Organic conjugated polymer fluorescent material for blood latent fingerprint development and preparation method and application thereof

Abstract

This invention provides an organic conjugated polymer fluorescent material for developing latent fingerprints in blood, its preparation method, and its applications, relating to the field of conjugated polymer technology. The structural formula of the organic conjugated polymer of this invention is as follows: wherein Ar is or R1 is H, a C1-C16 alkyl group, a C1-C16 alkoxy group, or a C1-C16 alkylthiol group; R2 is H or a C1-C16 alkyl group; x is 0 or 0.01; and n is a natural number from 1 to 300. The polymer of this invention exhibits high sensitivity, superior development performance, and strong anti-interference capabilities.

Description

Technical Field

[0001] This invention relates to the field of conjugated polymer technology, and in particular to an organic conjugated polymer fluorescent material that can be used for blood latent fingerprint development, its preparation method, and its application. Background Technology

[0002] Fingerprints, as direct evidence of individual identity, possess high specificity and stability, helping to quickly identify suspects and narrow down the scope of investigation. Blood fingerprints, as a common type of evidence in criminal cases, are a crucial element in forensic eccentricity and crime scene investigation, directly impacting the efficiency and impartiality of case solving.

[0003] In judicial practice, blood fingerprints are categorized into latent and visible types. Latent fingerprints are often blurred and difficult to see due to small blood volume, high dilution, or long time, requiring special methods to enhance them. Visible fingerprints, when affected by complex backgrounds, also require enhancement techniques to improve contrast and clarity. Currently, blood fingerprint detection technology primarily uses scientific methods to reveal blood fingerprints left at crime scenes, including chemical reagent treatment, physical enhancement methods, or modern biotechnology. In current judicial practice, the detection and revealing of blood fingerprints mainly rely on a series of chemical reagents, such as protein dyes, tetramethylbenzidine, luminol, and ninhydrin. These reagents react chemically with specific components in the blood, thereby revealing the outline and details of the fingerprint. However, most blood fingerprint revealing methods have certain limitations, mainly including the following aspects:

[0004] (1) Traditional methods have poor resistance to background interference, and the darker colors may not be suitable for dark backgrounds, pose a risk of false positives, and may cause biotoxicity; (2) The display effect of traditional methods may be time-limited, and the display effect may be unsatisfactory for older or improperly processed blood fingerprints, making it difficult to extract fingerprint information completely; (3) Traditional blood fingerprint display methods have poor controllability and are easily affected by various factors such as environment, temperature, and humidity, resulting in insufficient clarity and stability of fingerprint display; (4) Although some new methods have high sensitivity, they do not have fluorescence, so the fingerprint visualization effect is not good; (5) Most traditional and new methods have a single color, which is difficult to adapt to background interference of different colors and textures on site. Thus, their application scope and effect are limited to a certain extent.

[0005] With the rapid development of science and technology, emerging technologies such as nanomaterials, immunoassay, and hyperspectral imaging are gradually gaining prominence, bringing new possibilities for the accurate and efficient detection and visualization of blood fingerprints. However, despite the significant advantages these emerging technologies have demonstrated in the field of blood fingerprint detection, their high cost and relatively limited applicability make widespread application difficult at present. Therefore, developing new materials and methods to achieve simple, rapid, and clear visualization of blood fingerprints remains a crucial challenge that urgently needs to be addressed.

[0006] Fluorescent conjugated polymers possess advantages such as strong light-harvesting ability, tunable chemical structure and emission color, and good processability, making them widely used in optoelectronic devices, biological detection, and disease diagnosis to amplify fluorescence sensing signals. In recent years, many researchers have also applied this material to latent fingerprint detection. However, its application in blood fingerprint detection is relatively limited. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides an organic conjugated polymer fluorescent material for the development of latent blood fingerprints, its preparation method, and its application, achieving highly efficient development of blood fingerprints.

