Water-soluble organic fluorescent molecules, methods of making and use in fingerprint detection

Abstract

The application discloses water-soluble organic fluorescent molecules, a preparation method thereof and application thereof in fingerprint detection, belongs to the field of criminal investigation science, and the obtained molecules all have good latent fingerprint developing effect. Three kinds of water-soluble organic fluorescent molecules prepared by the application have the structural formula: the molecules are designed into organic salts, the water solubility of the molecules is increased, the detection environment is more green, the TTC-1 and TTC-2 molecules both have the aggregation-induced emission (AIE) property, the light emission is stronger, and the latent fingerprint developing is more favorable. The fluorescent molecules have excellent light emission property, good solubility and fast enrichment speed of the fingerprint, and can be accurate to the tertiary structure of the fingerprint, the image of the fingerprint is clear, and the resolution is high.

Description

Technical Field

[0001] This invention belongs to the field of criminal investigation science, specifically relating to water-soluble organic fluorescent molecules, their preparation methods, and their application in fingerprint detection. Background Technology

[0002] With the rapid development of the information age, people's demands for personal information security in daily life are increasing. Confirming personal identity and its uniqueness is crucial, especially in criminal investigation and forensic medicine, where biometrics has always been the most challenging and deceptive aspect of case analysis. Fingerprint imaging technology can provide extremely valuable and powerful evidence, linking individuals with objects, locations, and specific activities, greatly improving the efficiency of case solving. For fingerprint imaging to be successful, the fingerprint on the object's surface must first be located and recorded. Therefore, researchers in this field have been dedicated to optimizing existing fingerprint imaging technologies or developing new fingerprint detection mechanisms, including improving the detection efficiency, sensitivity, and selectivity of secretory components in fingerprints. Furthermore, fingerprint detection involves three levels of detail to verify personal characteristics. Level 1 structure mainly reveals the overall ridge flow pattern, representing the macroscopic structure of the fingerprint; Level 2 structure mainly reveals some detailed points, including ridge terminations, bifurcations, and lakes; while Level 3 structure mainly reveals all the dimensional attributes of the ridges, including sweat pores, width, shape, and edge contours. Generally, level 2 and level 3 fingerprint structures have significant reference value in criminal investigations, especially the level 3 fingerprint structure features, which can further confirm fingerprint information. However, they are rarely used in automatic fingerprint identification technology because they require high-quality fingerprint images. This urgently necessitates the development of detection reagents that can detect level 3 fingerprint structures.

[0003] As is well known, fingerprint imaging relies on the interaction between fingerprint surface residues and dyes. Therefore, developing dyes with excellent lipophilicity and high sensitivity is a key research focus. Organic fluorescent molecules, with their advantages of easy preparation, high sensitivity, and strong lipophilic-lipid interactions, are well-suited for latent fingerprint development. Currently, organic fluorescent molecules (such as ninhydrin) have been developed for latent fingerprint detection, but the resulting fingerprint images have low signal-to-noise ratios and poor water solubility. Furthermore, existing organic fluorescent latent fingerprint detection reagents, due to their lipophilic and hydrophobic nature, often employ powder coating methods, which are not environmentally friendly. Developing solution-based latent fingerprint detection reagents to replace powder coating methods can reduce pollution from the detection molecules themselves; however, the use of organic solvents can damage the fingerprint. Therefore, developing water-soluble organic molecules has become paramount. On the one hand, aqueous solutions do not damage the fingerprint, effectively preserving the original fingerprint structure and facilitating the development of the fingerprint's tertiary structure; they also have no irritating odor, significantly reducing pollution and making the detection process greener and healthier. On the other hand, water-soluble detection reagents are more conducive to atomization, solving the problem of latent fingerprint detection in complex scenarios. Furthermore, developing molecules with aggregation-induced emission (AIE) properties helps enhance luminescence, which can improve the resolution of fingerprint images. Modifying organic fluorescent molecules with excellent luminescence properties to form organic salt fluorescent molecules increases the water solubility of the molecules without affecting their inherent luminescence properties. This approach offers low preparation costs, high sensitivity, and high fingerprint image resolution, demonstrating broad application prospects. Summary of the Invention

[0004] This invention provides water-soluble organic fluorescent molecules, their preparation methods, and their applications in fingerprint detection. The prepared water-soluble organic fluorescent molecules can rapidly enrich the oils on latent fingerprints, down to the tertiary structure of the fingerprint, exhibiting high sensitivity and high resolution.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A water-soluble organic fluorescent molecule, the structure of which is: Formula TTC-1, TTC-2 or Formula TTC-3.

