An application method of organic long afterglow material for solvent water content detection, acid vapor visualization, red long afterglow and dynamic anti-counterfeiting

Abstract

The application discloses an application method of an organic material based on an aggregation-induced emission / room-temperature phosphorescence dual characteristic, adopts N,N-di(2-pyridyl)-4-bromoaniline (abbreviated as NNPA) as a light-emitting unit, and is applied to solvent water content detection, acid vapor visualization, red long afterglow and dynamic anti-counterfeiting. The method comprises the following steps: (1) a standard curve between the two is established by utilizing the fact that the fluorescence emission peak of NNPA in a tetrahydrofuran / water system continuously red shifts with water content; (2) acid vapor visualization detection is realized based on the change of afterglow retention time caused by protonation; (3) dynamic anti-counterfeiting is realized by taking NNPA and an ethanol solution of NNPA and rhodamine B as anti-counterfeiting ink, combining different afterglow retention times and acid-caused afterglow quenching / alkali-caused recovery characteristics; and (4) red long afterglow is obtained by utilizing the Förster resonance energy transfer between NNPA and rhodamine B through melt blending.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic materials technology and information security technology, specifically involving a multimodal detection method based on organic room temperature phosphorescent (RTP) materials and a dynamic anti-counterfeiting and information encryption constructed using its long afterglow characteristics. Background Technology

[0002] The trace water content in organic solvents is crucial to the progress of chemical reactions, drug quality, and food safety. The traditional Karl Fischer method is cumbersome and requires toxic reagents; while existing fluorescent probe methods often suffer from aggregation-induced quenching (ACQ) or nonlinear inversion of fluorescence signals in high water content regions, making it difficult to achieve wide-range, high-precision quantitative detection.

[0003] Furthermore, acidic vapors are prevalent in industrial production and laboratory environments, and are corrosive and harmful to health. Existing acidic gas detection methods mostly rely on electrochemical sensors or complex optical instruments, making it difficult to achieve low-cost, naked-eye-visualized, rapid on-site screening.

[0004] In the field of anti-counterfeiting technology, traditional fluorescent anti-counterfeiting technology faces challenges due to its low technical threshold and ease of replication and counterfeiting. Although long-afterglow materials (phosphorescent powder) provide anti-counterfeiting measures in the time dimension, existing inorganic long-afterglow materials usually contain rare earth or heavy metal elements and have poor flexible processing performance; while most pure organic long-afterglow materials have short afterglow time, low brightness, and lack multiple response characteristics to external stimuli, making it difficult to meet the needs of high-end dynamic encryption. Summary of the Invention

[0005] The present invention aims to address the deficiencies in the prior art and provide a new application for a class of organic long afterglow materials based on N,N-bis(2-pyridyl)-4-bromoaniline (NNPA), specifically providing an application method for quantitative moisture content, visualization of acid vapor, and dynamic anti-counterfeiting.

[0006] The technical solution of the present invention is as follows: An application method for organic long-afterglow materials used in moisture quantification, acid vapor visualization, and dynamic anti-counterfeiting, employing N,N-bis(2-pyridyl)-4-bromoaniline (NNPA) as the core functional material, includes at least one of the following applications: (1) A fluorescence quantitative detection method for moisture content in organic solvents; (2) A time-resolved visual detection method for acid vapor; (3) A multi-dimensional dynamic anti-counterfeiting encryption method based on long afterglow characteristics.

[0007] (4) Preparation method of red long afterglow.

[0008] Furthermore, the quantitative moisture detection method utilizes the "wet aggregate" effect of NNPA. When NNPA is in dry THF solvent, intramolecular charge transfer is limited, and the emission peak is located at a shorter wavelength. With the addition of water, water molecules form a hydrogen bond network at the aggregate interface, enhancing the solvation effect and causing a significant red shift in the fluorescence emission peak. Unlike traditional AIEgens, which show a signal reversal trend at high water content, NNPA exhibits a monotonic red shift characteristic across the entire water volume fraction range of 0% to 90%. Specifically, in the low water content range of 0% to 15%, the emission peak exhibits a nonlinear and rapid red shift with increasing water content. This range has extremely high optical response sensitivity to trace amounts of water, which can be determined by the nonlinear fitting formula (y1 = 415.17 - 32.27 / (1 + x / 12.09) ^1.21, R1). 2 = 0.97075) to achieve precise quantification of trace amounts of water; exhibiting excellent linearity within the range of 15% to 90% (y2 = 394.23 + 0.435x, R2) 2 = 0.99343), thus it can be used as a "spectral ruler" to accurately achieve rapid screening of moisture content over a wide range.

