Organic conjugated polymer fluorescent material capable of being used for bloody latent fingerprint development as well as preparation method and application of organic conjugated polymer fluorescent material

Abstract

The invention provides an organic conjugated polymer fluorescent material for bloody latent fingerprint development as well as a preparation method and application thereof, and relates to the technical field of conjugated polymers. The structural formula of the organic conjugated polymer is as follows: # imgabs 0 #, Ar is # imgabs 1 # or # imgabs 2 #, R1 is H, C1-C16 alkyl, C1-C16 alkoxy or C1-C16 alkyl sulfydryl, R2 is H or C1-C16 alkyl, x is 0 or 0.01, and n is 0 or 0. N is a natural number ranging from 1 to 300. The polymer provided by the invention has the advantages of high sensitivity, excellent display performance and excellent anti-interference capability.

Description

Technical Field

[0001] The invention relates to the technical field of conjugated polymers, and in particular to an organic conjugated polymer fluorescent material that can be used for blood latent fingerprint visualization, and a preparation method and application thereof. Background Art

[0002] As direct evidence of individual identity, fingerprints are highly specific and stable, which helps to quickly identify suspects and narrow the scope of investigation. As one of the common evidences in criminal cases, the detection and appearance of blood fingerprints is a key link in forensic evidence and crime scene investigation, which is directly related to the efficiency and fairness of case detection.

[0003] In judicial practice, blood fingerprints are divided into two categories: latent and visible. Latent fingerprints are blurred and difficult to see due to small amounts of blood, high dilution or long periods of time, and require special methods to enhance; visible fingerprints also require certain enhancement techniques to improve contrast and clarity when affected by complex backgrounds. At present, blood fingerprint detection technology mainly uses scientific means to reveal blood fingerprints left at the crime scene, including chemical reagent treatment, physical enhancement methods or modern biotechnology. In current judicial practice, the detection and visualization 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 to reveal the outline and details of the fingerprints. However, most blood fingerprint visualization methods have certain limitations, mainly including the following aspects:

[0004] (1) Traditional methods have poor anti-background interference ability, and the darker color may not be suitable for dark backgrounds, and there is a risk of false positives and possible biological toxicity; (2) The visualization effect of traditional methods may be limited by time. For older or improperly processed blood fingerprints, the visualization effect may not be ideal, resulting in difficulty in completely extracting fingerprint information; (3) Traditional blood fingerprint visualization 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 visualization; (4) Although some new methods are highly sensitive, they do not have fluorescence, so the fingerprint visualization effect is not good; (5) Most traditional and new methods have a single color and are difficult to adapt to background interference of different colors and textures at the scene. This limits their application scope and effect to a certain extent.

[0005] With the rapid development of science and technology, emerging technologies such as nanomaterials, immune technology, and hyperspectral imaging have gradually emerged, bringing new possibilities for the accurate and efficient detection and visualization of blood fingerprints. However, although emerging technologies have shown great advantages in the field of blood fingerprint detection, their high cost and relatively limited scope of application make it difficult to be widely used in large-scale promotion. Therefore, the development of new materials and methods to achieve simple, fast, and clear visualization of blood fingerprints is still an important problem that needs to be solved urgently.

[0006] Fluorescent conjugated polymers have the advantages of strong light-capturing ability, adjustable chemical structure and emission color, and good processability. They can be used to amplify fluorescent sensing signals and are widely used in optoelectronic components, biological detection, and disease diagnosis. In recent years, many researchers have also applied this material to the field of latent fingerprint detection. However, its application in blood fingerprint detection is relatively rare. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides an organic conjugated polymer fluorescent material that can be used for blood latent fingerprint visualization, and a preparation method and application thereof, thereby achieving efficient visualization of blood latent fingerprints.

[0008] In a first aspect, the present invention provides an organic conjugated polymer that can be used for blood latent fingerprint visualization, and its structural formula is as follows:

[0009]

[0010] Among them, Ar is or R1 is H, C1-C16 alkyl, C1-C16 alkoxy or C1-C16 alkanethio, R2 is H or C1-C16 alkyl, x is 0 or 0.01; n is a natural number of 1-300.

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

[0012]

[0013]

[0014] n=1-300.