[0008] In a first aspect, the present invention provides an organic conjugated polymer that can be used for developing latent blood fingerprints, the structural formula of which is as follows:

[0009]

[0010] Where Ar is or R1 is H, a C1-C16 alkyl group, a C1-C16 alkoxy group, or a C1-C16 alkylthiol group; R2 is H or a C1-C16 alkyl group; x is 0 or 0.01; n is a natural number from 1 to 300.

[0011] In one embodiment of the present invention, the organic conjugated polymer has any of the following structural formulas:

[0012]

[0013]

[0014] n = 1 - 300.

[0015] In a second aspect, the present invention provides a method for preparing the above-mentioned organic conjugated polymer, comprising using M1, M2, and SO-Br2 as raw materials to carry out a Suzuki coupling reaction.

[0016] Among them, M1 is 2,7-bis(4,4,5,5-tetramethyl-1,3-dioxaborane-2-yl)-9,9-dioctylfluorene, M2 is 2,7-dibromo-9,9-dioctylfluorene, and SO-Br2 is 3,7-dibromo-S,S-dioxodibenzothiophene.

[0017] In one embodiment of the present invention, the raw material further includes Ar-Br2, wherein the Ar-Br2 is BT-Br2 or DTBT-Br2; BT-Br2 is 4,7-dibromobenzo[c][1,2,5]thiadiazole, and DTBT-Br2 is 4,7-bis(5-bromothiophene-2-yl)benzo[c][1,2,5]thiadiazole.

[0018] In one embodiment of the present invention, the molar ratio of M1, M2, SO-Br2, and Ar-Br2 is 50:(39-40):10:1.

[0019] In one embodiment of the present invention, the preparation method specifically includes the following steps:

[0020] (1) The raw materials, organic solvent and alkaline reagent are mixed to obtain the first mixture;

[0021] (2) Add palladium catalyst to the first mixture to carry out a coupling reaction, and then add end-capping agent to carry out an end-capping reaction to obtain the second mixture;

[0022] (3) The second mixture is subjected to precipitation, filtration, washing and drying to obtain an organic conjugated polymer.

[0023] In one embodiment of the present invention, in step (1), the organic solvent is any one or more of toluene, xylene, tetrahydrofuran, N,N-dimethylformamide, and 1,4-dioxane.

[0024] In one embodiment of the present invention, in step (1), the alkaline reagent is any one or more of tetraethylammonium hydroxide, triethylamine, and N,N-diisopropylethylamine.

[0025] In one embodiment of the present invention, in step (1), the raw materials include M1, M2, SO-Br2 and Ar-Br2 in a molar ratio of 50:(39-40):10:1.

[0026] In one embodiment of the present invention, in step (2), the palladium catalyst is any one or more of palladium acetate, tetra(triphenylphosphine)palladium, palladium chloride, diphenylvinylbis(benzomethylene)palladium, and tri(diphenylethylene)bis(benzomethylene)palladium.

[0027] In one embodiment of the present invention, in step (2), a ligand is added to the palladium catalyst to increase its catalytic activity. Specifically, the ligand is a phosphine ligand, preferably, the phosphine ligand is any one or more of tricyclohexylphosphine, triphenylphosphine, XPhos, and SPhos.

[0028] In one embodiment of the present invention, in step (2), the molar percentage of palladium catalyst to M2 is 0.5 mol%-5 mol%, and the molar ratio of the ligand to palladium catalyst is (1-3):1.

[0029] In one embodiment of the present invention, in step (2), the capping agent includes phenylboronic acid and bromobenzene.

[0030] In one embodiment of the present invention, in step (2), the coupling reaction temperature is 60-90℃ and the time is 6-24h; the end-capping reaction time is 6-12h.

[0031] In one embodiment of the present invention, in step (3), the second mixture is precipitated in methanol and filtered, the filter residue is washed with acetone, and the washed filter residue is dried under vacuum.

[0032] In a third aspect, the present invention provides a blood latent fingerprint developing reagent comprising the above-mentioned organic conjugated polymer.

