Full-Color Tunable Fluorescent and Chemiluminescent

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Full-Color Tunable Fluorescent and Chemiluminescent Supramolecular Nanoparticles for Anti-Counterfeiting Inks Minzan Zuo, Weirui Qian, Tinghan Li, Xiao-Yu Hu, Juli Jiang, and Leyong Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14110 • Publication Date (Web): 22 Oct 2018 Downloaded from http://pubs.acs.org on October 23, 2018

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ACS Applied Materials & Interfaces

Full-Color Tunable Fluorescent and Chemiluminescent Supramolecular Nanoparticles for Anti-Counterfeiting Inks Minzan Zuo,† Weirui Qian,† Tinghan Li,† Xiao-Yu Hu,*†,‡ Juli Jiang, *† and Leyong Wang, *†,§ †

Key Laboratory of Mesoscopic Chemistry of MOE and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, China. E-mail: [email protected] (XH), [email protected] (JJ), [email protected] (LW). ‡ Applied Chemistry Department, School of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, 211100, China. § School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China. ABSTRACT: A drive for anti-counterfeiting technology has attracted considerable interests in developing nanomaterials with a wide range of colors and tunable optical properties in solid-state. Herein, with a series of conjugated polymers and based on the host-guest driven self-assembly strategy, a color-tunable supramolecular nanoparticle-based system is reported, in which full-color as well as white fluorescence can be achieved. Moreover, this fluorescent platform exhibits reversible photoswitching between quenching and emission by noncovalently introducing a photoresponsive energy acceptor. In addition, an efficient chemiluminescence system with high intensity can also be obtained in a similar manner by introducing a H2O2-responsive energy donor. Significantly, chemiluminescence is advantageous over fluorescence since there is no need for external light irradiation. More importantly, these acceptor/donor-loaded supramolecular nanoparticles exhibit fluorescence/chemiluminescence modulation ability in both solution and solid state. Therefore, this supramolecular system can be employed as fluorescent security inks for anti-counterfeiting strategies and provide a proof-of-principle application. KEYWORDS: color-tunable, supramolecular nanomaterials, chemiluminescence, energy transfer, anti-counterfeiting

INTRODUCTION Full-color tunable nanomaterials with stimuli responsibility are promising candidates for organic light-emitting diodes,1−3 security inks,4−12 and chemical biosensors among other functionalities.13,14 However, achieving full-color fluorescence, especially white-light emission has been proven to be a great challenge, mainly because of the difficulty in preventing the adverse intermolecular energy transfer.15−19 Conjugated polymers (CPs) possess excellent semiconductive and optoelectronic properties, and they can display various colors by changing the primary structures of the main chains. Moreover, compared with the isolated chain, CPs with higher ordered backbone structures in the aggregated state exhibit quite different fluorescent properties.20,21 Meanwhile, the formed individual nanoparticles aggregated with each other can prevent the intermolecular energy transfer. Hence, fully tunable emission colors and white fluorescence can be acquired by altering the proportion of red, green, and blue (RGB) fluorescent nanoparticles.22 Especially, it is of particular interest to develop photoluminescent materials that are able to respond to external stimuli with reversible changes. Akagi‟s group has reported some excellent work concerning photochemically colour-tuneable materials based on conjugated polymer nanospheres.20,22 However, most of the reported approaches for introducing functional groups to the CPs chains are achieved by covalent integration, which not only increases the difficulty of synthesis but also limits the access to large libraries of photoelectric materials. From this

perspective, delicate design of luminescence-tunable nanomaterials directed by supramolecular strategy is highly appealing. Taking advantage of the fact that different types of molecules can be noncovalently incorporated into unique architectures that assembled based on host-guest interaction, functional supramolecular aggregates could be achieved with no additional synthetic effort. 23−27 In addition, highly ordered aggregates can provide spatial organization for donor/acceptor to guarantee the efficient energy transfer and precisely controllable functions.28−33 Based on the above supramolecular strategy, Guo et al. have recently reported the construction of broad-spectrum tunable photoluminescent nanomaterials.29 Moreover, Tian et al. demonstrated that host–guest complex could be used to develop multicolor photoluminescence including white-light emission.18 However, a highly efficient chemiluminescence system, which can achieve full-color as well as white fluorescence under ambient conditions based on the supramolecular platform is virtually unexplored, which stands for a novel strategy for the construction of excellent optoelectronic devices without the need for any external light irradiation. Herein, de novo design of multi-responsive water-soluble CPs nanoparticles based on supramolecular host-guest assembly has been developed (Figure 1). The compact assembly of the host-guest complexes contributed to the enhanced intramolecular Förster resonance energy transfer (FRET) of the guests. Thus full-color emission, especially white-light fluorescence could be obtained by mixing the RGB photoresponsive vesicles at a certain proportion. Such smart materials with chemi1

