Organic fluorescent material with AIE performance and preparation method and application thereof

Abstract

The invention discloses an organic fluorescent material with AIE performance and a preparation method and application thereof, and belongs to the technical field of AIE materials.The AIE material with water solubility is prepared by modifying the structure of AIE micromolecules, latent fingerprint development under a soaking method can be achieved by means of the AIE performance, and the AIE performance is improved. Due to the water solubility, the aqueous solution of the material can be developed by using an ultrasonic atomizer through a spraying method; in addition, a layered double hydroxide (LDHs) loading strategy is utilized, aggregation of AIE molecules on a solid-phase interface is promoted through electrostatic interaction, and effective development of porous material fingerprints through a powder method is achieved; the organic fluorescent material with AIE performance prepared by the invention can realize optimal latent fingerprint detection in different scenes by using a soaking method, a spraying method and a powder spraying method.

Description

Organic fluorescent materials with AIE properties, their preparation methods and applications Technical Field

[0001] This invention belongs to the field of AIE materials technology, specifically relating to organic fluorescent materials with AIE properties, their preparation methods, and applications. Background Technology

[0002] Fingerprint evidence is the most reliable means of biometric identification due to its uniqueness and stability. However, over 90% of fingerprints collected at crime scenes are latent fingerprints, tiny traces formed by secretions such as sweat and sebum that are invisible to the naked eye and require special imaging techniques to reveal. Even more challenging is the low success rate of existing technologies in practical applications, particularly in detecting fingerprints on porous materials, against complex backgrounds, or in aged fingerprints. This directly impacts the accuracy of forensic identification and the efficiency of case investigation.

[0003] The hierarchical structure of latent fingerprints determines their evidentiary value. The structure of latent fingerprints is divided into three levels. The first level encompasses the macroscopic features of the fingerprint; the second level includes detailed features such as ridge bifurcation, endpoints, and islands; these two levels constitute the main basis for current fingerprint comparison. The third level focuses on microscopic morphology such as sweat pores and ridge edges. Although it requires higher resolution developing techniques, it provides more accurate individual identification information. Because latent fingerprints are invisible, various methods have been developed to visualize them. Traditional physical and chemical developing methods, such as the ninhydrin method, cyanoacrylate fumigation method, and magnetic powder method, while effective under specific conditions, generally suffer from limitations such as complex operation, high toxicity, and poor selectivity. In recent years, fluorescent materials have shown great potential in the field of latent fingerprint detection due to their high sensitivity, high contrast, and rapid response characteristics. In particular, organic fluorescent dyes, with their tunable molecular structures and mature synthesis methods, provide ample space for the development of novel developing agents.

[0004] However, traditional organic fluorescent materials face the fundamental challenge of aggregation-induced quenching (ACQ) in practical applications. When fluorescent molecules aggregate at high concentrations or in a solid state, the π-π stacking between molecules leads to enhanced nonradiative transitions, resulting in a sharp decrease in fluorescence intensity. This phenomenon severely restricts the practical application of fluorescent materials in latent fingerprint detection. In recent years, research on aggregation-induced emission (AIE) materials has solved this problem. These materials exhibit increased fluorescence intensity even during aggregation. AIE fluorescent probes, through hydrophilic-hydrophobic interactions, can achieve rapid and efficient latent fingerprint development and are currently under extensive research.

[0005] Despite the immense potential of AIE materials in latent fingerprint detection, existing systems still suffer from significant shortcomings. First, most AIE materials require a mixture of organic solvents and water to induce aggregation. The use of organic solvents not only poses a health risk to operators but also damages biological evidence such as DNA in fingerprints, affecting subsequent multi-dimensional forensic analysis. Second, even with the development of water-soluble AIE probes, traditional solution immersion or spraying methods are extremely ineffective when processing porous materials (such as wood, leather, and paper). The solution penetrates into the material, resulting in severe background fluorescence and blurred fingerprint details. This technical bottleneck severely limits the practical application of AIE materials in complex crime scenes. Furthermore, existing research largely focuses on optimizing single development modes, lacking a systematic multi-mode integration strategy, making it difficult to meet the diverse needs of different substrate materials and scene conditions. Therefore, developing a multi-mode latent fingerprint development system based on a single AIE material holds promise for improving the application of AIE materials in this field. Summary of the Invention

[0006] This invention provides organic fluorescent materials with AIE properties, their preparation methods, and applications. By modifying the structure of AIE small molecules, water-soluble AIE materials are prepared. The prepared materials can achieve latent fingerprint development based on their AIE properties, and can achieve optimal latent fingerprint detection in different scenarios using immersion, spraying, and powder spraying methods.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] There are two types of organic fluorescent materials with AIE properties, each with different emission colors and lipid-water partition coefficients, named RA-1 and RA-2, respectively, with the following structures:

[0009] .

[0010] A method for preparing organic fluorescent materials with AIE properties includes the following steps:

[0011] S1: Pyridine-4-boronic acid, 2-bromothiophene and catalyst are placed in a reaction flask, wherein the molar ratio of pyridine-4-boronic acid and 2-bromothiophene is 1:(1-1.2). Solvent is added, the reaction system is kept oxygen-free, and the reaction is carried out under reflux at 105℃ for 6-12 hours by Suzuki coupling reaction to obtain compound R1.

