CN113444195A

CN113444195A - Preparation method of atypical polymerization-induced luminescent aliphatic polyamide

Info

Publication number: CN113444195A
Application number: CN202110695837.2A
Authority: CN
Inventors: 严骏杰; 杨敏; 潘栋辉; 徐宇平; 王立振; 赵富宽; 张波
Original assignee: Jiangsu Institute of Nuclear Medicine
Current assignee: Jiangsu Institute of Nuclear Medicine
Priority date: 2021-06-23
Filing date: 2021-06-23
Publication date: 2021-09-28
Anticipated expiration: 2041-06-23
Also published as: CN113444195B

Abstract

The invention discloses a preparation method of atypical polymerization-induced luminescent aliphatic polyamide, which comprises the steps of dissolving N-ACHCT and allylamine in dioxane, and stirring overnight at room temperature; adding tricarboxyethylphosphine into the mixture, and stirring; adding DMPA as a photoinitiator and exposing the reaction mixture to UV radiation; the resulting mixture was purified by precipitation in ether and dried under vacuum to yield a viscous solid. Aliphatic polyamides having amide units and substructures are prepared according to the present invention, and aliphatic polyamides containing primary, secondary and tertiary amides exhibit different PIEs due to different local chemical environments and self/non-self intermolecular forces. The research not only can provide the correlation between the structure of the aliphatic polyamide and the NTIL, but also can provide a new research idea for the PIE of the aliphatic polymer.

Description

Preparation method of atypical polymerization-induced luminescent aliphatic polyamide

Technical Field

The invention belongs to the technical field of fluorescent polymer preparation, and particularly relates to a preparation method of atypical polymerization-induced luminescent aliphatic polyamide.

Background

Since Carothers' initiative in the 20 th century, polyamide has been developed as one of the most important high-performance engineering materials, and is widely used in the fields of machinery, textiles, electrical equipment, molding and the like. Fluorescence studies of polyamides have historically not been considered as important as their outstanding mechanical properties. Amides exhibit neither absorption nor fluorescence due to forbidden transitions, whereas aliphatic amides typically exhibit fluorescence quenching due to electron transfer. Therefore, strategies for synthesizing fluorescent polyamides generally rely on the modification of (aromatic) conjugated units. Until recently, many electron-rich heteroatom units have been shown to fluoresce, not only accelerating the development of unconventional intrinsic fluorescence (NTIL), but also extending the conventional fluorescent paradigm; at the same time, several new fluorescence theories such as Aggregation Induced Emission (AIE), cluster emission (CTE), and Polymerization Induced Emission (PIE) have also been established.

It is imperative to design and synthesize aliphatic fluorescent polyamides with tunable structures, and to further differentiate the NTIL that modulates its diversity.

Disclosure of Invention

This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.

The invention provides a preparation method of atypical polymerization-induced luminescent aliphatic polyamide.

In order to solve the technical problems, the invention provides the following technical scheme: a method for preparing an atypical polymerization-induced luminescent aliphatic polyamide, which comprises dissolving N-ACHCT and allylamine in dioxane, and stirring at room temperature overnight; adding tricarboxyethylphosphine into the mixture, and stirring; adding DMPA as a photoinitiator and exposing the reaction mixture to UV radiation; the resulting mixture was purified by precipitation in ether and dried under vacuum to yield a viscous solid.

As a preferred embodiment of the method for preparing the atypical polymerization-induced luminescent aliphatic polyamide according to the present invention: the addition amount of the N-ACHCT and the allylamine is 95.4mg and 0.6 mmol; the addition amount of the allylamine was 37.6mg and 0.66mmol, and the addition amount of the dioxane was 0.6 mL.

As a preferred embodiment of the method for preparing the atypical polymerization-induced luminescent aliphatic polyamide according to the present invention: the adding amount of the tricarboxyphosphine is 10mM, and the stirring is carried out for 0.5-1.5 h.

As a preferred embodiment of the method for preparing the atypical polymerization-induced luminescent aliphatic polyamide according to the present invention: the addition amount of the DMPA is 0.5-2 wt%, and the UV irradiation time is 20-40 min.

