Aggregation-induced emission fluorophore precursor suitable for preparing luminescent polymer and application of aggregation-induced emission fluorophore precursor

Abstract

The invention discloses a novel method for preparing a light-emitting polymer with wide fluorescence by coupling an aggregation-induced emission fluorophore precursor (AIE fluorescent precursor) with a universal polymer through mechanochemistry. The invention also discloses an AIE fluorescent precursor with the following main structural formula: AIE,

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 567,904, filed on March 20, 2024, the disclosure of which is incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to an aggregation-induced emission (AIE) fluorophore compound suitable for preparing a luminescent polymer, and applies the compound to information storage and encryption display. Background Art

[0004] Mechanical radicals generated by mechanical stimuli such as grinding, milling, or stretching offer a unique pathway for mechanoradic coupling, facilitating the construction of elaborate molecular structures. The application of mechanical stress to polymer chains is sufficient evidence for the scission of covalent bonds, leading to the formation of reactive macromolecular radicals. These macromolecular radicals can then participate in subsequent reactions with different molecules, paving the way for the creation of new material entities or initiating polymerization processes. This rapidly growing interest is attributed to the simplicity, cost-effectiveness, and versatility of the mechanoradic coupling process, as well as the unique properties and wide range of applications of the resulting materials.

[0005] The synthesis of luminescent polymer materials via mechano-radical coupling is a particularly interesting area of ​​exploration. This innovative strategy entails the fusion of non-luminescent radical species to form novel compounds that can emit light in response to mechanical agitation, thus providing a streamlined route to the development of functional materials.

[0006] Despite this, the field of constructing functional light-emitting polymers through mechanical forces remains a largely unexplored area. In particular, how to introduce functional groups into non-specialty polymers in the solid state to produce materials with strong luminescent properties is a great challenge. Furthermore, the process of using mechanical supports to impart fluorescence to polymers faces several challenges, including complex polymerization requirements and the widespread problem of aggregation-caused quenching (ACQ), which significantly reduces the luminescence efficiency when the material is in an aggregated or solid state. Therefore, simple precursors and faster manufacturing methods are highly needed to combine mechanical free radical methods and functional luminescent groups to form highly fluorescent polymers. Summary of the Invention

[0007] The present invention discloses a novel method for preparing light-emitting polymers with a wide range of fluorescence by mechanochemically coupling aggregation-induced emission fluorophore precursors (AIE pre-fluorophores, hereinafter referred to as AIE fluorophores) with general polymers. A series of AIE groups connected to 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) radicals (or its derivatives) were synthesized as AIE fluorophores, which initially exhibited weak fluorescence due to intramolecular quenching. The mechanical coupling of these AIE fluorophores with macromolecular free radicals was generated by mechanical stirring of the general polymer, resulting in a significant enhancement of the fluorescence within the resulting AIE-modified light-emitting polymers.

[0008] The present invention also discloses the effects of different AIE fluorescent precursors and universal polymers, promoting tunable absorption and emission across the visible-near-infrared (NIR) spectrum. The AIE-modified polymers demonstrate applications in stimulus-responsive information storage and encrypted displays. The present invention avoids complex chemical synthesis and enables the direct production of highly luminescent polymers from readily available polymers and AIE fluorescent precursors.

[0009] In one embodiment, the present invention discloses an aggregation-induced emission fluorophore precursor (hereinafter referred to as an AIE fluorescent precursor) suitable for preparing a light-emitting polymer. The AIE fluorescent precursor has the following main structural formula:

[0010]

[0011] wherein R1, R2, R3 and R4 are independently selected from linear, branched, or cyclic alkyl groups, alkylphenyl groups, alkylthienyl groups, and other alkyl aromatic groups containing 2 to 40 carbon atoms, and wherein one or more non-adjacent carbon atoms are optionally substituted by –O–, –S–, –C(O)–, –C(O–)–O–, –O–C(O)–, –O–C(O)–O–, or –C≡C–, and wherein one or more hydrogen (H) atoms are optionally replaced by fluorine (F), chlorine (Cl), bromine (Br), iodine (I), or cyanide (CN), or represent aromatic, heteroaromatic, aryloxy, heteroaryloxy, aromatic carbonyl, heteroaromatic carbonyl, aromatic carbonyloxy, heteroaromatic carbonyloxy, aryloxycarbonyl, or heteroaryloxycarbonyl groups having a ring of 4 to 30 atoms, and these ring molecules are unsubstituted or substituted by one or more non-aromatic groups;

[0012] wherein R5 has structural formula (I) or structural formula (II):

[0013] Donor-π bridge- (I)

[0014] Donor-Acceptor-π Bridge- (II)

[0015] The π bridges are independently selected from the following groups:

[0016]

[0017] wherein the receptors are independently selected from the following groups:

[0018]

[0019] Where R5 is independently selected from the following groups:

[0020]

[0021]

[0022]

[0023] In another embodiment, the present invention discloses a method for preparing a light-emitting polymer, comprising:

[0024] Providing the aforementioned AIE fluorescent precursor;

[0025] Provides general polymers;

[0026] delivering an AIE fluorescent precursor and a universal polymer into a container to form a mixture;

[0027] performing mechanochemical agitation on the mixture in the container to form a reaction mixture, wherein macromolecular radicals generated by the mechanochemical agitation of the general polymer can covalently interact with radical sites of the AIE fluorescent precursor, resulting in the formation of new covalent bonds, thereby forming an aggregation-induced emission (AIE-modified) light-emitting polymer; and

[0028] The reaction mixture is purified to remove any unreacted free radicals and other low molecular weight residues to obtain the final product of the light-emitting polymer.

[0029] In another embodiment, the present invention discloses a security document, comprising:

[0030] a substrate; and

[0031] a marking layer having coded information, formed by printing the aforementioned light-emitting polymer, wherein the marking layer is formed or placed on a substrate;

[0032] The light-emitting polymer has the characteristic of absorbing light with a wavelength lower than 400 nm, and when the light-emitting polymer is exposed to ambient sunlight, the light-emitting polymer does not show any color and does not emit fluorescence;

[0033] Wherein, under the irradiation of light below 400nm, the light-emitting polymer absorbs light with a wavelength below 400nm, thereby emitting fluorescence or showing color, and generating a readable contrast difference between the marking layer with coded information and the substrate.

[0034] In yet another embodiment, the present invention discloses a dual-mode security document, comprising:

[0035] a substrate; and

[0036] a marking layer having coded information, formed by printing the aforementioned light-emitting polymer, the marking layer being placed on the substrate and forming a plurality of regions;

[0037] The light-emitting polymer has the characteristic of absorbing ultraviolet light. When the light-emitting polymer is exposed to ambient sunlight, the light-emitting polymer does not show any color and does not emit fluorescence.