[0009] Furthermore, the described acid vapor visualization detection method is based on the protonation response mechanism of NNPA. The pyridine nitrogen atom in the NNPA molecule is Lewis basic; when exposed to acidic vapor, the nitrogen atom protonates to form a cation, disrupting the original intramolecular charge transfer channels and enhancing the non-radiative transition rate, leading to rapid quenching of room-temperature phosphorescence. Since the degree of quenching is directly related to the acid concentration, a semi-quantitative naked-eye analysis of the acid concentration can be achieved by observing the rate at which the afterglow disappears after the UV lamp is turned off.

[0010] Furthermore, the dynamic anti-counterfeiting encryption method utilizes the intrinsic long afterglow characteristic of NNPA and its energy transfer characteristics after blending with dyes. NNPA crystals (prepared by slow diffusion of petroleum ether into a dichloromethane-saturated solution of NNPA) can continuously emit a green afterglow for approximately 3 seconds after the 365 nm ultraviolet light is turned off; by blending with Rhodamine B (RhB) (NNPA:RhB mass ratio = 100:3), the green phosphorescence can be converted to red emission using the Förster resonance energy transfer (FRET) mechanism, with an afterglow time of approximately 0.8 seconds. This significant difference in lifetime allows for information encryption in the temporal dimension: both red and green patterns are visible immediately after the light is turned off; as time progresses, the red afterglow disappears first, leaving only the green pattern; eventually, all afterglow disappears. This dynamic change is extremely difficult to counterfeit. To apply this technology to flexible carriers, this invention provides a simple method for preparing long-afterglow filter paper: Ordinary qualitative filter paper is immersed in a 25 mg / mL anhydrous ethanol solution of NNPA for 10-30 minutes, then removed and dried in a 40-60°C forced-air drying oven to obtain a first filter paper with green afterglow characteristics. Another filter paper is immersed in a mixed ethanol solution of NNPA and Rhodamine B (RhB), where the NNPA concentration is 25 mg / mL and the mass ratio of NNPA to RhB is 100:3, for 10-30 minutes, then removed and dried to obtain a second filter paper with red afterglow characteristics. By cutting, folding, and assembling the above filter papers, a three-dimensional long-afterglow origami model with spatiotemporal dual encryption characteristics can be constructed. This model exhibits preset dynamic three-dimensional pattern changes at different delay times, greatly increasing the complexity and difficulty of cracking the anti-counterfeiting structure.

[0011] Furthermore, this invention provides a time-dependent dynamic writing encryption method based on in-situ coordination: using an anhydrous ethanol solution of NNPA as the first ink, and an ethanol / water solution of NNPA and aluminum trichloride (AlCl3) (ethanol:water = 50:1) as the second ink. The concentration of NNPA in both inks is 25 mg / mL, and the concentration of AlCl3 is 12.5 mg / mL. The fluorescence emission of the second ink shows a significant redshift compared to the first ink, and its long afterglow lifetime is shorter. By combining these two inks on a substrate, after ultraviolet light is turned off, different areas sequentially appear and disappear over time due to differences in afterglow lifetime (different decay rates), forming a dynamically evolving encrypted information stream, thereby achieving an advanced anti-counterfeiting function that can be verified without complex equipment.

[0012] The beneficial effects of this invention are as follows: (1) High detection sensitivity and wide linear range: Moisture detection covers the range from trace to large amount, solving the problem of signal distortion of traditional fluorescent probes in the high moisture content area.

[0013] (2) Visualization and portability: Acid vapor detection does not require an external power supply or complex reading equipment. The danger level can be determined by observing the duration of the afterglow with the naked eye, making it suitable for emergency monitoring.

[0014] (3) High security anti-counterfeiting: It combines multiple encryption dimensions such as spectrum, lifetime and stimulus response, especially time-gated decryption technology, which greatly improves the threshold for counterfeiting.