As a preferred embodiment of the method for preparing the atypical polymerization-induced luminescent aliphatic polyamide according to the present invention: the preparation method of the N-ACHCT comprises the steps of mixing D, L-homocysteine thiolactone hydrochloride (3.07g, 0.02mol) and triethylamine (5.56g, 0.055mol), adding into 50mL dichloromethane, and forming a suspension under the ice bath condition; adding acetyl chloride (2.36g, 0.03mol) dropwise for more than 20min, and stirring the obtained mixed solution at room temperature overnight; adding 20mL of dichloromethane, filtering, washing, and extracting with dichloromethane; the organic layer was dried over anhydrous sodium sulfate and evaporated in vacuo; and performing silica gel column chromatography on the obtained product to obtain a white powdery product N-ACHCT.

As a preferred embodiment of the method for preparing the atypical polymerization-induced luminescent aliphatic polyamide according to the present invention: the atypical fluorescent aliphatic polyamide has a structural formula shown as a formula (I):

wherein n is 5 to 100.

The invention has the beneficial effects that: aliphatic polyamides having amide units and substructures are prepared according to the present invention, and aliphatic polyamides containing primary, secondary and tertiary amides exhibit different PIEs due to different local chemical environments and self/non-self intermolecular forces. The present inventors have discovered that PIE properties can be modulated by altering intermolecular hydrogen bonding interactions in the polyamide structure. The research not only can provide the correlation between the structure of the aliphatic polyamide and the NTIL, but also can provide a new research idea for the PIE of the aliphatic polymer.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise. Wherein:

FIG. 1 shows the absorption spectra in THF, fluorescence spectra and quantum yields in DMF of thiolactone monomer (M1-M5) and polyamide (P1-P5).

FIG. 2 shows the molecular orbital levels of the P1-P7 polyamide repeating units.

FIG. 3 is a photo-physical characterization of P1.

FIG. 4 shows the dynamic monitoring of the polymerization reaction of P1 by UV spectroscopy and fluorescence spectroscopy.

FIG. 5 shows photophysical properties of P1, P6 and P8 in different environments.

FIG. 6 is a photo-physical characterization of P9-P13.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with examples are described in detail below.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.

Synthesis of N-substituted thiolactone library: the N-substituted thiolactone library is prepared from_D,L-homocysteine thiolactone and various acid chlorides or chloroformates. Generally, will_D,LHomocysteine thiolactone hydrochloride (0.02mmol) was mixed with 2.2 equivalents of triethylamine in 50mL of DCM to form a suspension. An equivalent amount of acid chloride or chloroformate was then added dropwise in an ice bath, and the mixture was stirred at room temperature overnight. The reaction mixture was then diluted with DCM, filtered, washed with brine and extracted twice with DCM. Anhydrous Na for organic layer₂SO₄Dried, concentrated, and purified by silica gel column chromatography to obtain the product.

Aminolysis of N-substituted thiolactones by cyclic secondary amines: all aminolysis reactions of N-substituted thiolactones are carried out with equivalent ratios of thiolactone to cyclic secondary amine. Typically, the ammonolysis reaction is carried out in deoxygenated chloroform and is carried out overnight at 30 ℃. Then, the product is directly subjected to¹H，¹³C NMR and HRMS analysis. The influence of the solvents, thiolactones of different substituents, amines (cyclic secondary, cyclic tertiary, primary and linear secondary) on the aminolysis reaction is carried out in a similar manner.

Synthesis of methacrylamide monomer (M1-M8): sulphur synthesis by one potThe ring-opening reaction of the lactone and the michael addition reaction of the mercapto-methacrylate to produce the methacrylamide monomer. Mixing N-MAHCT (37.1mg, 0.2mmol) and PEG₅₀₀(100.2mg, 0.2mmol) was dissolved in 1mL anhydrous THF/DMSO (v/v ═ 1/1) and deoxygenated with argon for 10 minutes. Then, an equivalent amount of secondary cyclic amine was added to the mixture and stirred overnight at 30 ℃ in the dark. All methacrylamide monomers were purified by silica gel column chromatography to remove unreacted reagents. Methacrylamide monomers derived from aminolysis of primary amines were prepared in a similar manner.