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cal sensing behavior could selectively detect ferric ion in aqueous solution. Furthermore, reliant on noncovalent selfsorting encapsulation, a photoresponsive energy acceptor (dithienylethene derivative) could be spatially positioned at the hydrophobic layer of the formed vesicles. Reversible photoswitching between emission and quenching of the vesicles could be achieved by simple irradiation with UV or visible light. More importantly, we further realized the construction of chemiluminescence vesicles based on the reaction of H2O2 with a peroxalate derivative that occurred within the vesicles, where CPs can be excitated chemically. The greatest advantage of the chemiluminescence is their autoluminescent property, which can achieve efficient light emission without

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any external light excitation. Notably, compared with the reported small-molecule chemiluminescent probes,34,35 which are low emissive and unstable. Such water-soluble selfluminescent polymeric supramolecular nanoparticles exhibited high brightness with long-lasting time that could be observed by naked eyes. Therefore, we have successfully developed a highly efficient chemiluminescence system, which can achieve full-color as well as white fluorescence under ambient conditions. Moreover, the above mentioned multi-responsive properties of the nanoparticles could be maintained in both solution and solid state, allowing us to develop a platform in which the tunable supramolecular nanomaterials can be employed as fluorescent security inks for anti-counterfeiting strategies.

Figure 1. Schematic illustration of the full-color tunable fluorescent and chemiluminescent nanomaterials based on supramolecular platform.

RESULTS AND DISCUSSION Noncovalent Interactions of the Supramolecular SelfAssembly System. Three different types of CPs were designed and synthesized as guest molecules (G) generating red, green, and blue fluorescence (Scheme S1−S3 and Figure S1−S7, Supporting Information), i.e., polyfluorene (PF)

containing 5 mol% of dithienylbenzothiadiazole (DBT) unit (G1), poly(fluorene-thienylene) (G2), and poly(fluorenephenylene) (G3). Table S1 shows the molecular weights of these guests as measured by gel permeation chromatography (GPC). The weight-average molecular weights of these guests range from 9.1×103 to 1.9×104 with a polydispersity index (from 2.4 to 2.8, Table S1, Supporting 2


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Information). Utilizing water-soluble pillar[5]arene (WP5) as a host molecule, we first investigated the thermodynamics of the host-guest interactions prior to the aggregation behavior of host-guest complex. Herein, a model compound G′ (1butanaminium) which is able to mimic the binding site of G was designed, and then isothermal titration calorimetry (ITC) experiments (Figure S11, Supporting Information) confirmed the formation of host-guest complex between WP5 and G′ in a 1:1 binding stoichiometry with an association constant of 7.3 × 104 M-1. Such high binding affinity might be driven by the cooperative C−H···π, electrostatic, as well as hydrophobic interactions, contributing to the formation of a stable amphiphilic host-guest complex. It is noteworthy that WP5 + G1, WP5 + G2, and WP5 + G3 solutions could yield pure red, green, and blue fluorescence, respectively. However, free G1 and G2 solutions exhibited reddish purple and cyan fluorescence (Figure 2). To verify that the above phenomenon was caused by aggregation-induced intramolecular energy transfer based on the self-assembled host-guest complex, not merely the simple electrostatic interaction, the fragment unit of WP5, hydroquinone-O,O‟-diacetic acid disodium salt (M) was taken as a control compound to investigate its complexation with G1, G2, and G3, respectively, only driven by electrostatical interaction. As presented in Figure 2, colors in M + G1, M + G2, and M + G3 solutions displayed limited changes compared with free G group, which is consistent with our hypothesis.

Figure 2. (a) Fluorescent images of free G1, G2, and G3 solutions and their mixture. (b) Fluorescent images of M + G1, M + G2, and M + G3 solutions and their mixture. (c) Fluorescent images of WP5 + G1, WP5 + G2, and WP5 + G3 fluorescent solutions and their mixture. White-light emission can only be obtained in the mixed solutions of WP5 + G1, WP5 + G2, and WP5 + G3 at an appropriate ratio. (d) Fluorescent images of WP5 + G1, WP5 + G2, and WP5 + G3 solutions with tunable light emission covering the full color range (λex = 365 nm).

