Water-sensitive fluorescent microgel inks to produce verifiable information for highly secured anti-counterfeiting

Abstract

The decryption and verification of encrypted information via a simple and efficient method is always difficult and challenging in the field of information security. Herein, a series of water-sensitive fluorescent microgels are fabricated for highly secured anti-counterfeiting with authenticity identification. The initial negatively charged microgels (MG) are made up of N-isopropylacrylamide (NIPAM), acrylic acid (AAc) and anthracen-9-yl acrylate (9-ANA, blue fluorescent monomer). The prepared MGs can bind cationic fluorescent dyes such as 5-aminofluorescein (FITC, green fluorescent dye) and rhodamine B (Rh B, red fluorescent dye) via electrostatic interaction, emitting multi-fluorescent colors based on the fluorescence resonance energy transfer (FRET) process. Furthermore, the fluorescence colors of MG-derived systems can be rapidly changed by swelling in water, which can block the FRET process and change the aggregation state of dyes. With the assistance of inkjet printing, multi-color security patterns can be designed and encoded, which can be revealed by UV irradiation and further verified by water stimulation. This study has pioneered a novel strategy to verify the authenticity of decrypted information, which greatly improves the security level of information.

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New concepts

The rapid advancement of technology has fueled a heightened demand for anti-counterfeiting labels, prompting the need for efficient methods in high-security label production. This study focuses on the development of advanced encryption labels capable of decoding and authenticating encoded information. It explores water-responsive multicolor fluorescent microgel systems, formed by combining microgels with cationic fluorescent dyes like FITC and Rh B. Synthesized from NIPAM, AAc, and 9-ANA, these microgels expand rapidly in water, altering the fluorescence colors. Leveraging this, multi-color anti-counterfeiting labels are created using inkjet printing, revealing concealed information under UV light and undergoing water-based authentication. This research provides a robust methodology for crafting secure, easily decipherable anti-counterfeiting materials to meet the evolving needs of authentication in a technologically driven landscape.

Introduction

The rapid development of science and technology has brought convenience for our life, but also provided an opportunity for criminals to seek profits by making false information or commodities. The appearance of anti-counterfeiting labels has effectively reduced the occurrence of such incidents to a certain extent.^1–5 Nevertheless, common commercial security labels are generally manufactured through established procedures or methods, and hence their high predictability and low security have led to the emergence of corresponding fake anti-counterfeiting labels. Therefore, it is urgent to develop new anti-counterfeiting materials and adopt cutting-edge anti-counterfeiting techniques.^6–12

Fluorescent anti-counterfeiting labels have attracted wide attention due to the characteristic of fluorescence color concealment, which means that it can only be displayed at a specific excitation wavelength.^13–19 For instance, Wu and colleagues¹⁰ encoded multiple fluorescent patterns on a shape memory hydrogel, and the hidden informations could only be decrypted under UV irradiation after shape recovery. Wang and coworkers²⁰ combined an oxygen-sensitive probe with an oxygen permeable polymer matrix to achieve high security of multilevel information. The concealed message could only be visible when exposed to a certain concentration of oxygen under UV light. Unlike conventional fluorescent anti-counterfeiting strategies, these elegant attempts can improve the security of the message by adding decryption procedures. However, they cannot eradicate the trouble caused by the imitation of fluorophores with similar colors.^7,21–23

A security label with dynamic change of fluorescence color can make up for the inherent defects that static fluorescence has brought.^24–28 Wang's team fabricated dual-mode anti-counterfeiting patterns by photo-responsive supramolecular polymers consisting of anthracene-endoperoxide and energy acceptor fluorescent molecules. The process of FRET could be subtly regulated by either a gas-induced polymerization process or a photo-triggered anthracene–peroxide–lactone conversion, resulting in high-contrast fluorescence variations in three separate states.²⁹ Previously, our group designed a urea-containing hydrogel for protecting multistage information, where a protonated fluorescent unit could coordinate with various metal ions to load fluorescent information. When exposed to urea solution, the hidden information could be quickly displayed and erased during the procedure.³⁰ Though controllable dynamic fluorescence transformation has successfully been achieved, it is still a huge challenge to quickly and effectively identify the authenticity of decrypted information. Moreover, another challenge encountered in dynamic coding of multicolor fluorescence patterns is how to improve the accuracy and complexity of loading information.

