A fluorescent conjugated polyelectrolyte containing a phenylboronic acid side group and a preparation method thereof

Abstract

The application discloses a fluorescent conjugated polyelectrolyte containing a benzene boronic acid side group and a preparation method thereof. A diethynyl monomer containing a dimethylamino side group and a dibromoarene monomer are respectively synthesized, and a conjugated polyelectrolyte precursor containing a dimethylamino side group is synthesized through a Sonogashira coupling reaction; after a quaternary ammoniation reaction and removal of a protective group, the fluorescent conjugated polyelectrolyte containing the benzene boronic acid side group is obtained. In the application, a benzene boronic compound containing a benzene boronic acid group and a dimethylamino group are introduced into a side group of a conjugated polymer in the form of a stable quaternary ammonium salt through a substitution reaction, a large number of benzene boronic acid groups capable of reversibly covalently combining with molecules with an o-diol structure are introduced into the side group of the conjugated polymer while water solubility of the polymer is endowed, and thus the performance of the polymer is changed, and the application has application prospects in the fields of chemistry, biological imaging, carbohydrate detection and the like.

Description

Technical Field

[0001] This invention relates to a fluorescent conjugated polyelectrolyte, and more particularly to a polyfluorene-based fluorescent conjugated polyelectrolyte containing high-density phenylboronic acid side groups and its preparation method. Background Technology

[0002] The molecular backbone of conjugated polymers possesses a large delocalized electronic structure, enabling signal transmission throughout the entire conjugated chain and thus enhancing the signal to some extent (see Chem Rev. 2007, 107, 1339-1386). Therefore, they offer advantages in terms of fluorescence signal form and quantum efficiency. Compared to other materials, conjugated polymers possess numerous advantages as fluorescent materials, such as simple synthesis, tunable chemical structure and emission color, relatively low cost, low toxicity, strong resistance to photobleaching, and good stability (see Chem. Rev. 2000, 100, 1605-1644). Consequently, they are widely used in fields such as bioimaging and sensing.

[0003] In recent years, fluorescent conjugated polymers have seen rapid development in the field of biosensing. This is because these polymers, after side group ionization, become conjugated polyelectrolytes. They possess both the excellent properties of conjugated polymers mentioned above and good water solubility, as their side chains generally contain charged quaternary ammonium salts or carboxylate structures. An increasing number of conjugated polyelectrolytes are being selected for molecular research in aqueous media, such as the detection and imaging of nucleic acids, proteins, or cells in vivo (see: Adv. Mater. 2008, 20, 2959-2964; Angew. Chem. Int. Ed. 2009, 48, 4300-4316).

[0004] Boric acid, as an important intermediate in organic chemistry, participates in various processes such as chemical synthesis, drug research, and molecular recognition (see Biomol. Chem. 2019, 17, 683-691). Boric acid can reversibly covalently bind to Lewis bases and polyols, and therefore has been used as a receptor for carbohydrate detection and in related cell and tissue imaging (see Analyst. 2020, 145, 719-744). Currently, there are few reports on introducing phenylboronic acid groups into the side groups of polymers. Only a very few studies have introduced boronic acid groups into the side groups of polythiophene through the quaternization reaction of pyridineboronic acid with alkyl bromides, preparing hydrophilic polymers for the detection of carbohydrates such as glucose and fructose (see Chem. Eur. J. 2008, 14, 1648-1653). Another literature reports a conjugated polymer nanoparticle containing phenylboronic acid side groups (see: ACS Appl. Polym. Mater, 2021, 3, 4543-4553). First, a polyfluorene-benzothiazole backbone was synthesized, with repeating units containing two terminal amino-terminal side groups. Then, polyethylene glycol and phenylboronic acid groups were modified to the side groups via amidation between amino and carboxyl groups. This polymer itself is insoluble in water and needs to be prepared as nanoparticles for stable dispersion in water; furthermore, after amidation, each repeating unit contains only one phenylboronic acid side group. In summary, the currently reported fluorescent conjugated polymers containing phenylboronic acid side groups have limitations in their applications in chemical, biological imaging, and trace evidence analysis.