Synthesis of N-homocysteine thiolactone methacrylate (N-MAHCT): d, L-homocysteine thiolactone hydrochloride (6.14g, 0.04mol) was added to 150mL of chloroform and ice-cooled to form a suspension; methacryloyl chloride (5.02g, 0.048mol) was added to the mixture; after that, triethylamine (9.70g,0.096mol) was added dropwise over 20min and the suspension gradually turned into a reddish solution. The solution was stirred in an ice bath for 2 hours and traced by thin layer chromatography. The reaction mixture was washed with brine (60 ml. times.2), extracted with chloroform (60 ml. times.2), and the organic phase was dried over sodium sulfate and filtered. The resulting solution was concentrated to a volume of 50mL and slowly added to 100mL of hexane, the precipitated powder was isolated by filtration and dried under vacuum for 2h, yield: 83.9 percent.¹H NMR(300MHz,CDCl3)δ6.37–6.17(m,1H),5.78(s,1H),5.41(t,J＝1.4Hz,1H),4.54(ddd,J＝12.7,6.8,5.7Hz,1H),3.40(td,J＝11.8,5.1Hz,1H),3.28(ddd,J＝11.4,7.0,1.3Hz,1H),3.09–2.94(m,1H),1.99(s,2H),1.80-2.05(m,2H).13C NMR(101MHz,Chloroform-d)δ205.78,168.59,139.06,120.78,59.41,31.59,27.53,18.50.

Synthesis of Linear Polyamide: the corresponding linear polyamides obtained from methacrylamide monomers were prepared by free radical polymerization (P1-P8). In the case of P1, 1mL of M1(100.1mg) THF solution containing 0.5 wt% AIBN was added to a glass tube and two freeze-thaw cycles were performed to exclude air. The tube was then sealed under vacuum and subsequently placed in a preheated oil bath at 65 ℃. After a predetermined time, the resulting mixture was purified by precipitation into a mixed solvent of ether/hexane (1/1, v/v), and dried under vacuum for 3 hours to give a viscous light-colored or pale-yellow product. Yield: 67.3 percent.

Preparation of P9: N-ACHCT (N-acetylhomocysteine thiolactone) (95.4mg, 0.6mmol) and allylamine (37.6mg, 0.66mmol) were dissolved in 0.6mL dioxane (dioxane) and stirred at room temperature overnight; TCEP (tricarboxyethylphosphine) (10mM) was added to the mixture and stirred for 1h (to reduce possible conjugated disulfide bonds); thereafter, DMPA (benzoin dimethyl ether) (1 wt%) was added as a photoinitiator and the reaction mixture was exposed to UV (365nm UV lamp, power 9W) irradiation for 30 minutes; precipitation in diethyl ether was used to purify the resulting mixture and dried under vacuum for 3 hours to give P9 as a viscous solid. Yield: 78.4 percent.

P14 was prepared similarly to P10 in DMSO, except that no PEG was added₅₀₀To consume the thiol group.

Synthesis of N-acetyl homocysteine thiolactone (N-ACHCT): d, L-homocysteine thiolactone hydrochloride (3.07g, 0.02mol) and triethylamine (5.56g, 0.055mol) are mixed and added into 50mL DCM (dichloromethane), and suspended matters are formed under ice bath conditions; adding acetyl chloride (2.36g, 0.03mol) dropwise for more than 20min, and stirring the obtained mixed solution at room temperature overnight; 20mL of DCM was added, filtered, washed and extracted with DCM (40 mL. times.2); the organic layer was dried over anhydrous sodium sulfate and evaporated in vacuo; the obtained product is chromatographed by a silica gel column to obtain a white powdery product. Yield: 61.4 percent.

¹H NMR(400MHz,CDCl3)δ6.01(s,1H),4.52(dt,J＝12.8,6.4Hz,1H),3.36(ddd,J＝12.2,11.4,5.1Hz,1H),3.26(ddd,J＝11.4,6.9,1.3Hz,1H),2.95(dddd,J＝12.1,6.6,5.1,1.3Hz,1H),2.05(s,3H),1.92(qd,J＝12.4,6.9Hz,1H).

For P11, P12 and P13, prepared by free radical polymerization of the corresponding commercial monomers of N-isopropyl methacrylamide, N-dimethyl methacrylamide and methacrylamide, and purification in diethyl ether yielded white powders. Yield: 85.4% (P11), 92.7% (P12), 96.3% (P13).