[0007] The preparation method of the above-mentioned water-soluble organic fluorescent molecules includes the following steps:

[0008] Preparation of TTC-1 molecules: The final TTC-1 molecule with carboxylate was obtained by a one-step palladium-catalyzed Suzuki coupling reaction. The specific synthetic route is as follows:

[0009]

[0010] Preparation of TTC-2 molecules: The terminal dimethylamino group undergoes a one-step methylation reaction with iodomethane to form a quaternary ammonium salt, yielding the final TTC-2 molecule. The specific synthetic route is as follows:

[0011]

[0012] Preparation of TTC-3 molecules: TTC-3 molecules with pyridine cations were obtained in one step by the condensation reaction of aldehyde and methyl groups in an alkaline environment. The specific synthetic route is as follows:

[0013]

[0014] In the above-described method, the preparation of TTC-1 molecule (potassium 5-(4-(diphenylamino)phenyl)thiophene-2-carboxylate): the molar ratio of reactants 5-bromothiophene-2-carboxylic acid and (4-(diphenylamino)phenyl)boronic acid in the palladium-catalyzed Suzuki coupling reaction is 1:(1-1.2), preferably 1:1.2; the catalyst is tetratetraphenylphosphine palladium or bistriphenylphosphine palladium chloride, preferably tetratetraphenylphosphine palladium; the molar ratio of 5-bromothiophene-2-carboxylic acid to tetratetraphenylphosphine palladium is 1:(0.06-0.08), preferably 1:0.06; the reaction is carried out in a basic ring... The reaction is carried out under alkaline conditions, preferably with potassium carbonate to maintain the alkaline environment. The molar ratio of 5-bromothiophene-2-carboxylic acid to potassium carbonate is 1:(6-10), preferably 1:6. The solvent used is a mixture of 1,4-dioxane and water or a mixture of toluene and water, preferably a mixture of 1,4-dioxane and water. The volume ratio of 1,4-dioxane to water is 3:1. The amount of solvent added is 5-8 times the amount of feed, preferably 5 times. The reaction is carried out under reflux conditions and an argon atmosphere. The reaction temperature is 105-110°C, preferably 105°C. The reaction time is 0.5-5 h, preferably 1 h.

[0015] Preparation of TTC-2 molecule (3'-(benzo[d]thiazol-2-yl)-4'-hydroxy-N,N,N-trimethyl-[1,1'-biphenyl]-4-amino): The molar ratio of 2-aminobenzylthiol and 5-bromosalicylic acid aldehyde in the synthesis of L1 by the aldehyde-amine condensation-oxidative cyclization method is (1.1-1.3):1, preferably 1.1:1; the solvent used is dimethyl sulfoxide (DMSO); the reaction is carried out under reflux at a temperature of 180-200°C, preferably 195°C; the reaction time is 0.5-2 h, preferably 1 h.

[0016] In the synthesis of L2, the molar ratio of product L1 to (4-(dimethylamino)phenyl)boronic acid in the palladium-catalyzed Suzuki coupling reaction is 1:(1-1.1), preferably 1:1; the catalyst is tetratetraphenylphosphine palladium or bis(triphenylphosphine)palladium chloride, preferably tetratetraphenylphosphine palladium; the molar ratio of 5-bromothiophene-2-carboxylic acid to tetratetraphenylphosphine palladium is 1:(0.06-0.08), preferably 1:0.06; the reaction is carried out under alkaline conditions, preferably with potassium carbonate to maintain the alkaline environment, and 5-bromothiophene-2-carboxylic acid... The molar ratio of acid to potassium carbonate is 1:(6-10), preferably 1:6. The solvent used is a mixture of 1,4-dioxane and water or a mixture of toluene and water, preferably a mixture of 1,4-dioxane and water. The volume ratio of 1,4-dioxane to water is 3:1. The amount of solvent added is 5-8 times the amount of feed, preferably 5 times. The reaction is carried out under reflux conditions and an argon atmosphere. The reaction temperature is 105-110°C, preferably 105°C. The reaction time is 16-20 h, preferably 16-18 h.