[0005] According to literature reports, dimethylamino groups can undergo efficient quaternization reactions with terminal bromine compounds under mild reaction conditions to generate water-soluble salts (see: J. Am. Chem. Soc. 2004, 126, 9845-9853). However, there are currently no reports on the preparation of conjugated polymers containing high-density dimethylamino side groups via coupling. Since the dimethylamino group can partially affect the catalytic process in the coupling reaction, the preparation of polymer precursors containing high-density dimethylamino groups requires careful selection and optimization of the catalyst used in the polymerization process and its dosage. Quaternization reactions between high-density dimethylamino groups in the polymer precursor and benzyl bromide can not only introduce phenylboronic acid groups into the side groups of the conjugated polymer, but also simultaneously generate quaternary ammonium salts on the side groups, giving them good water solubility. Under alkaline conditions, the phenylboronic acid groups interact with molecules in the aqueous environment through covalent bonding, which holds promise for improving various application properties in chemical, biological, and other fields, and has significant practical implications. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a simple and efficient synthesis process for a polyfluorene-based fluorescent conjugated polyelectrolyte containing high-density phenylboronic acid side groups, which yields a product with good water solubility and bright fluorescence, as well as its preparation method.

[0007] The technical solution of this invention is to provide a fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups, the structural formula of which is: , Where n is the number of repeating units, n = 8 to 21.

[0008] The present invention also provides a method for preparing a fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups, comprising the following steps: (1) By molar amount, 1 part of 2,5-bis(3'-(N,N-dimethylamino)propyl)-1,4-bis(trimethylsilylacetylene)benzene, 2~2.5 parts of n-Bu4NF and 1100~1200 parts of tetrahydrofuran were stirred until the solid dissolved. After stirring at room temperature for 0.5~1 hours, the mixture was extracted, rotary evaporated, purified by neutral alumina column chromatography and dried to obtain a diacetylene monomer, denoted as M1. The structural formula of the monomer M1 is: ; (2) Under anhydrous and oxygen-free conditions, by molar amount, 1 part of dibromoaromatic monomer M2 and 1 part of monomer M1 obtained in step (1), 0.015-0.05 parts of tetra(triphenylphosphine)palladium dichloride, 0.015-0.05 parts of cuprous iodide, 100-200 parts of diisopropylamine, and 200-300 parts of toluene are added to a reactor and mixed and stirred. The mixture is reacted for 30-50 hours under argon protection and at a temperature of 70-75°C. After filtration, recrystallization, centrifugation, and drying, a conjugated polyelectrolyte precursor is obtained, denoted as PFPE-NMe2. The structural formula of the monomer M2 is: ; The structural formula of the precursor PFPE-NMe2 is: , Where n is the number of repeating units, n = 8~21; (3) By amount of substance, 1 part of the precursor PFPE-NMe2 prepared in step (2) is mixed with 3500~3600 parts of tetrahydrofuran, and 35~55 parts of 4-bromomethylphenylboronic acid pinacol ester is added under oil bath conditions at 60~66℃ for reaction. The reaction time is 48~72 hours. During the reaction, 400~900 parts of methanol are added in 2~3 times. After the reaction is completed, the mixture is cooled to room temperature, and 35~55 parts of 4-bromomethylphenylboronic acid and 80~100 parts of hydrochloric acid are added. After stirring for 20~40 minutes, the mixture is placed in a mixed solvent with a volume ratio of acetone / diethyl ether of 1:9~1:7 to precipitate. After centrifugation and drying, a fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups is obtained.

[0009] The fluorescent conjugated polyelectrolyte solution containing phenylboronic acid side groups provided by this invention has reversible covalent bonding between the phenylboronic acid side groups and vicinal diols under alkaline conditions. Therefore, it has great application prospects in the fields of chemistry, biological imaging, and carbohydrate detection.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a novel strategy for synthesizing polyelectrolyte precursors containing high-density dimethylamino side groups by selecting appropriate catalyst types and optimizing their dosage, so as to introduce higher density phenylboronic acid groups in subsequent quaternization reactions. The synthesis is simple and economical.