In the past decade, thiolactone chemistry has shown great competitiveness in the precise synthesis and double modification of polymers. In general, aminolysis of thiolactones is very goodReadily react with primary amines to form linear secondary amides with a molecular thiol group formed on the pendant group. However, thiolactones are generally not reactive with linear secondary or tertiary amines. Interestingly, in the comparative ammonolysis of N-methacrylic acid homocysteine thiolactone (N-MAHCT) and tetrahydropyrrole (equivalent charge ratio), the reaction was carried out by¹H，¹³C Nuclear Magnetic Resonance (NMR) and High Resolution Mass Spectrometry (HRMS) demonstrated complete ring opening and quantitative conversion of the thiolactone to the tertiary amide. The aminolysis reaction of N-MAHCT is applicable to other secondary cyclic amines (e.g., piperidine, azapentane, piperazine, 1-methylpiperazine, morpholine and indoline), and the aminolysis efficiency is related to the pKa value of the amine. Although pyrroles and imidazoles also have secondary amine units, their low nucleophilicity does not allow the ring opening of N-MAHCT, nor do cyclic tertiary amines (e.g., 1-methylpiperidine) or linear secondary amines (e.g., diethylamine). In addition, this Cyclic Secondary Amine Mediated Ammonolysis (CSAMA) reaction is effective in a variety of solvents and also in a variety of N-substituted homocysteine thiolactone systems.

CSAMA of thiolactones enriches the amide structure in polyamides. For example, N-MAHCT is aminolyzed by orthogonal PEGylation of pyrrolidine, piperidine, azapentane, piperazine, morpholine to produce a series of methacrylamide monomers (M1-M5) with both secondary and tertiary amides (FIG. 1), with typical absorption and weak fluorescence signals at 325nm and 355nm, respectively. By conventional free-radical polymerization, the resulting polyamides (P1-P5) have higher quantum yields (. PHI.) than the monomers (FIG. 1 h). The absorption signal of P1-P5 is still around-325 nm, but E_mThe wavelength (360-443nm) has a certain red shift. Despite similar molecular weights, differences in the substructures (ring size and heteroatoms in the cyclic amine) result in different degrees of fluorescence enhancement. Of these, P1 showed the highest Φ (see fig. 1h for testing in DMF, Φ 9.6% for P1 in water) and the greatest fluorescence enhancement (79-fold). Due to the influence of solvents and environment, P1-P5 exhibit different photophysical parameters in various solvents.

To investigate the NTIL of these aliphatic polyamides, we prepared two additional monomers (M6, M7) as controls, in which the N-MAHCT was ring-opened by primary amines (N-butylamine and ethanolamine) to giveThe corresponding polyamides (P6, P7) have only secondary amides in the structure. The molecular orbital energy levels of the polyamide repeating units were calculated using the Density Functional Theory (DFT), and as shown in fig. 2, the Highest Occupied Molecular Orbital (HOMO) among all sulfur atoms is located on the amide orbital, but the Lowest Unoccupied Molecular Orbital (LUMO) shows a different distribution. For P1-P5, the LUMOs are located predominantly on the adjacent orbitals of the carbonyl and tertiary amides, and are less occupied by the orbitals of the secondary amide and sulfur atoms. Whereas for P6-P7, the LUMOs are occupied by a chain between the amide and the carbonyl group. From the energy level of the polyamide, secondary amides with larger cyclic amine rings have higher LUMO and HOMO energies, while secondary amides have lower LUMO and HOMO energies than tertiary amides. The lowest energy gap of P1, 5.921eV, indicates that the conjugation and electron delocalization of P1 are the greatest among all polyamides, both of which contribute to the potential fluorescence. To obtain more photophysical information from polyamides, we further determined that they are at varying excitation wavelengths (λ)_ex) Fluorescence emission spectrum of (1). The P1-P7 all show double distribution in the emission spectrum, and one group of emission is 375nm (E)_m375) About, another group is above 420nm (>E_m420). The emission of the former is almost equal to λ_exIndependently of the emission of the latter and lambda_exIt is related. Lambda was previously observed in related studies of graphene quantum dots_exA sum of_exUnrelated NTIL coexists due to quantum dot surface defect states and size effects. To obtain more detailed information, we analyzed the excitation regions (E) at each designation _m375 of [ E ]_x255，E_x300]And>E_m420 [ E ]_x345，E_x390]) The next two sets of emitted offset wavelengths. Interestingly, at different λ_exE of P1-P3_mThe 375 wavelength is nearly constant, but the presence of other oxygen or nitrogen atoms in P4 and P5 causes the emission wavelength (λ)_em) A slight blue shift. P6 and P7 have typical absorption peaks at 363nm and with lambda due to the difference of amides in the polyamide_exIn E_mA greater blue shift (Δ λ) at 375_em>15nm) and their Φ value in water is lower than P1. On the other hand, theAmong the polyamides, there are polyamides in which,>E _m420 with lambda_exIs increased to exhibit a red-shifted lambda_em([E _x345，E_x390]). Wherein P1 exhibits a minimal bathochromic shift λ_em(8nm) without significant fluorescence intensity reduction, the maximum Φ was obtained. These results indicate the different properties of the two groups of NTILs for aliphatic polyamides.

