Luminescent Oxygen-Sensitive Ink to Produce Highly Secured Anticounterfeiting Labels by Inkjet Printing

Large Capacity of Data Storage and Information Encryption in Optical Encoder Disk by Integrating Phase Angle and Time Lock Based on Luminescence Metal Nanoclusters

The traditional "matrix" symbol patterns from the luminescence materials are mainly involved in a 2D plane, which seriously limits the information security and storage capacity. Here, a novel strategy is designed to extend two additional dimensions into a 2D plane by integrating time-gated response and phase angle changes of luminescent patterns. The strong orange fluorescence assemblies in an optical encoder disk are obtained after adding metal ions (Zn2+ or Al3+) and ammonia into copper nanoclusters (CuNCs) mainly due to aggregation-induced emission (AIE) behavior. The number of CuNCs-based aggregates is closely related to rotating angle changes. On the contrary, these aggregates can be reversibly dissembled upon exposing to adenosine triphosphate (ATP) in concomitant with their luminescence quenching. Their different quenching rates are on-demand controlled by the coordination reaction kinetics between ATP and metal ions in different pH value, which is conducive to the design of a series of time-locked information. The encoding patterns comprehensively utilize the static and dynamic characteristics of materials by rotating the phase angle at the specific time. The phase angle and time double locks is added into 2D plane to form a 4D storage models, which realizes higher-level information encryption and larger data storage capacity.

Time-Division Multiplexing Physical Unclonable Functions Based on Multicolor Phosphorescent Carbon Dots

Phosphorescent materials offer a promising approach to information encryption due to their long luminescence lifetimes and high signal-to-noise ratios. However, fixed phosphorescent patterns are vulnerable to imitation over time, limiting their effectiveness in advanced encryption. Here, a time-division multiplexing physical unclonable function (TDM-PUF) label utilizing multicolor phosphorescent carbon dots (CDs) is proposed that leverages variations in wavelength and lifetime to construct time-resolved, multidimensional cryptographic protocols. Efficient multi-color phosphorescence in CDs is achieved by enhancing intersystem crossing, suppressing non-radiative transitions through confinement effects, and regulating emission spectra via energy transfer. The random spatial distribution and unpredictable emissions of phosphorescent CDs significantly enhance the complexity of the PUF system, thereby fortifying its defenses against mimicry attacks. Furthermore, this PUF system exhibits multiple optical responses over time, allowing correct information recognition only at specified time nodes, achieving time-resolved anti-counterfeiting. Finally, by segmenting PUF labels based on emission color and time channels, non-overlapping multicolor and multi-time segments are achieved, enabling highly secure time-division multiplexed encryption. The study provides a competitive anti-counterfeiting label and inspires the development of novel anti-counterfeiting strategies.

Multi-wavelength luminescent sensor by lanthanide complex doped amino-clay for visual ofloxacin detection

Fluoroquinolone antibiotic residues, ofloxacin (OFX) have aroused more attention because of their serious influence on surface water and food area, which seriously affect human health. Herein, a visible and high-performance sensor method for detecting OFX is fabricated successfully by co-assembling bimetallic Ln3+ (Eu3+/Tb3+) and amino-clay named Eu1Tb9(BZ)@AC. By changing the ultraviolet excitation wavelength, the sensor displayed high sensitivity and low detection limit to OFX in different modes of detection OFX, which are ratiometric luminescent sensor and turn-on luminescent sensor approaches. The luminescent response mechanisms of the sensor toward ofloxacin are further investigated, which is exploited to build an anticounterfeiting platform by doping the sensor into PVA. This work provides a new direction for the preparation of multifunctional materials based on the co-assembly of lanthanide complexes with luminescent nano clay and offers a new platform in the fields of antibiotic detection and anti-counterfeiting.