[0011] 2. The polyfluorene-based fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups provided by this invention exhibits bright blue fluorescence in polar solvents and possesses excellent photostability. The side groups of the polyelectrolyte have an irregular structure, which can prevent polymer chain aggregation to a certain extent, thus having significant application value and practical significance.

[0012] 3. The fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups prepared in this invention is introduced into the side groups of the conjugated polymer through a quaternization reaction between dimethylamino and benzyl bromide. Simultaneously, the side groups form a quaternary ammonium salt structure, resulting in a conjugated polyelectrolyte with excellent water solubility, making it suitable for various applications in aquatic environments, especially in chemical, biological imaging, and carbohydrate detection fields, where it has great application potential. It possesses significant application value and practical significance.

[0013] 4. The fluorescent conjugated polyelectrolyte prepared in this invention contains a higher density of phenylboronic acid side groups compared with existing reports, which can provide more sites for reversible covalent binding with vicinal diols under alkaline conditions, and is expected to provide better performance in fields such as bioimaging and carbohydrate detection. Attached Figure Description

[0014] Figure 1 This is a synthetic route diagram of the phenyl-containing diacetylene monomer M1 provided in Example 1 of the present invention; Figure 2 This is a synthetic route diagram of the dibromoaromatic monomer M2 prepared in Example 1 of the present invention; Figure 3 This is a synthetic route diagram of the precursor polymer PFPE-NMe2 and the fluorescent conjugated polyelectrolyte PFPE-PBA containing phenylboronic acid side groups provided in Example 1 of the present invention; Figure 4 , 5 6 and 7 are the NMR spectra of monomer M1, monomer M2, polymer precursor PFPE-NMe2 and conjugated polyelectrolyte PFPE-PBA prepared in Example 1 of the present invention, respectively. Figure 8 The infrared spectra of M1, monomer M2, polymer precursor PFPE-NMe2 and conjugated polyelectrolyte PFPE-PBA prepared in Example 1 of this invention are shown. Figure 9 This is a photophysical performance data diagram of the fluorescent conjugated polyelectrolyte PFPE-PBA containing phenylboronic acid side groups prepared in Example 2 of this invention. Implementation

[0015] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. Example 1

[0016] 1. Synthesis of monomers M1 and M2 (1) See Appendix Figure 1 It is a synthetic route diagram for the monomer M1 required to prepare fluorescent conjugated polymers.

[0017] Figure 1 Preparation of compound 1 (2,5-dibromohydroquinone): Hydroquinone (4.26 g, 0.039 mol) was added to a flask, followed by 20 mL of acetic acid and stirring until slightly dissolved. Then, 4 mL of bromine (dissolved in 18 mL of acetic acid) was added dropwise over 3 hours. The mixture was reacted overnight at below 10 °C using an ice-water bath. The solvent was removed by filtration through a Buchner funnel. The filtered solid was recrystallized from methanol / deionized water to give pure white crystals, which were dried under vacuum overnight (3.52 g, yield 32.9%).

[0018] Figure 1Preparation of compound 2 (1,4-bis(3'-(N,N-dimethylamino)propyl)-2,5-dibromobenzene): 2,5-Dibromohydroquinone (2.67 g, 10 mmol) and 3-(dimethylamino)chloropropane hydrochloride (3.16 g, 20 mmol) were placed in a 100 mL round-bottom flask, and DMSO (30 mL) was added to dissolve the solid particles. Subsequently, finely ground KOH (8.40 g, 0.15 mol) was added. The reaction mixture was stirred overnight at 20 °C. After the reaction was complete, the reaction mixture was poured into ice water and allowed to stand for 12 hours. The mixture was filtered through a Buchner funnel under reduced pressure. The solid was washed three times with ice water to give a white solid (3.75 g, yield 42.8%). Figure 1 Preparation of compound 3 (2,5-bis(3'-(N,N-dimethylamino)propyl)-1,4-bis(trimethylsilylacetylene)benzene): Compound 2 (2.18 g, 5 mmol), CuI (0.026 g, 0.14 mmol), (PPh3)2PdCl2 (0.145 g, 0.20 mmol), and diisopropylamine (20 mL) were added to a 100 mL round-bottom flask under argon atmosphere. The substrate was stirred until dissolved, and trimethylacetylene silicon (1.5 mL) was added dropwise to the mixture. The mixture was stirred at room temperature for 1 hour, then refluxed for 12 hours. The reaction was terminated and cooled to room temperature. After filtration, the filtrate was collected, and the solvent was removed under reduced pressure to give a black solid. The crude product was purified by silica gel column chromatography (dichloromethane / ethyl acetate / triethylamine, 100:50:1, v / v). After removing the solvent, a brown solid (2.05 g, yield 86.9%) was obtained.