Concentration is a key parameter for adjusting NTIL and determining the fluorescence emission center. Therefore, we treated different concentrations of P1(0.5, 2, 4, 8, 16, 32mg mL)^-1Aqueous solution and bulk P1) were characterized (UV/Vis and fluorescence spectra) (fig. 3). As shown in FIGS. 3a-3b, the typical absorption peak at 320nm of P1 in water is proportional to the concentration (R)²0.9990), higher concentrations can be assured at longer wavelengths (λ)>350nm) has a strong absorption peak. When changing lambda_exAll aqueous solutions of P1 were at-375 nm (E)_m375) And 440nm (E)_m440) There are two distinct sets of emission signals (fig. 3c-3l), while bulk P1 exhibits only a single emission signal at 446 nm. When the concentration exceeds 16mg mL^-1When E is greater_m375 grows non-linearly and reaches the platform; in contrast, even at concentrations as high as 32mg mL^-1，E _m440 still show a linear increase in fluorescence intensity (R)²0.9992). Fluorescence excitation spectroscopy confirmed the presence of two separate fluorescence emission centers in P1 (fig. 3n), with a maximum of λ_exRespectively located at-300 nm (E)_x300) And 375nm (E)_x375)。

In the fluorescence spectrum of the aqueous solution of P6, a major maximum excitation peak (E) was detected_x370) And E is_x302 is the shoulder signal, but not the independent maximum excitation peak. In water and corresponding E of body P6_m437nm and 429nm respectively. Thus, different amides in aliphatic polyamides result in distinct NTILs. For P1, E_mFluorescence lifetime of 375: (<τ>) 0.58/3.89ns (τ 1/τ 2), and E _m440 have a longer lifetime of 1.43/4.58ns (τ 1/τ 2) (FIG. 3 o). Of P1 due to increased structural steric hindrance<τ>The value is longer in the bulk state than in water. In addition, under continuous light irradiation, both groups of fluorescence are photostable, superior to fluorescein 5-isoThiocyanate (FITC), comparable to quinine sulfate (fig. 3 p). It should be noted that the dual emission of the aliphatic polyamide comes from different fluorescence centers, but not from the fluorescence states or quantum confinement λ_exRelying on the phenomenon of polychromatic emission. The emitting material can be used not only with different lambda_exExcitation, and also prevention of decrease in Fluorescence Intensity (FI).

Based on these observations, the NTIL of the aliphatic polyamide in our study system essentially conforms to the characteristics of PIE (polymerization induced luminescence). We monitored the polymerization of P1 dynamically by uv spectroscopy and fluorescence spectroscopy (fig. 4). Notably, the molecular weight of P1 increased with increasing polymerization time, with enhanced absorption peak signals at 324nm and 351 nm. M1 is weakly fluorescent, with lambda at 300nm and 375nm_exThe values of Φ at s were 2.6% and 0.5%, respectively. As the polymerization proceeds, E_mThe FI of 375 was continuously increased to 8h and phi increased to 4.0%. On the other hand, E_mThe FI of 440 showed an upward trend, but at 8h it slightly decreased. This reduction or quenching of fluorescence may be due to self-absorption and/or exciton interaction, E_mThe final Φ of 440 is close to 9%. As the polymerization proceeds, the small molecules are converted to oligomers and polymers with more chain entanglement, and the tyndall effect clearly indicates clustering or aggregation of P1 after polymerization (fig. 4 d). The DFT calculation was then used to study the change in the optimal geometric conformation of P1 as the number of repeating units (n) increased. FIG. 4e shows that as n increases from 1 to 3, the distance of adjacent carbonyl groups increases from

Is reduced to

The distance between the amine and the adjacent carbonyl group (with the cyclic amine) is selected from

Is reduced to

. With amines and adjacent carbonylsThe bond angle between the radicals (and the cyclic amine) decreases from 107.6 ° to 106.9 °. All these conformational changes indicate that the molecular chains of P1 rotate and pack into a more compact structure after polymerization, resulting in an increase in fluorescence.