[0015] In a second aspect of the present invention, a method for preparing the above-mentioned organic conjugated polymer is provided, comprising using M1, M2, and SO-Br2 as raw materials, and performing a Suzuki coupling reaction to obtain:

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

[0017] In one embodiment of the present invention, the raw material also 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-di(5-bromothiophen-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 comprises the following steps:

[0020] (1) mixing a raw material, an organic solvent and an alkaline reagent to obtain a first mixture;

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

[0022] (3) The second mixture is precipitated, filtered, washed and dried 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, tetrakis(triphenylphosphine)palladium, palladium chloride, diphenylvinyldi(benzomethylene)palladium, and tris(diphenylethylene)di(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 the palladium catalyst to M2 is 0.5 mol%-5 mol%, and the molar ratio of the ligand to the palladium catalyst is (1-3):1.

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

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

[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 vacuum dried.

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

[0033] The fourth aspect of the present invention provides the use of the above organic conjugated polymer or blood latent fingerprint revealing reagent in detecting blood fingerprints.

[0034] A fifth aspect of the present invention provides a method for detecting latent fingerprints in blood, using the above-mentioned organic conjugated polymer or latent fingerprint visualization reagent for detection.

[0035] In one embodiment of the present invention, the method for detecting latent blood fingerprints comprises covering a latent blood fingerprint developing reagent on an object carrying fingerprints, allowing the object to stand, and photographing the latent blood fingerprints after development under ultraviolet light irradiation with a wavelength of 300 to 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 visualization of blood fingerprints on non-permeable surfaces is achieved, solving the problem of poor visualization effect of traditional blood fingerprint visualization methods. The visualization effect of traditional methods may be limited by time. For older or improperly processed blood fingerprints, the visualization effect may not be ideal, making it difficult to completely extract fingerprint information.

[0038] (2) The polymer of the present invention has high sensitivity, excellent display performance and anti-interference ability. Due to the optimized design of the polymer structure and the fluorescent characteristics, it can still maintain a high anti-interference ability in a complex environment, thereby ensuring the accuracy and reliability of fingerprint display and solving the problem of the narrow application range of traditional methods.

[0039] (3) The multicolor polymer brush display method of the present invention is easy to operate, has a short display process, and is fast. The powder can be stored and carried conveniently, which is conducive to meeting the needs of various crime scenes and solves the problem of complicated operation procedures 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 has excellent display effects on a variety of non-permeable objects such as glass, marble, ceramics, stainless steel, etc., and can clearly display the details of blood fingerprints (sweat pores, etc.) to the third level, 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 cost, simple synthesis operation, short cycle, and suitable for industrial mass production and practical promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0044] Figure 3 is the cyclic voltammetry curve (CV) of the polymer;

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

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

[0047] Figure 6 The comparison of the display effects of red, green and blue fluorescent polymer powders and amino black and tetramethylbenzidine methods;

[0048] Figure 7 Grayscale value comparison chart of tetramethylbenzidine, amino black 10B and copolymer development method (CG is the blank control group) DETAILED DESCRIPTION

[0049] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations 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 included in the scope that the present invention is intended to protect.

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

[0051] Example 1 Synthesis of polymer PF-SO10

[0052] The monomers 2,7-di(4,4,5,5-tetramethyl-1,3-dioxaborolan-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-dioxydibenzothiophene (SO-Br2, 22.4 mg, 0.06 mmol) were added to a two-necked round-bottom flask containing toluene (9 mL) and tetraethylammonium hydroxide aqueous solution (20 wt / v%, 0.9 mL).

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

[0054] Phenylboric acid (25 mg) and bromobenzene (0.2 mL) were added in sequence, and the reaction was carried out for 12 h for end-capping. After the reaction was completed, the mixture was precipitated in methanol (250 mL) and filtered. The filter residue was washed with acetone through a Soxhlet extractor, and the washed filter residue was vacuum dried to obtain the product.

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

[0056] The monomers 2,7-di(4,4,5,5-tetramethyl-1,3-dioxaborolan-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-dioxydibenzothiophene (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 tetraethylammonium hydroxide aqueous solution (20 wt / v%, 0.9 mL).