[0033] In a fourth aspect, the present invention provides the application of the above-mentioned organic conjugated polymer or blood latent fingerprint developing reagent in the detection of blood fingerprints.

[0034] In a fifth aspect, the present invention provides a method for detecting latent blood fingerprints, using the aforementioned organic conjugated polymer or latent blood fingerprint developing reagent.

[0035] In one embodiment of the present invention, the method for detecting latent blood fingerprints includes covering a fingerprint-loaded object with a latent blood fingerprint developing reagent, allowing it to stand, and then photographing the developed latent blood fingerprint under ultraviolet light with a wavelength of 300-400 nm.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The functional groups of the polymer of the present invention have an affinity for hemoglobin. By designing the types of functional groups and adjusting the density of functional groups, the accurate development of blood fingerprints on non-permeable surfaces is achieved, solving the problem of poor development effect of traditional blood fingerprint development methods. The development effect of traditional methods may be limited by time. For older or improperly processed blood fingerprints, the development effect may be unsatisfactory, making it difficult to extract fingerprint information completely.

[0038] (2) The polymer of the present invention has high sensitivity, superior development performance and anti-interference ability. Due to the optimized design of the polymer structure and its fluorescence properties, it can maintain a high level of anti-interference ability in complex environments, thereby ensuring the accuracy and reliability of fingerprint development and solving the problem of the narrow application range of traditional methods.

[0039] (3) The multicolor polymer brushing method of the present invention is simple to operate, has a short development process, and is fast. The powder is easy to store and carry, which is conducive to adapting to the needs of various crime scenes and solves the problem of cumbersome operation process of traditional methods.

[0040] (4) The polymer of the present invention has a fluorescent effect, which can effectively deal with the background interference problem of complex patterns or dark background surfaces. It exhibits excellent display effect on a variety of non-permeable objects such as glass, marble, ceramics, and stainless steel, and can clearly display the details of blood fingerprints (sweat pores, etc.) up to the third level, thus solving the problem of poor anti-background interference ability of traditional methods.

[0041] (5) The method of the present invention has low cost and short synthesis cycle. The raw materials of the present invention are all chemical raw materials, which are easy to obtain, low in cost, simple to synthesize, and short in cycle, making them suitable for industrial mass production and practical application. Attached Figure Description

[0042] Figure 1 This is a schematic diagram illustrating the synthesis strategy of this fluorescent conjugated polymer material;

[0043] Figure 2 Thermogravimetric (left) and thermal stability (right) spectra of fluorescent conjugated polymer materials;

[0044] Figure 3 The cyclic voltammetry (CV) curves of the polymer are shown.

[0045] Figure 4 The ultraviolet-visible absorption spectrum and photoluminescence (PL) spectrum of the polymer;

[0046] Figure 5 The infrared spectrum of the polymer;

[0047] Figure 6 A comparison of the development effects of red, green, and blue fluorescent polymer powders with those of the amino black and tetramethylbenzidine methods;

[0048] Figure 7 This is a comparison of grayscale values ​​for the development methods of tetramethylbenzidine, amino black 10B, and copolymers (CG represents the blank control group). Detailed Implementation

[0049] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0050] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0051] Example 1: Synthesis of polymer PF-SO10

[0052] The monomers 2,7-bis(4,4,5,5-tetramethyl-1,3-dioxaborane-2-yl)-9,9-dioctylfluorene (M1, 192.6 mg, 0.3 mmol), 2,7-dibromo-9,9-dioctylfluorene (M2, 131.5 mg, 0.24 mmol), and 3,7-dibromo-S,S-dioxodibenzothiophene (SO-Br2, 22.4 mg, 0.06 mmol) were added to a two-necked round-bottom flask containing toluene (9 mL) and an aqueous solution of tetraethylammonium hydroxide (20 wt / v%, 0.9 mL).

[0053] Palladium acetate (2.0 mg) and tricyclohexylphosphine (4.0 mg) were added to the mixture. Under nitrogen protection, the mixture was heated to 85 °C and stirred for 24 h.