Polymers with PIE typically exhibit fluorescence in both solution and bulk. E _x300 results in E of P1_mThere is a 12nm gap between the water and the bulk, and E _x375 does not cause E_m440 (fig. 4 f). Rigid structures are known to reduce the flexibility of the polymer chain and limit the non-radiative decay pathways, and therefore generally increase the corresponding Φ. Thus, tert-butyl methacrylate replaces PEG₅₀₀Rigid and hydrophobic aliphatic polyamide P8 was produced. Similar to P1, P8 also has two fluorescence emission centers that can be excited at 300 and 380nm, respectively. In FIG. 4g, E _x300 emission peak blue-shifts to E_m353 and has the same emission wavelength in DMF and bulk. In contrast, E_x380nm of emission. Blue shifted lambda_emUsually implying the creation of a rigid environment. Thus, the different blue-shifted wavelengths in the emission spectra show different packing/aggregation of the molecules in bulk P1 and P8. For P1 and P8, longer λ in solution and bulk_exAll have a higher phi and a longer emission peak<τ>Values (fig. 4h, 4 i). Unlike AIE, P1 shows strong fluorescence even at concentrations as low as-0.05 mM in THF (solvent), in E _m375 and E_mThe values of Φ at 434 were 4.5% and 15.1%, respectively. Furthermore, when water (poor solvent) is added to a DMF solution of P8, at E _x300 or E_xNo AIE effect was observed at 380 (fig. 4 j).

Analysis of the structure of P1, possible fluorophores were tertiary and secondary amides, and the derivatives from PEG were excluded₅₀₀And polyPEG₅₀₀Interference of fluorescence. Notably, secondary amides can form intermolecular hydrogen bonds, while tertiary amides cannot, but both can form hydrogen bonds with protic solvents. As shown in FIG. 5a, P1, P6 and P8 are at 1525cm^-1The coexistence of a secondary amide and a tertiary amide with similar amide | | | bands in P1 and P8 at 1633cm^-1With a lower amide | band. At 3550-0cm^-1In the range of 3514cm^-1Typical NH stretching free peaks were observed at 3295, 3295 and 3303cm^-1The NH bands with hydrogen bonds detected correspond to P1, P6 and P8, respectively. In short, more secondary amide units and more rigid structures provide the bulk polyamide with stronger intermolecular hydrogen bonding interactions. Due to heavy water (D)₂O) has a stronger hydrogen bonding interaction than water and has been shown to stabilize the proton transfer rate between dye and solvent, thus increasing both FI and Φ. The materials were not removed, at different concentrations (1-32mg mL)^-1) E in heavy water _m440 ratio of E in water _m440 are stronger, but E _m375 showed no significant difference in weight (fig. 5 b). Also, pH plays a crucial role in NTIL of polymers due to nitrogen atoms. E _m440 showed the strongest fluorescence under neutral conditions, with a slight decrease in FI in both acidic and basic environments (fig. 5 c). In contrast, E _m375 exhibit enhanced fluorescence under acidic conditions, a phenomenon commonly found in polymers containing nitrogen atoms and mostly associated with protonation of the nitrogen atom. In the structure of P1, cyclic secondary amines have greater strain than linear secondary amides due to the polar solvent (H)₂O), N protonation of cyclic tertiary amides is appreciated and thus may lead to potential fluorescence enhancement in acidic environments. Furthermore, due to the importance of heteroatoms (N, O, S and P) in NTILs, we also tested the fluorescence of P1 interacting with oxidizing agents. As shown in fig. 5d-5e, with H₂O₂(3eq) incubation, E _m375 FI slightly increased and incubation with ammonium persulfate (APS, 3eq) gave E_mThe FI of 375 increases by 40%. In contrast, E_mFI of 440 shows a decrease in fluorescence upon oxidation, while addition of APS (3eq) P1 to an aqueous solution would result in E_mFI of 440 was reduced by 63%. Addition of H₂O₂And APS may provide additional hydrogen bonding interactions between the amide and the oxidizing agent while reducing intermolecular hydrogen bonding interactions between the amide, thereby reducing E _m440, fluorescence of the sample. The UV-Vis spectrum shows that a new absorption peak appears at 362nm, and the absorption at 323nm is obviously reduced, which shows thatE _m375 and E _m440 differ in their fluorescent properties.