[0038] Wherein, under ultraviolet light irradiation, the light-emitting polymer absorbs ultraviolet light, thereby emitting light with a first set of wavelengths in the marking layer with coded information, which displays color or emits fluorescence;

[0039] The characteristic of the light-emitting polymer is that when the light-emitting polymer is exposed to polar solvent vapor, it interacts with the polar solvent molecules, thereby causing the emission wavelength to red-shift;

[0040] Among them, when exposed to ultraviolet light and the vapor of a polar solvent at the same time, the light-emitting polymer is exposed to the vapor of a polar solvent, thereby red-shifting the first set of wavelengths to the second set of wavelengths under ultraviolet light, showing color or emitting fluorescence, and converting the encoded information layer into a decoded information layer.

[0041] The above description is only a summary of the technical solution of the present invention. The following provides a complete embodiment of the present invention in conjunction with the accompanying drawings to make it easier for those skilled in the art to understand the operation process and its objectives, features and advantages of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be fully understood from the following detailed description of the complete embodiments with reference to the accompanying drawings, in which:

[0043] Figure 1 The synthetic pathways of B-tp, G-tp, Y-tp, O-tp, and R-tp are shown.

[0044] Figure 2 The chemical structures of B-tp, G-tp, Y-tp, O-tp, and R-tp are shown.

[0045] Figure 3a The synthetic pathways of B-tp, G-tp, Y-tp, O-tp, and R-tp are shown. Figure 3b The electron spin resonance (ESR) signals of B-tp, G-tp, Y-tp, O-tp and R-tp in THF solution are shown, g = 1.97. Figure 3c The electron spin resonance (ESR) signals of B-tp, G-tp, Y-tp, O-tp and R-tp in the solid state are shown, g = 1.92. Figure 3d Shown are the normalized absorption spectra of B-tp, G-tp, Y-tp, O-tp, and R-tp in the solid state. Figure 3e The solid-state photoluminescence (PL) spectra of B-tp, G-tp, Y-tp, O-tp, and R-tp are shown. The corresponding graphs were measured under sunlight and UV light.

[0046] Figure 4a Schematic diagram of the reaction of B-tp reduction to B-tp-H. Figure 4b The PL spectrum of B-tp in a THF / water mixture (1:9 vol%) and the fluorescence turn-on after addition of ascorbic acid at the same water fraction are shown. (The inset photographs are taken before and after addition of ascorbic acid to the O-tp solution.) Figure 4c The adsorption process of B-tp is shown as D0→D2( 2 CT 2,FC ) and non-radiative emission process D1( 2 ET 1,min )→D0 corresponding electronic transition molecular orbital. Figure 4d Calculated energy levels and proposed mechanism showing the luminescence behavior of B-tp. Figure 4e The adsorption process of B-tp-H is shown as S0→S1( 1 CT 1,FC ) and non-radiative emission process S1( 1 CT 1,min )→S0 corresponding electronic transition molecular orbital. Figure 4f The calculated energy levels and proposed mechanism for the luminescence behavior of B-tp-H are shown. The blue arrows correspond to absorption, the red arrows to emission, and the black dashed arrows to non-radiative processes.

[0047] Figure 5a Schematic diagram of the reaction process for preparing fluorescent plastics from general polymers via mechano-radical coupling with AIE fluorescent precursors. (Inset: photos of a PS and B-tp mixture before and after ball milling under sunlight and 365 nm UV light.) Figure 5b Gel permeation chromatography (GPC) traces of polystyrene (PS) and mixtures of polystyrene with AIE fluorescent precursors (B-PS, G-PS, Y-PS, O-PS, and R-PS) after ball milling are shown. Figure 5cShown are the electron spin resonance (ESR) signals of B-tp, G-tp, Y-tp, O-tp, R-tp, PS, and the obtained mixtures of PS and pre-AIE fluorophores (B-PS, G-PS, Y-PS, O-PS, and R-PS) in the solid state at g = 1.92.

[0048] Figure 6a The photoluminescence (PL) spectra of PS, B-tp, and AIE fluorescent precursor-attached PS (B-PS) are shown. Figure 6b The photoluminescence (PL) spectra of PS, G-tp, and AIE fluorescent precursor-attached PS (G-PS) are shown. Figure 6c The photoluminescence (PL) spectra of PS, Y-tp, and AIE fluorescent precursor-attached PS (Y-PS) are shown. Figure 6d The photoluminescence (PL) spectra of PS, O-tp, and AIE fluorescent precursor attached PS (O-PS) are shown. Figure 6e The photoluminescence (PL) spectra of PS, R-tp, and AIE fluorescent precursor-attached PS (R-PS) are shown. Figure 6f Shown are the normalized absorption spectra of PS, B-PS, G-PS, Y-PS, O-PS, and R-PS in the solid state. Figure 6g The obtained photoluminescence (PL) spectra of the AIE fluorescent precursor-attached PS (B-PS, G-PS, Y-PS, O-PS, and R-PS) in the solid state are shown. Figure 6h The obtained AIE fluorescent precursor-attached PMMA (B-PMMA, G-PMMA, Y-PMMA, O-PMMA, and R-PMMA) photoluminescence (PL) spectra in the solid state are shown. Figure 6i The obtained AIE fluorescent precursor-attached PPS (B-PPS, G-PPS, Y-PPS, O-PPS, and R-PPS) photoluminescence (PL) spectra in the solid state are shown. Figure 6j The photoluminescence quantum yield (PLQY) of the AIE fluorescent precursor and its attached polymer is shown.

[0049] Demonstrate information encryption 3D printing and pattern generation. Figure 7a Showing the 3D printing process and the creation of the fluorescent word "AGGREGATE". Figure 7b Shows the changes in the fluorescent PS film after treatment with methanol. Figure 7c Schematic diagram showing the fabrication, assembly, writing, and reading of dual-mode information encryption patterns. DETAILED DESCRIPTION

[0050] definition

[0051] In this application, when an element or component is referred to as being included in and / or selected from a list of enumerated elements or components, it is understood that the element or component can be any of the enumerated elements or components, or the element or component can be selected from a group consisting of two or more of the enumerated elements or components. Furthermore, it is understood that the elements, compound group properties, apparatuses, or methods described herein may be combined in various ways, whether explicitly or implicitly herein, without departing from the spirit and scope of the present teachings.

[0052] Unless expressly stated otherwise, use of the terms "including," "comprising," "having," or "having" are generally accepted to be open ended and non-limiting.

[0053] The singular is used herein to include the plural (and vice versa) unless otherwise expressly stated. Furthermore, when the term "about" is used before a quantitative value, this patent also includes the specific quantitative value itself, unless otherwise expressly stated. When the term "about" is used herein, it means within a range of ±10% from the standard value, unless otherwise stated or inferred.

[0054] The order in which the steps are performed is not critical, as long as the guidelines in the patent remain valid. In addition, two or more actions may be performed simultaneously.

[0055] “λ ex ” here refers to the excitation wavelength.

[0056] The term "aggregation-induced luminescence quenching" or "ACQ" as used herein refers to the phenomenon that aggregation of π-conjugated fluorophores significantly reduces the fluorescence intensity of the fluorophore. The formation of aggregates is believed to "quench" the luminescence of the fluorophore.

[0057] The term "aggregation-induced emission" or "AIE" as used herein refers to a phenomenon in which compounds exhibit significantly enhanced luminescence when aggregated in the amorphous or crystalline (solid state) but exhibit weak or almost no luminescence in dilute solution.

