Dual-mode Anti-counterfeiting

With the development of information technology and economy, the demand for anti-counterfeiting technology is becoming increasingly urgent in many fields such as food, medicine, clothing, and communication. The most common single color anti-counterfeiting is limited due to its single mode practical application. Herein we present a multimode anti-counterfeiting film based on Y-TCPP/DBCZ PVA composite gel film (Figure 6a). Considering the risk of MOF being damaged by direct exposure to alkali, writing with PVA dispersion of DBCZ and MOF is more suitable than applying MOF and DBCZ onto PVA films. We prepared multifunctional gel 1 (a dispersion of 1 mg MOF, 100 mg PVA, and 4 mL water), gel 2 (a dispersion of 0.2 mg DBCZ, 100 mg PVA, and 4 mL water), and gel 3 (a dispersion of 1 mg MOF, 0.2 mg DBCZ, 100 mg PVA, and 4 mL water) as ink for writing. Afterwards, use multifunctional gel 1, 2, and 3 to write the numbers ”1”, ”3”, and ”6” on the substance, respectively. Due to insufficient sample size to construct continuous strokes, additional multifunctional gel is added to the corresponding stroke. After drying and cross-linking, the composite gel film is immersed in a Tris solution with pH=13. After the fluorescence turns red, excess alkaline solution is wiped off and dried. The dried film exhibits obvious red ”1”, blue ”3”, and rose red ”6” under excitation of 365 nm light. After turning off ultraviolet light, a yellow-green ”3” and a faintly visible ”6” can be seen. After soaking the film in an artificial sweat solution at pH=4.7 for 20 minutes and drying, the light red ”1”, blue ”3”, and light purple ”6” were displayed under excitation of 365 nm light. After turning off ultraviolet light, the yellow-green ”3” remains unchanged from before sweat treatment, and the weaker lightness ”6” is clearly visible (Figure 6b). These experimental results prove the application prospect of Y-TCPP/DBCZ PVA mixed gel in dual-mode anti-counterfeiting materials, and show the application value of organic afterglow materials with adjustable solid emission in anti-counterfeiting.

Conclusions

Based on the advantage of Y-TCPP MOF for OH^- specific response, a two-color stimulus response gel was constructed in combination with DBCZ PVA system, and a sweat pH sensing and anti-counterfeiting mode that is economical, applicable, easy to prepare and operate was found. A MOF with specific response to OH- was synthesized and combined with the DBCZ PVA system to construct a stimulus responsive thin film material with fluorescence red blue color changing with pH, which has good repeatability. The phosphorescence of the mixed system exhibits a significant decrease in emission intensity and luminescence lifetime at pH=13. The above spectroscopy results are visible to the naked eye. A sweat pH sensor was constructed and exhibited different luminescence changes under different conditions. The effect of different pH sweat on luminescence may be used for health testing. A fluorescent phosphorescent composite anti-counterfeiting material has been constructed, which can achieve dual-mode anti-counterfeiting performance. Under alkaline and sweat conditions, it exhibits different fluorescence and phosphorescence properties visible to the naked eye.

Experimental

Materials

Yttrium nitrate hexahydrate (Y(NO₃)₃·6H₂O, 99.9%), 7H-dibenzo[c, g]carbazole (DBCZ, 98%), polyvinyl alcohol 1799 (PVA, 1799 type, alcoholysis degree 98-99%), lactate (90%) were purchased from Aladdin Co., Ltd. Tetra-(4-carboxyphenyl) porphyrin (TCPP, 95%) was purchased from Leyan Co., Ltd. Glutaraldehyde (25% aqueous solution), hydrochloric acid (36%-38% HCl aqueous solution), urea (99.0%), glucose (AR), tris-(hydroxymethyl)aminomethane (Tris, 99.5%), sodium hydroxide (NaOH, 99%) sodium chloride (NaCl, 99.5%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Artificial sweat were purchased from Shenzhen Zhongwei equipment co., LTD. All other solvents and reagents were of analytical grade and used as received. Milli-Q water (18.2MΩ·cm) was used in all cases.

Instruments

Use GeminiSEM 500 to record the scanning electron microscope (SEM) image and the X-ray energy dispersion spectrum (EDS) image. The steady-state fluorescence and phosphorescence measurements were obtained on the Hitachi F-4600 fluorescence spectrophotometer at room temperature. X-ray photoelectron spectroscopy (XPS) was performed on ESCALAB 250Xi X-ray photoelectron spectrometer. X-ray diffraction (XRD) was performed on the Rigaku SmartLab 9kW. Use SHIMADZU UV-2700 PC spectrophotometer to measure UV-vis absorption spectrum. Fourier transform infrared spectroscopy (FT-IR) was measured by using BRUKER TENSOR II.

Preparation of Y-TCPP MOF

The synthesis method is taken from the previous report.^[27] TCPP (21.0 mg, 0.0266 mmol) was completely dissolved in DMF (45.0 mL) in a 100 mL round bottom flask. Y(NO₃)₃·6H₂O (15.0 mg, 0.0392 mmol) was dissolved in 3 mL ultra-pure water. Then Y(NO₃)₃ solution was added into TCPP solution and stirred evenly. The mixture was stirred and heated to 60 °C for 2 h, further heated to 100 °C for 2 h. After cooling, the reacted liquid was centrifuged at 10000 rpm for 25 min, collected the precipitation, and washed twice with ethanol to obtain brown solid. The brown product attached to the bottle wall could be dispersed by soaking in anhydrous ethanol. Finally, Y-TCPP was stored in ethanol and need to be shaken to uniform dispersion before use. The concentration of the dispersion solution is obtained by measuring a quantitative liquid in a bottle and weighing the solid after drying in a vacuum oven at 60 °C for 30 hours.

Preparation of Y-TCPP/DBCZ PVA mixed gel

100 mg of PVA was added into a glass bottle containing 4 mL of ultra-pure water, and heated at 90 °C until it is completely dissolved. After cooling, 1 mg of centrifuged Y-TCPP MOF was added and the mixed solution was ultrasoniced until well-distributed. 1 mg of DBCZ was dissolved in 0.1 mL of ethanol and ultrasoniced until it is fully dissolved. 20 μL DBCZ solution was added to PVA solution and stirred for 0.5 h. The dispersion solution is light brown and unobvious turbidity was observed. 0.1 mL of sample was dropped onto a glass sheet and dried in air at 40 °C for 1 hour to form the gel film.

Preparation of water-resistant mixed gel

0.15 mL of 25% glutaraldehyde, 0.25 mL of concentrated hydrochloric acid and 2.6 mL of acetone was stirring evenly as the cross-linking solution. The gel film was completely immersed in a 5 mL beaker containing 3 mL cross-linking solution for 5 min, then take it out and blow off the excess liquid with nitrogen, placed in a ventilated environment for 1 h. The gel film is stable and can not be eroded by water.

Supporting Information

The supporting information for this article is available on the WWW under https://doi.org/10.1002/cjoc.2023xxxxx.

Acknowledgement

This study was supported by the Basic Research Fund for the Central Universities (WK3450000006).

References