[0054] Phenylated boric acid (25 mg) and bromobenzene (0.2 mL) were added sequentially, and each reaction was allowed to proceed for 12 h for end-capping. After the reaction was complete, the mixture was precipitated in methanol (250 mL) and filtered. The filter residue was washed with acetone using a Soxhlet extractor, and the washed residue was dried under vacuum to obtain the product.

[0055] Example 2: Synthesis of polymer PF-SO10-BT1

[0056] The monomers 2,7-bis(4,4,5,5-tetramethyl-1,3-dioxaborane-2-yl)-9,9-dioctylfluorene (M1, 192.6 mg, 0.3 mmol), 2,7-dibromo-9,9-dioctylfluorene (M2, 128.2 mg, 0.234 mmol), 3,7-dibromo-S,S-dioxabenzothiophene (SO-Br2, 22.4 mg, 0.06 mmol), and 4,7-dibromobenzo[c][1,2,5]thiadiazole (BT-Br2, 1.8 mg, 0.006 mmol) were added to a two-necked round-bottom flask containing toluene (9 mL) and an aqueous solution of tetraethylammonium hydroxide (20 wt / v%, 0.9 mL).

[0057] Palladium acetate (2.0 mg) and tricyclohexylphosphine (4.0 mg) were added to the mixture. Under nitrogen protection, the mixture was heated to 85 °C and stirred for 24 h.

[0058] Phenylated boric acid (25 mg) and bromobenzene (0.2 mL) were added sequentially, and each reaction was allowed to proceed for 12 h for end-capping. After the reaction was complete, the mixture was precipitated in methanol (250 mL) and filtered. The filter residue was washed with acetone using a Soxhlet extractor, and the washed residue was dried under vacuum to obtain the product.

[0059] Example 3 Synthesis of polymer PF-SO10-DTBT1

[0060] The monomers 2,7-bis(4,4,5,5-tetramethyl-1,3-dioxaborane-2-yl)-9,9-dioctylfluorene (M1, 192.6 mg, 0.3 mmol), 2,7-dibromo-9,9-dioctylfluorene (M2, 128.2 mg, 0.234 mmol), 3,7-dibromo-S,S-dioxadibenzothiophene (SO-Br2, 22.4 mg, 0.06 mmol), and 4,7-bis(5-bromothiophene-2-yl)benzo[c][1,2,5]thiadiazole (DTBT-Br2, 2.7 mg, 0.006 mmol) were added to a two-necked round-bottom flask containing toluene (9 mL) and an aqueous solution of tetraethylammonium hydroxide (20 wt / v%, 0.9 mL).

[0061] Palladium acetate (2.0 mg) and tricyclohexylphosphine (4.0 mg) were added to the mixture. Under nitrogen protection, the mixture was heated to 85 °C and stirred for 24 h.

[0062] Phenylated boric acid (25 mg) and bromobenzene (0.2 mL) were added sequentially, and each reaction was allowed to proceed for 12 h for end-capping. After the reaction was complete, the mixture was precipitated in methanol (250 mL) and filtered. The filter residue was washed with acetone using a Soxhlet extractor, and the washed residue was dried under vacuum to obtain the product.

[0063] Example 4 Polymer Performance Testing

[0064] 1. Thermogravimetric and thermal stability testing

[0065] Using TA TGA Q5000 and Netzzch DSC 300 respectively under nitrogen flow at 15℃ min -1 and 10℃min -1 The thermal performance was tested at the heating rate, and the results are as follows: Figure 2 As shown. It can be seen that the glass transition temperature (T) of all polymers... g s) all reached 100℃, decomposition temperature (T) d It has high thermal stability at around 400℃.

[0066] 2. Polymer molecular weight and thermal properties testing

[0067] The proton NMR spectra of the polymer were measured using a Bruker Ascend™ 400 micrometer with deuterated chloroform and tetramethylsilane as solvent and internal standard, respectively. 1 ¹H NMR). The number-average molecular weight (Mn) was determined using an Agilent 1260 Infinity analyzer with polystyrene and tetrahydrofuran as standards and eluents, respectively. nThe results are shown in Table 1.