[0058] "Luminescence intensity" as used herein refers to the amount of fluorescence / phosphorescence typically measured using a fluorescence spectrometer or fluorescence microscope; "fluorophore" or "fluorescence source" as used herein refers to a molecule that exhibits fluorescence; "luminescence source" or "luminophore" as used herein refers to a molecule that exhibits luminescence;

[0059] Here, "AIEgen" refers to a molecular cluster that exhibits AIE properties.

[0060] As used herein, a "donor" material refers to an organic material, such as an organic nanoparticle material, in which holes serve as the primary current or charge carriers.

[0061] As used herein, an "acceptor" material refers to an organic material, such as an organic nanoparticle material, in which electrons are the primary current or valence charge carriers.

[0062] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0063] AIE fluorescent precursors and their characteristics

[0064] The synthesis of light-emitting polymer materials via mechano-radical coupling is a particularly interesting area of ​​exploration. This innovative strategy entails the fusion of non-emissive radical species to form novel compounds that emit light in response to mechanical agitation, thus providing a streamlined route to the development of functional materials.

[0065] The emergence of aggregation-induced luminogens (AIE luminogens, hereinafter referred to as AIE luminogens) has become a beacon of hope, providing a convincing countermeasure to ACQ. AIE luminogens are different in that they exhibit enhanced emission in the aggregated state, which is a result of restricted intramolecular motions (RIM), thereby mitigating non-radiative decay pathways. Although progress has been made in embedding AIE luminogens into polymer matrices through blending, copolymerization or grafting techniques, the exploration of direct integration through mechanical-radical coupling to enhance luminescence is still in its infancy. This can be attributed to the lack of appropriately engineered fluorescent precursors for such processes, as well as the lack of effective and optimized coupling strategies.

[0066] In a first embodiment, the present invention provides an aggregation-induced emission fluorophore precursor (hereinafter referred to as an AIE fluorescent precursor) suitable for preparing a light-emitting polymer, wherein the AIE fluorescent precursor has the following main structural formula:

[0067]

[0068] wherein R1, R2, R3 and R4 are independently selected from linear, branched, or cyclic alkyl groups, alkylphenyl groups, alkylthienyl groups, and other alkyl aromatic groups containing 2 to 40 carbon atoms, and wherein one or more non-adjacent carbon atoms are optionally substituted by –O–, –S–, –C(O)–, –C(O–)–O–, –O–C(O)–, –O–C(O)–O–, or –C≡C–, and wherein one or more hydrogen (H) atoms are optionally replaced by fluorine (F), chlorine (Cl), bromine (Br), iodine (I), or cyanide (CN), or represent aromatic, heteroaromatic, aryloxy, heteroaryloxy, aromatic carbonyl, heteroaromatic carbonyl, aromatic carbonyloxy, heteroaromatic carbonyloxy, aryloxycarbonyl, or heteroaryloxycarbonyl groups having a ring of 4 to 30 atoms, and these ring molecules are unsubstituted or substituted by one or more non-aromatic groups;

[0069] wherein R5 has structural formula (I) or structural formula (II):

[0070] Donor-π bridge- (I)

[0071] Donor-Acceptor-π Bridge- (II)

[0072] The π bridges are independently selected from the following groups:

[0073]

[0074] wherein the receptors are independently selected from the following groups:

[0075]

[0076] Where R5 is independently selected from the following groups:

[0077]

[0078]

[0079]

[0080] In this embodiment, under ultraviolet excitation, the aggregation-induced emission fluorophore precursor exhibits very weak fluorescence in the free radical form and strong fluorescence in the reduced form.

[0081] In a preferred embodiment, the aggregation-induced emission fluorophore precursors are independently selected from the following group:

[0082]

[0083]

[0084] In this embodiment, in order to realize materials that emit light across the entire visible light region, the present invention designs a series of AIE fluorescent precursors with donor-acceptor-π (DA-π) characteristics, such as blue (B-tp), green (G-tp), yellow (Y-tp), orange (O-tp) and red (R-tp) compounds. The synthetic reaction pathways for preparing blue (B-tp), green (G-tp), yellow (Y-tp), orange (O-tp) and red (R-tp) compounds are as follows: Figure 1 and Figure 3a shown.

[0085] By selecting specific donor, acceptor and π-bridge moieties, the intramolecular charge transfer (ICT) effect of these AIE fluorescent precursors was carefully tuned. The AIE fluorescent precursors were functionalized with 4-hydroxy-2,2,6,6-tetramethylpiperidinyl 1-oxyl through Suzuki coupling, hydrolysis and Stieglich esterification reactions, aiming to achieve blue (B-tp), green (G-tp), yellow (Y-tp), orange (O-tp) and red (R-tp) luminescence. The free radical signals of the obtained AIE fluorescent precursors were confirmed by electron spin resonance (ESR) spectroscopy. All AIE fluorescent precursors exhibited strong ESR signals, whether in THF solution ( Figure 3b ) or in solid state ( Figure 3c ), which matches well with the signal of TEMPO in the literature. Subsequently, the absorption spectrum of the AIE fluorescent precursor was measured in the solid state. With the increase of ICT, the absorption maximum showed a gradual red shift, that is, B-tp, G-tp, Y-tp, O-tp and R-tp were at 386, 413, 427, 484 and 546 nm, respectively ( Figure 3d Interestingly, although all of these AIE fluorescent precursors possess typical AIE moieties, the luminescence observed by the naked eye and photoluminescence (PL) spectroscopy is almost non-existent or very weak ( Figure 3e ).

[0086] In order to confirm the molecular structure and elucidate the luminescent properties of the AIE fluorescent precursor, ascorbic acid was used as a chemical reagent to quench the free radical sites present in the compound. For example, taking B-tp as a prototype, in the presence of ascorbic acid (i.e., vitamin C), the nitroxide radical part (NO·) was reduced to a hydroxylamine group (N-OH), thereby forming its reduced form B-tp-H ( Figure 4a ). In addition, if Figure 4bAs shown, a B-tp solution initially exhibited negligible fluorescence under UV excitation, but its luminescence was significantly enhanced upon treatment with ascorbic acid at room temperature. This exhibited distinct blue fluorescence, indicating that B-tp rapidly responded to the free radical quenching effect of ascorbic acid. Similarly, other members of the AIE fluorescent precursor family exhibited significantly enhanced emission when treated with ascorbic acid, also demonstrating the efficient quenching of free radicals in these systems.