[0017] In the methylation reaction during the synthesis of TTC-2, the molar ratio of 3-(benzo[d]thiazol-2-yl)-4'-(dimethylamino)-[1,1'-biphenyl]-4-ol to iodomethane is 1:(1.5-1.8), preferably 1:1.5; the solvent used is acetone or tetrahydrofuran, preferably acetone; the reaction temperature is 20-35℃, preferably 30℃; and the reaction time is 8-12h, preferably 8-10h.

[0018] Preparation of TTC-3 molecule ((E)-4-(2-(9H-fluorene-2-yl)vinyl)-1-(2-hydroxyethyl)pyridine-1-onium): The molar ratio of reactant 9H-fluorene-2-carboxaldehyde and 1-(2-hydroxyethyl)-4-methylpyridine-1-onium in the condensation reaction is (1.1-1.4):1, preferably 1.2:1; piperidine is 1-2 drops, preferably 2 drops; ethanol or toluene is used as the solvent, preferably ethanol, to maintain a homogeneous reaction, the reaction temperature is 80-85℃, preferably 80℃; the reaction time is 16-24h, preferably 16-18h.

[0019] The above reaction was purified by means of filtration, water washing, extraction, drying and column chromatography. Filtration was carried out by water pump filtration, water washing was carried out with distilled water or saturated potassium bicarbonate solution, and extraction solvent was ethyl acetate or dichloromethane. Drying was carried out with anhydrous sodium sulfate. Column chromatography was carried out using column chromatography methods well known in the art, with silica gel of 200-300 mesh and eluent of petroleum ether and dichloromethane (v / v) or dichloromethane and methanol (v / v).

[0020] The above-mentioned water-soluble organic fluorescent molecules are used to detect latent fingerprints. The preparation of the detection reagents and the latent fingerprint detection process include the following steps:

[0021] (a) Weigh a certain amount of water-soluble organic fluorescent molecules and dissolve them in pure water to obtain the detection reagent;

[0022] (b) Gently press your fingerprint onto different substrate materials to obtain the latent fingerprint to be tested on different substrates;

[0023] (c) Chemical impregnation method: Take a small amount of solution from step (a) and gently drop it onto the latent fingerprint to be tested in step (b). After 5 to 10 seconds, preferably 5 seconds, gently absorb the surface solution with a dropper. Gently absorb any remaining solvent with absorbent paper. Irradiate the fingerprint with a 3W 365nm UV handheld lamp and take a picture with a mobile phone to obtain the fingerprint image.

[0024] (d) Atomization method: Add the solvent from step (a) into the atomizer, spray the atomized liquid onto the latent fingerprint to be tested in step (b) for 5-10 seconds, irradiate with a 3W 365nm ultraviolet handheld lamp, and take a picture with a mobile phone to obtain the fingerprint image.

[0025] In step (a), prepare 1×10 -3 mol·L -1 The mother liquor is then gradually diluted to prepare test reagents of different concentrations; the organic solvent can be dichloromethane, tetrahydrofuran, methanol, etc., with tetrahydrofuran being preferred; the substrates used in step (b) include glass slides, tin foil, iron sheets, and A4 paper; the nebulizer in step (d) is a commercially available nano-sized nebulizer.