[0019] Figure 1 Preparation of monomer M1: Compound 3 (1.42 g, 3 mmol) was placed in a 100 mL flask, and 20 mL of tetrahydrofuran was added and stirred until the solid dissolved. Then, 6 mL of n-Bu4NF (1 M) dissolved in tetrahydrofuran was added. The mixture was stirred at room temperature for 0.5 hours. After the reaction was completed, 30 mL of deionized water was added to the reaction mixture, and the mixture was extracted with 3 × 100 mL of dichloromethane. The organic phases were combined, and anhydrous sodium sulfate was added to remove water. Excess solvent was removed by rotary evaporation under reduced pressure to obtain a crude product, which was purified on a neutral alumina column using dichloromethane / petroleum ether (2:1, v / v) as eluent to give a light brown solid (0.82 g, yield 83.1%). 1 H NMR (400 MHz, CDCl3, ppm): δ 6.98 (s, 2H), 4.03(t, J= 8.5 Hz, 4H), 3.33 (s, 2H), 2.48 (t, J = 9.6 Hz, 4H), 2.25 (s, 12H), 1.95 (t, 4H). 13 C NMR (100 MHz, CDCl3, ppm): δ 153.93, 117.80, 113.27, 82.50,79.68, 77.30, 77.04, 76.72, 67.84, 56.23, 45.52, 27.41. FTIR (cm -1 ): 3160,2966, 2938, 2854, 2817, 2775, 1492, 1459, 1386, 1226, 1033, 964, 873, 730.Elemental Anal. Calcd for C 20 H 28 N2O2 (%): C, 73.14; H, 8.95; N, 8.53. Found: C, 67.71; H, 8.32; N, 8.18. See appendix Figure 4 It is the NMR spectrum of monomer M1 provided in this embodiment, which is... Figure 4 It can be seen that the structure of monomer M1 is correct.

[0020] (2) See Appendix Figure 2 This is the synthetic route diagram for monomer M2 required for the preparation of fluorescent conjugated polymer in this embodiment. In this embodiment, monomer M2 is 2,7-dibromo-9,9-bis(3'-(N,N-dimethylamino)propyl)fluorene.

[0021] Figure 2Preparation of monomer M2: Under argon atmosphere, 2,7-dibromofluorene (3.05 g, 9.4 mmol) and 60 mL DMSO were added to a flask and stirred until dissolved. Tetrabutylammonium bromide (60 mg) and 8 mL of 50% sodium hydroxide aqueous solution were then added. Under argon atmosphere, 20 mL of a DMSO solution of 3-dimethylaminochloropropane hydrochloride (3.51 g, 22 mmol) was added dropwise to the mixture. The reaction mixture was stirred at room temperature for 6 hours. The reaction was stopped, and the solution was diluted with 50 mL of water to dissolve all the salts. The product was extracted with diethyl ether (3 × 100 mL) and washed with deionized water (3 × 100 mL) and saturated sodium chloride (100 mL). The combined organic layers were dried over MgSO4, filtered, and the solvent was removed under reduced pressure to obtain a crude product as a green solid. The crude product was recrystallized in MeOH / H2O to give white crystals (2.15 g, yield 47.8%). 1 H NMR (400 MHz, CDCl3,ppm): δ 7.52 (d, 2H), 7.47 (s, 3H), 7.44 (s, 1H), 1.99 (m, 14H), 1.69 (s,4H), 0.75 (m, 4H). 13 C NMR (100 MHz, CDCl3, ppm): δ 152.19, 139.31, 130.61,126.38, 121.84, 121.45, 77.56, 77.24, 76.93, 59.77, 55.50, 45.53, 37.78,22.22. FTIR (cm -1 ): 2965, 2937, 2856, 2822, 2776, 1454, 1403, 1371, 1272,1130, 1052, 1016, 673. Elemental Anal. Calcd for C 23 H 30 Br2N2 (%): C, 55.89; H, 6.12; N, 5.67. Found: C, 55.31; H, 6.04; N, 5.91.