Long-chain crosslinker-induced patterning on an elastic polymer film for robust and reversible information encryption/decryption

While reversible information encryption and decryption are readily achievable with hydrogels, this process presents a significant challenge when applied to elastic polymer films. This is due to the inherent chemical stability of anhydrous polymer films which significantly increases the difficulty of information writing. In this study, we propose a solvent-free radical polymerization method for chemical patterning on the elastic film of poly(styrene-butadiene-styrene) (SBS). Unlike short chain crosslinkers-induced patterning, which increases the brittleness of the film, the long-chain crosslinkers are chemically bonded with the chains of SBS. This not only enhances the mechanical stability of film, but also improves its softness and robustness (the strength increases 1.8 times and the toughness increases 2.3 times), thereby greatly extending its durability for information encryption and decryption. When patterned with a photomask, the crosslinked regions maintain transparency upon acetone absorption, while the non-crosslinked regions become opaque due to an acetone-induced phase change. Upon removal of acetone, these opaque regions can be restored to transparency. Compared with hydrogels liable to water loss and deformation, the patterned films show greater stability, retaining pattern encryption/decryption functions after 30 days in a natural environment without special storage. The rate of this phase transition is directly related to the degree of crosslinking. Therefore, by adjusting the degree of crosslinking, the patterned films can undergo multistage encryption/decryption in response to acetone, providing a promising method for information security and storage.

High-Security Data Encryption Enabled by DNA Multi-Strand Solid-Phase Hybridization and Displacement in Inkjet-Printed Microarrays

Multicolor fluorescent encryption systems that respond to specific stimuli have drawn widespread attention to data storage and encryption due to their low cost and facile data access. However, existing encryption systems are limited by encryption materials, restricting their encryption depth. This study uses DNA molecules as encryption materials that offer exceptional specificity and encryption depth within sequences. With inkjet-printed microarrays on a solid-phase interface, a multicolor fluorescent data storage system based on DNA hybridization and strand displacement is developed, achieving an encryption system with high encryption depth and flexibility. DNA strands, modified with different fluorescent labels, are delivered onto solid-phase interfaces containing a DNA self-assembled monolayer (SAM) via inkjet printing, forming multicolor fluorescent data microarrays. Data storage and encryption are achieved through the hybridization of fluorescent DNA strands for data presentation and interference with the DNA SAM at the interface between the solid phase and droplets. Interference DNA strands can be removed by DNA strand displacement for decryption. The encryption depth of this system is determined by the design of the DNA sequences and the combination of multiple DNA strands, showcasing its outstanding encryption ability. Meanwhile, high-throughput inkjet printing accelerates the data writing process, further enhancing the system efficiency. With DNA solid-phase reaction in inkjet-printed microarrays, this system provides a scalable and robust strategy for high-depth and efficient data encryption.

Dual-Emissive Iridium(III) Complex with Aggregation-Induced Emission: Mechanistic Insights into Electron Transfer for Enhanced Hypoxia Detection in 3D Tumor Models

Accurate oxygen detection and measurement of its concentration is vital in biological and industrial applications, necessitating highly sensitive and reliable sensors. Optical sensors, valued for their real-time monitoring, nondestructive analysis, and exceptional sensitivity, are particularly suited for precise oxygen measurements. Here, we report a dual-emissive iridium(III) complex, IrNPh2, featuring "aggregation-induced emission" (AIE) properties and used for sensitive oxygen sensing. IrNPh2 exhibits dual emissions at 450 and 515 nm, with 515 nm triplet-state emission demonstrating remarkable oxygen sensitivity due to its long-lived excited state (12.12 μs) and high quantum yield (68%). Stern-Volmer analysis reveals a notable quenching constant (Ksv = 12.44%-1) and an ultralow detection limit of 0.0397%, emphasizing its superior performance. The oxygen quenching mechanism is driven by electron transfer (ET), supported by computational studies showing the lowest-unoccupied molecular orbital (LUMO) alignment of IrNPh2 with the πg* orbitals of triplet oxygen, leading to superoxide radical (O2•-) formation. Electron paramagnetic resonance (EPR) studies further confirm this pathway. Biological evaluations using a three-dimensional (3D) U87-MG glioma spheroid model highlight the ability of IrNPh2 to detect hypoxic regions, with significant fluorescence enhancement under hypoxia and minimal cytotoxicity (>80% viability at 100 μM). With high sensitivity, low detection limits, and biocompatibility, IrNPh2 emerges as a promising candidate for oxygen sensing in environmental and biomedical applications, especially tumor hypoxia detection.