[0026] Beneficial Effects: This invention provides water-soluble organic fluorescent molecules, their preparation methods, and their applications in fingerprint detection. By designing the molecules as organic salts, their water solubility is increased. On one hand, this results in no irritating odor, significantly reducing environmental pollution and making the detection process greener and healthier. On the other hand, the aqueous solution reagent is more conducive to atomization, solving the problem of latent fingerprint detection in complex scenarios. The three organic salt fluorescent molecules TTC-1 to TTC-3 in this invention all possess excellent luminescence properties, good solubility, rapid fingerprint enrichment, and high sensitivity. They can all accurately detect the tertiary structure of fingerprints, producing clear images with high resolution. Furthermore, they are suitable for different substrate materials and application scenarios, and are expected to replace existing commercial latent fingerprint developers. Moreover, the synthesis and preparation of the TTC-1 molecule is simple, basically covering basic chemistry experiments for university students, and its application is novel, highly practical, and has significant practical value. Attached Figure Description

[0027] Figure 1 This is the synthetic route for water-soluble organic fluorescent molecules in the embodiments of the present invention;

[0028] Figure 2 The UV-Vis absorption spectrum of water-soluble organic fluorescent molecules in tetrahydrofuran in this embodiment of the invention (c = 1 × 10⁻⁶) -5M);

[0029] Figure 3 The emission spectrum of the water-soluble organic fluorescent molecule in tetrahydrofuran in this embodiment of the invention is shown (c = 1 × 10⁻⁶). - 5 M, λ ex TTC-1 =380nm,λ ex TTC-2 =380nm,λ ex TTC-3 =470nm);

[0030] Figure 4 The following are emission spectra of water-soluble organic fluorescent molecules in different two-component mixed solvents in embodiments of the present invention. The mixed solvents are mixtures of good and bad solvents, wherein (a) TTC-1 has tetrahydrofuran as the good solvent and n-hexane as the bad solvent; (b) TTC-2 has acetonitrile as the good solvent and water as the bad solvent (c = 1 × 10⁻⁶). -5 M, λ ex TTC-1 / TTC-2 =380nm);

[0031] Figure 5 This is a schematic diagram illustrating two different latent fingerprint development methods using water-soluble organic fluorescent molecules in embodiments of the present invention;

[0032] Figure 6 Color images showing the latent fingerprint development effect of the water-soluble organic fluorescent molecule TTC-1 on different substrate materials using the immersion method in embodiments of the present invention (c = 1 × 10⁻⁶). -4 M; fingerprint color is bright blue;

[0033] Figure 7 Color images showing the latent fingerprint development effect of the water-soluble organic fluorescent molecule TTC-1 on different substrate materials using the atomization method in this embodiment of the invention (c = 5 × 10⁻⁶). -4 M; fingerprint color is bright blue;

[0034] Figure 8 The images show detailed analysis (a) of the water-soluble organic fluorescent molecule TTC-1 in a glass slide using the immersion method in an embodiment of the present invention, and a detailed comparison (b) of the immersion method on a glass slide and tin foil (the fingerprint color is bright blue).

[0035] Figure 9 This is an example of latent fingerprint development images and detailed analysis of water-soluble organic fluorescent molecules TTC-2 and TTC-3 on a glass slide using the immersion method in embodiments of the present invention (c = 1 × 10⁻⁶). -4 M; (a) is TTC-2, fingerprint color is yellow-green; (b) is TTC-3, fingerprint color is orange-yellow). Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0037] The structural formulas of water-soluble organic fluorescent molecules are as follows:

[0038]

[0039] like Figure 1 As shown, the method for preparing the above-mentioned water-soluble organic fluorescent molecules includes:

[0040] Synthesis of TTC-1

[0041]

[0042] In a 250 ml two-necked round-bottom flask, 5-bromothiophene-2-carboxylic acid (5.00 g, 17.30 mmol), (4-(diphenylamino)phenyl)boronic acid (3.94 g, 19.02 mmol), potassium carbonate (9.55 g, 69.18 mmol), and tetraphenylphosphine palladium (1.20 g, 1.04 mmol) were dissolved in a solution of 1,4-dioxane and water in a 3:1 ratio. The reaction was carried out at 105 °C under reflux for 20 h.