Dense molecular packing/aggregation can inhibit nonradiative decay pathways and increase NTILs. Since pegylation made P1 less viscous and difficult to shape, we selected P8 bulk material and compressed the powder into tablets. The increase in the concentration of local intermolecular hydrogen bonds of the secondary amide increased phi of the P8 tablet by 32.3%. Despite the similarity of the respective fluorescence patterns, the P8 powder/tablet has different doublets E at 350/336 and 461/471nm, respectively_mA value which is also different therefrom<τ>Values and excitation spectra (fig. 5 h). The P8 tablet is longer than the powder due to increased structural rigidity<τ>(E_m440). However, E _m375 of<τ>Foreshortening, which often occurs during fluorescence quenching. Considering E of P1 and P8_m375 showed fluorescence reduction or quenching in either concentrated solution or bulk material, we concluded that E _m375 are related to solvents and further investigated for the fluorescence properties of aliphatic polyamides in solvents with different hydrogen bonding interactions. Overall, P1 in DMF (E)_m377，E_m438) And CHCl₃(E _m375，E_m438) Also exhibits dual emission and concentration dependent fluorescence exhibits similar characteristics as in water. However, CHCl₃In E_m375 FI weaker than DMF and FI in water, with the highest E _m438/E _m375 fluorescence intensity ratio. This solvent effect is common in NTIL, probably due to the interaction of the solvent with the polymer segments that affect the degree of polymerization.

In addition, low temperature conditions can inhibit molecular movement of the substance and have a significant effect on fluorescence. At 77K, aqueous P1 solution (5mg mL)^-1) At a different lambda than that of body P1_exLower has a similar emission spectrum and a maximum of E_ms are at 420 and 426nm, respectively (FIGS. 5i-5 j). Notably, no emission peak was observed between 330-380nm in aqueous solutions at this concentration due to the limitation and absence of hydrogen bonding interactions. The fluorescence of aqueous P1 and bulk P1 at 77K increased 6.9 and 4.1 times, respectively, compared to the sample at 298K. Due to molecular vibration in the frozen stateDecrease, E of P1_mShifted in the blue by-12-15 nm. For P8, a similar fluorescence distribution appeared at 77K, but due to its inherently rigid structure, the fluorescence enhancement from 298K to 77K was greatly limited, resulting in a much smaller growth space than P1 (FIGS. 5 m-5P). Combining these results, we speculate that E _m440 are derived from secondary amides and are involved in their intermolecular hydrogen bonding interactions; and E _m375 are derived from tertiary amides and depend on hydrogen bonding interactions with the solvent.

To validate our hypothesis that different amides lead to different PIE, we synthesized a series of aliphatic polyamides containing various amides, the chemical structure of which is shown in fig. 6 a. In particular, P9 and P10 have only secondary amides, wherein the sulfur atoms and/or PEG doping are distributed in the main chain and/or side chains of the polyamide. P11, P12 and P13 have only secondary, tertiary and primary amides, respectively, without heteroatom or PEG doping. FIG. 6c reveals that P9 has a single E at 385 and 487nm, respectively_xAnd E_m. The adjacent doublets E at 338 and 373nm appeared in the P10 fluorescence spectrum due to the presence of additional secondary amines in the polymer backbone_xs and corresponding E appears at 416 and 438nm_mAnd s. However, in the aqueous P10 solution and in the bulk P10, the lambda was varied_exWhile observing only a single E_m. This also occurs in P11 with double E at 258 and 333nm_xs, single E at-423 nm_m. For P12, a typical single fluorescence center (E) was also obtained_x265 and E_m335). However, P13 did not fluoresce in water, but did not fluoresce in CHCl₃Fluorescence was detected, indicating that proton transfer between the primary amide and water is likely to occur, as is also observed in cycloaliphatic fluorescent poly (amide-imide). In addition, we have also specifically studied λ_exFluorescence emission spectra of dependence, concentration dependence and low temperature experiments to confirm the fluorescence emission centers of these polyamides. P9 has the highest Φ (40.6% in water),<τ>values (τ 1 ═ 2.52ns in water, τ 2 ═ 12.54ns) and maximum freeze-induced FI enhancement (8.8 times in water) (fig. 6b, 6h-6 i). All aqueous solutions of the polyamides showed a Tyndall effect and a reckoned count rate (DCR) measured by Dynamic Light Scattering (DLS)Significant aggregation was seen, while P9 possessed the highest DCR (fig. 6 b). The molecular interactions between polyamides were then explored by FTIR spectroscopy. FIG. 6j shows that only 3279cm was found in P9^-1NH telescopic bands with hydrogen bonding, whereas 3459cm were present in both P10 and P11^-1Free NH telescopic band. These results indicate that the hydrogen bonding interactions in the main chain polyamide are stronger than those in the side chain polyamides, and that the sulfur atom may enhance the hydrogen bonding interactions between the polyamides. We then also calculated that the more pronounced spatial separation of the homo, and LUMOs of the MOs, P9 and P10 of the P9-P12 repeat unit resulted in a lower oscillation intensity of the glue and suppression of non-radiative relaxation, thus retaining more fluorescence than P11 and P12. Interestingly, 3428cm at P13^-1A strong free NH elastic band was observed, while at 3227cm^-1A weak hydrogen-bonded N-H stretch band was observed, which well explains the fluorescent properties of P13 and confirms that intermolecular hydrogen bonding does contribute to the NTIL of aliphatic polyamides. Compared with P9, PEG modification (excluding cross-linking of polyamide) improves the flexibility of P10 but reduces the fluorescence intensity, and phi is reduced to 2.0%. Without pegylation, the resulting polyamide (P14) can further raise Φ to 8.8%, but weak hydrogen bonding interactions in the system cannot further enhance Φ. In general, different classes of amides in aliphatic polyamides have different PIEs and their photophysical properties can be easily adjusted by modifying the intermolecular forces between the polyamide structures or with the environment. Compared to the traditional aliphatic polyamides with NTIL at the present stage, the aliphatic polyamides of the present invention have adjustable amide types, controllable amide distribution and variable chemical environment. These advantages motivate us to explore the relationship of the structure of aliphatic polyamides to NTIL. Notably, aliphatic polyamides have PIE characteristics rather than AIE. The various amides have different intermolecular hydrogen bonding interactions and provide distinguishable fluorescence emission centers for the polyamides. These PIEs are λ_exDependent on, but distinct from, the polychromatic emission from the set of fluorescent states. Furthermore, the in situ generated thiol groups can be used to dope and tune the fine structure of aliphatic polyamides by thiol click chemistry, and thus produceOr for regulating the environmental intermolecular forces of aliphatic NTILs. Our studies not only demonstrate how to distinguish PIE of various aliphatic polyamides by means of thiolactone chemistry to achieve a detailed substructure of amide species and amide chains and doped heteroatoms, but also extend the scope of PIE and NTIL.