[0087] To elucidate the underlying reasons for the significant difference in fluorescence between B-tp and B-tp-H, their emission mechanisms were computationally analyzed by (time-dependent) density functional theory [(TD-)DFT] at the B3LYP / 6-31G* level ( Figure 4c ).like Figure 4d As shown in Figure 2, the predicted optical energy gap of B-tp is 2.97 eV (f = 0.73), which can be attributed to the D0-D2 transition rather than the D0-D1 transition with negligible oscillator strength (f ~ 0). In addition, the calculation shows that after the absorption process, B-tp easily undergoes a non-radiative transition from the D2 state to the D1 state near the Frank Condon (FC) conformation. This transition leads to the formation of a D1 state with local excitation (LE) characteristics, which is denoted as 2 LE 1,FC , where the superscripts represent state diversity. Subsequently, excited state structural relaxation (ESSR) occurs, leading to the energy minimum conformation of the D1 state, marked as 2 ET 1,min This involves the electrons from the TEMPO fragment (p O ) transitions from the p orbital of the O atom in the TPA fragment (π TPA ) of the π orbital, indicating the existence of a photoinduced electron transfer (PET) pathway. 2 ET 1,min The minimum state indicates that the oscillator strength is close to 0, reaching the D0 state. 2 LE 1,FC arrive 2 ET 1,min This shift effectively quenches the radiative decay, explaining the decaying fluorescence observed in B-tp.

[0088] In contrast, the calculations for B-tp-H show a clear S0-S1 absorption at 3.04 eV (f = 0.74, Figure 4e and Figure 4f). It is worth noting that during the ESSR, the electronic state remains unchanged and only the geometric changes occur. The S1-S0 radiative transition is quite strong and fast (2.24 eV, f = 0.07), considering that the 0.05 cm -1 Given the relatively insignificant spin-orbit coupling (SOC) constant, the intersystem crossing (ISC) quenching pathway from S1 to T1 is thought to be inefficient. Consequently, the B-tp-H molecule favors fluorescence in the S1 state. In summary, it is hypothesized that the reduced fluorescence in B-tp is primarily due to a significant PET effect generated by the TEMPO radical moiety. Following quenching of the radical signature by reduction, oxidation, or quenching by another radical, the resulting species should exhibit substantial "turn-on fluorescence."

[0089] Synthesis and Characterization of AIE Fluorescent Precursor Series

[0090] Synthesis of methyl 5-(4-(diphenylamino)phenyl)thiophene-2-carboxylate (1)

[0091] A mixture of (4-(diphenylamino)phenyl)boronic acid (1.00 g, 3.46 mmol), methyl 5-bromothiophene-2-carboxylate (913 mg, 4.15 mmol), Pd(dppf)Cl2 (127 mg, 0.17 mmol) and K2CO3 (2.39 g, 17.3 mmol) was dissolved in THF / water (18 / 9 mL) and stirred at 80 ° C overnight under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was extracted with chloroform and washed with water and brine. After concentration under reduced pressure, the crude product was purified by column chromatography (stationary phase: silica gel; eluent: DCM) to give a light yellow oily product (1.16 g, 87%). 1 H NMR (400MHz, CDCl3) δ7.77(d,J=3.9Hz,1H),7.51(d,J=8.7Hz,2H),7.31(t,J=7 .9Hz,4H),7.22(d,J=3.9Hz,1H),7.17(s,4H),7.13–7.06(m,4H),3.92(s,3H). 13 C NMR(101MHz, CDCl3)δ162.81,151.41,148.53,147.18,134.59,130.80,129.45,127.00,126.87,124.95,123.61,122.88,122.56,52.14.MS(ESI):calculated for C 24 H 19NO2S:385.1136,found:385.1130.

[0092] Synthesis of B-tp

[0093] Compound 1 (1.00 g, 2.60 mmol) was dissolved in THF (10 mL), and then aqueous LiOH (2 M, 20 mL) was added. The mixture was heated at 80°C overnight and quenched by adding excess aqueous HCl to form a precipitate. The mixture was filtered and the residual solid was washed three times with water. The carboxylic acid intermediate was dried under reduced pressure at 60°C and used in the next step without further purification. The carboxylic acid, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH, 501 mg, 2.91 mmol), N,N′-dicyclohexylcarbodiimide (DCC, 1.00 g, 4.85 mmol), and 4-dimethylaminopyridine (DMAP, 59 mg, 0.49 mmol) were then dissolved in anhydrous DCM (20 mL) under a nitrogen atmosphere. The mixture was stirred at room temperature overnight and purified by column chromatography (stationary phase: silica gel; eluent: DCM diluted to DCM:Et2O=100:1) to give a pale yellow solid product (886 mg, 65% after two-step purification). MS (ESI): calculated for C 32 H 33 N2O3S·:525.2212,found:548.2112(M+Na).

[0094] Synthesis of methyl 4-(7-(4-(1,2,2-triphenylvinyl)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)benzoate (2)

[0095] A mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzo[c][1,2,5]thiadiazole (1.00 g, 2.58 mmol), methyl 4-bromobenzoate (610 mg, 2.84 mmol), (2-(4-bromophenyl)ethene-1,1,2-triyl)triphenyl (1.17 g, 2.84 mmol), Pd(dppf)Cl2 (94 mg, 0.13 mmol), and K2CO3 (3.56 g, 25.8 mmol) was dissolved in THF / water (26 / 13 mL) and stirred at 80°C overnight under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was extracted with chloroform and washed with water and brine. After concentration under reduced pressure, the crude product was purified by column chromatography (stationary phase: silica gel; eluent: DCM) to give the product as a pale yellow solid (650 mg, 42%). 1H NMR(400MHz, CDCl3)δ8.23(d,J=8.1Hz,2H),8.07(d,J=8.1Hz,2H),7.83–7.74(m,4H) ,7.24(d,J=8.1Hz,2H),7.20–7.11(m,13H),7.08(dd,J=7.0,2.8Hz,2H),3.99(s,3H). 13 C NMR (101MHz, CDCl3) δ166.91,153.91,144.10,143.71,143.65,143.61,141.84,141.62,140.45,135.02,133.75,131.83,131.69,131 .49,131.40,131.37,129.87,129.71,129.19,128.67,128.46,127.85,127.77,127.67,126.64,126.57,52.26.MS(ESI):calculated for C 40 H 28 N2O2S:600.1871,found:600.1864.

[0096] Synthesis of G-tp

[0097] Compound 2 (500 mg, 0.83 mmol) was dissolved in THF (10 mL), and then a LiOH aqueous solution (2 M, 10 mL) was added. The mixture was heated at 80 ° C overnight and the reaction was quenched by adding excess HCl aqueous solution to form a precipitate. The mixture was filtered and the residual solid was washed three times with water. The carboxylic acid intermediate was dried under reduced pressure at 60 ° C and used in the next step without further purification. Then, the carboxylic acid, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH, 158 mg, 0.92 mmol), N, N'-dicyclohexylcarbodiimide (DCC, 317 mg, 1.54 mmol) and 4-dimethylaminopyridine (DMAP, 19 mg, 0.15 mmol) were dissolved in anhydrous DCM (10 mL) under a nitrogen atmosphere. The mixture was stirred at room temperature overnight and purified by column chromatography (stationary phase: silica gel; eluent: DCM diluted to DCM:Et2O=100:1) to give a yellow solid product (376 mg, 61% after two-step purification). MS (ESI): calculated for C 48 H 42 N3O3S·:740.2947,found:762.2851(M+Na).