[0043] After the reaction was completed and cooled to room temperature, the reaction solution was sequentially filtered, extracted, washed, dried, and purified. The cooled reaction solution was poured into a small amount of silica gel (200-300 mesh) and filtered to obtain a clear, dark green solution. The aqueous phase of the reaction solution was first extracted with dichloromethane solution, and the lower organic layer was removed. When the residue in the aqueous phase was found to be small, the organic phase was washed three times with saturated potassium bicarbonate aqueous solution. After standing and separating the layers, the organic phase was collected. Anhydrous sodium sulfate solid was added to the washed organic phase, and the mixture was stirred, filtered, and rotary evaporated to remove dichloromethane. The product was then dried under vacuum to obtain the final dark green product (5-(4-(diphenylamino)phenyl)thiophene-2-carboxylate potassium) (TTC) with a yield of 60-75%.

[0044] NMR data of TTC-1 molecules: 1 H NMR (400MHz, DMSO-d6) δ7.53(d,J=8.7Hz,2H),7.30(td,J=7.9,1.7Hz,4H),7.21(t,J=2.8Hz,2H),7.04(dd,J=13.2,7.4Hz,6H),6.96(d,J=8.7Hz,2H)

[0045] Synthesis of TTC-2

[0046]

[0047] In a 100 mL two-necked round-bottom flask, 2-aminobenzylthiol (1.37 g, 11.0 mmol) and 5-bromosalicylic acid aldehyde (2.01 g, 10.0 mmol) were dissolved in dimethyl sulfoxide (5 mL). The reaction was stirred at 195 °C for 1 hour, then cooled, and recrystallized with n-hexane (20 mL) to give white solid 2, with a yield of 93.54%.

[0048] NMR data of intermediate L1: 1 H NMR (400MHz, CDCl3) δ12.63(s,1H),8.02(d,J=8.1Hz,1H),7.94(d,J=7.9Hz,1H),7. 80(d,J=2.2Hz,1H),7.55(t,J=7.6Hz,1H),7.51–7.42(m,2H),7.02(d,J=8.8Hz,1H).

[0049]

[0050] In a 100 mL two-necked round-bottom flask, intermediate L1 (0.92 g, 3 mmol), (4-(dimethylamino)phenyl)boronic acid (0.49 g, 3 mmol), potassium carbonate (4.14 g, 30 mmol), tetrakis(triphenylphosphine)palladium (0.35 g, 0.3 mmol), 1,4-dioxane (24 mL), and water (8 mL) were added. The mixture was refluxed at 105 °C for 18 h under argon protection. After the reaction was completed, the mixture was filtered while hot. The filtrate was cooled to room temperature and washed with water (3 × 20 mL) and saturated brine (20 mL). The organic layer was dried with anhydrous sodium sulfate and extracted with ethyl acetate. The mixture was concentrated under reduced pressure, and the residue was purified by preparative thin-layer chromatography using silica gel (eluent: petroleum ether: dichloromethane = 2:1) to obtain the target compound L2, which was a pale yellow solid with a yield of 53.47%.

[0051] L2 NMR data: 1 H NMR (400MHz, CDCl3) δ12.46(s,1H),8.01(d,J=8.1Hz,1H),7.92(d,J=8.0Hz,1H),7.83(s,1H),7.58(d,J=8.6H z,1H),7.51(t,J=9.4Hz,3H),7.43(d,J=7.5Hz,1H),7.15(d,J=8.5Hz,1H),6.84(d,J=8.2Hz,2H),3.01(s,6H).

[0052]

[0053] Intermediate L2 (0.20 g, 0.58 mmol) was added to a 25 mL two-necked round-bottom flask, and iodomethane (0.13 g, 0.87 mmol) was dissolved in acetone (10 mL). The mixture was stirred at room temperature for 10 h under argon protection. After the reaction was completed, the mixture was cooled to room temperature, excess acetone solvent was removed, and the final yellow product was obtained by recrystallization with a mixed solvent of methanol and n-hexane, with a yield of 90%.