[0012] S2: Compound R1 and N-bromosuccinimide (NBS) are placed in a reaction flask with a molar ratio of 1:(1-1.4). A solvent is added, and the reaction system is kept oxygen-free. Compound R2 is obtained by Wohl-Ziegler reaction for 6-12 hours.

[0013] S3: Place compound R2, precursor and catalyst in a reaction flask, add solvent, keep the reaction system oxygen-free, and react under reflux to obtain intermediate product;

[0014] S4: Place the intermediate product, 2-bromoethanol and catalyst in a reaction flask, add solvent, keep the reaction system oxygen-free, and obtain the target compound RA-1 or the target compound RA-2 through a nucleophilic substitution reaction under reflux conditions.

[0015] In the steps described above, the reaction system is preferably carried out under an argon atmosphere to ensure an oxygen-free environment.

[0016] When the target compound is RA-1, the specific process of S3 is as follows: R2, diphenylamine and catalyst are placed in a reaction flask, the molar ratio of compound R2 to diphenylamine is 1:(1-1.2), solvent is added, the reaction system is kept oxygen-free, and compound A1 is obtained by Buchwal-Hartwig amination reaction for 12 hours under reflux conditions.

[0017] When the target compound is RA-2, the specific process of S3 is as follows: R2, 4-(diphenylamino)phenylboronic acid and catalyst are placed in a reaction flask, and the molar mass ratio of compound R2 to 4-(diphenylamino)phenylboronic acid is 1:(1-1.2). Solvent is added, the reaction system is kept oxygen-free, and compound A2 is obtained by Suzuki coupling reaction under reflux conditions for 6-12 hours.

[0018] When the target compound is RA-1, the specific process of S4 is as follows: Compound A1, 2-bromoethanol and catalyst are placed in a reaction flask, wherein the molar ratio of A1 to 2-bromoethanol is 1:(1-2.4); solvent is added, the reaction system is kept oxygen-free, and compound RA-1 is obtained by nucleophilic substitution reaction under reflux conditions for 48 hours.

[0019] When the target compound is RA-2, the specific process of S4 is as follows: compound A2, 2-bromoethanol and catalyst are placed in a reaction flask, wherein the molar ratio of A2 to 2-bromoethanol is 1:(1-2.4), solvent is added, the reaction system is kept oxygen-free, and compound RA-2 is obtained by nucleophilic substitution reaction under reflux conditions for 48 hours.

[0020] The organic fluorescent material with AIE properties prepared above can be used for latent fingerprint detection, and latent fingerprint detection can be achieved in different scenarios using immersion method, spray method and powder spraying method.

[0021] When using the powder spraying method to detect fingerprints in porous materials, RA-2@LDHs composite material was obtained by loading RA-2 with layered double metal hydroxides (LDHs). The electrostatic interaction promotes the aggregation of AIE molecules at the solid-phase interface, thus achieving effective development of fingerprints in porous materials by the powder spraying method.

[0022] Beneficial Effects: This invention provides organic fluorescent materials with AIE properties, their preparation methods, and applications. By modifying the structure of AIE small molecules, water-soluble AIE materials are prepared, and their photophysical and latent fingerprint detection properties are verified. The latent fingerprint detection material provided by this invention can achieve latent fingerprint development using the immersion method due to its AIE properties, while its water solubility allows for development using an ultrasonic atomizer via spraying. Furthermore, a layered double hydroxide (LDH) loading strategy is utilized to promote the aggregation of AIE molecules at the solid-phase interface through electrostatic interactions, achieving effective development of fingerprints on porous materials using the powder spraying method. The material of this invention can achieve optimal latent fingerprint detection in different scenarios using immersion, spraying, and powder spraying methods. Attached Figure Description

[0023] Figure 1 is a flowchart of the preparation process of organic fluorescent materials with AIE performance in the embodiments of the present invention;

[0024] Figure 2 is a flowchart of the preparation process of the RA-2@LDHs composite material in the embodiment of the present invention;

[0025] Figure 3 shows the concentrations of RA-1 and RA-2 in toluene (1×10⁻⁶). -5 (a) Normalized UV-Vis absorption spectrum and (b) Normalized emission spectra with λ wavelengths of 464 nm and 466 nm in M);

[0026] Figure 4 shows the UV-Vis absorption spectra of aqueous solutions of RA-1(a) and RA-2(b) at different concentrations. Inset: linear relationship curves of absorbance of RA-1(a) at 469 nm and RA-2(b) at 459 nm as a function of concentration, and photographs of aqueous solutions of the two at different concentrations.

[0027] Figure 5 shows (a) the different THF ratios (f) of RA-1 in a THF / water mixture. n Emission spectrum under (λ), inset: maximum emission wavelength (λ) max The curves showing the variation of RA-1 with different proportions in a THF / water mixture (c=5×10) -5 M); (b) RA-2 in different THF / water mixtures (f n Emission spectrum under (λ), inset: maximum emission wavelength (λ) maxThe curves showing the variation of RA-2 with different proportions in a THF / water mixture (c=1×10) -5 (m); (c) The image shows the change in RA-1 emission intensity after adding different proportions of THF to the water; (d) The image shows the change in RA-2 emission intensity after adding different fractions of THF to the water.

