A norbornene binary copolymer containing AIE donor acceptor and having FRET effect and preparation method thereof

Abstract

The present invention constructs a FRET system of a binary copolymer with polynorbornene as the main chain, and belongs to the technical field of organic chemical synthesis and polymer materials. The present invention uses norbornene ring-opening metathesis polymerization to adjust the ratio of the donor and the acceptor, thereby obtaining a series of customized luminescent copolymers with FRET effect. In this invention, as the ratio of the donor and the acceptor decreases, we find that the system gradually changes from blue light to red light, and the efficiency of FRET transmission increases.

Description

Technical Field

[0001] The invention belongs to the technical field of organic chemistry and polymer materials, and particularly relates to a norbornene binary copolymer having a FRET effect and comprising an AIE donor acceptor and a preparation method thereof. Background Art

[0002] In 1948, Foster first proposed the concept of Fluorescence resonance energy transfer (FRET). FRET refers to the phenomenon that energy is transferred from the donor fluorophore to the acceptor fluorophore under excitation conditions when the emission spectrum of the donor fluorophore overlaps with the absorption spectrum of the acceptor fluorophore to a certain extent and the distance between the two fluorophores is in the range of 1-10 nm. The specific process is that after the donor fluorescent molecule is excited, since the distance between the donor and the acceptor is constant and the energy difference between the vibrational energy levels of the ground state and the excited state between the donor and the acceptor is appropriate, the excited donor fluorescent molecule will transfer part or all of the energy to the acceptor fluorescent molecule, causing the acceptor fluorescent molecule to be excited. Since the whole process does not involve the mediation of photons, there is no radiation.

[0003] The phenomenon of fluorescence energy resonance transfer is generally divided into intramolecular fluorescence energy resonance transfer and intermolecular fluorescence energy resonance transfer. Intramolecular fluorescence resonance transfer is the energy transfer that occurs by combining the donor and the acceptor in a single molecule through covalent bonds. Intermolecular fluorescence resonance transfer generally has two situations. One is that the donor and the acceptor are dispersed in a certain medium (such as clay, metal oxides, polyvinyl chloride, etc.), and then the distance between the two is within 1-10 nm by making a thin film to achieve fluorescence energy resonance transfer. The other is to anchor the donor and the acceptor to the polymer backbone through polymerization reaction. The efficiency of intermolecular fluorescence energy resonance transfer varies depending on the ratio of donor and acceptor. The first situation has been analyzed and studied, while the effect of the donor-acceptor ratio in the polymer on FRET sensing has not been explored. Summary of the invention

[0004] The purpose of the present invention is to anchor the easily synthesized blue fluorescence emitting donor TPE monomer M1 and the red fluorescence emitting acceptor TPE monomer M2 with AIE properties to the polynorbornene main chain. By adjusting the ratio of donor to acceptor, a series of norbornene copolymers are obtained and their FRET sensing efficiency is explored.

[0005] The technical solution adopted by the present invention is:

[0006] The chemical structure of a norbornene binary copolymer having a FRET effect and comprising an AIE donor acceptor is shown in Formula 1 below:

[0007]

[0008] Formula 1.

[0009] The present invention provides a method for preparing a norbornene binary copolymer having a FRET effect and comprising an AIE donor acceptor, and the steps are as follows:

[0010]

[0011] (1) Synthesis of Monomer M1: Compound 1 and Compound 2 are dissolved in a first solvent, and a dehydrating agent, dicyclohexylcarbodiimide (DCC) and a catalyst, 4-dimethylaminopyridine (DMAP) are added. After the reaction is completed, a white solid compound M1 is obtained by treatment.

[0012] (2) Synthesis of Monomer M2: Compound 3 and Compound 4 are dissolved in a second solvent, a small amount of potassium iodide (KI) is added, and the mixture is reacted at reflux temperature. After the reaction is completed, a red solid compound M2 is obtained by treatment.

[0013] (3) Synthesis of copolymer P1: Monomer M1 and monomer M2 were dissolved in a first solvent, and a Grubbs III catalyst (G3) was added. After the polymerization was completed, vinyl ethyl ether was added to terminate the polymerization and quench the polymerization, and copolymer P1 was obtained.

[0014] Preferably, the first solvent is super dry dichloromethane, and the second solvent is acetonitrile.

[0015] Preferably, in step (1), the molar ratio of compound 1 to compound 2 is 1:0.8-1.8, and in step (2), the molar ratio of compound 1 to compound is 1:1-1.5.

[0016] Preferably, the reaction time in step (1) is 12-36 h, the reaction time in step (2) is 24-72 h, and the reaction time in step (3) is 10-30 min.

[0017] Preferably, the reaction temperature of steps (1) and (3) is room temperature 20-30°C, and the reaction temperature of step (2) is 80-90°C.