[0068] Table 1 Test Results

[0069]

[0070] The results show that the polymer has a uniform molecular weight distribution and good thermal stability.

[0071] 2. Electrochemical properties of polymers

[0072] Electrochemical performance was measured using a CHI660E electrochemical workstation with cyclic voltammetry (CV) at a scan rate of 50 mV / s. -1 The working electrode, counter electrode, reference electrode, and electrolyte solution were graphite, platinum wire, Ag / AgCl, and 0.1 mol L, respectively. -1 Tetrabutylammonium hexafluorophosphate in acetonitrile solution.

[0073] The cyclic voltammetry (CV) curve of the polymer is as follows: Figure 3 As shown, detailed data is presented in Table 2. Based on the empirical formula E... HOMO =-(E ox +4.80-E fer )(eV) and E LUMO =-(E red +4.80-E fer (eV), the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were obtained, respectively. ox E red and E fer These are the polymer oxidation potential, reduction potential, and ferrocene oxidation potential (Fc / Fc). + The HOMO energy levels of PF-SO10, PF-SO10-BT1, and PF-SO10-DTBT1 are identical, which is because the HOMO energy levels are mainly dominated by the electron-donating units of the polymer. Compared to PF-SO10, the LUMO energy levels of PF-SO10-BT1 and PF-SO10-DTBT1 are lower due to the strong electronegativity of the BT units. Electrochemical band gap (E g CV ) and optical band gap (E g opt The inconsistency between the two may be due to the low content of BT and DTBT units in the polymer, resulting in lower absorption at longer wavelengths.

[0074] Table 2 Cyclic Voltmeter Detection Data

[0075]

[0076] 3. UV-Vis absorption and PL spectra of the polymer in toluene solution and thin film

[0077] The UV-Vis absorption spectrum and photoluminescence (PL) spectrum of the polymer were measured using a MAPADA UV-6100S UV-Vis spectrophotometer and an F97 fluorescence spectrophotometer, respectively. The results are as follows: Figure 4 As shown.

[0078] The UV-Vis absorption and PL spectra of PF-SO10, PF-SO10-BT1, and PF-SO10-DTBT1 in toluene solution are as follows: Figure 4 As shown in (a) and (b), the strong absorption peak at 389 nm can be attributed to the π-π* transition of conjugated fluorene. Figure 4 (a)). In Figure 4 In (b), the emission peak at 431 nm belongs to the PF-SO segment, while the emission peaks around 520 and 619 nm belong to the BT and DTBT units, respectively. The absorption spectrum of the polymer in the thin film is similar to that in solution. Figure 4 (c)). Figure 4 (d) shows the blue light emission spectra of the polymers in the thin film. The blue light emission intensities of PF-SO10-BT1 and PF-SO10-DTBT1 are significantly reduced, while PF-SO10-BT1 is almost completely quenched. The main emission peaks of PF-SO10-BT1 and PF-SO10-DTBT1 are redshifted to 533 nm and 631 nm, respectively. This is mainly due to the enhanced intermolecular interactions and energy transfer in the thin film state.

[0079] 4. Infrared spectrum of polymers

[0080] Fourier transform infrared (FT-IR) spectroscopy measurements from 4000 to 400 cm⁻¹ -1 Thermo Fisher Scientific Nicolet iS10 infrared spectrometer was used for testing via the dry potassium bromide pellet method. The results are as follows: Figure 5 As shown.

[0081] Example 5: Application of organic conjugated polymer fluorescent materials for detecting blood fingerprints

[0082] 1. Blood fingerprint deposition

[0083] Before testing, all substrate surfaces underwent rigorous treatment. First, they were thoroughly cleaned with a 75% ethanol solution to remove surface impurities, and then allowed to air dry under ambient conditions to ensure that the substrates were clean and free of contaminants.