[0028] Figure 6 shows the molecular surface orbital distributions of HOMO and LUMO for RA-1 and RA-2 obtained based on the B3LYP / 6-31G* algorithm;

[0029] Figure 7 shows fingerprint images and grayscale analysis obtained by soaking in RA-2 aqueous solution at different concentrations and times. (a) Different concentrations, (b) Different times, (c) Grayscale analysis of the blue line in Figure a, (d) Grayscale analysis of the blue line in Figure b (fingerprint images were taken under 365 nm light excitation).

[0030] Figure 8 shows (a) fluorescence response of common substances in LFPs using 60 μL RA-2 detection solution under 365 nm UV irradiation, (b) dynamic light scattering (DLS) analysis of RA-2 in aqueous solution (40 μM), (c) transmission electron microscopy (TEM) image of RA-2 (40 μM), and (d) RA-2 (40 μM) in a solution containing 1 × 10⁻⁶ ions. -4 DLS analysis of M oleic acid (OA) in a 10% methanol aqueous solution, (e)RA-2 (40 μM) in a solution containing 1×10 -4 TEM in a 10% methanol aqueous solution of M oleic acid (OA);

[0031] Figure 9 shows (a) the development of LFPs on glass using composite materials: the top image is under sunlight and the bottom image is under 365 nm light excitation; from left to right are kaolin, cellulose, starch, hydrotalcite and montmorillonite; (b) images of LFPs on glass developed on RA-2@LDHs (different mass ratios) and the gray values ​​on the blue lines.

[0032] Figure 10 shows the (a) infrared spectrum and (b) X-ray diffraction spectrum of LDHs, RA-2, and RA-2@LDHs;

[0033] Figure 11 shows TEM images of the composite materials: (a) RA-2, (b) LDHs, and (c) RA-2@LDHs.

[0034] Figure 12 shows the Br elemental analysis of the composite material, (a) RA-2, (b) RA-2@LDHs;

[0035] Figure 13 shows the evaluation of the latent fingerprint detection effect of three processing methods: immersion method (a), spray method (b), and powder application method (c): level 1 detail of LFP image, blue line gray value, and level 2-3 detail of LFP (under 365nm light excitation).

[0036] Figure 14 shows the detection of LFPs by immersion method using freshly prepared RA-2 aqueous solution (40 μM) and solution stored for 3 months;

[0037] Figure 15 shows the natural aging of LFPs after development by immersion method for 1-7 days, and the gray value analysis of the blue-lined part.

[0038] Figure 16 shows the detection of LFPs by spray method using freshly prepared RA-2 aqueous solution (40 μM) and solution stored for 3 months. The analysis was carried out by measuring the change in fluorescence intensity between the fingerprint ridges and grooves in the blue lines.

[0039] Figure 17 shows the LFPs after natural aging for 1-7 days using the spray method, and the grayscale value analysis of the blue-lined part; Figure 18 shows the RGB true color photographs of LFPs on different substrates developed by RA-2 (under 365 nm light excitation). Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0041] Example 1

[0042] Synthesis of compound R1

[0043] In a 250 mL double-necked reaction flask, pyridine-4-boronic acid (1.22 g, 10 mmol), 2-bromothiophene (1.63 g, 10 mmol), tetrakis(triphenylphosphine)palladium (0.58 g, 0.5 mmol), and potassium carbonate (2.7 g, 20 mmol) were dissolved in 20 mL of water and 100 mL of a mixed solution of 1,4-dioxane. The reaction was carried out at 105 °C for 6–12 h under reflux in a nitrogen atmosphere. The mixture was then cooled to room temperature, washed three times with saturated brine (50 mL), and extracted with ethyl acetate. The organic layer was dried over anhydrous MgSO4, concentrated under reduced pressure, and the residue was purified by preparative thin-layer chromatography using silica gel (eluent: ethyl acetate: petroleum ether = 1:1) to obtain the target compound R1 (1.8 g, 8.9 mmol), which was a white solid with a yield of 89%. 1H NMR (400 MHz, DMSO-d6)δ8.58–8.56 (m, 2H), 7.81 (dd, J = 3.7, 1.2 Hz, 1H), 7.74 (dd, J = 5.1, 1.1 Hz, 1H),7.66 – 7.63 (m, 2H), 7.22 (dd, J = 5.1, 3.7 Hz, 1H).

[0044] Example 2

[0045] Synthesis of compound R2

[0046] In a 250 ml single-necked flat-bottom flask, R1 (0.96 g, 6 mmol) and N-bromosuccinimide (1.2 g, 6.6 mmol) were dissolved in a mixture of 50 ml acetic acid and 50 ml dichloromethane. The reaction was carried out under nitrogen atmosphere in the dark for 6–12 h. The mixture was concentrated under reduced pressure, and the residue was purified by preparative thin-layer chromatography using silica gel (eluent: ethyl acetate: petroleum ether = 1:1) to obtain the target compound R2 (0.892 g, 3.72 mmol), which was a yellowish-white solid with a yield of 62%. 1H NMR (400 MHz, DMSO-d6) δ 8.58 (d, J = 6.2 Hz, 2H), 7.67 (d, J = 3.9 Hz, 1H), 7.61 (d, J =6.2 Hz, 2H), 7.36 (d, J = 3.9 Hz, 1H).