As a class of stimulus-responsive gels,^13,31–36 polymeric microgels have the advantages of designability in terms of fast responsiveness and printable sizes, which is expected to be used for fluorescent labels via inkjet printing technology. Especially, such microgels show a rapid response to water stimulation, accompanied by changes in volume/morphology. Herein, anionic microgels (MG) were constructed by copolymerization of N-isopropylacrylamide (NIPAM), acrylic acid (AAc) and anthracen-9-yl acrylate (9-ANA) (Scheme 1(A)), which displayed blue fluorescence and exhibited rapid and conspicuous volume changes in the presence or absence of water (Fig. S1, ESI†). The conspicuous volume changes stemmed the robust hydrogen bonding between water molecules and polymer chains, which facilitated the swift expansion of the microgel upon exposure to water, thus achieving rapid response times. Moreover, the deprotonated MG microgels could bind various cationic fluorescent dyes via electrostatic interaction. As typical representatives of cationic dyes, rhodamine B (Rh B, red dye) and protonated 5-aminofluorescein (FITC, green dye) were selected for obtaining MG-derived systems with multicolor fluorescence emission (Scheme 1(B)). The MG-derived systems showed excellent fluorescence discoloration ability upon water stimulation (Scheme 1(C)), which could block the FRET process between the anthracene groups and the cationic dyes. In the meanwhile, the fluorescent color could also be affected by the aggregation state of dyes, which changed during microgel swelling. The instant dynamic fluorescence color-changing ability gave microgels the potential to be fluorescent anti-counterfeiting inks (Scheme 1(D)). Assisted by an inkjet printer, a large-area information could be encoded, which could be read upon exposure to UV light and further identified the authenticity by water stimulation (Scheme 1(E)–(G)). This study is the first to achieve high security levels by verifying the decrypted information, providing ideas for the development of novel anti-counterfeiting materials.

Scheme 1 Schematic illustration of multicolor fluorescent inks for information encryption. (A) The chemical composition of fluorescent microgel inks. Microgel structures and the ensuing fluorescence color alterations within MG-derived microgels, comprising MG, MG-RhB, and MG-FITC, across dehydration (B) and hydration (C). (D)–(G) The information printed with multicolor fluorescent inks, which can be displayed under UV light and verified by water stimulation.

Results and discussion

Synthesis and characterization of MG-derived systems

Poly(NIPAM-co-AAc-co-9-ANA) microgels (MG) were synthesized by a radical terpolymerization of NIPAM, AAc and 9-ANA (emitting blue fluorescence) via an emulsion polymerization method (Fig. 1(A)). ¹H nuclear magnetic resonance (NMR) spectroscopy was conducted to reveal that 9-ANA has been successfully introduced into the microgel networks (Fig. 1(B)). The prepared hydrated microgels with an average diameter of 155.8 nm (Fig. 1(C)) exhibited negative charges (Fig. S2, ESI†), which provided anchoring points for the introduction of positive fluorescent dyes. In addition, SEM images (Fig. 1(D) and Fig. S3, ESI†) showed that the swollen microgels were perfectly spherical and homogeneous. Furthermore, the microgels exhibited exceptional photophysical properties due to the existence of blue fluorescent emitter 9-ANA. As shown in Fig. 1(E), the MG solution displayed a blue fluorescence when excited at wavelengths ranging from 250 to 400 nm, especially at 254 nm (Fig. 1(F)), which was also recorded by confocal laser scanning microscopy (CLSM) (Fig. 1(G)). One thing that needs to be pointed out is that the particle size of the microgels significantly decreased to less than 100 nm after dehydration (Fig. S4, ESI†), which laid the foundation for the change of fluorescence colors. It could be preliminarily proved that the fluorescence intensity of MG is greatly weakened in the dry state (Fig. S5–S7, ESI†), which is caused by the aggregation-induced quenching (ACQ) effect of anthracene groups.

Fig. 1 Morphology, composition and photophysical studies of prepared microgels. (A) The synthesis routine of MG. (B) ¹H NMR spectrum of MG. (C) DLS data and (D) SEM image of MG. (E) PL mapping spectra and (F) fluorescence spectra of MG solution. Insets: Photographs of the corresponding MG solution. (G) CLSM image of MG.

