the separation and processing of intermediates and improving the synthesis efficiency.

[0072] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A small molecule fluorescent dye with an emission wavelength exceeding 1300 nm, characterized in that, The structure of the fluorescent dye is shown below: The molecular formula of the fluorescent dye is C 42 H 30 N3O + It has a molecular weight of 592.2383, a maximum absorption wavelength of 1180 nm, and a maximum emission wavelength of 1304 nm.

2. A method for preparing a fluorescent dye as described in claim 1, characterized in that, The synthesis route is shown below: Includes the following steps: (1) Dissolve phenoxazine and benzyl chloride in 1,2-dichloroethane, add triethylamine, reflux, concentrate, crystallize and recrystallize to obtain compound of formula 1; (2) Dissolve the compound of formula 1 in dichloromethane, add liquid bromine dropwise under ice bath conditions, and after the reaction is completed, quench, extract, crystallize and recrystallize to obtain the compound of formula 2; (3) The compound of formula 2, 1-methyl-2-phenylindoleazine, potassium acetate and palladium acetate were dissolved in N,N-dimethylformamide and refluxed under nitrogen protection. The compound of formula 3 was obtained by extraction, drying and column chromatography. (4) Dissolve the compound of formula 3 in dichloromethane, add perchloric acid solution dropwise, and after the reaction is completed, neutralize, extract, dry and column chromatography to obtain the target fluorescent dye of formula 4.

3. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of phenoxazine to benzyl chloride and triethylamine is 1:3 to 7:3 to 7.

4. The preparation method according to claim 2 or 3, characterized in that: Step (1) The reflux temperature is 75-85℃, and the reaction time is measured by TLC until the phenoxazine disappears.

5. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of the compound shown in Formula 1 to liquid bromine is 1:1.8 to 3.

0.

6. The preparation method according to claim 2 or 5, characterized in that, In step (2), the bromination temperature is -5 to 5℃, and stirring is continued for 0.5 to 3 h after the bromine is added.

7. The preparation method according to claim 2, characterized in that, In step (3), the molar ratio of the compound shown in Formula 2 to 1-methyl-2-phenylindoleazine, potassium acetate, and palladium acetate is 1:1.9 to 4:4 to 7:0.05 to 0.

25.

8. The preparation method according to claim 2 or 7, characterized in that, Step (3) The reflux temperature is 105-115°C, and the reaction time is measured by TLC until the compound of formula 2 disappears.

9. The preparation method according to claim 2, characterized in that, In step (4), the mass fraction of the perchloric acid solution is 70% to 72%.

10. The preparation method according to claim 9, characterized in that, When the compound of Formula 3 is ≤0.6 g, the perchloric acid solution is 15 mL; When 0.6g < compound of formula 3 ≤ 2g, the perchloric acid solution is 25 mL; When the compound of Formula 3 is greater than 2 g, the amount of perchloric acid solution should be increased by 5 mL for every 1 g increase.

Images