[0015] (4) Green and environmentally friendly: The materials are simple to synthesize, and the anti-counterfeiting ink uses ethanol as a solvent, which avoids the use of heavy metals and meets environmental protection requirements. Attached Figure Description

[0016] Figure 1 , Figure 2 and Figure 3 These are the proton, carbon, and mass spectra of the target product NNPA obtained in Example 1; Figure 4 (a) Normalized UV-Vis absorption spectra of NNPA in different solvents; (b) Fluorescence emission spectra of NNPA in different solvents (concentration 1×10⁻⁶). −5 (c) Fluorescence emission spectra of NNPA under different pH conditions. (d) NNPA (1×10⁻⁶ mol / L). −5 mol / L) in different water volume fractions ( f w Fluorescence emission spectrum of the THF / H2O mixture (Illustration: THF / H2O mixture before aggregation) f w =0% and after aggregation ( f w =60%) Tyndall effect). (e) NNPA in THF / H2O mixture system f w Variations in fluorescence emission intensity and peak maximum (Illustration:) f w Fluorescence micrographs of the THF / H2O mixture at 60% and 90% concentrations. (f) f w Linear relationship with fluorescence emission peak position in the ranges of 0%–15% and 15%–90%.

[0017] Figure 5 (a) NNPA in glassy DMSO solution (77 K, 1×10⁻⁶) −5 mol / L, λ ex(a) Afterglow photographs of NNPA crystal at 365 nm and NNPA crystal at room temperature. (b) Normalized fluorescence and delayed emission spectra of NNPA crystal at room temperature (delay time = 1 ms). (c) Phosphorescence decay curve of NNPA crystal at 519 nm (λ) ex =365 nm).

[0018] Figure 6 (a) Photographs of NNPA:RhB composites with different mass ratios (100:1, 100:3, 100:5, 100:10, and 100:50) under 365 nm UV irradiation (left) and after excitation is stopped (right). (b) Normalized phosphorescence emission spectrum of NNPA crystals and absorption spectrum of solid-state RhB. (c) Attenuation curves of NNPA:RhB (100:3) composites at wavelengths of 519 nm (green, corresponding to FRET donor emission) and 605 nm (red, corresponding to FRET acceptor emission).

[0019] Figure 7 (a) Information encryption based on NNPA@filter paper and NNPA@RhB@filter paper, and (b) a three-dimensional origami structure. (c) Information writing and multi-layer encryption using secure NNPA ink (0.05 g NNPA dissolved in 2 mL anhydrous ethanol). (d) Dynamic information encryption based on NNPA@filter paper and NNPA@AlCl3@filter paper.

[0020] Figure 8 Fluorescence spectra of NNPA crystals after fumigation with (a) 1 mol / L, (b) 4 mol / L, (c) 8 mol / L and (d) 12 mol / L hydrochloric acid vapor.

[0021] Figure 9 Fluorescence and afterglow images of NNPA crystals after treatment with (a) 1 mol / L, (b) 4 mol / L, (c) 8 mol / L and (d) 12 mol / L hydrochloric acid vapor and triethylamine fumigation.

[0022] Figure 10 Fluorescence and afterglow images of filter paper loaded with NNPA and different metal salts (NNPA : M²⁺ / M³⁺ = 2 : 1, mass ratio). Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] Example 1 2,2'-Dipyridylamine (1.0 g, 5.8 mmol), 1,4-dibromobenzene (2.6 g, 11.6 mmol), cesium carbonate (4.7 g, 14.5 mmol), and cuprous iodide (0.11 g, 0.58 mmol) were dissolved in DMAC (10 mL). The resulting mixture was heated under reflux for 5 hours. After cooling to room temperature, it was extracted three times with ethyl acetate and saturated brine. The combined organic phases were dried over anhydrous Na₂SO₄. The crude product was concentrated under reduced pressure by rotary evaporation and purified by silica gel column chromatography using ethyl acetate / petroleum ether (EA / PE, v / v = 1:15) as eluent to give the target product as a white solid. Yield: 80%. Melting point: 124 °C.

[0025] Example 2 Accurately weigh 3.26 mg of NNPA solid and place it in a 100 mL volumetric flask. Dilute to volume with anhydrous tetrahydrofuran (THF) to obtain a concentration of 1 × 10⁻⁶ mg. -4 The stock solution was prepared at mol / L. Ten blank vials were prepared, and 0.2 mL of the above THF solution was added to each vial using a pipette. Then, 1.8 mL, 1.6 mL, 1.4 mL, 1.2 mL, 1.0 mL, 0.8 mL, 0.6 mL, 0.4 mL, 0.2 mL, and 0 mL of THF were added sequentially. Then, 0 mL, 0.2 mL, 0.4 mL, 0.6 mL, 0.8 mL, 1.0 mL, 1.2 mL, 1.4 mL, 1.6 mL, and 1.8 mL of distilled water were added sequentially. The solutions were sonicated for 1 minute and allowed to stand overnight to prepare the desired solutions. f w THF / H₂O mixed solutions with concentrations of 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% were used. A fluorescence spectrophotometer was used, with the excitation wavelength set to 330 nm, to record the fluorescence emission spectra in the range of 350 nm to 650 nm. f w Plot a graph with the x-axis representing the maximum emission wavelength and the y-axis representing the maximum emission wavelength. f w Nonlinear and linear curves were obtained by fitting within the ranges of 0-15% and 15-90%, respectively.