The host-guest interaction between WP5 and G′ was further confirmed by 1H NMR spectroscopy (Figure S10, Supporting

Information), and the result revealed that the protons of the alkyl chain moiety in compound G′ underwent remarkable upfield chemical shifts due to the shielding effect, indicating that the alkyl chain moiety was encapsulated into the electronrich cavity of WP5. However, no chemical shift changes could be observed in the control group by using M of as host molecule (Figure S10, Supporting Information). These results demonstrated that WP5 can induce more compact aggregation of G via host-guest interaction, which in return facilitated the efficient energy transfer and was directly reflected by the visual color changes of G. However, M can decrease the charge repulsion of G merely by electrostatic interaction but without the host-guest complexing ability, which led to only modest changes in color (Figure 2 and Figure S8, Supporting Information). Further evidence for our assumption came from the investigation of Tyndall effect (Figure S9, Supporting Information). Notable opalescence with obvious Tyndall effect could be observed in WP5 + G1, WP5 + G2, and WP5 + G3 solutions, suggesting the formation of large amounts of nanoparticles. On the contrary, neither free G nor the control group exhibited distinct Tyndall effect, indicating that both of them displayed a scattered state and could hardly form largesized aggregates. Therefore, we could produce full-color as well as white-light emission (R : G : B = 8 : 5 : 1 ) by regulating the volume ratios of three pure RGB colors generated from WP5 + G1, WP5 + G2, and WP5 + G3 solutions (Figure S18, Supporting Information). However, the same luminescence manner including white-light could not be reproduced either by free G or by M + G1, M + G2, and M + G3 solutions (Figure 2). Dynamic light scattering (DLS) tests further demonstrated that the average diameters of the nanoaggregates assembled by WP5⊃G1, WP5⊃G2, and WP5⊃G3 complexes are 84, 72, and 71 nm, respectively (Figure S12a−c, Supporting Information). Transmission electron microscopy (TEM) images confirmed the formation of spherical nanoparticles with comparable diameters to the DLS results (Figure S12d−f, Supporting Information). ζ-potential assays of the formed WP5⊃G1, WP5⊃G2, and WP5⊃G3 nanoparticles were measured to be −44.75, −41.86, and −49.90 mV, respectively, suggesting their good stability (Figure S13a−c, Supporting Information). In addition, we further performed the long-term stability analysis based on the size changes of the nanoparticles. DLS results showed that the average diameters of these nanoparticles did not show obvious changes within one week, indicating the good stability of these inks (Figure S24a, Supporting Information). Actually, these nanoparticles are highly stable for several weeks with no agglomeration or precipitation. Moreover, fluorescence lifetimes of the WP5⊃G1, WP5⊃G2, and WP5⊃G3 nanoparticles were measured to be 2.3×103, 5.4×102, and 3.0×102 ps, respectively (Figure S14 and Table S2, Supporting Information). And their fluorescence quantum yields were further evaluated as 7.9%, 6.9%, and 8.7%, respectively (Figure S15−S17 and Table S2, Supporting Information). Chemical Sensing Property of the Supramolecular SelfAssembly System. The current system was proved to be a potential chemical sensor for metal ions (Figure 3). Taking WP5⊃G2 nanoparticles for example, recognition profiles of the chemosensor toward several ions were identified, i.e., Zn 2+, Al3+, Ca2+, Mg2+, Ni2+, Cu2+, and Fe3+. As seen in Figure 3a, when 10 equiv. of Fe3+ was added to the WP5⊃G2 nanoparticle solution, the fluorescent intensity was drastically 3



decreased, which could be easily distinguished by the naked eyes. However, different from Fe3+, none of the remaining ions could induce obvious fluorescence quenching phenomenon, revealing the specific selectivity of this nano-chemosensor to Fe3+. Similar fluorescence quenching could also be observed both in WP5⊃G1 and WP5⊃G3 systems when adding equal equiv. of Fe3+ (Figure 3b), but such fluorescence quenching could not be observed for the free G solution (Figure 3c).