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

[0058] Phenylboric acid (25 mg) and bromobenzene (0.2 mL) were added in sequence, and the reaction was carried out for 12 h for end-capping. After the reaction was completed, the mixture was precipitated in methanol (250 mL) and filtered. The filter residue was washed with acetone through a Soxhlet extractor, and the washed filter residue was vacuum dried to obtain the product.

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

[0060] The monomers 2,7-di(4,4,5,5-tetramethyl-1,3-dioxaborolan-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-dioxydibenzothiophene (SO-Br2, 22.4 mg, 0.06 mmol), and 4,7-di(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 tetraethylammonium hydroxide aqueous solution (20 wt / v%, 0.9 mL).

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

[0062] Phenylboric acid (25 mg) and bromobenzene (0.2 mL) were added in sequence, and the reaction was carried out for 12 h for end-capping. After the reaction was completed, the mixture was precipitated in methanol (250 mL) and filtered. The filter residue was washed with acetone through a Soxhlet extractor, and the washed filter residue was vacuum dried to obtain the product.

[0063] Example 4 Performance Testing of Polymers

[0064] 1. Thermogravimetric and thermal stability testing

[0065] The samples were analyzed by TA TGA Q5000 and Netzzch DSC 300 under nitrogen flow at 15 °C min -1 and 10℃min -1 The thermal performance was tested at a heating rate of Figure 2 As shown. It can be seen that the glass transition temperature (T g s) all reached 100℃, and the decomposition temperature (T d s) has high thermal stability at around 400°C.

[0066] 2. Molecular weight and thermal properties testing of polymers

[0067] The H NMR spectra of the polymers were measured using Bruker Ascend TM 400 with deuterated chloroform and tetramethylsilane as solvent and internal standard, respectively. 1 H NMR). The number average molecular weight (M) was determined using Agilent 1260 Infinity with polystyrene and tetrahydrofuran as the standard and eluent, respectively. n) and polydispersity index (PDI). The results are shown in Table 1.

[0068] Table 1 Test results

[0069]

[0070] It can be seen from the results that the molecular weight distribution of the polymer is uniform and has good thermal stability.

[0071] 2. Electrochemical properties of polymers

[0072] The electrochemical performance was tested by cyclic voltammetry (CV) with 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 -1 Tetrabutylammonium hexafluorophosphate in acetonitrile.

[0073] The cyclic voltammetry (CV) curve of the polymer is shown in Figure 3 The detailed data are shown in Table 2. According to the empirical formula E HOMO =-(E ox +4.80-E fer )(eV) and E LUMO =-(E red +4.80-E fer )(eV), and the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels were obtained. ox ,E red and E fer are the oxidation potential, reduction potential of the polymer and the oxidation potential of ferrocene (Fc / Fc + ) values. The HOMO energy levels of PF-SO10, PF-SO10-BT1, and PF-SO10-DTBT1 are the same, which is due to the fact that the HOMO energy level is mainly dominated by the electron-donating unit of the polymer. Compared with PF-SO10, the LUMO energy levels of PF-SO10-BT1 and PF-SO10-DTBT1 are reduced due to the strong electronegativity of the BT unit. The electrochemical band gap (E g CV ) and the optical band gap (E g opt ) may be due to the lower content of BT and DTBT units in the polymer, resulting in lower absorption at long wavelengths.

[0074] Table 2 Cyclic voltammetry test data

[0075]

[0076] 3. UV-Vis absorption and PL spectra of polymers in toluene solutions and films

[0077] The UV-visible absorption spectrum and photoluminescence (PL) spectrum of the polymer were measured using a MAPADA UV-6100S UV-visible spectrophotometer and a F97 fluorescence spectrophotometer, respectively. Figure 4 shown.