Multicolor fluorescence emission based on MG-derived systems

MG containing negative-charged carboxylate functional groups could bind positively charged fluorophores by electrostatic interaction, thus achieving multicolor fluorescence emission (Fig. 2(A)). As two simple and easily available fluorescent dyes, rhodamine B (Rh B) and 5-aminofluorescein (FITC) were selected because they are positively charged or easily protonated. Herein, the MG-derived systems, including MG-FITC (only adding FITC), MG-Rh B (only adding Rh B) and MG-1F1R (adding FITC and Rh B in a molar ratio of 1 : 1), were obtained by immersing pristine MG powder into a solution containing Rh B or FITC or both, before being dried. Following the incorporation of cationic dyes, the zeta potentials of the MG derivative systems are recorded as −0.5 mV (MG-FITC) and −3.1 mV (MG-Rh B) (Fig. S8, ESI†), which were higher than that of pure MG, indicating the successful anchoring of cationic dyes. Nevertheless, the introduction of cationic dyes did not have any effect on the microgel size (Fig. S9, ESI†), which were stable even after three months of storage (Fig. S10, ESI†). Additionally, it was feasible to verify the attachment of FITC and Rh B to the various MG-derived systems by utilizing an attenuated total reflection Fourier transform infrared spectrometer (ATR-FTIR). As shown in Fig. 2(B), the spectra of MG-FITC, MG-1F1R and MG-Rh B showed several additional bands in comparison to that of pure MG. The stretching vibration of ring ethers had a developing absorption peak at 1340 cm⁻¹ in the MG-FITC spectrum (green line). The five-membered cyclic lactone was responsible for creating the new peak at 1108 cm⁻¹. Besides, the spectrum of MG-Rh B (orange-red line) showed additional distinguishing bands at 1328 and 1261 cm⁻¹, which derived from the carboxylic acid group and aromatic ether in Rh B, respectively. Moreover, the bands at 1640 cm⁻¹ of MG were shifted to 1633 cm⁻¹ after the addition of FITC and Rh B, which stemmed from electrostatic interaction between carboxylate and dyes. The emerging and alteration of these bands were all present in the spectrum of MG-1F1R (yellow line).

Fig. 2 Multicolor fluorescence based on MG-derived systems. (A) The diagram of multicolor microgels fabricated by adding positively charged fluorescent dyes FITC, Rh B or both, respectively. (B) ATR-FTIR spectra and (C) fluorescent spectra of MG, MG-FITC, MG-1F1R and MG-Rh B. PL mapping spectra of MG-FITC (D), MG-1F1R (E) and MG-Rh B (F) powder at room temperature.

The introduction of fluorescent dyes had a great effect on the fluorescent properties of microgels. Compared with MG, the fluorescence intensity of other microgels systems significantly decreased at 380–480 nm as shown in the fluorescent spectra (Fig. 2(C)). A singular fluorescence peak was detected at 530 nm for MG-FITC, and a prominent peak emerged at 590 nm in the case of MG-Rh B. Correspondingly, in the MG-1F1R system, two distinct peaks were apparent at 530 nm and 585 nm. It was possible that the whole network contracted due to the electrostatic interactions between polymer chains and fluorescent dyes in the dry MG-derived systems, resulting in a fluorescence resonance energy transfer. This conjecture could be firstly confirmed by PL mapping spectra of the MG-derived systems. As depicted in Fig. 2(D)–(F), the MG-derived systems showed a common feature in which the intensity of the blue luminous center decreased and new luminous centers appeared.