[0098] Synthesis of methyl 4-(7-(4-(2,2-bis(4-methoxyphenyl)-1-phenylvinyl)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)benzoate (3)

[0099] A mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzo[c][1,2,5]thiadiazole) (1.00 g, 2.58 mmol), methyl 4-bromobenzoate (610 mg, 2.84 mmol), 4,4'-(2-(4-bromophenyl)-2-phenylethene-1,1-diyl)bis(methoxybenzene) (1.33 g, 2.84 mol), Pd(dppf)Cl2 (94 mg, 0.13 mmol) and K2CO3 (3.56 g, 25.8 mmol) was dissolved in THF / water (26 / 13 mL) and stirred at 80°C overnight under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was extracted with chloroform and washed with water and brine. After concentration under reduced pressure, the crude product was purified by column chromatography (stationary phase: silica gel; eluent: DCM) to give the product as a pale orange solid (680 mg, 40%). 1 H NMR (400MHz, CDCl3) δ8.23(d,J=8.4Hz,2H),8.07(d,J=8.4Hz,2H),7.85–7.75(m,4H),7.22(d,J=8.3Hz,2H),7.20–7.09 (m,5H),7.06(d,J=8.7Hz,2H),6.99(d,J=8.7Hz,2H),6.69(dd,J=12.3,8.7Hz,4H),3.99(s,3H),3.77(d,J=2.3Hz,6H). 13 C NMR (101MHz, CDCl3) δ166.92,158.26,158.15,153.96,153.93,144.74,14 4.18,141.87,140.81,138.71,136.33,136.30,134.65,133.84,132.69,13 2.65,131.72,131.54,129.86,129.69,129.18,128.69,128.48,127.80,127.70,126.23,113.19,113.02,55.13,55.11,52.24.MS(ESI):calculated forC 42 H 32 N2O4S:660.2083,found:660.2072.

[0100] Synthesis of Y-tp

[0101] Compound 3 (500 mg, 0.76 mmol) was dissolved in THF (10 mL), and then a LiOH aqueous solution (2 M, 10 mL) was added. The mixture was heated at 80 ° C overnight and the reaction was quenched by adding excess HCl aqueous solution to form a precipitate. The mixture was filtered and the residual solid was washed three times with water. The carboxylic acid intermediate was dried under reduced pressure at 60 ° C and used in the next step without further purification. Then, carboxylic acid, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH, 143 mg, 0.84 mmol), N, N'-dicyclohexylcarbodiimide (DCC, 287 mg, 1.39 mmol) and 4-dimethylaminopyridine (DMAP, 17 mg, 0.14 mmol) were dissolved in anhydrous DCM (10 mL) under a nitrogen atmosphere. The mixture was stirred at room temperature overnight and purified by column chromatography (stationary phase: silica gel; eluent: DCM diluted to DCM:Et2O=100:1) to give a yellow solid product (406 mg, 67% after two-step purification). MS (ESI): calculated for C 50 H 46 N3O5S·:800.3158,found:823.3129(M+Na).

[0102] Synthesis of methyl 4-(7-(4-(bis(4-methoxyphenyl)amino)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)benzoate (4)

[0103] A mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzo[c][1,2,5]thiadiazole (1.00 g, 2.58 mmol), methyl 4-bromobenzoate (610 mg, 2.84 mmol), 4-bromo-N,N-bis(4-methoxyphenyl)aniline (1.09 g, 2.84 mmol / L), Pd(dppf)Cl2 (94 mg, 0.13 mmol) and K2CO3 (3.56 g, 25.8 mmol) was dissolved in THF / water (26 / 13 mL) and stirred at 80°C overnight under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was extracted with chloroform and washed with water and brine. After concentration under reduced pressure, the crude product was purified by column chromatography (stationary phase: silica gel; eluent: DCM) to give a light red solid product (561 mg, 38%). 1H NMR (400MHz, CDCl3) δ8.22(d,J=8.0Hz,2H),8.07(d,J=8.0Hz,2H),7.85(d,J=8.3Hz,2H),7.81(d,J=7.5Hz,1H),7. 74(d,J=7.4Hz,1H),7.17(d,J=8.4Hz,4H),7.09(d,J=8.3Hz,2H),6.89(d,J=8.4Hz,4H),3.99(s,3H),3.84(s,6H). 13 C NMR (101MHz, CDCl3) δ166.93,156.27,154.09,153.96,149.20,142.01,140.43,133.99,130.82,129.89,12 9.85,129.51,129.10,128.88,128.49,127.15,126.63,119.57,114.82,55.53,52.23.MS(ESI):calculated for C 34 H 27 N3O4S:573.1722,found:573.1718.

[0104] Synthesis of O-tp

[0105] Compound 4 (500 mg, 0.87 mmol) was dissolved in THF (10 mL), and then a LiOH aqueous solution (2 M, 10 mL) was added. The mixture was heated at 80 ° C overnight and the reaction was quenched by adding excess HCl aqueous solution to form a precipitate. The mixture was filtered and the residual solid was washed three times with water. The carboxylic acid intermediate was dried under reduced pressure at 60 ° C and used in the next step without further purification. Then, the carboxylic acid, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH, 166 mg, 0.97 mmol), N, N'-dicyclohexylcarbodiimide (DCC, 332 mg, 1.61 mmol) and 4-dimethylaminopyridine (DMAP, 20 mg, 0.16 mmol) were dissolved in anhydrous DCM (10 mL) under a nitrogen atmosphere. The mixture was stirred at room temperature overnight and purified by column chromatography (stationary phase: silica gel; eluent: DCM diluted to DCM:Et2O=100:1) to give a red solid product (386 mg, 62% after two-step purification). MS (ESI): calculated for C 42 H 41 N4O5S·:713.2798,found:736.2698(M+Na).

[0106] Synthesis of methyl 4-(9-(4-(bis(4-methoxyphenyl)amino)phenyl)naphtho[2,3-c][1,2,5]thiadiazol-4-yl)benzoate (5)

[0107] A mixture of 4,9-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)naphtho[2,3-c][1,2,5]thiadiazole (1.00 g, 2.28 mmol), methyl 4-bromobenzoate (540 mg, 2.51 mmol), 4-bromo-N,N-bis(4-methoxyphenyl)aniline (964 mg, 2.51 mmol), Pd(dppf)Cl2 (84 mg, 0.11 mmol), and K2CO3 (3.15 g, 22.8 mmol) was dissolved in THF / water (22 / 11 mL) and stirred at 80°C overnight under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was extracted with chloroform and washed with water and brine. After concentration under reduced pressure, the crude product was purified by column chromatography (stationary phase: silica gel; eluent: DCM) to give a pale purple solid product (526 mg, 37%). 1 H NMR (400MHz, CDCl3) δ8.33(d,J=8.3Hz,2H),8.25–8.18(m,1H),7.94(ddd,J=7.1,4.0,2.2Hz,1H),7.77(d,J=8.3Hz,2H),7.51(d ,J=8.7Hz,2H),7.43–7.34(m,2H),7.26(d,J=8.9Hz,4H),7.16(d,J=8.7Hz,2H),6.93(d,J=9.0Hz,4H),4.03(s,3H),3.85(s,6H). 13 C NMR (101MHz, CDCl3) δ166.96,156.34,151.48,151.22,148.88,141.60,140.46,132.06,132.02,131.78,131.48,131.37,12 9.79,129.76,128.04,127.64,127.45,127.20,126.85,126.48,126.05,118.78,114.85,55.53,52.31.MS(ESI):calculated for C 38 H 29 N3O4S:623.1879,found:623.1872.