[0054] TTC-2 NMR data: 1 H NMR (400MHz, DMSO-d6) δ11.79(s,1H),8.54(d,J=2.4Hz,1H),8.17(d,J=7.9Hz,1H),8.12–8.03(m,3H),7.98–7.9 2(m,2H),7.82(dd,J=8.6,2.5Hz,1H),7.60–7.53(m,1H),7.50–7.44(m,1H),7.23(d,J=8.6Hz,1H),3.66(s,9H).

[0055] Synthesis of TTC-3

[0056]

[0057] In a 100 mL two-necked round-bottom flask, 9H-fluorene-2-carboxaldehyde (0.53 g, 2.75 mmol) and 1-(2-hydroxyethyl)-4-methylpyridin-1-onium (0.50 g, 2.30 mmol) were dissolved in ethanol (40 mL). Two drops of piperidine were added dropwise, and the mixture was stirred at 80 °C for 16 h under argon protection. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was concentrated under reduced pressure. The residue was purified by thin-layer chromatography using silica gel (eluent: dichloromethane: methanol = 20:1) to obtain an orange-yellow solid, TTC-3, with a yield of 65%.

[0058] TTC-3 NMR data: 1H NMR (400MHz, DMSO-d6) δ 8.93–8.89 (d, J = 6.4Hz, 2H), 8.30–8.26 (d, J = 6.4Hz, 2H), 8.17 (d, J = 16.3Hz, 1H), 8.04–8.00 (m, 2H), 7.97 (d, J = 7.3Hz, 1H), 7.81 (d, J = 8.0Hz, 1H), 7.67–7.59 (m, 2H), 7.40–

[0059] 7.36(dt,J=20.2,7.4Hz,2H),5.31(s,1H),4.61–4.58(t,J=4.9Hz,2H),4.01(s,2H),3.89–3.84(q,J=4.9Hz,2H).

[0060] The following tests were performed on the water-soluble organic fluorescent molecules prepared above:

[0061] Test Example 1: Absorption Spectroscopy Test of TTC-1 to TTC-3 Molecules

[0062] Using tetrahydrofuran as a solvent, TTC-1, TTC-2, and TTC-3 were prepared to a concentration of 1×10⁻⁶. -5 mol·L -1 The sample solution was analyzed, and then, using a TU-1900 UV-Vis spectrophotometer with a 1 cm quartz cuvette, a baseline scan of the toluene solvent was performed (scanning range: 200–800 nm). After background subtraction, the sample solution was scanned, and its UV-Vis absorption spectrum was measured. The results are shown in [Figure number missing]. Figure 2 ,from Figure 2 We can see that TTC-1 and TTC-2 molecules have the strongest light absorption ability at around 370nm.

[0063] Test Example 2: Emission Spectroscopy Test of TTC-1 to TTC-3 Molecules

[0064] Using tetrahydrofuran as a solvent, TTC-1, TTC-2, and TTC-3 were prepared to a concentration of 1×10⁻⁶. -5 mol·L -1 The sample solution was then tested using a Hitachi F-4600 fluorescence spectrophotometer at room temperature. The excitation and emission spectra are as follows: Figure 3 As shown in the figure, the maximum emission wavelengths of the three molecules in the tetrahydrofuran solution are 460 nm and 460 nm, respectively.

[0065] Test Example 3: AIE performance test of TTC-1 to TTC-3 molecules

[0066] In systems with both good and poor solvents, the emission of molecules increases with the increase of the poor solvent. Taking TTC-1 as an example, for instance... Figure 4 As shown in (a), the good solvent is tetrahydrofuran, and the poor solvent is n-hexane. The emission gradually increases with the increase of the poor solvent, consistent with typical aggregation-induced emission (AIE) properties. Similarly, the TTC-2 molecule also exhibits AIE properties, such as... Figure 4 As shown in (b), the TTC-3 molecule does not have this property.