Water-induced fluorescence discoloration of MG-derived systems

Owing to the volume change of microgels during the swelling–deswelling process, the interaction between fluorescent dyes and polymer chains, as well as the distance between them and anthracene groups changed, leading to the variation of fluorescence color. Specifically, the MG-FITC sample emitted green fluorescence (530 nm) in its initial dry state. However, the fluorescence color changed to blue (415 nm) after water treatment, accompanied by a decrease in the fluorescence intensity at 530 nm and an increase at 420 nm (Fig. 3(A)). Relatively, other MG-derived systems, including MG-1F1R and MG-Rh B, also showed obvious red shifts of their fluorescent color before and after swelling in water (Fig. 3(B) and (C)). As can be seen in the CIE 1931 chromaticity diagram (Fig. 3(D)), the various microgels exhibited obvious differences in color transformation. MG-FITC underwent a fluorescence transition from green to blue, and MG-Rh B exhibited a color transformation from orange to red. Additionally, MG-1F1R similarly showed a color alteration from yellow to red. To verify the reversibility of the discoloration process, fluorescence intensities of blue, green and red emission peaks were monitored. As shown in Fig. 3(E), there was no discernible decline in the fluorescence intensity and the corresponding ratios of these microgels after six consecutive cycles of hydration–dehydration, which documented the outstanding reversibility of the fluorescence switch. This interesting phenomenon was possibly due to the synergistic effect of FRET and ACQ in the aggregation state and dispersion state of MG-derived systems (Fig. 3(F), (G) and Fig. S11, ESI†). To be specific, the fluorescence emission intensity of Rh B can be enhanced due to the elimination of the ACQ effect^37–39 when the microgels expanded in response to water stimulation, while the FRET effect between cationic dyes and anthracene units would be interrupted. Moreover, these microgel systems have impressive UV light stability even when exposed to continuous UV light for 150 min (Fig. S12, ESI†).

Fig. 3 Water-triggered color variation of MG-derived systems. Fluorescent spectra of MG-FITC (A), MG-1F1R (B) and MG-Rh B (C) before and after treated with water. Insets: Corresponding photographs of the fluorescent color variation. (D) The fluorescent color coordinates of MG, MG-FITC, MG-1F1R, MG-Rh B and their change after treated with water in the CIE 1931 chromaticity diagram. (E) The cyclic fluorescent changes of MG, MG-FITC, MG-1F1R and MG-Rh B during the sequential process of hydration and dehydration. (F) and (G) The schematic diagram of the conjecture mechanism.

Mechanism of fluorescence discoloration in MG-derived systems

To better understand the mechanism of fluorescence discoloration, both experimental tests and theoretical simulations have been conducted. As shown in Fig. 4(A), pure MG displayed a broad emission peak in the blue region, spanning from 380 to 500 nm (λ_ex = 254 nm). By design, this emission spectrum precisely overlapped with the UV absorption spectra of both FITC (380–530 nm) and Rh B (380–600 nm), providing the potential occurrence of FRET. To test this hypothesis, the density functional theory (TD-DFT) calculations of conformation optimization, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) electron densities of 9-ANA, FITC and Rh B were obtained.^40,41 Compared with the HOMO–LUMO energy gap of 9-ANA (2.271 eV), FITC and Rh B had lower energy gaps calculated as 2.160 eV and 1.883 eV, indicating the possibility of electron transfer from anthracene moieties to cationic fluorescent dyes (FITC and Rh B) (Fig. 4(B)). Furthermore, alterations in the fluorescence quantum efficiency and fluorescence lifetime concerning MG-FITC and MG-Rh B served as corroborative evidence for the occurrence of the FRET process. In comparison to pure MG (Fig. 4(C)), the fluorescence quantum efficiency of both MG-FITC and MG-Rh B exhibited a reduction within the wavelength range of 385–500 nm, declining from 20.82% to 7.93% and 7.17%, respectively. Conversely, within the range of 500–700 nm, there was a notable increase in the fluorescence efficiency, rising from 3.17% to 17.85% for MG-FITC and a substantial enhancement to 67.28% for MG-Rh B, which signified an improvement in MG-derived systems without 9-ANA (Fig. S12 and S13, ESI†). These results provided good evidence that the FRET process occurred. Nevertheless, the quantum efficiency of MG-FITC and MG-Rh B increased in the range of 385–500 nm and decreased in the range of 500–700 nm after water exposure. Especially, the quantum efficiency at 500–700 nm was not much different from that of hydrated MG-derived one without 9-ANA, indicating that the FRET process was blocked. In addition, the fluorescence lifetime of MG-derived systems is also much longer than that of those without 9-ANA. Interestingly, hydrated MG-derived systems exhibit fluorescence lifetimes that were comparable to those observed in the absence of 9-ANA (Fig. S14 and S15, ESI†), which highlights the role of hydration in modulating FRET. Pure MG (425 nm) maintained a nearly constant fluorescence lifetime (Fig. S16, ESI†), but the fluorescence lifetimes of MG-FITC (530 nm) and MG-Rh B (585 nm) decreased from 11.1 ns and 8.9 ns to 5.1 ns and 1.85 ns, respectively, when water was involved (Fig. 4(D) and (E)). These findings all demonstrated that the FRET process between the energy acceptor (MG-FITC or MG-Rh B) and the energy donor (MG) was inhibited.