[0084] Six representative non-permeable substrates were selected to comprehensively evaluate the effectiveness of the revealing strategy on different substrates. These substrates included light-colored / transparent white ceramics and glass, black-painted copper-zinc alloy sheets on dark substrates, patterned marble with complex backgrounds, and highly reflective silver stainless steel and mirrors. In the experiment, volunteers uniformly used fingerprints containing 5 microliters of blood, pressing them vertically onto the different substrates.

[0085] 2. Blood fingerprints appear

[0086] Low-cost and highly stable alginate particles were used as the grinding aid, with a grinding ratio of sodium alginate to the fluorescent polymers prepared in Examples 1-3 of 500:1 (m / m). A soft-bristled brush with flexible tendrils was selected as the tool to pick up the polymer powder and alginate mixture and gently brush the blood fingerprint to avoid damaging the ridge details. The fingerprint images were detected using a VSC8000 document examination instrument in 365nm ultraviolet light mode to detect the fluorescence effect of the blood fingerprint, and then the fingerprint images were captured and fixed using the camera control module of the document examination instrument.

[0087] To evaluate the development effect, two common traditional blood fingerprint development methods were selected as controls: Amine Black 10B (AB) and Tetramethylbenzidine (TMB). The preparation method for Amine Black 10B was as follows: 1.2g of Amine Black 10B was added to 10ml of glacial acetic acid and 95ml of anhydrous ethanol, and stirred thoroughly until completely dissolved. The resulting mixed solution was used as the development reagent. Simultaneously, 20ml of acetic acid and 180ml of anhydrous ethanol were mixed to prepare a detergent. The preparation method for Tetramethylbenzidine was as follows: 0.5g of TMB was dissolved in 50ml of anhydrous ethanol, heated in a water bath until dissolved, and then 5ml of 30% hydrogen peroxide solution was added dropwise, stirred, and set aside. Since TMB and Amine Black 10B were solutions, to avoid blurring of the fingerprint lines when developing the fingerprint using a spray method, the blood fingerprint needed to be fixed first. Anhydrous ethanol was used as the fixative, and was dropped onto the surface of the blood fingerprint three times.

[0088] Specific results are as follows Figure 6 As shown in the figure, the experimental results show that undeveloped blood fingerprints are visible on these substrates but have low contrast; while the developed fingerprint lines have significantly improved clarity and contrast, and emit strong fluorescence under a 365nm ultraviolet light source. This enhances blood fingerprint patterns on various non-permeable substrates and effectively solves the problem of low contrast on complex backgrounds (marble) and dark background surfaces. The developed fingerprints can exhibit 2-3 levels of ridge detail. The experimental results also show that alginate has almost no impact on the fluorescence effect of the copolymer and does not damage the ridge details.

[0089] 3. Gray value calculation

[0090] Grayscale values ​​are a common method for evaluating image contrast. A high dynamic range of grayscale values ​​means high contrast. For fingerprint images, the difference in grayscale values ​​represents the contrast between fingerprint peaks and valleys. The larger the grayscale value range, the stronger the contrast between the fingerprint and the background, thus making the fingerprint image more recognizable.

[0091] The RGB image was converted to an 8-bit grayscale image using the grayscale calculation software Image J. The blood fingerprint image obtained in the above experiment was selected using the software's built-in analysis function, and the grayscale value range was calculated to generate a grayscale range curve, which quantitatively evaluated the image contrast effect.