Figure 3. (a) Fluorescence emission spectra of WP5⊃G2 nanoparticle solution ([WP5] = 50 μM; [G2] = 0.08 mg/mL) upon addition of 10 equiv. (0.5 mM) of different ions (λex = 365 nm). Inset: Corresponding fluorescent images. (b) Fluorescent images of WP5⊃G1, WP5⊃G2, and WP5⊃G3 nanoparticle solutions upon addition of 10 equiv. (0.5 mM) of Fe3+ ([WP5] = 50 μM, [G1] = 0.06 mg/mL, [G2] = 0.08 mg/mL, [G3] = 0.07 mg/mL, λex = 365 nm). (c) Fluorescent images of free G1, G2, and G3 solutions upon addition of 10 equiv. (0.5 mM) of Fe3+ ([G1] = 0.06 mg/mL, [G2] = 0.08 mg/mL, [G3] = 0.07 mg/mL, λex = 365 nm).

The above observations can be explained by the high binding ability of anionic WP5 with Fe3+, which contributes to the formation of WP5-Fe3+ complexes,36 and finally results in the efficient electron transfer from the polymer backbone to the formed WP5-Fe3+ complex. Consequently, the fluorescence was obviously quenched.37 For the free G solution, the repulsive force between cationic G and Fe3+ impedes the formation of metal complexes. Thus, electron transfer is inhibited and the fluorescence response will not take place. To further confirm the interactions between these nanoparticles and Fe3+, fluorescence spectra of the nanoparticle solutions were monitored upon gradual titration of Fe3+ (Figure S19a−c, Supporting Information). It turned out that the fluorescence intensity decreased to 10%−15% of their original values in the presence of 6 equiv. of Fe3+, and the fluorescence was completely quenched upon adding 15 equiv. of Fe3+. Considering that a strong chelator might switch off the complexation between WP5 and Fe3+, resulting in a remarkable enhancement of the fluorescence emission, EDTA was added as a competitive chelator to the nanoparticle

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solutions pre-treated with 6 equiv. of Fe3+. Upon gradually increasing the concentration of EDTA, fluorescence intensity could be reversibly recovered, reaching to 90% of the original values (Figure S19d−f, Supporting Information). Photoresponsive Property of the Supramolecular SelfAssembly System. To fabricate photoswitchable nanomaterials based on alternate UV/visible light irradiation, small molecules with broad-spectrum tunability can be used as ideal acceptors. Dithienylethene derivatives are recognized as promising photochromic materials due to their excellent ability to undergo photoisomerization between open and closed forms. Therefore, luminescence of CPs with dithienylethene moieties approaching to the main chains can be dynamically controllable, which is essential for the construction of optoelectronic devices.38,39 After systematic screening, 1, 2-Bis(2,4-dimethyl-5-phenyl-3-thienyl)3,3,4,4,5,5-hexafluorocyclopentene (DE), a dithienylethene derivative was chosen as an acceptor, since its absorption band at the closed form cover the visible region, which is essential for the FRET effect from the donor (CPs nanoparticles) to the acceptor (DE closed form). Driven by noncovalent encapsulation, the hydrophobic DE molecule was entrapped into the nanoparticles in a self-sorting behavior. According to the DLS measurements, the size of DE-loaded aggregates including DE-WP5⊃G1, DE-WP5⊃G2, and DEWP5⊃G3 increased to 160, 175, and 133 nm, respectively (Figure S20a−c, Supporting Information). Moreover, TEM results showed that the diameter of the nanoparticles negative stained with uranyl acetate is around 150 nm, which is in good agreement with the above DLS result. Meanwhile, the contrast of periphery and central parts of the spherical structures is easily distinguishable, indicating the formation of hollow vesicular structures (Figure S20d−f, Supporting Information). ζ-potential assays of the DE-loaded vesicles were recorded as −43.20 (DE-WP5⊃G1), −46.30 (DE-WP5⊃G2), and −54.20 mV (DE-WP5⊃G3), respectively (Figure S13d−f, Supporting Information). Subsequently, photoswitching of DE-loaded vesicles between fluorescence and quenching was investigated. As shown in Figure 4a−c, the characteristic absorption bands of DE moiety in the open form (250 nm) decreased after irradiating with UV light for 40−60 s. Meanwhile, the absorption bands corresponding to the closed form of DE moiety (350 and 550 nm) increased obviously, indicating the efficient photoisomerization of DE from open to closed state. Moreover, the absorption spectrum of DE-loaded vesicles could be restored by subsequent irradiation with visible light for 5−8 min, which confirmed the reversible photoisomerization of DE from closed to open form. Photoluminescence (PL) spectra of DE-WP5⊃G1, DEWP5⊃G2, and DE-WP5⊃G3 vesicular solutions with DE in the open form produced emission bands at 628, 496, 417 nm, in correspondence with red, green, and blue fluorescence, respectively. Upon irradiating with UV light for 40−60 s, fluorescence intensities were drastically decreased (Figure 4d−f). As a control, no appreciable intensity change was detected for the blank nanoparticles without DE loading (Figure S21a−c, Supporting Information), implying that fluorescence quenching might be caused by the FRET from the nanoparticles in their excited state to DE. Subsequently, DE in the closed state released energy by a non-radiative transition, leading to the obvious fluorescence quenching. The