It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims

1. A preparation method of atypical polymerization-induced luminescent aliphatic polyamide is characterized in that: comprises dissolving N-ACHCT and allylamine in dioxane, and stirring at room temperature overnight; adding tricarboxyethylphosphine into the mixture, and stirring; adding DMPA as a photoinitiator and exposing the reaction mixture to UV radiation; precipitation in ether was used to purify the resulting mixture and dried under vacuum to give a viscous solid.

2. The method for producing an atypical polymerization-induced luminescent aliphatic polyamide as claimed in claim 1, wherein: the addition amount of the N-ACHCT and the allylamine is 95.4mg and 0.6 mmol; the addition amount of the allylamine was 37.6mg and 0.66mmol, and the addition amount of the dioxane was 0.6 mL.

3. The method for producing an atypical polymerization-induced luminescent aliphatic polyamide as claimed in claim 1 or 2, characterized in that: the adding amount of the tricarboxyphosphine is 10mM, and the stirring is carried out for 0.5-1.5 h.

4. The method for producing an atypical polymerization-induced luminescent aliphatic polyamide as claimed in claim 1 or 2, characterized in that: the addition amount of the DMPA is 0.5-2 wt%, and the UV irradiation time is 20-40 min.

5. The method for producing an atypical polymerization-induced luminescent aliphatic polyamide as claimed in claim 1 or 2, characterized in that: the preparation method of the N-ACHCT comprises the steps of mixing 3.07g of D, 0.02mol of L-homocysteine thiolactone hydrochloride with 5.56g of triethylamine, 0.055mol of D, L-homocysteine thiolactone hydrochloride, adding the mixture into 50mL of dichloromethane, and forming suspended matters under the ice bath condition; dropwise adding 2.36g and 0.03mol of acetyl chloride, wherein the dropwise adding process is more than 20min, and stirring the obtained mixed solution at room temperature overnight; adding 20mL of dichloromethane, filtering, washing, and extracting with dichloromethane; the organic layer was dried over anhydrous sodium sulfate and evaporated in vacuo; and performing silica gel column chromatography on the obtained product to obtain a white powdery product N-ACHCT.

6. The method for producing an atypical polymerization-induced luminescent aliphatic polyamide as claimed in claim 1 or 2, characterized in that: the atypical fluorescent aliphatic polyamide has a structural formula shown as a formula (I):

wherein n is 5 to 100.