[0026] Example 3 NNPA crystals or their ethanol solution were coated onto filter paper and dried (0.05 g NNPA dissolved in 2 mL anhydrous ethanol) to prepare a detection card. A 12 mol / L concentrated hydrochloric acid solution was placed in a beaker, with an inverted small bottle placed inside, and the crystals or detection card placed on top. A larger inverted beaker was then placed outside, exposing the crystals or detection card to the volatile HCl vapor. The crystals or detection card were irradiated with a 365 nm UV lamp for 60 seconds, then the light source was turned off. The duration of afterglow was recorded at different times until it was almost invisible. The process was repeated in a low-concentration acidic environment, recording the duration of afterglow at different times under the same acidic conditions until it was almost invisible, thus achieving a naked-eye graded warning for acid vapor concentration.

[0027] Example 4 0.5 g of NNPA was dissolved in 20 mL of anhydrous ethanol and sonicated until completely dissolved to obtain green afterglow ink. 0.5 g of NNPA and 15 mg of Rhodamine B were dissolved in 20 mL of anhydrous ethanol and sonicated until completely dissolved to obtain red afterglow ink. Filter paper sheets measuring 10 × 20 cm were immersed in the two inks respectively, removed and dried after 30 minutes to obtain filter papers with different afterglows. Two "birds" folded from the NNPA filter paper and NNPA@RhB filter paper respectively showed blue and red fluorescence under ultraviolet light; after the light was turned off, they exhibited green and red phosphorescence. Thanks to the significant difference in afterglow duration, the afterglow of the red bird disappeared within 0.6 seconds, leaving only the green bird visible. This dynamic conversion of phosphorescence from planar to three-dimensional space demonstrates enormous commercial potential in the field of smart packaging. Based on the two filter papers with different afterglow colors and different afterglow retention times, a digital encryption codebook was constructed. Under ultraviolet light, the two substrates exhibit blue and red fluorescence, respectively, making the coded information invisible. However, once excitation stops, the afterglow color (green / red) and pattern shape correspond to a specific numerical code (0–9). Crucially, time-resolved decryption can be achieved by utilizing the difference in dynamic decay behavior: the red afterglow decays faster than the green, revealing the correct code ("0304") only within a specific time window (0 s), while the information cannot be deciphered during dynamic observation (1–3 s).

[0028] Example 5 Commercially available filter paper was selected as the substrate. The green afterglow ink from Example 4 was used to write "SAFE" and "安全". It is invisible under sunlight, but shows bright blue fluorescence when excited by 365 nm ultraviolet light; after turning off the ultraviolet lamp, bright green phosphorescence appears. It is worth noting that this ink exhibits reversible protonation / deprotonation behavior. Fumigation with acidic vapor can quench the phosphorescence and enhance the fluorescence visibility, while subsequent fumigation with triethylamine can restore the original room temperature phosphorescence (RTP), confirming the erasable property of this ink.

[0029] Example 6 Weigh 0.5 g of NNPA, and then weigh 0.25 g of various metal salts including: AlCl3, Cd(ClO4)2, Ni(ClO4)2, Co(ClO4)2, Fe(ClO4)3, Cu(ClO4)2, Mg(ClO4)2, Zn(ClO4)2, Ca(ClO4)2 or Ba(ClO4)2. Dissolve them in 20 mL of ethanol and 0.4 mL of water, and perform ultrasonic treatment. Immerse the filter paper with a size of 1 × 2 cm into the mixture for 30 minutes, take it out and dry it to obtain filter paper with different afterglows.

[0030] Example 7 Use the ethanol solution of NNPA in Example 4 and the ethanol aqueous solution of NNPA and AlCl3 in Example 6 to write "HELLO". Due to the protonation effect induced by the hydrolysis of AlCl3, the written words with the two inks have differences in fluorescence color (blue vs cyan) and afterglow lifetime, successfully realizing a dynamic anti-counterfeiting pattern ("HELLO" turning into "1110"). These multi-stimulus response behaviors verify the potential of NNPA as an advanced information security multifunctional platform.