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Figure 4. Photoresponsive behavior of DE-loaded vesicles with the irradiation of UV (λex = 365 nm) or visible light (λ = 520 nm). Changes of the UV–visible absorption spectra of DE-WP5⊃G1 (a), DE-WP5⊃G2 (b), and DE-WP5⊃G3 (c) vesicular solutions in water; and the changes of fluorescence emission spectra of DEWP5⊃G1 (d), DE-WP5⊃G2 (e), and DE-WP5⊃G3 (f) vesicular solutions in water. Inset: Corresponding fluorescent changes (λex = 365 nm).

fluorescence could be regenerated by visible light irradiation for 5−8 min (Figure 4d−f). Photoswitching of fluorescence from white to RGB fluorescence was further explored by introducing small molecule dyes, i.e. rhodamine B, calcein, and quinoline sulfate to generate the corresponding orange-red, green, and blue fluorescence, respectively (Figure S22a, Supporting Information). As shown in Figure S22a, by replacing a certain RGB color of the vesicles with the above dyes of the same color, three different RGB systems were prepared. And for each system, two types of photoresponsive vesicles and one small fluorescent molecule were involved. By mixing the above RGB colors in each system at an appropriate ratio, white fluorescence could also be generated. Furthermore, upon irradiating with UV light, fluorescence of the photoresponsive vesicles was quenched owning to the photoisomerization of DE. However, fluorescence of the dye still remained because of their non-photoresponsibility, resulting in the observation of the corresponding color of the dyes. Therefore, the white light emission could be successfully switched to orange-red, green, and blue, respectively (Figure S22a, Supporting Information). In addition, the above results were consistent with the changes in fluorescence intensities that a slightly fluorescence decrease of the small-molecule dyes and a drastically fluorescence decline of the photoresponsive vesicles were observed (Figure S22b−d, Supporting Information). Chemiluminescent Property of the Supramolecular SelfAssembly System. The present system was further explored as chemiluminescent materials when doping with an energy donor. Herein, a hydrophobic peroxyoxalate, bis-(2, 4, 5-

trichloro-6-(pentyloxycarbonyl)phenyl)oxalate (CPPO) was incorporated into the WP5⊃G1, WP5⊃G2, and WP5⊃G3 nanoparticles as a chemiluminescent substrate. Since CPPO could be oxidized by H2O2, affording a high energy intermediate 1, 2-dioxetanedione, which could then give rise to the excited nanoparticles and induced the efficient chemiluminescent without external excitation. 40 Accordingly, the chemiluminescence behavior of the generated CPPOWP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 vesicles was measured by adding excessive H2O2 to the tested solutions. As seen in Figure 5c, the luminescence spectra of CPPOWP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 are basically identical to their fluorescence spectra, indicating efficient chemiluminescence have been generated by chemically initiated electron exchange (CIEE) from 1, 2dioxetanedione to G1, G2, and G3, respectively. The chemiluminescence colors for the CPPO-WP5⊃G1, CPPOWP5⊃G2, and CPPO-WP5⊃G3 vesicles in aqueous solution were further depicted in the CIE (Commission Internationale de l‟Eclairage) xy chromaticity diagram (Figure 5a). The CIE coordinates of CPPO-WP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 vesicular solutions were determined as (x, y) = (0.60, 0.30), (0.17, 0.53), and (0.15, 0.05), respectively. Moreover, the mixed solution with a volume ratio 20:10:1 (R : G : B) showed a color coordinate of (0.31, 0.32), which is very close to that of pure white-light emission (0.33, 0.33) and can be perceived as white-light emission. Notably, the formed CPPO-WP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 vesicles exhibited much stronger chemiluminescence than those small molecule chemiluminescent dyes, and they could be clearly observed by naked eyes (Figure 5b). Additionally, these chemiluminescent systems are water-soluble and have a long-lasting effect, in which the efficient luminescence could persist for over 20 min. Based on the previous work, it is speculated that inorganic salts could not only accelerate the reaction rate between CPPO and H2O2, but also could induce the formation of more compact aggregation, which will lead to more effective energy transfer and significantly enhanced

Figure 5. (a) CIE 1931 chromaticity diagram showing the chemiluminescent color coordinates of CPPO-WP5⊃G1, CPPOWP5⊃G2, and CPPO-WP5⊃G3 vesicles as well as white light emission. (b) Images of chemiluminescent CPPO-WP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 vesicles in aqueous solution upon addition of excessive H2O2. (c) Corresponding chemiluminescence spectra of the CPPO-WP5⊃G1, CPPOWP5⊃G2, and CPPO-WP5⊃G3 vesicular solutions as well as white light emission.