Fig. 4 The mechanism of fluorescence discoloration in the MG-derived systems. (A) The normalized UV absorption spectra of Rh B and FITC, and the fluorescence emission spectra of MG. (B) LUMO and HOMO of structure-optimized 9-ANA, FITC and Rh B based on DFT calculations. (C) The quantum efficiency of MG, and MG-FITC, MG-Rh B before and after water treatment in the 385–500 nm range and the 500–700 nm range, respectively. (D) The fluorescent lifetime of MG-FITC at 530 nm before and after water treatment. (E) The fluorescent lifetime of MG-Rh B at 585 nm before and after water treatment. Two-dimensional COS synchronous spectra and asynchronous spectra generated from MG-FITC (F) and MG-Rh B (G) with different water contents wherein red and blue colors are defined as positive and negative intensity, respectively. (H) Mechanism of fluorescence processes in the MG-derived systems.

To gain insights into the changes of chemical groups in MG-derived systems with or without water involved, FTIR spectroscopy was conducted. The peaks at 1385 and 1367 cm⁻¹ were related to the methyl vibration of –C(CH₃)₂ in the polymer chains, the peak at 1640 cm⁻¹ corresponded to the –COO⁻, and the peak at 1539 cm⁻¹ was attributed to hydrogen bonds between C=O and N–H. Overall, the introduction of water molecules could cause the changes in the conformation of polymer chains and their interaction with fluorescent dyes (Fig. S17–S19, ESI†). To further analyze the dynamic process, ordinary FTIR spectra were converted to 2D correlation spectra (2DCOS).^42,43 The synchronous and asynchronous 2D-IR spectra of MG-FITC (Fig. 4(F)) and MG-Rh B (Fig. 4(G)) in the range of 1680–1350 cm⁻¹ were recorded. The Φ (v₁₆₄₀, v₁₅₃₉), Φ (v₁₆₄₀, v₁₃₈₅) and Φ (v₁₆₄₀, v₁₃₆₇) in the synchronous spectrum and Ψ (v₁₆₄₀, v₁₅₃₉), Ψ (v₁₆₄₀, v₁₃₈₅), Ψ (v₁₆₄₀, v₁₃₆₇) in the asynchronous spectrum were positive and negative, respectively. According to the Noda rule, the shifts of the peaks at 1539, 1385 and 1367 cm⁻¹ were earlier than that at 1640 cm⁻¹, indicating that the swelling process of microgels precedes the dissolution of electrostatic interactions between molecular chains and fluorescent dyes. In other words, the FRET process would be gradually interrupted with the swelling of microgels.

Based on the analysis of the above optical properties, the mechanism of the FRET process between the energy donor (9-ANA) and the energy acceptor (FITC and Rh B) could be successfully documented, as shown in Fig. 4(H). During the FRET process, the majority of the photoexcited singlet excitons (S1^H) in the dry microgels matrix were transferred directly to the singlet excited state (S1^G), resulting in the radiating decay from S1^G to the ground state and achieving efficient fluorescence emission. Meanwhile, the other part of the excitons (S1^H) emitted blue fluorescence in the form of radiative decay. Therefore, the dehydrated microgel entities exhibited a composite manifestation of diverse fluorescent hues, wherein MG corresponded to blue fluorescence, MG-FITC emitted a green fluorescence, and MG-Rh B was orange. When water was introduced, the FRET process from S1^H to S1^G was restricted, which enhanced blue emission and diminished green/red emission.

Anti-counterfeiting application of MG-derived systems

The fluorescent variation of microgels under water stimulation opens up a new way for advanced information encryption. Utilizing MG-derived systems as fluorescent inks, various information, including patterns, numbers, letters, could be written/printed with the assistance of a pen or an inkjet printer (Fig. S20, ESI† and Fig. 5(A)). As a proof of concept, the printed bouquet demonstrated the capacity for instantaneous alteration of its fluorescent coloration when subjected to water, with the ability to revert to its original state upon subsequent water evaporation (Fig. 5(B) and Movie S1, ESI†). Additionally, a series of binary code encryption tags was prepared using a method that integrated binary encoding with fluorescent colors as a cryptographic mechanism. Initially, the binary data were segmented based on fluorescent colors (blue, green, and orange), and subsequently decrypted to reveal the hidden information as “GHB” (Fig. 5(C) and Movie S2, ESI†). Upon exposure to water stimulation, the fluorescent color corresponding to the information emerged, allowing the retrieval of the accurate information “Rh B” by arranging the same color codes in blue and red. This approach amalgamates fluorescent labeling with color coding, ensuring both concealment and the ability to decode through specific steps, thereby guaranteeing security and confidentiality. It's worth mentioning that the encryption–decryption process could be repeated for multiple cycles, ensuring the stability of stored information (Fig. S21, ESI†).