[0047] Example 3

[0048] Synthesis of compound A1

[0049] In a 100 mL double-necked reaction flask, diphenylamine (0.338 g, 2 mmol), R2 (0.517 g, 2.15 mmol), sodium tert-butoxide (0.382 g, 4 mmol), tri-tert-butylphosphine tetrafluoroborate (0.116 g, 0.4 mmol), and tris(dibenzylacetone)palladium (0.1 g, 0.1 mmol) were dissolved in 50 mL of toluene. The mixture was refluxed at 120 °C for 12 h under nitrogen protection, then cooled to room temperature, washed three times with saturated brine (50 mL), and extracted with ethyl acetate. The organic layer was dried over anhydrous MgSO4, concentrated under reduced pressure, and purified by preparative thin-layer chromatography using silica gel (eluent: ethyl acetate: petroleum ether = 1:1) to obtain the target compound A1 (0.39 g, 1.2 mmol), which was a green solid with a yield of 60%. 1 H NMR (400 MHz, DMSO-d6) δ 8.50 – 8.46 (m, 2H), 7.64 (d, J = 4.0 Hz, 1H), 7.52 – 7.48 (m, 2H),7.39 – 7.34 (m, 4H), 7.13 (dd, J = 11.3, 7.5 Hz, 6H), 6.69 (d, J = 4.0 Hz,1H).

[0050] Example 4

[0051] Synthesis of compound A2

[0052] In a 100 mL double-necked reaction flask, 4-(diphenylamino)phenylboronic acid (0.3 g, 1 mmol), R2 (0.24 g, 1 mmol), tetra(triphenylphosphine)palladium (0.06 g, 0.05 mmol), and potassium carbonate (0.276 g, 2 mmol) were dissolved in 40 mL of a mixture of 1,4-dioxane and 10 mL of water. The reaction was carried out under nitrogen protection and reflux at 105 °C for 6–12 h, followed by cooling to room temperature. The mixture was washed three times with saturated brine (50 mL) and extracted with ethyl acetate. The organic layer was dried over anhydrous MgSO4 and concentrated under reduced pressure. The residue was purified by preparative thin-layer chromatography using silica gel (eluent: ethyl acetate: petroleum ether = 1:1) to obtain the target compound (0.32 g, 0.8 mmol). It was a yellow solid with a yield of 80%. 1H NMR (400 MHz, DMSO-d6) δ 8.56(d, J = 5.2 Hz, 2H), 7.81 (d, J = 3.9 Hz, 1H), 7.62 (d, J = 8.7 Hz, 4H), 7.50(d, J = 3.9 Hz, 1H), 7.37 – 7.31 (m, 4H), 7.13 – 7.04 (m, 6H), 6.99 (d, J =8.7 Hz, 2H).

[0053] Example 5

[0054] Synthesis of compound RA-1

[0055] In a 100 ml two-necked flask, Al (0.32 g, 1 mmol), 2-bromoethanol (0.186 g, 1.5 mmol), tetrabutylammonium iodide (0.36 g, 1 mmol), and potassium iodide (0.6 g, 4 mmol) were dissolved in 100 ml of acetonitrile. The mixture was refluxed at 70 °C for 48 h under nitrogen protection. The solution was filtered, washed with acetonitrile, and dried to give RA-1 (0.28 g, 0.6 mmol), which was a red solid (0.28 g, 0.75 mmol), with a yield of 75%. 1H NMR (400 MHz, DMSO-d6) δ 8.56 (d, J = 6.8Hz, 2H), 8.07 (d, J = 4.4 Hz, 1H), 7.99 (d, J = 6.7 Hz, 2H), 7.48 (d, J = 8.0Hz, 4H), 7.38 – 7.27 (m, 6H), 6.51 (d, J = 4.4 Hz, 1H), 5.20 (t, J = 5.2 Hz, 1H), 4.41 (t, J = 5.0 Hz, 2H), 3.78 (q, J = 5.1 Hz, 2H).

[0056] Example 6

[0057] Synthesis of compound RA-2

[0058] In a 100 mL two-necked flask, A2 (0.4 g, 1 mmol), 2-bromoethanol (0.186 g, 1.5 mmol), tetrabutylammonium iodide (0.36 g, 1 mmol), and potassium iodide (0.6 g, 4 mmol) were dissolved in 100 mL of acetonitrile. The mixture was refluxed at 70 °C for 48 h under nitrogen protection. The solution was filtered, washed with acetonitrile, and dried to give RA-2 (0.31 g, 0.6 mmol), a deep red solid, in 60% yield.1 H NMR (400 MHz, DMSO-d6) δ 8.84 (d, J = 6.8 Hz, 2H), 8.32 (d,J = 6.9 Hz, 2H), 8.28 (d, J = 4.1 Hz, 1H), 7.72 – 7.68 (m, 3H), 7.37 (t, J =7.9 Hz, 4H), 7.13 (dd, J = 18.2, 7.4 Hz, 6H), 7.00 (d, J = 8.7 Hz, 2H), 5.25(t, J = 5.3 Hz, 1H), 4.54 (t, J = 4.9 Hz, 2H), 3.84 (q, J = 4.8 Hz, 2H).