[0022] See appendix Figure 5 It is the NMR spectrum of monomer M2 provided in this embodiment, by Figure 5 It can be seen that the structure of monomer M2 is correct.

[0023] 2. Preparation of fluorescent conjugated polyelectrolytes containing high-density phenylboronic acid side groups in repeating units See appendix Figure 3This is the synthetic route diagram for preparing the fluorescent conjugated polymer in this embodiment.

[0024] (1) Preparation of the precursor polymer PFPE-NMe2: The experimental setup was evacuated three times. Under argon protection, M1 (0.082 g, 0.25 mmol), M2 (0.12 g, 0.25 mmol), (PPh3)2PdCl2 (0.0142 g, 0.02 mmol), and CuI (0.0042 g, 0.02 mmol) were added to a flask. Then, dry DIPA (3 mL) and toluene (8 mL) were added to the flask under argon. The mixture was refluxed under argon for 48 hours and then cooled to room temperature. The mixture was filtered through a filter with a pore size of 0.22 μm. The filtrate was concentrated under reduced pressure and added dropwise to 100 mL of n-hexane and placed in the upper part of the refrigerator overnight. After centrifugation (3 min, 3000 rpm), the precipitate was collected and then dried under vacuum for 24 hours to obtain a dark red solid (0.16 g, yield 83.5%). 1 H NMR(400 MHz, CDCl3, ppm): δ 7.8 – 7.3 (m, 6H), 7.09 (s, 1H), 4.10 (s, 4H), 2.52(d, 4H), 2.28 (s, 12H), 2.00 (s, 16H), 1.74 (s, 8H), 0.79 (s, 4H). FTIR (cm -1 ): 2954, 2856, 2817, 2773, 1498, 1460, 1205, 1052, 840, 723, 694. ElementalAnal. Calcd for C 43 H 57 BrN4O2 (%): C, 69.62; H, 7.74; N, 7.55. found: C, 65.24; H, 6.35; N, 6.12. GPC: M̅ w = 14.0 kDa; M̅ n = 6.2 kDa; Đ = 2.26, the number of repeating units n is approximately 10.

[0025] See appendix Figure 6 This is the NMR spectrum of the precursor polymer PFPE-NMe2 provided in this embodiment, which is... Figure 6 It can be seen that the precursor polymer PFPE-NMe2 has the correct structure.