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chemiluminescent emission of the acceptor.29 Therefore, we further prepared these CPPO-loaded vesicles in PBS solution to investigate the improvement in chemiluminescence (Supporting Movie 1). As expected, although the chemiluminescence-time was shortened, much stronger brightness could be monitored compared with that in aqueous solution (Supporting Movie 2). Notably, very few reports have achieved the construction of full-color emission system with highly efficient chemiluminescence in aqueous solution, especially based on a novel supramolecular strategy. Anti-counterfeit Investigation of the Supramolecular Self-Assembly System. Considering that this kind of multistimuli-responsive supramolecular material not only has good stability (Figure S24b, Supporting Information), but also can achieve tunable color emission in water, it is promising for applications in security inks and anti-counterfeiting technology (Figure 6). As shown in Figure 6a, using the blank nanoparticle WP5⊃G1, WP5⊃G2, and WP5⊃G3 aqueous solutions as inks, three letters “RGB” could be written on a paper and revealed by UV light. When applying Fe3+ ink onto the surface of the pre-existing “RGB” images, additional information could be attached. Moreover, this additional information could be reversibly erased with EDTA ink. In addition, the DE-WP5⊃G1, DE-WP5⊃G2, and DEWP5⊃G3 inks are also applicable for anti-counterfeiting technology (Figure 6b). By loading different inks in pens, we could draw a fluorescent flower with these three kinds of inks, i.e., blank WP5⊃G1 ink for red petals, DE-WP5⊃G2 ink for green scape and leaves, and DE-WP5⊃G3 ink for blue pistil. Upon being irradiated with UV light (λ = 254 nm) for 40 s, images for the blue pistil as well as the green scape and leaves vanished because of fluorescence quenching caused by the photoisomerization of DE moiety. However, the fluorescent image of the red petals was not influenced due to the absence of the DE moiety in the blank WP5⊃G1 ink. Furthermore, the images of pistil, scape, and leaves could be restored by irradiation with visible light for 5 min. Thus, these security inks exhibit anti-counterfeiting features through choosing different combinations of WP5⊃G1, WP5⊃G2, and WP5⊃G3 inks with DE-WP5⊃G1, DE-WP5⊃G2, and DEWP5⊃G3 inks. Subsequently, to explore the potential application of the present platform as chemiluminescent inks, CPPO-WP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 solutions were written on white papers. As seen in Figure 6c, upon adding H2O2 to the pre-existing images, efficient chemiluminescence was visible to the naked eyes. By contrast, no appreciable chemiluminescence could be observed when writing the information with WP5⊃G1, WP5⊃G2, and WP5⊃G3 inks in the absence of CPPO (Figure S23, Supporting Information). During this handwriting experiment, the CIEE process was not impeded and the chemiluminescence was well retained in the solid state. Therefore, stimulus-responsive modulation of chemiluminescence in the solid state can be achieved under ambient conditions, offering us an available opportunity for applications in security inks.

CONCLUSION In summary, we have successfully developed multiplex fluorescent systems in aqueous media based on the supramolecular self-assembly strategy, where the functionalities can be well-modulated through entrapping different small molecules. Herein, host-guest interaction could

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Figure 6. (a) Adding and erasing information reversibly on the blank WP5⊃G1, WP5⊃G2, and WP5⊃G3 fluorescent ink with Fe3+ (middle) and EDTA (down) aqueous solution, respectively. (b) Reversibly photoswitching behavior of the flower image drawn with blank WP5⊃G1 ink (red petals), DE-WP5⊃G2 ink (green scape and leaves) and DE-WP5⊃G3 ink (blue pistil) by UV and visible light stimuli. (c) Images written with CPPOWP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 under natural light (up), and the corresponding chemiluminescent behavior upon adding H2O2 on the pre-existing images (down).