Fig. 5 Inkjet printing of encrypted fluorescent patterns. (A) Schematic diagram of inkjet printing process and programmed patterns printed by using fluorescent microgels (MG, MG-FITC and MG-Rh B) in three colors as inks. (B) Photograph of the printed bouquet pattern before and after water stimulation under UV light of 254 nm. (C) The printed multicolor binary codes can be decrypted into fake information and correct information, depending on the presence or absence of water. (D) Photograph of a paragraph printed by using tri-chromic fluorescent inks, respectively displaying words “safe, materials, gel” and “safe” before and after water stimulation under UV light of 254 nm (scale bar: 1 cm).

In the pursuit of enhancing security measures, the integration of commercial inks with microgel fluorescent inks was undertaken. Consequently, certain seemingly inconsequential patterns or messages printed with commercial inks remained discernible under visible light. However, the authentic content became visible under UV illumination or upon exposure to water. To illustrate, one could only see the window and the moon, clouds outside under natural light, but one could see the hidden QR code under the UV light (Fig. S22A, ESI†). Similarly, visible light revealed solely the presence of a tree trunk and branches, but UV light exposure unveiled yellow and green fruits. Furthermore, the red fruits became visible upon contact with water (Fig. S22B, ESI†). As depicted in Fig. 5(D), three words including “safe”, “materials”, “gel” could be discerned through color recognition in the poem when subjected to UV light. However, nothing but background was shown under visible light (Fig. S23, ESI†). When exposed to water stimulation, a single word, “safe”, with altered coloration became apparent, thereby facilitating the differentiation between authentic and counterfeit information. As indicated above, these features give rise to a new encryption method, which can further improve the security level. It is worth noting that our fluorescent patterns can be stored for more than one year (Fig. S24, ESI†).

Conclusions

In summary, we have presented a series of printable microgels with fluorescence color-changing properties in response to water for highly secured anti-counterfeiting. The initial poly(NIPAM-co-AAc-co-9-ANA) microgel (MG) was fabricated by the copolymerization of NIPAM, AAc and 9-ANA (blue fluorescence emitter). Owing to the existence of carboxylic groups, MG can bond with cationic fluorescent dyes such as FITC and Rh B via electrostatic interaction, obtaining MG-derived systems called MG-FITC and MG-Rh B. These microgels exhibited multicolor fluorescence in the dry state based on FRET between anthracene moieties and cationic fluorescent dyes. When exposed to water, the FRET process can be interrupted, and aggregation degree of Rh B is decreased, accompanied by remarkable fluorescent switches. Given the dramatic differences in fluorescent properties before and after water treatment, our microgels can serve as smart inks to print confidential information with the assistance of inkjet printing technology. The encoded information decrypted under UV irradiation can be rapidly verified by water stimulation. In a word, our strategy provides a new idea to decrypt hidden information with high security level in a simple way, which is expected to have potential applications in fields such as anti-counterfeiting labels.

Author contributions

Hui Shang: methodology, data curation, formal analysis, investigation, writing – original draft. Xiaoxia Le: conceptualization, formal analysis, writing – review & editing, supervision. Yu Sun: data curation, supervision Shuangshuang Wu: data curation, supervision. Yu Wang: supervision. Patrick Théato: writing – review & editing. Tao Chen: supervision, conceptualization.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Key R&D Program of China (2022YFB3204300), the National Natural Science Foundation of China (52103246), the Zhejiang Provincial Natural Science Foundation of China (LQ22E030015), the Natural Science Foundation of Ningbo (2023J408, 20221JCGY010301), the Ningbo International Cooperation Project (2023H019), and the Sino-German Mobility Program (M-0424).

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4mh00210e

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