[0026] (2) Preparation of the conjugated polyelectrolyte PFPE-PBA: PFPE-NMe2 (0.075 g, 0.1 mmol) and tetrahydrofuran (10 mL) were placed in a 100 mL flask and stirred until the polymer dissolved. 4-Bromomethylphenylboronic acid pinacol ester (1.20 g, 4 mmol) was added to the flask under oil bath conditions at 60 °C. During this process, approximately 3 mL of methanol was added once a solid appeared in the flask, consuming a total of 9 mL of methanol. After reacting for 48 hours, heating was stopped and the mixture was cooled to room temperature. 4-Bromomethylphenylboronic acid (0.85 g, 4 mmol) and hydrochloric acid (0.5 mL) were added, and the reaction was stopped after stirring at room temperature for 30 minutes. Most of the solvent in the reaction mixture was removed by vacuum distillation, and the precipitate was placed in 100 mL of a mixed solvent (acetone / ethyl ether, 1:9, v / v) and left overnight in the upper part of a refrigerator. The precipitate was collected by centrifugation (3 minutes, 3000 rpm) and then dried under vacuum for 24 hours to give a dark red solid (0.12 g, yield 79.3%). 1 H NMR (400 MHz, CD3OD, ppm): δ 8.25 – 7.0 (m, 22H), 4.6(s, 4H), 4.25 (s, 4H), 3.75 (s, 4H), 3.12 (s, 8H), 2.70 (s, 6H), 2.50 (s,4H), 1.20 (s, 16H), 1.30 (s, 10H). FTIR (cm -1 ): 3384, 2785, 1654, 1467, 1438,1369, 1207, 1049, 1024, 848, 761. Elemental Anal. Calcd for C 71 H 89 B4Br5N4O 10 (%): C, 53.26; H, 5.60; N, 3.50. found: C, 56.15; H, 6.50; N, 2.09. See appendix Figure 7 This is the NMR spectrum of the polyelectrolyte PFPE-PBA provided in this embodiment, which is... Figure 7 It can be seen that the structure of the polyelectrolyte PFPE-PBA is correct.

[0027] See appendix Figure 8 It is the infrared spectrum of monomers M1 and M2 and polymers PFPE-NMe2 and PFPE-PBA in this embodiment, derived from... Figure 8 This further confirms the correctness of the structures of monomers M1 and M2 and polymers PFPE-NMe2 and PFPE-PBA. Example 2

[0028] This embodiment measures the photophysical properties of the polymer PFPE-PBA synthesized in Example 1. See Appendix. Figure 9 The polymer PFPE-PBA is readily soluble in common polar solvents such as methanol and water. Its maximum absorption wavelength is around 400 nm, and its maximum emission wavelength is around 460 nm.

Claims

1. A fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups, characterized in that... Its structural formula is: ， Where n is the number of repeating units, n = 8 to 21.

2. A method for preparing the fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups as described in claim 1, characterized in that... The steps include the following: (1) By molar amount, 1 part of 2,5-bis(3'-(N,N-dimethylamino)propyl)-1,4-bis(trimethylsilylacetylene)benzene, 2~2.5 parts of n-Bu4NF and 1100~1200 parts of tetrahydrofuran were stirred until the solid dissolved. After stirring at room temperature for 0.5~1 hours, the mixture was extracted, rotary evaporated, purified by neutral alumina column chromatography and dried to obtain a diacetylene monomer, denoted as M1. The structural formula of the monomer M1 is: ； (2) Under anhydrous and oxygen-free conditions, by molar amount, 1 part of dibromoaromatic monomer M2 and 1 part of monomer M1 obtained in step (1), 0.015-0.05 parts of tetra(triphenylphosphine)palladium dichloride, 0.015-0.05 parts of cuprous iodide, 100-200 parts of diisopropylamine, and 200-300 parts of toluene are added to a reactor and mixed and stirred. The mixture is reacted for 30-50 hours under argon protection and at a temperature of 70-75°C. After filtration, recrystallization, centrifugation, and drying, a conjugated polyelectrolyte precursor is obtained, denoted as PFPE-NMe2. The structural formula of the monomer M2 is: ； The structural formula of the precursor PFPE-NMe2 is: ， Where n is the number of repeating units, n = 8~21; (3) By amount of substance, 1 part of the precursor PFPE-NMe2 prepared in step (2) is mixed with 3500~3600 parts of tetrahydrofuran, and 35~55 parts of 4-bromomethylphenylboronic acid pinacol ester is added under oil bath conditions at 60~66℃ for reaction. The reaction time is 48~72 hours. During the reaction, 400~900 parts of methanol are added in 2~3 times. After the reaction is completed, the mixture is cooled to room temperature, and 35~55 parts of 4-bromomethylphenylboronic acid and 80~100 parts of hydrochloric acid are added. After stirring for 20~40 minutes, the mixture is placed in a mixed solvent with a volume ratio of acetone / diethyl ether of 1:9~1:7 to precipitate. After centrifugation and drying, a fluorescent conjugated polyelectrolyte containing phenylboronic acid side groups is obtained.

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