[0078] The UV-visible absorption spectra and PL spectra of PF-SO10, PF-SO10-BT1 and PF-SO10-DTBT1 in toluene solution are shown in Figure 2. Figure 4 (a) and (b). The strong absorption peak at 389 nm can be attributed to the π-π* transition of conjugated fluorene ( Figure 4 (a)). Figure 4 In (b), the emission peak at 431 nm belongs to the PF-SO fragment, 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 film is similar to that in the solution ( Figure 4 (c)). Figure 4 (d) is the PL spectrum of the polymer in the film. The blue light emission intensity of PF-SO10-BT1 and PF-SO10-DTBT1 is significantly reduced, while PF-SO10-BT1 is almost completely quenched. The main emission peaks of PF-SO10-BT1 and PF-SO10-DTBT1 are red-shifted to 533nm and 631nm, respectively. This is mainly due to the enhancement of intermolecular interactions and energy transfer in the film state.

[0079] 4. Infrared Spectroscopy of Polymers

[0080] Fourier transform infrared (FT-IR) spectroscopy measurements from 4000 to 400 cm -1 The test was performed using the Thermo Fisher Nicolet iS10 infrared spectrometer by the dry potassium bromide tablet method. The results are as follows Figure 5 shown.

[0081] Example 5: Using organic conjugated polymer fluorescent materials to detect blood fingerprints

[0082] 1. Blood fingerprint deposition

[0083] Before testing, all substrate surfaces were strictly treated. They were first thoroughly cleaned with 75% ethanol solution to remove surface impurities, and then naturally dried under ambient conditions to ensure that the substrate was clean and free of contamination.

[0084] Six representative non-permeable objects were selected to comprehensively evaluate the effects of the visualization strategy on different substrates. These substrates include light / transparent white ceramics and glass, black painted copper-zinc alloy sheets with dark substrates, marble with complex background patterns, and highly reflective silver stainless steel and mirrors. In the experiment, volunteers uniformly used fingerprints containing 5 microliters of blood and pressed vertically on different substrates.

[0085] 2. Blood fingerprints appear

[0086] Alginate particles with low cost and strong stability were used as grinding auxiliary materials, and the grinding ratio of sodium alginate and the fluorescent polymer prepared in Examples 1-3 was 500:1 (m / m). A soft brush with flexible tendrils was selected as a tool to pick up the mixture of polymer powder and alginate, and the blood fingerprint was gently brushed to avoid damaging the ridge details of the lines. The fingerprint image was taken using a VSC8000 document inspection instrument, and the 365nm ultraviolet irradiation mode was selected to detect the fluorescence effect of the blood fingerprint, and then the camera control module of the document inspection instrument was used to shoot and fix the fingerprint image.

[0087] In order to evaluate the development effect, two common traditional blood fingerprint development methods were selected as controls, including amino black 10B (AB) and tetramethylbenzidine (TMB). The preparation method of amino black 10B is to add 1.2g of amino black 10B to 10ml of glacial acetic acid and 95ml of anhydrous ethanol and stir until completely dissolved. The resulting mixed solution is used as a development reagent. At the same time, 20ml of acetic acid and 180ml of anhydrous ethanol are mixed to prepare a detergent. The preparation method of tetramethylbenzidine is to dissolve 0.5g of TMB in 50ml of anhydrous ethanol, heat it in a water bath to dissolve it, and then drop 5ml of 30% hydrogen peroxide solution, stir it and set it aside. Since TMB and amino black 10B are solutions, in order to avoid the diffusion and blurring of the fingerprint lines when the fingerprint is displayed by spraying, the blood fingerprint needs to be fixed first. The experiment uses anhydrous ethanol as a fixative, which is dripped on the surface of the blood fingerprint and repeated 3 times.

[0088] Specific results such as Figure 6 As shown. From the experimental results, it can be seen that the undeveloped blood fingerprints on these substrates are visible but with low contrast; while the clarity and contrast of the fingerprint lines after development are significantly improved, and strong fluorescence is emitted under a 365nm ultraviolet light source, which can enhance the blood fingerprint patterns on various non-permeable objects and effectively solve the problem of low contrast of blood fingerprints on complex backgrounds (marble) and dark background surfaces. The developed fingerprints can show 2-3 levels of ridge details. The experimental results also show that alginate has almost no effect on the fluorescence effect of the copolymer, and does not damage the line details.

[0089] 3. Gray value calculation

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

[0091] The grayscale calculation software Image J was used to convert the RGB image into an 8-bit grayscale image. The blood fingerprint image obtained in the above experimental process was selected through the analysis function of the software to calculate the grayscale value range, generate the grayscale range curve, and quantitatively evaluate the image contrast effect.