induce compact aggregation of the water-soluble polymeric dyes, which in return enhanced the intramolecular FRET effect of G to display pure RGB color as well as the white light emission. Moreover, reversible regulation of quenching and emission of the fluorescence nanoparticles could be achieved via adding Fe3+ and EDTA, respectively. By introducing DE moiety into the supramolecular nanoparticles through noncovalent interaction, photoresponsive fluorescent vesicles could be realized, and the fluorescence of DE-loaded vesicles could be quenched by UV irradiation and subsequently restored by visible light due to the FRET effect between dyes and the energy acceptor DE moiety. Furthermore, varying volume ratio between the RGB vesicles allows for efficient white light emission and fine-tuning of the white light to RGB could also be achieved by replacing the photoresponsive vesicles with small fluorescent molecules of the corresponding color. Notably, water-soluble chemiluminescent materials could be easily obtained by introducing CPPO moiety as an energy donor. When responding to H2O2, such a system could be well-tuned in fullcolor range including white light emission with naked-eye visible high chemiluminescence intensity. More importantly, the present system is easy to work in both water and solid state, thus it can be applied as potential inks for anti-counterfeiting strategies. The current platform paves a new avenue for protecting information based on supramolecular nanomaterials featuring multiple stimuli responsiveness.

MATERIALS AND METHODS Preparation of the supramolecular nanoparticle solutions. The blank WP5⊃G1, WP5⊃G2, and WP5⊃G3 nanoparticle solutions were prepared as follows: Compounds G1 (0.30 mg), G2 (0.40 mg), and G3 (0.35 mg) were dissolved in DMF (100 μL), respectively. Subsequently, the above solutions were added separately to WP5 aqueous solution (50 μM, 5 mL) during ultrasonication within 30 s to generate the nanoparticle solutions in water. The DE-WP5⊃G1, DE-WP5⊃G2, and DE-WP5⊃G3 nanoparticle solutions were prepared as 6


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follows: Compounds G1 (0.60 mg), G2 (0.80 mg), and G3 (0.70 mg) were dissolved in DE (0.20 mg)-containing DMF solution (100 μL), respectively. The above mixed solutions were added separately to WP5 aqueous solution (0.1 mM, 5 mL) during ultrasonication within 30 s to generate the nanoparticle solutions in water. The CPPO-WP5⊃G1, CPPOWP5⊃G2, and CPPO-WP5⊃G3 nanoparticle solutions were prepared as follows: Compounds G1 (0.60 mg), G2 (0.80 mg), and G3 (0.70 mg) were dissolved in CPPO (0.30 mg)containing DMF solution (100 μL), respectively. The above mixed solutions were added separately to WP5 aqueous solution (0.1 mM, 5 mL) during ultrasonication within 30 s to generate the nanoparticle solutions in water. Ink writing tests. The blank WP5⊃G1, WP5⊃G2, and WP5⊃G3 supramolecular inks for writing were prepared by mixing WP5 (50 μM) with G1 (0.06 mg/mL), G2 (0.08 mg/mL), and G3 (0.07 mg/mL), respectively in water at 25 °C as the method mentioned above. Typically, inks were written on a white paper and the Fe3+ ink (0.3 mM) was used to add information on the pre-existing images. Moreover, the additional information was erased with EDTA ink (1.0 mM). DEWP5⊃G2 and DE-WP5⊃G3 inks were prepared with DE (0.1 mM), WP5 (0.1 mM), G2 (0.16 mg/mL), and G3 (0.14 mg/mL) in water at 298 K by using the same procedure mentioned above. Typically, different inks were used to draw a flower image on a white paper (blank WP5⊃G1 ink for the red petals, DE-WP5⊃G2 ink for the green scape and leaves, and DE-WP5⊃G3 ink for the blue pistil). When irradiated the flower image with the UV light (254 nm) by an ultraviolet lamp (4 W) for 40–60 s, the section drawn by DE-WP5⊃G2 and DE-WP5⊃G3 inks disappeared. Upon subsequent irradiation with visible light (520 nm, 20W) for 5–8 min, the disappeared parts were completely recovered. Whereas, the section drawn by WP5⊃G1 ink was not influenced when irradiated with the UV or visible light. CPPO-WP5⊃G1, CPPOWP5⊃G2, and CPPO-WP5⊃G3 inks were prepared with CPPO (0.1 mM), WP5 (0.1 mM), G1 (0.12 mg/mL), G2 (0.16 mg/mL), and G3 (0.14 mg/mL) in water at 25 °C by using the same procedure mentioned above. Typically, different inks were written on a white paper in the dark and H2O2 was added to the pre-existing images.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. http://pubs.acs.org. Synthesis and relevant characterization details, and supporting photographs. (PDF) Video of the chemiluminescent nanoparticles solution. (AVI)

AUTHOR INFORMATION Corresponding Author [email protected] (XH); [email protected] (JJ); [email protected] (LW).