[0018] Preferably, the post-treatment method of step (1) is washing with water, filtering, extracting, spin drying, column chromatography and drying, the post-treatment of step (2) is spin drying, column chromatography and drying, and the post-treatment of step (3) is spin drying, recrystallization and drying.

[0019] Preferably, in step (3), the ratio of monomer M1 to monomer M2 is 1:0, 50:1, 30:1, 20:1, 10:1, 5:1 and 3:1.

[0020] The invention discloses a norbornene binary copolymer with FRET effect and containing AIE donor and acceptor. The copolymers with different donor and acceptor ratios have different colors under a 365 nm ultraviolet lamp, and the system changes from blue to red as the donor and acceptor ratio decreases.

[0021] The present invention discloses a norbornene binary copolymer having FRET effect and comprising AIE donor and acceptor. With the decrease of the donor-acceptor ratio, under 360 nm laser excitation, the blue fluorescence at 470 nm will gradually weaken, while the red fluorescence at 620 nm will gradually increase, and the FRET efficiency will also gradually increase. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the H NMR spectrum (CDCl3) of the monomer M1 in Example 1;

[0023] Figure 2 is the nuclear magnetic hydrogen spectrum (CDCl3) of the monomer M2 in Example 1;

[0024] Figure 3 : is a molecular weight table of copolymer P1 with different donor-acceptor ratios in Example 1;

[0025] Figure 4 is an overlapping diagram of the emission spectrum of the donor monomer M1 and the absorption spectrum of the acceptor monomer M2 in Example 2;

[0026] Figure 5 The pictures of copolymer P1 with different donor-acceptor ratios in Example 2 under 365 nm ultraviolet light irradiation;

[0027] Figure 6 : The fluorescence emission spectra of copolymer P1 with different donor-acceptor ratios in Example 2. DETAILED DESCRIPTION Embodiment 1:

[0028] A method for synthesizing a norbornene binary copolymer having a FRET effect and containing an AIE donor acceptor of the present invention comprises the following steps:

[0029] (1) Synthesis of monomer M1: Compounds 1, 2, 3, and 4 can be synthesized according to the literature method. Compound 1 (0.12 g, 0.55 mmol) and compound 2 (0.30 g, 0.55 mmol) were dissolved in 30 mL of ultra-dry dichloromethane. After stirring for ten minutes, dicyclohexylcarbodiimide (0.14 g, 0.66 mmol) and 4-dimethylaminopyridine (0.07 g, 0.55 mmol) were added thereto. The mixture was reacted at room temperature for 36 hours under a nitrogen atmosphere. After the reaction was complete, 15 mL of ultrapure water was added and stirred for 20 minutes. DCU was filtered to remove the DCU. The organic layer was extracted after washing with 10 mL of 0.01 M dilute hydrochloric acid. The organic layer was dried over anhydrous sodium sulfate and then spin-dried onto a column. 0.34 g of white solid M1 was obtained by column chromatography using petroleum ether: dichloromethane (1:5) as the eluent, with a yield of 82%.

[0030] The white solid M1 obtained above was measured by a nuclear magnetic resonance instrument (Varian instrument 400 MHz), and the data are as follows:

[0031] 1 H NMR (400 MHz, CDCl3) δ (ppm): δ 7.20 (s, 1H), 7.18 (s, 1H), 7.08 (q, J = 2.4 Hz, 8H), 7.00 (q, J = 4.5, 3.7 Hz, 6H), 6.96 (s, 1H), 6.94 (s,1H), 6.16 (s, 2H), 4.10 (s, 2H), 3.44 (d, J = 2.8 Hz, 2H), 3.38 (d, J = 1.8Hz, 2H), 1.57 (s, 1H).

[0032] (2) Synthesis of monomer M2: Compound 3 (0.10 g, 0.40 mmol), compound 4 (0.20 g, 0.40 mmol) and potassium iodide (0.02 g, 0.12 mmol) were dissolved in 10 mL of ultra-dry acetonitrile. The mixture was refluxed at 80 °C for 48 hours. After the solvent was dried, the crude product was purified by silica gel chromatography (dichloromethane: methanol = 15:1) to obtain 0.22 g of red solid compound M2 with a yield of 73%.

[0033] The red solid compound M2 obtained above was measured by a nuclear magnetic resonance instrument (Varian instrument 400 MHz), and the data are as follows:

[0034] 1H NMR (400 MHz, CDCl3) δ (ppm): 9.15 (d, J = 6.3 Hz, 2H), 7.93 (d, J= 6.4 Hz, 2H), 7.59 (d, J = 16.1 Hz, 1H), 7.34 (d, J = 8.1 Hz, 2H), 7.14-6.87(m, 11H), 6.62 (t, J = 8.3 Hz, 4H), 6.17 (t, J = 4.3 Hz, 1H), 5.87 (dd, J =6.0, 3.0 Hz, 1H), 4.90 (t, J = 8.0 Hz, 2H), 4.10 (m, 2H), 3.72 (s, 6H), 3.14(s, 1H), 2.93 (dt, J = 8.6, 3.9 Hz, 1H), 2.88 (s, 1H), 2.39 (t, J = 7.2 Hz,2H), 1.41 (d, J = 8.4 Hz, 1H), 1.33 (d, J = 11.2 Hz, 2H), 1.25 (d, J = 8.6Hz, 2H).