[0108] Synthesis of R-tp

[0109] Compound 5 (500 mg, 0.80 mmol) was dissolved in THF (10 mL), and then a LiOH aqueous solution (2 M, 10 mL) was added. The mixture was heated at 80 ° C overnight and the reaction was quenched by adding excess HCl aqueous solution to form a precipitate. The mixture was filtered and the residual solid was washed three times with water. The carboxylic acid intermediate was dried under reduced pressure at 60 ° C and used in the next step without further purification. Then, carboxylic acid, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-OH, 152 mg, 0.89 mmol), N, N'-dicyclohexylcarbodiimide (DCC, 304 mg, 1.48 mmol) and 4-dimethylaminopyridine (DMAP, 18 mg, 0.15 mmol) were dissolved in anhydrous DCM (10 mL) under a nitrogen atmosphere. The mixture was stirred at room temperature overnight and purified by column chromatography (stationary phase: silica gel; eluent: DCM diluted to DCM:Et2O=100:1) to give a purple solid product (336 mg, 55% after two-step purification). MS (ESI): calculated for C 46 H 43 N4O5S·:763.2954,found:763.2960. AIE Modified light-emitting polymer and method for forming the same

[0110] In a second embodiment, the present invention provides a method for preparing a light-emitting polymer, comprising:

[0111] Providing the AIE fluorescent precursor as described in the first embodiment;

[0112] Providing a general polymer, which may include polystyrene (PS), polymethylmethacrylate (PMMA) or polyphenylene sulfide (PPS);

[0113] delivering an AIE fluorescent precursor and a universal polymer into a container to form a mixture;

[0114] performing mechanochemical agitation on the mixture in the container to form a reaction mixture, wherein macromolecular radicals generated by the mechanochemical agitation of the general polymer can covalently interact with radical sites of the AIE fluorescent precursor, resulting in the formation of new covalent bonds, thereby forming an aggregation-induced emission (AIE-modified) light-emitting polymer; and

[0115] The reaction mixture is purified to remove any unreacted free radicals and other low molecular weight residues to obtain the final product of the light-emitting polymer. The purification procedure may include gel permeation chromatography.

[0116] In a preferred embodiment, the container is a ball mill and the mechanochemical stirring is a ball milling process, wherein the ball milling speed is less than or equal to 1000 rpm and the ball milling time is less than or equal to 60 minutes.

[0117] In this example, the aggregation-induced emission (AIE-modified) luminescent polymer was produced using a solvent-free process. Preferably, the AIE-modified luminescent polymer was prepared by in-situ mechanoradical coupling of a general polymer with an AIE pre-fluorophore. This bypasses complex chemical synthesis and enables the direct preparation of bright luminescent materials with long fluorescence lifetimes and high quantum yields approaching 60% under optimal conditions.

[0118] Under ultraviolet excitation, the AIE-modified luminescent polymer exhibits weak fluorescence in a dilute solution state and strong fluorescence in the solid state. The AIE-modified luminescent polymer has a tunable, broad spectrum covering wavelengths from 400 to 900 nanometers.

[0119] In a preferred embodiment, a series of AIE fluorescent precursors from the first embodiment, such as blue (B-tp), green (G-tp), yellow (Y-tp), orange (O-tp) and red (R-tp) compounds, are provided for mechanochemical coupling with a series of commercially purchased polymers. Here, polystyrene (PS), polymethylmethacrylate (PMMA) or polyphenylenesulfide (PPS) obtained from Sigma-Aldrich Corp. are used as purchased without any additional purification steps. After applying a mechanical stimulus (such as ball milling), the polymer backbone breaks and produces macromolecular free radical intermediates. These emerging free radical species from the polymer can covalently link with the free radical sites of the AIE fluorescent precursor to form new covalent bonds. This coupling leads to the alleviation of the fluorescence quenching effect associated with free radicals, which ultimately manifests as strong fluorescence ( Figure 5a ).

[0120] For example, PS with a number average molecular weight (Mn) of 86.3 kDa and a polydispersity index (PDI) of 1.05 was used. The PS polymer was ball milled at 750 rpm for 30 minutes in the presence of the AIE fluorescent precursor B-tp. Figure 5a As shown in the inset, the resulting mixture exhibits distinct blue fluorescence under UV excitation. The reaction product is then purified, including dialysis and recovered by preparative gel permeation chromatography (GPC), to remove any unreacted free radicals and other low-molecular-weight residues, yielding a blue-emitting polymer, designated B-PS. Similar protocols can be used to synthesize other modified polymers.

[0121] To evaluate the molecular characteristics of the fluorescent modified PS samples, analytical GPC was performed. Figure 5b As shown in Figure 2, a consistent trend was observed in the modified PS samples (B-PS, G-PS, Y-PS, O-PS, and R-PS), where the decrease in Mn (10-17 kDa) was accompanied by an increase in PDI values ​​(1.24-1.25), indicating mechanical radical cleavage of homolytic covalent bonds within the PS matrix. In addition, ESR spectroscopy was used to evaluate the fluorescent polymers. Figure 5c ) and solution states, the absence of discernible signals in the ESR spectra indicates that the free radicals in the purified fluorescent products after the mechanochemical process are partially neutralized. In sharp contrast, the original AIE fluorescent precursors (B-tp, G-tp, Y-tp, O-tp, and R-tp) exhibit distinct EPR signals. Through these observations, transformative mechanochemical coupling has been confirmed to be an effective method for producing light-emitting polymers, thereby expanding the innovative application potential of AIE materials in the field of polymer science.

[0122] After preparing the AIE-modified luminescent polymer, its photophysical properties were evaluated in detail. First, PL spectra were recorded to elucidate the luminescent characteristics of the material ( Figure 6a-Figure 6e ). It was observed that pure PS was non-fluorescent, while the AIE fluorescent precursor alone exhibited negligible fluorescence. However, the modified PS showed strong fluorescence covering the entire visible spectrum from blue (B-PS), green (G-PS), yellow (Y-PS), orange (O-PS), and red (R-PS). Notably, the emission of R-PS can extend to the near-infrared (NIR) region.

[0123] Furthermore, the photoluminescence quantum yields (PLQYs) were comprehensively tabulated. The data revealed that the standalone AIE fluorescent precursors exhibited extremely low PLQYs. In stark contrast, the materials synthesized via the mechano-radical coupling route displayed significantly enhanced QYs compared to the pristine reactants, highlighting the effectiveness of the coupling process in generating highly fluorescent polymers.

[0124] The emission dynamics of the AIE fluorescent precursor and AIE modified PS were carefully characterized. The fluorescence lifetime (τ F ) is about 0.30ns, and the specific lifetime is recorded as follows: τ F(B-tp) =0.28ns,τ F(G-tp) =0.26ns,τ F(Y-tp) =0.32ns,τ F(O-tp) =0.31ns,τ F(R-tp) = 0.32ns. It is worth noting that the lifetime of the modified PS is significantly prolonged compared with the corresponding structure of the AIE fluorescent precursor, and the recorded lifetimes are as follows: τ F(B-PS) =0.72ns,τ F(G-PS) =1.66ns,τ F(Y-PS) =2.60ns,τ F(O-PS) =6.84ns,τ F(R-PS) = 12.98 ns, indicating strong fluorescence.