[0092] The results are as follows Figure 7 As shown, compared to the original blood fingerprint, the fingerprint developed using the red-green-blue fluorescent conjugated polymer exhibited a significant increase in the grayscale range across all substrate surfaces. Looking at the grayscale value variations of all developed images on different substrates, the average grayscale values ​​of the fingerprint and background differed across substrates due to varying substrate brightness, resulting in different grayscale baselines. Furthermore, the original grayscale range of the substrates also varied due to factors such as self-reflection (mirrors and stainless steel) and complex patterns (marble). Compared to TMB and amino black, the red-green-blue fluorescent conjugated polymer showed a larger range of grayscale value differences, confirming that the blood fingerprint development strategy based on this patent effectively enhances contrast in all situations.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. The application of a blood latent fingerprint developing reagent in the detection of blood fingerprints, characterized in that, The organic conjugated polymer structure of the latent blood fingerprint is as follows: , where Ar is ,or R1 is H, a C1-C16 alkyl group, a C1-C16 alkoxy group, or a C1-C16 alkylthiol group; R2 is H or a C1-C16 alkyl group; x is 0 or 0.01; n is a natural number from 1 to 300.

2. The application as described in claim 1, characterized in that, The organic conjugated polymer has any of the following structural formulas: , , , n=1-300.

3. The application as described in claim 2, characterized in that, The method for preparing the organic conjugated polymer includes using M1, M2, and SO-Br2 as raw materials and carrying out a Suzuki coupling reaction. Among them, M1 is 2,7-bis(4,4,5,5-tetramethyl-1,3-dioxaborane-2-yl)-9,9-dioctylfluorene, M2 is 2,7-dibromo-9,9-dioctylfluorene, and SO-Br2 is 3,7-dibromo-S,S-dioxodibenzothiophene.

4. The application as described in claim 3, characterized in that, The raw materials in the preparation method of the organic conjugated polymer also include Ar-Br2, wherein the Ar-Br2 is BT-Br2 or DTBT-Br2; BT-Br2 is 4,7-dibromobenzo[c][1,2,5]thiadiazole, and DTBT-Br2 is 4,7-bis(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole.

5. The application as described in claim 4, characterized in that, The molar ratio of M1, M2, SO-Br2, and Ar-Br2 is 50:(39-40):10:

1.

6. The application as described in claim 4, characterized in that, The preparation method of the organic conjugated polymer specifically includes the following steps: (1) The raw materials, organic solvent and alkaline reagent are mixed to obtain a first mixture; (2) Add palladium catalyst to the first mixture to carry out a coupling reaction, and then add end-capping agent to carry out an end-capping reaction to obtain the second mixture; (3) The second mixture is subjected to precipitation, filtration, washing and drying to obtain an organic conjugated polymer.

7. The application as described in claim 6, characterized in that, In step (1), the organic solvent is any one or more of toluene, xylene, tetrahydrofuran, N,N-dimethylformamide, and 1,4-dioxane; In step (1), the alkaline reagent is any one or more of tetraethylammonium hydroxide, triethylamine, and N,N-diisopropylethylamine; In step (2), the palladium catalyst is any one or more of palladium acetate, tetra(triphenylphosphine)palladium, palladium chloride, diphenylvinylbis(benzomethylene)palladium, and tri(diphenylvinyl)bis(benzomethylene)palladium; In step (2), a ligand is added to the palladium catalyst to increase its catalytic activity; The ligand is a phosphine ligand, and the phosphine ligand is any one or more of tricyclohexylphosphine, triphenylphosphine, XPhos, and SPhos; In step (2), the molar percentage of palladium catalyst to M2 is 0.5 mol%-5 mol%, and the molar ratio of the ligand to palladium catalyst is (1-3):1; In step (2), the capping agent includes phenylboronic acid and bromobenzene; In step (2), the coupling reaction temperature is 60-90℃ and the time is 6-24h; the end-capping reaction time is 6-12h. In step (3), the second mixture is precipitated in methanol and filtered, the filter residue is washed with acetone, and the washed filter residue is dried under vacuum.

8. A method for detecting latent blood fingerprints, characterized in that, The following organic conjugated polymers were used for the detection of latent fingerprints in blood. , where Ar is ,or R1 is H, a C1-C16 alkyl group, a C1-C16 alkoxy group, or a C1-C16 alkylthiol group; R2 is H or a C1-C16 alkyl group; x is 0 or 0.01; n is a natural number from 1 to 300.

Images