[0059] Example 7

[0060] Synthesis of composite material RA-2@XXX

[0061] 50 mg of RA-2 solid powder was co-dispersed with 1 g of substrate material in 30 ml of methanol. The substrate material was selected as inexpensive, readily available, and highly absorbent, including kaolin, cellulose, starch, hydrotalcite, and montmorillonite. The resulting suspension was sonicated at 40 W for 10 minutes, and then the solid product was obtained by centrifugation (9000 rpm, 3 min). o After being dried in an oven at C for 12 hours, the powder was ground into powder and sieved through a 100-mesh sieve to obtain 1.3 g of pink composite material.

[0062] The photophysical properties and latent fingerprint detection performance of the prepared materials described above will be verified below.

[0063] Test Example 1

[0064] RA-1 and RA-2 in toluene (c = 1×10) -5 The UV-Vis absorption spectrum of M is shown in Figure 3(a). Two distinct absorption bands were observed, with the shorter wavelength absorption peak attributed to the aromatic structures within the two molecules. 1The transition is a π-π* transition. The maximum absorption peak at longer wavelengths is attributed to intramolecular ICT, specifically at 467 nm and 481 nm. This redshift difference is mainly due to the different electron-donating abilities of the electron-donating groups diphenylamine and triphenylamine in the two molecules. Similarly, this can also be seen from the emission spectrum in Figure 3(b). The electron-donating ability of diphenylamine in RA-1 is not as strong as that of triphenylamine in RA-2, which also leads to the redshift of emission. RA-1 emits a yellow-green light at 545 nm in toluene, while RA-2 emits an orange-yellow light at 586 nm, showing a redshift of 41 nm. This longer wavelength emission is beneficial for improving the contrast of latent fingerprints after development and the ability to resist background fluorescence interference.

[0065] Test Example 2

[0066] Taking RA-1 as an example, aqueous solutions of different concentrations were prepared as shown in Figure 4. Figure 4(a) shows the UV-Vis absorption spectra at different concentrations, with a maximum absorption peak at 469 nm. A linear fit was performed by plotting the concentration against the absorbance at 469 nm, and the fitting constant was close to 1, satisfying the Lambert-Beer law, indicating complete solubility within this range. Due to the low degree of intramolecular conjugation of RA-1, the absorbance was low at low concentrations, and its water solubility was only measured at 30-50 μM. In contrast, as shown in Figure 4(b), RA-2 exhibits more comprehensive water solubility at 10-50 μM. As shown in Table 1, the lipid-water partition coefficients of the two were tested, with RA-1 showing a coefficient of 0.38. Compared to RA-1, RA-2 has an additional lipophilic benzene ring, resulting in increased lipophilicity, with a lipid-water partition coefficient of 1.31. Increased lipophilicity is more conducive to the binding of fluorescent probes to lipids in fingerprints.

[0067] Table 1. Lipid-water partition coefficients (P) of RA-1 and RA-2

[0068] C o (μM)C w (μM)C o / C w P = Log (C o / C w )RA-1106.0643.932.410.38RA-2285.9614.0420.361.31 surface

[0069] Test Example 3

[0070] Excellent water solubility is one of the necessary conditions for latent fingerprint developers, but even more important is their luminescent properties in the aggregated state, which is related to the effectiveness of latent fingerprint development. Therefore, the AIE performance of the compounds was studied. To investigate the AIE performance of RA-1 and RA-2, their fluorescence emission characteristics in a mixed solvent system were tested. It is worth noting that since both RA-1 and RA-2 are highly polar compounds and exhibit some solubility in water, water was used as the good solvent in this experiment, while tetrahydrofuran (THF) was used as a poor solvent that induces molecular aggregation, which is the opposite of the role of the solvent in traditional AIE testing. As shown in Figure 5(ab), the emission spectra of both were tested in a mixed solution of THF and water. With the increase of THF content, the molecules gradually began to aggregate, and the fluorescence intensity increased significantly; when the THF content was 80%, the brightness reached its maximum, and further addition of THF at this point did not increase the brightness, exhibiting a clear AIE phenomenon (Figure 5c-d). The difference is that RA-1 showed better fluorescence emission at high concentrations (c = 5 × 10⁻⁶). -5 The AIE phenomenon was only observed at M), and the fluorescence intensity increased approximately 12-fold from the dispersed state (THF content 0%) to the aggregated state (THF content 80%). In contrast, RA-2 showed a significantly lower fluorescence intensity at low concentrations (c = 1×10⁻⁶). -5 The fluorescence intensity of RA-2 was enhanced by 29 times, indicating a more significant fluorescence enhancement. RA-1 has a diphenylamine substituent with two rotating benzene rings, while RA-2 has a triphenylamine substituent with three rotating benzene rings. When they aggregate, intramolecular motion is restricted (RIM), reducing nonradiative transitions and increasing luminescence efficiency. Compared to RA-1, RA-2 exhibits a greater degree of RIM after aggregation, resulting in a more pronounced AIE phenomenon and making it more promising as a latent fingerprint probe.