[0125] In addition, the data revealed a trend that the τ of the modified PS F Expands with the enhancement of Da interaction. τ F The extension of suggests more complex excited-state dynamics, possibly involving transitions between singlet and triplet states. The absorption and emission spectra of the modified PS are shown in Figures 2 and 3, respectively. Figure 6f and Figure 6g shown.

[0126] AIE fluorescent precursors were also mechanically free radical coupled with PMMA and PPS. Figures 6h to 6i As shown, the fluorescence profiles of all modified PMMA and modified PPS were thoroughly investigated, demonstrating desirable absorption and emission properties from the UV to the near-infrared region. Interestingly, the modified PPS exhibited a red-shifted emission maximum relative to their PS and PMMA counterparts when paired with the same AIE precursor, attributed to their intrinsically richer electronic interactions with the benzene rings and sulfur atoms (i.e., a more polar microenvironment). Figure 6j The PLQYs of these modified PMMA and PPS are also summarized. The data show that the AIE fluorescent precursors exhibit extremely low PLQY (~0%), while the modified polymers obtained after mechanical radical coupling significantly improve the PLQY to as high as 54.1%.

[0127] Application of information storage and encrypted display

[0128] In a third embodiment, the present invention provides a security document that can be applied to 3D printed documents, information-encoded documents, or anti-counterfeiting documents. The security document includes:

[0129] a substrate; and

[0130] a marking layer having coded information, formed by printing the aforementioned light-emitting polymer, wherein the marking layer is formed or placed on a substrate;

[0131] The light-emitting polymer has the characteristic of absorbing light with a wavelength lower than 400 nm, and when the light-emitting polymer is exposed to ambient sunlight, the light-emitting polymer does not show any color and does not emit fluorescence;

[0132] Wherein, under the irradiation of light below 400nm, the light-emitting polymer absorbs light with a wavelength below 400nm, thereby emitting fluorescence or showing color, and generating a readable contrast difference between the marking layer with coded information and the substrate.

[0133] In a fourth embodiment, the present invention provides a dual-mode security document that can be applied to 3D printed documents, information-encoded documents, or anti-counterfeiting documents. The dual-mode security document includes:

[0134] a substrate; and

[0135] a marking layer having coded information, formed by printing the aforementioned light-emitting polymer, the marking layer being placed on the substrate and forming a plurality of regions;

[0136] The light-emitting polymer has the characteristic of absorbing ultraviolet light. When the light-emitting polymer is exposed to ambient sunlight, the light-emitting polymer does not show any color and does not emit fluorescence.

[0137] Wherein, under ultraviolet light irradiation, the light-emitting polymer absorbs ultraviolet light, thereby emitting light with a first set of wavelengths in the marking layer with coded information, which displays color or emits fluorescence;

[0138] The characteristic of the light-emitting polymer is that when the light-emitting polymer is exposed to polar solvent vapor, it interacts with the polar solvent molecules, thereby causing the emission wavelength to red-shift;

[0139] Among them, when exposed to ultraviolet light and the vapor of a polar solvent at the same time, the light-emitting polymer is exposed to the vapor of a polar solvent, thereby red-shifting the first set of wavelengths to the second set of wavelengths under ultraviolet light, showing color or emitting fluorescence, and converting the encoded information layer into a decoded information layer.

[0140] In a preferred embodiment, the light-emitting polymer prepared using the second embodiment of the present invention shows significant innovative application potential in the field of additive manufacturing, especially in three-dimensional (3D) printing technology. A digital light processing (DLP) 3D printing device is used to produce a series of individual characters - G, R, E, A and T, which together form the acronym "GREAT". Figure 7a As shown, each character was designed to emit a unique and vibrant color—specifically, green, blue, yellow, orange, and red—by using modified PS materials. The characters synergistically combine to form the word "AGGREGATE," creating a complex display that appears uniform in color under ambient daylight but exhibits unique fluorescence properties at discrete wavelengths under UV illumination. This dichotomy in appearance under different lighting conditions strongly demonstrates the suitability of these fluorescent polymers for 3D printing applications.

[0141] Further highlighting the functional versatility of these materials, the polymers exhibited significant solvent-responsive fluorescence, a property that can be attributed to the TICT effect inherent in the AIE moiety. This phenomenon manifests as a red-shift in the emission wavelength when exposed to polar solvents. Remarkably, the magnitude of the observed emission wavelength red-shift is directly correlated with the DA intensity within the AIE moiety. Specifically, it can be seen that an increase in DA intensity leads to a more pronounced red-shift in the polymer emission. A series of polymer films were then fabricated using spin coating techniques, with each design displaying a different fluorescence. Figure 7b The transitions of these films upon exposure to methanol vapor were demonstrated. The film containing Y-PS initially featured bright yellow fluorescence, which subsequently shifted to orange-yellow fluorescence, while the O-PS film shifted from orange to red. Most strikingly, the R-PS film, which initially emitted red, underwent a transition extending into the near-infrared region, thereby evading visual detection. In contrast, the emission of the G-PS film shifted slightly from green to yellow-green, while the emission of the B-PS film remained unchanged. This compelling demonstration of tunable fluorescence highlights the potential of these AIE-based fluorescent polymers as responsive materials for advanced photonic and optoelectronic applications.

[0142] Please refer to Figure 7c, polymer films were fabricated using a spin-coating technique and organized into a 5 x 5 grid to construct a 3D fluorescent code, called Pattern I. In its initial state, Pattern I exhibits no discernible features under ambient daylight and only reveals the encoded information when exposed to ultraviolet light. A crucial transformation occurs when Pattern I is exposed to methanol vapor. This treatment induces a specific red shift in the emission wavelength, leading to the appearance of Pattern II. Previously hidden data associated with the URL of the research team's website is simultaneously decrypted. By scanning the altered pattern with a mobile phone camera under ultraviolet light, the hidden information can be made legible.

[0143] In contrast, any attempts to decrypt Pattern II using the same scanning process but under natural light conditions were unsuccessful as the embedded information remained obscured. This experimental validation establishes the practicality and effectiveness of dual-mode fluorescent 3D patterns, encrypted through the synergistic application of UV light and solvent vapor interaction. The method for fabricating such patterns is both efficient and simple, leveraging the inherent advantages of the modified polymer. These advantages include high fluorescence quantum yield and excellent film-forming ability, which conveniently eliminates the necessity for external dopants or the risk of dye leaching. The successful execution highlights the versatility and adaptability of AIE-active materials in the field of security technology, providing a new avenue for the development of complex, customizable encryption systems.