[0092] The results are as follows Figure 7 As shown. Compared with the original blood fingerprint, the gray value range difference of the fingerprint after using red, green and blue fluorescent conjugated polymers on all substrate surfaces has increased significantly. From the change of grayscale value of all developed images on different substrates, due to the different brightness of the substrates, the average grayscale values ​​of fingerprints and backgrounds on different substrates are different, and the grayscale baselines are different. In addition, due to factors such as self-reflection (mirror and stainless steel) and complex colors (marble), the original grayscale range of the substrate is also different. Compared with TMB and amino black, the grayscale value difference range of red, green and blue fluorescent conjugated polymers is larger, which confirms that the blood fingerprint visualization strategy based on this patent effectively enhances the contrast in all cases.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. An organic conjugated polymer that can be used for blood latent fingerprint visualization, characterized in that: Its structural formula is as follows: Among them, Ar is or R1 is H, C1-C16 alkyl, C1-C16 alkoxy or C1-C16 alkanethio, R2 is H or C1-C16 alkyl, x is 0 or 0.01; n is a natural number of 1-300.

2. The organic conjugated polymer according to claim 1, characterized in that Its structural formula is any of the following: n＝1-300。 3. A method for preparing an organic conjugated polymer according to claim 1 or 2, characterized in that: It includes using M1, M2 and SO-Br2 as raw materials to carry out Suzuki coupling reaction to obtain: Among them, M1 is 2,7-di(4,4,5,5-tetramethyl-1,3-dioxaborolan-2-yl)-9,9-dioctylfluorene, M2 is 2,7-dibromo-9,9-dioctylfluorene, and SO-Br2 is 3,7-dibromo-S,S-dioxydibenzothiophene.

4. The method for preparing an organic conjugated polymer according to claim 3, characterized in that: The raw materials 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-di(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole.

5. The method for preparing an organic conjugated polymer according to claim 3, characterized in that: The molar ratio of M1, M2, SO-Br2 and Ar-Br2 is 50:(39-40):10:

1.

6. The method for preparing an organic conjugated polymer according to claim 3, characterized in that: The preparation method specifically comprises the following steps: (1) mixing a raw material, an organic solvent and an alkaline reagent to obtain a first mixture; (2) adding a palladium catalyst to the first mixture to carry out a coupling reaction, and then adding a capping agent to carry out a capping reaction to obtain a second mixture; (3) The second mixture is precipitated, filtered, washed and dried to obtain an organic conjugated polymer.

7. The method for preparing an organic conjugated polymer according to 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; Preferably, in step (1), the alkaline agent is any one or more of tetraethylammonium hydroxide, triethylamine, and N,N-diisopropylethylamine; Preferably, in step (2), the palladium catalyst is any one or more of palladium acetate, tetrakis(triphenylphosphine)palladium, palladium chloride, diphenylvinyldi(benzomethylene)palladium, tris(diphenylethylene)di(benzomethylene)palladium; Preferably, in step (2), a ligand is added to the palladium catalyst to increase its catalytic activity; more preferably, the ligand is a phosphine ligand, and further preferably, the phosphine ligand is any one or more of tricyclohexylphosphine, triphenylphosphine, XPhos, and SPhos; Preferably, in step (2), the molar percentage of the palladium catalyst to M2 is 0.5 mol%-5 mol%, and the molar ratio of the ligand to the palladium catalyst is (1-3): 1; Preferably, in step (2), the end-capping agent comprises phenylboronic acid and bromobenzene; Preferably, in step (2), the coupling reaction temperature is 60-90°C, the time is 6-24h; the end-capping reaction time is 6-12h; Preferably, 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 vacuum dried.

8. A blood latent fingerprint visualization reagent, comprising the organic conjugated polymer according to claim 1 or 2.

9. Use of the organic conjugated polymer according to claim 1 or 2 or the blood latent fingerprint visualization reagent according to claim 8 in detecting blood fingerprints.

10. A method for detecting latent fingerprints, characterized in that: The detection is performed using the organic conjugated polymer described in claim 1 or 2 or the blood latent fingerprint development reagent described in claim 8.

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