[0071] Test Example 4

[0072] To further elucidate the relationship between photophysical properties and molecular structure, quantum chemical calculations were performed using DFT. Figure 6 shows the electron cloud distribution of the ionic compounds RA-1 and RA-2. It can be seen that the introduction of the D-π-A structure enhances the ICT effect of the molecules, and there is a significant separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LOMO). The N atom on pyridine acts as the main electron-withdrawing site, causing the LOMO energy levels of both molecules to be mainly distributed around pyridine. The HOMO, however, is distributed on the electron-donating groups diphenylamine and triphenylamine. Due to the difference in electron-donating ability, the HOMO of RA-1 is -8.08 eV, while the HOMO of RA-2, with its stronger electron-donating group, is -7.31 eV. This difference also results in a significant energy level gap ΔE between the two molecules. gThe energy levels decrease sequentially, resulting in a significant reduction in the energy difference between the HOMO and LUMO levels. This result is consistent with the redshift observed in the emission spectrum during the experiment.

[0073] Test Example 5

[0074] Based on the aforementioned studies on the photophysical properties and structure-activity relationship of RA-1 and RA-2, it was confirmed that RA-2 has greater application potential in latent fingerprint development due to its excellent water solubility, significant AIE properties, and good affinity for fingerprint lipids. Therefore, the performance of RA-2 as a latent fingerprint developer was systematically evaluated, including the optimization of three different application methods (solution immersion, spraying, and powdering), development mechanism, anti-aging properties, and applicability to various substrates.

[0075] Figure 7 preliminarily evaluates the effect of RA-2 aqueous solution on the development of latent fingerprints using the immersion method. Fingerprints on aluminum foil were immersed in RA-2 aqueous solutions of different concentrations for 30 seconds. After removing excess solution from the foil, fingerprint images were captured using a smartphone. Background fluorescence was removed using IMAGEJ software, and the development effect was further evaluated using grayscale analysis. At a low concentration of 10 μM, the fingerprint color was yellowish-green due to the degree of aggregation. At a high concentration of 50 μM, excessive RA-2 residue on the substrate stained the background, resulting in lower brightness in the processed fingerprint image. Based on comprehensive evaluation, 40 μM was the optimal concentration. Similarly, the effect of immersion time was studied using this concentration, and it was found that the brightness reached its upper limit after immersion for 5 seconds, confirming 5 seconds as the optimal development time.

[0076] While immersion methods can achieve good latent fingerprint development, their practical application is limited and they waste a significant amount of developing solution. In contrast, spraying is a better choice. Ultrasonic nebulizers, which spray uniform water droplets, are widely used in latent fingerprint examination. Water as a solvent does not damage the ultrasonic nebulizer, nor does it cause respiratory harm to the user. Spraying can also effectively develop latent fingerprints.

[0077] Test Example 6

[0078] Common substances in fingerprint residues include sodium chloride, glycine, urea, glucose, lysozyme, lactic acid, and lipids. Figure 8a shows the fluorescence response of RA-2 to these substances, revealing a bright orange fluorescence response only to lipids, indicating that the probe's AIE property is excited by lipid binding. Figures 8b and 8d show the DLS analysis of RA-2, showing that the particle size of RA-2 molecules at a concentration of 40 μM is approximately 186 nm, while with the addition of oleic acid, the particle size reaches 432 nm, indicating molecular aggregation. The corresponding TEM images (Figures 8c and 8e) also illustrate that the addition of oleic acid causes RA-2 aggregation: the originally dispersed RA-2 particles aggregate under the attraction of oleic acid, exhibiting a morphology of RA-2 encapsulated by oleic acid. Furthermore, the tests of the zeta potentials of the two substances in Table 2 show that the electrostatic potential decreases after the positively charged pyridinium salt is mixed with the negatively charged oleic acid, which is evidence of electrostatic interaction. The conclusion is that RA-2 molecules are attracted to lipids in fingerprint residues through electrostatic interactions, causing the probe molecules to emit and aggregate, restricting intramolecular movement, enhancing luminescence, and thus achieving the effect of fingerprint detection.

[0079] Table 2. DLS and zeta potential analysis of RA-2 (40 μM) by adding oleic acid to water (10% methanol).

[0080] CompoundD (nm)ζPotential (mV)OA--12.46RA-2186.6216.46RA-2+OA(100μM)432.129-2.19 surface

[0081] Test Example 7

[0082] Immersion and spray methods have inherent limitations in developing latent fingerprints on porous materials. Recent studies have shown that co-doping fluorescent molecules with absorbent materials can maintain the high contrast and brightness of organic fluorescent dyes while also developing fingerprints on special substrates. The RA-2 molecule was simply blended with common, inexpensive materials such as kaolin, cellulose, starch, hydrotalcite, and montmorillonite, and its effect on glass was tested, as shown in Figure 9(a). Montmorillonite, kaolin, and starch showed the lowest brightness, while cellulose, although bright, could not reveal the grooves of the fingerprint. The hydrotalcite-based material showed excellent results. Figure 9(b) shows the doping ratio of the composite materials. Composite materials with mass doping ratios of 1%, 5%, and 10% were applied to latent fingerprint detection, and the fingerprint images were subjected to background fluorescence removal and grayscale analysis. It can be seen that the 1% material has lower brightness, while the brightness of the 10% material is not significantly different from that of the 5% material, presumably because hydrotalcite has limited loading capacity for fluorescent molecules. Based on comprehensive grayscale analysis, the material with a mass doping ratio of 5% was determined to be the optimal choice.