[0144] The present invention provides a series of AIE fluorescent precursors with TEMPO radicals as precursors for mechanical radical coupling. In a preferred case, ball milling is used as a physical strategy for in situ mechanical radical coupling of universal polymers with AIE fluorescent precursors, thereby covalently embedding the AIE moiety into the polymer backbone. This method enables the easy conversion of non-luminescent polymers (including PS, PMMA, and PPS) into bright luminescent materials. The resulting AIE-modified luminescent polymers benefit from the inherent AIE moiety and exhibit long fluorescence lifetime and high PLQY.

[0145] Leveraging these advances, the present invention successfully utilized the resulting AIE-modified light-emitting polymers for 3D printing applications, achieving high fluorescence intensity with minimal material incorporation. Furthermore, the excellent film-forming ability of the light-emitting polymer facilitates the creation of thin films for information storage and encryption. The sensitivity of the AIE moiety to solvent polarity, coupled with the unique visibility of UV light, enables the formation of dual-mode encrypted 3D fluorescent patterns. Essentially, the intrinsically high quantum yield of solid-state AIE materials facilitates the efficient "turn-on" of fluorescence from fluorescent precursors. The mechanical radical coupling technique does not require complex chemical synthesis and has broad applicability across a variety of fluorescent precursors and polymers.

[0146] The above embodiments are only used to illustrate the principles of the present invention and should not be understood as any limitation to the present invention. The above embodiments can be modified by a person skilled in the art without departing from the scope of the present invention as defined by the following claims.

Claims

1. An aggregation-induced emission fluorophore precursor suitable for preparing a light-emitting polymer, wherein the aggregation-induced emission fluorophore precursor has the following main structural formula: wherein R1, R2, R3 and R4 are independently selected from linear, branched, or cyclic alkyl groups, alkylphenyl groups, alkylthienyl groups, and other alkyl aromatic groups containing 2 to 40 carbon atoms, and wherein one or more non-adjacent carbon atoms are optionally substituted by –O–, –S–, –C(O)–, –C(O–)–O–, –O–C(O)–, –O–C(O)–O–, or –C≡C–, and wherein one or more hydrogen (H) atoms are optionally replaced by fluorine (F), chlorine (Cl), bromine (Br), iodine (I), or cyanide (CN), or represent aromatic, heteroaromatic, aryloxy, heteroaryloxy, aromatic carbonyl, heteroaromatic carbonyl, aromatic carbonyloxy, heteroaromatic carbonyloxy, aryloxycarbonyl, or heteroaryloxycarbonyl groups having a ring of 4 to 30 atoms, and these ring molecules are unsubstituted or substituted by one or more non-aromatic groups; wherein R5 has structural formula (I) or structural formula (II): Donor-π bridge-(I) Donor-acceptor-π bridge-(II) The π bridges are independently selected from the following groups: wherein the receptors are independently selected from the following groups: Where R5 is independently selected from the following groups:

2. The aggregation-induced emission fluorophore precursor according to claim 1, wherein The aggregation-induced emission fluorophore precursors are independently selected from the following groups:

3. The aggregation-induced emission fluorophore precursor according to claim 1, wherein Under ultraviolet excitation, the aggregation-induced emission fluorophore precursor exhibits very weak fluorescence in the free radical form and strong fluorescence in the reduced form.

4. A method for preparing a light-emitting polymer, comprising: Providing the aggregation-induced emission fluorophore precursor (AIE pre-fluorophore) as claimed in claim 1; Providing generic polymers; delivering the aggregation-induced emission fluorophore precursor and the universal polymer to a container to form a mixture; The mixture in the container is subjected to mechanochemical agitation to form a reaction mixture in which macromolecular free radicals generated by mechanochemical agitation of the general polymer (macromolecular radicals) can covalently link with the free radical sites of the aggregation-induced emission fluorophore precursor, resulting in the formation of new covalent bonds, thereby forming an aggregation-induced emission-modified (AIE-modified) light-emitting polymer; and The reaction mixture is purified to remove any unreacted free radicals and other low molecular weight residues to obtain the final product of the light-emitting polymer.

5. The method according to claim 4, wherein The general polymer includes polystyrene (PS), polymethylmethacrylate (PMMA) or polyphenylene sulfide (PPS).

6. The method according to claim 4, wherein The container is a ball mill.

7. The method according to claim 4, wherein The mechanochemical stirring is a ball milling process.

8. The method according to claim 7, wherein The ball milling speed is less than or equal to 1000 rpm.

9. The method according to claim 7, wherein The ball milling time is less than or equal to 60 minutes.

10. The method according to claim 4, wherein The aggregation-induced emission (AIE-modified) light-emitting polymer is manufactured by a solvent-free process.

11. The method according to claim 4, wherein The aggregation-induced emission (AIE-modified) light-emitting polymer is prepared by in-situ mechanoradical coupling of a general polymer with an aggregation-induced emission fluorophore precursor (AIE pre-fluorophore).

12. The method according to claim 4, wherein Under ultraviolet excitation, the aggregation-induced emission (AIE-modified) light-emitting polymer exhibits weak fluorescence in a dilute solution state and strong fluorescence in a solid state.

13. The method according to claim 4, wherein The aggregation-induced emission (AIE-modified) light-emitting polymer has a wide spectrum that can be adjusted and covers a wavelength range of 400 to 900 nanometers.

14. The method according to claim 4, wherein The purification procedure involved gel permeation chromatography.

15. A security document comprising: a substrate; as well as a marking layer having coded information, formed by printing the light-emitting polymer prepared as claimed in claim 4, wherein the marking layer is formed or placed on a substrate; The light-emitting polymer has the characteristic of absorbing light with a wavelength lower than 400 nm, and when the light-emitting polymer is exposed to ambient sunlight, the light-emitting polymer does not show any color and does not emit fluorescence; Wherein, under the irradiation of light below 400nm, the light-emitting polymer absorbs light with a wavelength below 400nm, thereby emitting fluorescence or showing color, and generating a readable contrast difference between the marking layer with coded information and the substrate.

16. The method according to claim 15, wherein The security document includes a 3D printed document, an information-encoded document or an anti-counterfeiting document.

17. A dual-mode security document comprising: a substrate; as well as a marking layer having coded information, formed by printing the light-emitting polymer prepared as claimed in claim 4, wherein the marking layer is placed on the substrate and forms a plurality of regions; The light-emitting polymer has the characteristic of absorbing ultraviolet light. When the light-emitting polymer is exposed to ambient sunlight, the light-emitting polymer does not show any color and does not emit fluorescence. Wherein, under ultraviolet light irradiation, the light-emitting polymer absorbs ultraviolet light, thereby emitting light with a first set of wavelengths in the marking layer with coded information, which displays color or emits fluorescence; The characteristic of the light-emitting polymer is that when the light-emitting polymer is exposed to polar solvent vapor, it interacts with the polar solvent molecules, thereby causing the emission wavelength to red-shift; Among them, when exposed to ultraviolet light and the vapor of a polar solvent at the same time, the light-emitting polymer is exposed to the vapor of a polar solvent, thereby red-shifting the first set of wavelengths to the second set of wavelengths under ultraviolet light, showing color or emitting fluorescence, and converting the encoded information layer into a decoded information layer.

18. The method according to claim 17, wherein The dual-mode security document includes a 3D printed document, an information-encoded document, or an anti-counterfeiting document.

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