[0067] Test Example 4: Latent fingerprint development test of TTC-1 to TTC-3 molecules

[0068] Taking the TTC-1 molecule as an example, the feasibility of using the above-prepared water-soluble organic fluorescent molecule as a latent fingerprint developer is demonstrated. The specific process is as follows:

[0069] A precise amount of TTC-1 molecules (8.2 mg) was weighed using an electronic balance and dissolved in 20 ml of pure aqueous solution. The solution was then sonicated at room temperature until all the solid was completely dissolved, yielding a concentration of 1 × 10⁻⁶. -3 mol·L -1 The mother liquor was gradually diluted to 5×10⁻⁶. -4 mol·L -1 1×10 -4 mol·L -1 5×10 -5 mol·L -1 and 1×10 -5 mol·L -1 Using detection reagents with equal concentration gradients, latent fingerprints are collected in different substrates. The optimal detection concentration is determined by comparing the final fingerprint development results. Figure 5 As shown, development is performed using two methods: chemical impregnation and atomization. The specific steps are as follows:

[0070] Immersion method: Take a small amount of the above solution and gently drop it onto the latent fingerprint to be tested. After about 5 seconds, gently remove the surface solution with a dropper. Gently absorb any remaining solvent with absorbent paper. Irradiate the fingerprint with a 3W 365nm ultraviolet handheld lamp and take a picture with a mobile phone to obtain the fingerprint image.

[0071] Atomization method: Add a small amount of solution to the atomizer, spray the atomized liquid onto the latent fingerprint to be tested in step (b) for about 5 to 10 seconds, irradiate with a 3W 365nm ultraviolet handheld lamp, and take a picture with a mobile phone to obtain the fingerprint image.

[0072] The water-soluble organic fluorescent molecules in this invention can all produce high-resolution fingerprint images, accurate to the third-order structure of the fingerprint. A schematic diagram of the detection is shown below. Figure 6 As shown, its precise analytical structure is as follows: Figure 8 As shown in (a), it can be seen from the figure that the TTC-1 molecule can display the original secondary structure of the fingerprint, such as lakes, bifurcation and origin; it can also display the tertiary structure of the fingerprint, the sweat pore structure.

[0073] Figure 6 The study also demonstrated that the TTC-1 molecule has a certain ability to develop latent fingerprints on different substrate materials, such as glass plates, tin foil, iron sheets, wood, and A4 paper. The smooth surfaces of glass plates, tin foil, and iron sheets showed better results, while the detection effect on porous materials such as wood and A4 paper was relatively poor. This may be because there is less fingerprint grease adhering to the porous interface or the background of A4 paper is blue under 365nm ultraviolet light excitation, which affects the resolution of fingerprint development. Figure 8 (b) also compares in detail the fingerprints developed on glass slides and aluminum foil by the immersion method, and their fine structures are completely consistent, verifying the feasibility of the material in different substrates.

[0074] Figure 7 This demonstrates a novel atomization method that achieves good latent fingerprint development on various substrates, such as glass slides, aluminum foil, and iron sheets. Video 1 showcases a 5×10... -4 mol·L -1 The TTC-1 test reagent clearly revealed the latent fingerprint located in the aluminum foil in the atomization method.

[0075] For the TTC-1 molecule, the following advantages are available:

[0076] 1. Diverse detection methods: Not only can chemical impregnation be used to detect latent fingerprints, but atomization methods can also be used. Suitable for difficult-to-detect scenarios, such as vertical door handles and vertical beaker walls;

[0077] 2. Green and environmentally friendly, pollution-free: Its detection solvent is water, which does not require any organic solvents to dissolve it, and it has no irritating odor;

[0078] 3. User-friendly detection process: The detection can be completed using light in the commonly used 365nm wavelength band. The fingerprint color is bright blue, and the image resolution is high, making it visible to the naked eye.

[0079] 4. High sensitivity: Clear fingerprint images can be obtained after chemical immersion for about 5 seconds or atomization for 4 to 10 seconds;

[0080] 5. High applicability: Fingerprint detection can be performed on a variety of different substrate materials. Especially on tin foil, a fingerprint can be observed at a high resolution at 365nm after being lightly pressed and atomized by TTC molecules.