[0083] Test Example 8

[0084] Infrared characterization was performed on LDHs, RA-2 fluorescent molecules, and RA-2@LDHs composites. In the infrared spectrum (Figure 10a), hydrotalcite mainly exhibits a peak at 3460 cm⁻¹. -1 The stretching vibration peak of the hydroxyl group (OH) and the peak at 1365 cm⁻¹ -1 Interlayer carbonate (CO3) 2- The asymmetric stretching vibration peak of RA-2 fluorescent molecules. Characteristic peaks of RA-2 fluorescent molecules include: 1645 cm⁻¹. -1 Characteristic peak of the pyridine group; 1433 cm⁻¹ -1 The skeletal vibration peak of the thiophene ring; 1082 cm⁻¹ -1 The stretching vibration peak of the CO bond on the ethanol chain is observed. In the infrared spectrum of the RA-2@LDHs composite material, the characteristic absorption peaks of the above-mentioned hydrotalcite and RA-2 fluorescent molecules are clearly distinguishable, indicating that the RA-2 molecules have been successfully loaded onto the hydrotalcite. To determine the location of the fluorescent molecule loading, X-ray diffraction analysis was performed on the hydrotalcite and the composite material, as shown in Figure 10b. Characteristic peaks of hydrotalcite (003) and (006) were observed at 11.6° and 23.6°, indicating that the layered structure of hydrotalcite was not destroyed before and after loading the fluorescent molecules. Among them, the peak at 11.6° of the composite material loaded with fluorescent molecules did not show a shift to a lower angle or a widening of the half-peak width, indicating that the fluorescent molecules did not enter the interlayer of hydrotalcite. The weakening of the peak intensity indicates that the fluorescent molecules were loaded on the layered structure of hydrotalcite. To further understand its microstructure, TEM images of hydrotalcite, RA-2 and RA-2@LDHs were taken (Figure 11). Interestingly, RA-2 exhibits a granular morphology, unlike the layered structure of hydrotalcite. The surface of hydrotalcite loaded with fluorescent molecules changes from smooth to rough, indicating that RA-2 is loaded onto the surface of the hydrotalcite layers. The hydrotalcite layers contain negatively charged sites due to defects or other factors. In solution, the positively charged RA-2 is attracted and fixed to the hydrotalcite layers due to electrostatic interactions. As shown in Figure 12 regarding the elemental analysis of Br, the bromide ions carried by RA-2 are eventually released into the solution and removed after adsorption onto the hydrotalcite. Furthermore, the abundant hydroxyl groups on the surface of the hydrotalcite layers may lead to hydrogen bonding interactions with RA-2, ultimately making it easier for RA-2 to aggregate and adsorb onto the hydrotalcite layers.

[0085] Test Example 9

[0086] Figure 13 evaluates the development effect of latent fingerprints using three methods. Firstly, it can be observed that the fingerprint image obtained using the powder method has significant brightness under naked-eye observation, which helps to quickly locate the fingerprint in practical use. However, the high brightness also brings drawbacks, namely, the grooves on the fingerprint are also stained. This is reflected in the lowest point of the grayscale curve in Figure 13c, which is higher than the corresponding parts of the other two methods, reducing fingerprint discrimination. While the immersion method also has good brightness, the material itself has limitations: residual droplets after immersion and drying will also slightly stain the background, increasing the difficulty of latent fingerprint detection. For example, the fingerprint image in Figure 13a shows some color unevenness. In contrast, although the spray method does not provide a bright fingerprint image, the grayscale curve in Figure 13b confirms that the fingerprint discrimination is good. This is attributed to the fact that the small water droplets generated by the ultrasonic atomizer can accurately adhere to the fingerprint, achieving efficient development of latent fingerprints while saving developing reagents.

[0087] An important indicator for evaluating the effectiveness of latent fingerprint developers is the development of the fingerprint's tertiary structure. The primary structure refers to the macroscopic features of the fingerprint. The secondary structure refers to the shapes formed by different grooves on the surface, such as forks. The tertiary structure is the most detailed feature, referring to the details within the fingerprint grooves, such as individual sweat pores. As shown in Figure 13, all three development methods can reveal these details, indicating that the three application methods based on RA-2 have good development effects on latent fingerprints.