[0031] Example 8 A composite system was prepared by melt blending NNPA and rhodamine B at a mass ratio of 100:1, 100:3, 100:5, 100:10, and 100:50. This composite system can emit red long afterglow of 600 - 655 nm after turning off the ultraviolet light.

[0032] The structural characterization data of the obtained target product NNPA are shown as follows: 1 H NMR (500 MHz, CDCl3) 1H NMR (500 MHz, Chloroform-d) δ 8.34 (dd, J =5.0, 1.9 Hz, 2H), 7.61-7.55 (m, 2H), 7.50-7.46 (m, 2H), 7.09-7.05 (m, 2H),7.01 -6.94 (m, 4H). 13 C NMR (100 MHz, CDCl3) δ 157.67, 148.60, 143.97, 137.80,132.79, 128.67, 118.78, 118.55, 117.00. HRMS (MALDI-TOF): m / z 326.0296 [[M +H] + , Calculated value 326.0293]. Based on the above characterization data, the structure of the target compound is inferred as follows: NNPA.

Claims

1. A device for detecting water content in solvents, visualizing acid vapor, and displaying red long afterglow and dynamic properties. The method for applying organic long afterglow materials for anti-counterfeiting features: The method uses N,N-bis(2-pyridyl)-4-bromoaniline, abbreviated as NNPA, whose chemical structure is as follows. The application method includes at least one of the following applications: (1) a fluorescence quantitative detection method for water content in organic solvents; (2) a time-resolved visualization detection method for acid vapors; (3) a multi-dynamic anti-counterfeiting encryption method based on long afterglow characteristics; and (4) a red long afterglow based on Förster resonance energy transfer. 。 2. A fluorescence quantitative detection method for water content in organic solvents according to claim 1, characterized in that: NNPA was dissolved in the aqueous organic solvent to be tested to prepare a solution of 1×10⁻⁶. -5 A mol / L sample solution was prepared; the fluorescence emission spectrum of the sample solution was measured using a fluorescence spectrophotometer. The water content in the tested organic solvent was calculated based on the fluorescence emission peak position and a pre-established standard curve of "water volume fraction - emission wavelength". In the tetrahydrofuran / water system, the water volume fraction exhibited a non-linear relationship with the fluorescence emission peak position within the range of 0% to 15%, with the non-linear relationship being y1 = 415.17 - 32.27 / (1 + x / 12.09)^1.21, and the non-linear correlation coefficient R1. 2 = 0.97075; The water volume fraction in the range of 15% to 90% shows a linear relationship with the fluorescence emission peak position, with the linear relationship being y2 = 394.23 + 0.435x and the linear correlation coefficient R² = 0.99343.

3. A time-resolved visual detection method for acidic vapor as described in claim 1, characterized in that: The test card was prepared by coating NNPA crystals or a 25 mg / mL ethanol solution onto filter paper and drying it at 40-60°C. The crystals or test card were then exposed to the hydrochloric acid vapor environment to be tested. The material was excited with ultraviolet light at a wavelength of 365 nm for 60 seconds and then the light source was turned off. The duration of the afterglow of the material was recorded using the video recording function of a mobile phone. The concentration level of acidic vapor is determined by the duration of the afterglow; the higher the concentration of acidic vapor, the faster the afterglow quenches and the shorter its duration.

4. The multi-layered dynamic anti-counterfeiting encryption method based on long afterglow characteristics according to claim 1, characterized in that: A 25 mg / mL ethanol solution of NNPA was used as the green ink; a 25 mg / mL ethanol solution of NNPA with a mass ratio of 100:1 (NNPA to Rhodamine B) was used as the red ink. Filter paper was immersed in the two inks respectively, removed and dried after 30 minutes to obtain filter paper with different afterglow. Information encryption and anti-counterfeiting products were prepared by writing with the above inks or by cutting and shaping the filter paper with different afterglow and folding it in three dimensions. Different hidden information was read by irradiation and removal with ultraviolet light at different delay time periods.

5. The application method according to claim 4, characterized in that: The information encryption and anti-counterfeiting products can also be fumigated with hydrochloric acid vapor to quench the afterglow or change the fluorescence color of the treated area, thereby forming a second layer of encrypted information; subsequently, the information can be reproduced by fumigation with triethylamine.

6. The red long afterglow based on Förster resonance energy transfer according to claim 1, characterized in that: A composite system was prepared by melt blending NNPA and Rhodamine B at mass ratios of 100:1, 100:3, 100:5, 100:10, and 100:

50. This composite system can emit a long red afterglow of 600-655 nm after ultraviolet light is turned off.

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