[0081] Figure 9 The latent fingerprinting patterns of TTC-2 and TTC-3 are shown. Their secondary and tertiary structures are similar to those of the TTC-1 molecule, and they also exhibit good latent fingerprinting ability. TTC-1 through TTC-3 produced fingerprints of different colors: TTC-1 produced a bright blue fingerprint, TTC-2 a yellow-green fingerprint, and TTC-3 an orange-yellow fingerprint. A comprehensive comparison of TTC-1 through TTC-3 shows that TTC-2 and TTC-3 also possess the aforementioned characteristics. Figure 7 The advantages of TTC-1 molecular latent fingerprint detection are demonstrated, with TTC-1 showing particularly outstanding overall performance.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A water-soluble organic fluorescent molecule characterized in that, The structure of the molecule is as follows: , or .

2. The method for preparing the water-soluble organic fluorescent molecule according to claim 1, characterized in that, The preparation of TTC-1 includes the following steps: 5-bromothiophene-2-carboxylic acid and (4-(diphenylamino)phenyl)boronic acid in a molar ratio of 1:(1~1.2) are dissolved in a solvent with a palladium catalyst. Under alkaline reaction conditions, the reaction is carried out in a one-step palladium-catalyzed Suzuki coupling reaction at a reaction temperature of 105~110℃ and a reaction time of 0.5~5 h in an argon atmosphere to obtain the final TTC-1 molecule with carboxylate.

3. The method for preparing water-soluble organic fluorescent molecules according to claim 2, characterized in that, The solvent is a mixture of 1,4-dioxane and water or a mixture of toluene and water; the palladium catalyst used is tetra-triphenylphosphine palladium or bis-triphenylphosphine palladium chloride.

4. The method for producing a water-soluble organic fluorescent molecule according to claim 2 or 3, wherein The amount of solvent is 5 to 8 times the amount of feed; the molar ratio of the 5-bromothiophene-2-carboxylic acid to the palladium catalyst is 1:(0.06~0.08).

5. The method for preparing the water-soluble organic fluorescent molecule according to claim 1, characterized in that, Including the preparation of TTC-2: S1: 2-Aminophenylthiol and 5-bromosalicylic acid aldehyde in a molar ratio of (1.1~1.3):1 were dissolved in a solvent and reacted at a temperature of 180~200℃ for 0.5~2 h under reflux via aldehyde-amine condensation-oxidative cyclization to synthesize L1; S2: L1 and (4-(dimethylamino)phenyl)boronic acid in a molar ratio of 1:(1~1.1) were dissolved in a solvent, and L2 was synthesized by a one-step palladium-catalyzed Suzuki coupling reaction under reflux conditions of 105~110℃ and 16~20 h in an argon atmosphere while maintaining an alkaline reaction environment. S3: L2 and iodomethane in a molar ratio of 1:(1.5~1.8) are dissolved in a solvent, and methylation is carried out at a reaction temperature of 20~35℃ and a reaction time of 8~12 h to generate a quaternary ammonium salt, yielding the final TTC-2 molecule. The synthetic route is as follows: 。 6. The method for preparing water-soluble organic fluorescent molecules according to claim 5, characterized in that, The molar ratio of L1 to catalyst in S2 is 1:(0.06~0.08).

7. The method for preparing the water-soluble organic fluorescent molecule according to claim 1, characterized in that, Including the preparation of TTC-3: 9H-fluorene-2-carboxaldehyde and 1-(2-hydroxyethyl)-4-methylpyridine-1-onium in a molar ratio of (1.1~1.4):1 were dissolved in a solvent, and the condensation reaction of the aldehyde group and the methyl group was carried out in an alkaline environment at a reaction temperature of 80~85℃ and a reaction time of 16~24 h to obtain the TTC-3 molecule with pyridine cation.

8. The method for preparing water-soluble organic fluorescent molecules according to claim 7, characterized in that, The solvent is ethanol or toluene; an alkaline environment is maintained by adding 1-2 drops of piperidine.

9. Use of the water-soluble organic fluorescent molecule according to claim 1 for fingerprint detection, characterized in that, The detection reagent is prepared by dissolving water-soluble organic fluorescent molecules in pure water; latent fingerprints are detected by immersion or atomization methods.

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