[0088] Test Case 10

[0089] Material stability has always been a key focus in the field of latent fingerprint development. Since RA-2 is dissolved in a single solvent, water, no sedimentation occurred even after the developing solution was left to stand for 3 months, indicating good stability. The solutions before and after aging were used for latent fingerprint detection using immersion and spray methods, as shown in Figures 14 and 16. Analysis was performed by measuring the change in fluorescence intensity between the ridges and grooves of the fingerprint (blue lines), and the detection results showed little difference. Furthermore, the developed fingerprints were exposed to air for 1 to 7 days. The three fingerprints after aging showed little difference, indicating good anti-aging properties of the material (Figures 15 and 17). Due to the unique layered structure of hydrotalcite, it has good water absorption; conventional storage environments can cause it to become damp, affecting its performance. RA-2@LDHs exhibit severe agglomeration due to water absorption under natural aging conditions, which significantly interferes with practical applications. Therefore, the anti-aging properties of the composite powder are not as good as those of the developing solution.

[0090] Test Example 11

[0091] In practical applications, the complexity of fingerprint substrates has always been a major challenge in this field. Therefore, the fingerprint development effects of three different application methods on various substrates were studied. As shown in Figure 18, all three methods are effective for fingerprints on smooth surfaces, but their respective advantages and disadvantages are obvious. Firstly, the powder method shows higher brightness and contrast compared to the immersion and spray methods. Comparing the immersion and spray methods, on steel and coin substrates, the immersion method shows higher brightness, but due to inherent process defects, it causes dye to adhere around the fingerprint, reducing distinguishability. Porous materials have always been a challenge in fingerprint detection. Using common materials such as wood, leather, and napkins as examples, the fingerprint development effects of the three methods on these materials were studied. The immersion and spray methods failed to develop fingerprints, and the images showed only a patch of dye, while the powder method could reveal the fingerprint. In terms of substrate universality, the powder method is superior to the two solution methods.

[0092] The embodiments described above are merely preferred embodiments of the present invention, used to explain the invention and not to limit its scope. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. An organic fluorescent material with AIE performance, characterized in that, There are two types of organic fluorescent materials, named RA-1 and RA-2, with the following structures: 、 。 2. A method for preparing organic fluorescent materials with AIE properties, characterized in that, Includes the following steps: S1: Pyridine-4-boronic acid, 2-bromothiophene, and a catalyst were mixed and added to a solvent. The reaction system was kept oxygen-free, and the mixture was subjected to a Suzuki coupling reaction under reflux conditions to obtain compound R1. The reaction formula is as follows: S2: Compound R1 and N-bromosuccinimide were mixed and a solvent was added. The reaction system was kept oxygen-free. Compound R2 was obtained via the Wohl-Ziegler reaction. The reaction equation is as follows: S3: Compound R2, the precursor, and the catalyst are added to a solvent, and the reaction system is kept oxygen-free. The reaction is carried out under reflux to obtain an intermediate product, which is: or S4: The intermediate product, 2-bromoethanol, and catalyst were placed in a reaction flask, a solvent was added, and the reaction system was kept oxygen-free. Under reflux conditions, a nucleophilic substitution reaction was carried out to obtain the target compound RA-1 or the target compound RA-2, with the following structure: 、 。 3. The method for preparing organic fluorescent materials with AIE performance according to claim 2, characterized in that, The reaction system was oxygen-free and carried out under an argon atmosphere.

4. The method for preparing organic fluorescent materials with AIE performance according to claim 2 or 3, characterized in that, When the target compound is RA-1, the specific process of S3 is as follows: compound R2, diphenylamine and catalyst are placed in a reaction flask, the molar ratio of compound R2 to diphenylamine is 1:(1-1.2), solvent is added, the reaction system is kept oxygen-free, and compound A1 is obtained by Buchwal-Hartwig amination reaction under reflux conditions.

5. The method for preparing organic fluorescent materials with AIE performance according to claim 2 or 3, characterized in that, When the target compound is RA-2, the specific process of S3 is as follows: compound R2, 4-(diphenylamino)phenylboronic acid and catalyst are placed in a reaction flask, the molar mass ratio of compound R2 and 4-(diphenylamino)phenylboronic acid is 1:(1-1.2), solvent is added, the reaction system is kept oxygen-free, and compound A2 is obtained by Suzuki coupling reaction under reflux conditions for 12 hours.

6. The method for preparing an organic fluorescent material with AIE performance according to claim 2, characterized in that, The molar ratio of pyridine-4-boronic acid and 2-bromothiophene in S1 is 1:(1-1.2).

7. The method for preparing an organic fluorescent material with AIE performance according to claim 2, characterized in that, The molar ratio of compound R1 and N-bromosuccinimide (NBS) in S2 is 1:(1-1.4).

8. The method for preparing organic fluorescent materials with AIE performance according to claim 2, characterized in that, The molar ratio of the intermediate product to 2-bromoethanol in S4 is 1:(1-2.4).

9. The application of the organic fluorescent material with AIE performance as described in claim 1, characterized in that, The organic fluorescent material is used for latent fingerprint detection, and latent fingerprint detection can be achieved in different scenarios using immersion, spraying, or powder spraying methods.

10. The application of the organic fluorescent material with AIE performance according to claim 9, characterized in that, When using the powder spraying method to detect fingerprints in porous materials, RA-2@LDHs composite material is obtained by loading RA-2 with layered bimetallic hydroxide. Through electrostatic interaction, the aggregation of AIE molecules at the solid-phase interface is promoted, thus achieving effective development of fingerprints in porous materials by the powder spraying method.

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