[0035] (3) Synthesis of copolymer P1: Monomer M1 and monomer M2 were dissolved in 12 mL of ultra-dry dichloromethane in the following molar ratios of 1:0, 50:1, 30:1, 20:1, 10:1, 5:1 and 3:1, and reacted for 30 minutes in an anhydrous, oxygen-free and light-proof environment. Then 1 mL of vinyl ethyl ether was added and stirred for 15 minutes to cap the copolymer. The corresponding binary copolymer P1 was obtained by recrystallization with dichloromethane and petroleum ether several times. The Mn, Mw and PDI of the copolymers with different donor-acceptor ratios are shown in Figure 2. Figure 3 shown. Embodiment 2:

[0036] The binary norbornene copolymer obtained in Example 1 was firstly Figure 4 As shown, we found that there is a certain and effective spectral overlap between the fluorescence emission spectrum of monomer M1 and the ultraviolet absorption spectrum of monomer M2, which theoretically confirms the feasibility of fluorescence resonance transfer. At the same time, the copolymers with different donor-acceptor ratios were prepared into 15 μg / mL aqueous solutions. The study found that under the irradiation of a 365 nm hand-held ultraviolet lamp, as the donor-acceptor ratio decreased, the system gradually changed from pure blue to pure red. Next, the fluorescence emission spectra of the copolymer systems with different donor-acceptor ratios (test concentrations were all 15 μg / mL) under 360 nm laser excitation were tested. As shown Figure 6As shown in Figure 2, it can be clearly observed that as the donor-acceptor ratio decreases, the blue fluorescence at 470 nm gradually weakens, while the red fluorescence at 620 nm gradually increases, which is consistent with the Figure 5 This is attributed to the occurrence of the FRET phenomenon. Under the excitation condition, the energy of the donor M1 will be transferred to the acceptor M2, resulting in the gradual weakening of blue fluorescence and the gradual enhancement of red fluorescence.

[0037] The above only expresses the preferred embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications, improvements and substitutions can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A norbornene binary copolymer having a FRET effect and comprising an AIE donor acceptor, characterized in that: Its chemical structure is as follows: ； The x:y is 50:1, 30:1, 20:1, 10:1, 5:1 and 3:

1.

2. A method for preparing a norbornene binary copolymer having a FRET effect and containing an AIE donor acceptor as claimed in claim 1, characterized in that: The target copolymer was obtained by polymerizing the blue fluorescent norbornene monomer M1 as a donor and the red fluorescent norbornene monomer M2 as an acceptor in the FRET system under the action of a catalyst. The structural formula of the blue fluorescent norbornene monomer M1 is: ； The structural formula of the red fluorescent norbornene monomer M2 is: 。 3. The preparation method according to claim 2, characterized in that: The catalyst is a Grubbs third-generation catalyst, and the polymerization method is ring-opening metathesis polymerization.

4. The preparation method according to claim 2, characterized in that: The specific synthesis steps are as follows: ； (1) Synthesis of blue fluorescent norbornene monomer M1: Compound 1 and Compound 2 were dissolved in dichloromethane, and then dicyclohexylcarbodiimide and 4-dimethylaminopyridine were added to react under a nitrogen atmosphere. After the reaction was completed, pure white monomer M1 was obtained; (2) Synthesis of red fluorescent norbornene monomer M2: Compound 3 and compound 4 were dissolved in acetonitrile, potassium iodide was added, and the mixture was reacted under a nitrogen atmosphere. After the reaction was complete, the red monomer M2 was obtained by treatment. (3) Synthesis of copolymer P1: blue fluorescent monomer M1 and red fluorescent monomer M2 were dissolved in ultra-dry dichloromethane, and Grubbs III catalyst was added. After the polymerization was completed, the copolymer P1 was purified.

5. The preparation method according to claim 4, characterized in that: In the step (1), the molar ratio of compound 1 to compound 2 is 1:0.8-1.8, and the post-treatment method is washing with water, filtering, extracting, spin drying, column chromatography, and drying.

6. The preparation method according to claim 4, characterized in that: In the step (2), the molar ratio of compound 3 to compound 4 is 1:1-1.5, and the post-treatment is spin drying, column chromatography, and drying.

7. The preparation method according to claim 4, characterized in that: The purification method in step (3) is recrystallization.

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