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT

This work was supported by the National Basic Research Program of China (2014CB846004), the National Natural Science Foundation of China (No. 21572101, 21472089), and the National Natural Science Foundation of Jiangsu (No. BK20180055). Xiao-Yu Hu thanks the Alexander von Humboldt Foundation for a research fellowship.

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Figure 1. Schematic illustration of the full-color tunable fluorescent and chemiluminescent nanomaterials based on supramolecular platform. 149x145mm (300 x 300 DPI)


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Figure 2. (a) Fluorescent images of free G1, G2, and G3 solutions and their mixture. (b) Fluorescent images of M + G1, M + G2, and M + G3 solutions and their mixture. (c) Fluorescent images of WP5 + G1, WP5 + G2, and WP5 + G3 fluorescent solutions and their mixture. White-light emission can only be obtained in the mixed solutions of WP5 + G1, WP5 + G2, and WP5 + G3 at an appropriate ratio. (d) Fluorescent images of WP5 + G1, WP5 + G2, and WP5 + G3 solutions with tunable light emission covering the full color range (λex = 365 nm). 85x94mm (300 x 300 DPI)



Figure 3. (a) Fluorescence emission spectra of WP5⊃G2 nanoparticle solution ([WP5] = 50 μM; [G2] = 0.08 mg/mL) upon addition of 10 equiv. (0.5 mM) of different ions (λex = 365 nm). Inset: Corresponding fluorescent images. (b) Fluorescent images of WP5⊃G1, WP5⊃G2, and WP5⊃G3 nanoparticle solutions upon addition of 10 equiv. (0.5 mM) of Fe3+ ([WP5] = 50 μM, [G1] = 0.06 mg/mL, [G2] = 0.08 mg/mL, [G3] = 0.07 mg/mL, λex = 365 nm). (c) Fluorescent images of free G1, G2, and G3 solutions upon addition of 10 equiv. (0.5 mM) of Fe3+ ([G1] = 0.06 mg/mL, [G2] = 0.08 mg/mL, [G3] = 0.07 mg/mL, λex = 365 nm). 85x105mm (300 x 300 DPI)


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Figure 4. Photoresponsive behavior of DE-loaded vesicles with the irradiation of UV (λex = 365 nm) or visible light (λ = 520 nm). Changes of the UV–visible absorption spectra of DE-WP5⊃G1 (a), DE-WP5⊃G2 (b), and DE-WP5⊃G3 (c) vesicular solutions in water; and the changes of fluorescence emission spectra of DE-WP5⊃G1 (d), DE-WP5⊃G2 (e), and DE-WP5⊃G3 (f) vesicular solutions in water. Inset: Corresponding fluorescent changes (λex = 365 nm). 85x94mm (300 x 300 DPI)



Figure 5. (a) CIE 1931 chromaticity diagram showing the chemiluminescent color coordinates of CPPOWP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 vesicles as well as white light emission. (b) Images of chemiluminescent CPPO-WP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 vesicles in aqueous solution upon addition of excessive H2O2. (c) Corresponding chemiluminescence spectra of the CPPO-WP5⊃G1, CPPOWP5⊃G2, and CPPO-WP5⊃G3 vesicular solutions as well as white light emission. 84x57mm (300 x 300 DPI)


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Figure 6. (a) Adding and erasing information reversibly on the blank WP5⊃G1, WP5⊃G2, and WP5⊃G3 fluorescent ink with Fe3+ (middle) and EDTA (down) aqueous solution, respectively. (b) Reversibly photoswitching behavior of the flower image drawn with blank WP5⊃G1 ink (red petals), DE-WP5⊃G2 ink (green scape and leaves) and DE-WP5⊃G3 ink (blue pistil) by UV and visible light stimuli. (c) Images written with CPPO-WP5⊃G1, CPPO-WP5⊃G2, and CPPO-WP5⊃G3 under natural light (up), and the corresponding chemiluminescent behavior upon adding H2O2 on the pre-existing images (down). 84x56mm (300 x 300 DPI)



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Full-Color Tunable Fluorescent and Chemiluminescent

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