Patternable chiral Au nanocrystal-doped composite films for information encryption: the role of optical rotation

Optical information encryption technology has garnered significant attention in currency security, information protection, and personal identification. While optical metasurfaces are considered ideal platforms for information encryption, their high cost and time-intensive fabrication processes have limited their widespread applications. To address this, emergent chiroptical nanomaterials offer new opportunities for information encryption through their polarization capabilities. In this study, composite films consisting of chiral Au nanocrystals embedded in curable polymers are utilized as a patternable platform for information encryption. Theoretical simulations demonstrate that chiral Au nanocrystals can rotate linearly polarized light of different wavelengths in various directions. Notably, Au nanocrystals with opposite chirality show reversed optical rotation effects for linearly polarized light while exhibiting the same extinction properties for non-polarized light. Based on these investigations, patternable composite films with embedded chiral Au nanocrystals are fabricated, showcasing their potential to encode information via optical rotation. This work establishes the feasibility of chiral Au nanocrystals as a patternable platform for information encryption and presents a simple, convenient, and cost-effective approach for optical information security.

Coffee-Ring Mediated Thinning and Thickness-Dependent Dewetting Modes in Printed Polymer Droplets Coupled with Assembly of Quantum Dots for Anti-Counterfeiting

Molecular transport processes in printed polymer droplets hold enormous importance for understanding wetting phenomena and designing systems in applications such as encoding, electronics, photonics, and sensing. This paper studies thickness-dependent dewetting modes that are activated by thermal annealing and driven by interfacial interactions within microscopically confined polymeric features. The printing of poly(2-vinylpyridine) is performed in a regime where coffee-ring effects lead to strong thinning of the central region of the deposit. Thermal annealing leads to two different modes of dewetting that depend on the thickness of the central region. Mode I refers to the formation of randomly positioned small features surrounded by large hemispherical ones located along the periphery of the printed features and occurs when the central regions are thin. Observed at large central thicknesses, Mode II mediates significant molecular transport from edges toward the center of the printed droplet with thermal annealing and forms a hemispherical feature from the initial ring-like deposit. The selective adsorption of red, green, and blue emitting quantum dots over the poly(2-vinylpyridine) results in photoluminescent patterns. The selective assembly of photoluminescent quantum dots over patterned surfaces leads to deterministic and stochastic features beneficial to creating security labels for anti-counterfeiting applications.

Dynamic metal-ligand coordination enables a hydrogel with rewritable dual-mode pattern display

The realization of dual-mode information display in the same material is of great significance to the expansion of information capacity and the improvement of information security. However, the existing systems lose the ability to re-encode information once they are constructed. Here, dynamic metal-ligand coordination is introduced into a novel hydrogel-based optical platform that allows rewritable dual-mode information display. The hydrogel system consists of a hard lamellar structure of poly(dodecylglyceryl itaconate) (pDGI) and soft double networks of poly(acrylamide)/poly(acrylic acid) (PAAm/PAAc) containing fluorescent carbon dots (CDs). As the carboxylic acid groups can coordinate with metal ions such as Al3+, the layer spacing of the lamellar structure is reduced while CDs aggregate, leading to the blue shift of the structural color and the red shift of the fluorescent color. Additionally, the metal chelating agent, ethylenediaminetetraacetic acid (EDTA), is able to strip away Al3+ ions and restore the two colors, realizing an erasable dual-mode information display. This study opens up a path for the development of new materials and technologies for rewritable dual-mode information protection.

Traceable Optical Physical Unclonable Functions Based on Germanium Vacancy in Diamonds

Physical unclonable functions (PUFs) have emerged as an unprecedented solution for modern information security and anticounterfeiting by virtue of their inherent unclonable nature derived from distinctive, randomly generated physical patterns that defy replication. However, the creation of traceable optical PUF tags remains a formidable challenge. Here, we demonstrate a traceable PUF system whose unclonability arises from the random distribution of diamonds and the random intensity of the narrow emission from germanium vacancies (GeV) within the diamonds. Tamper-resistant PUF labels can be manufactured on diverse and intricate structural surfaces by blending diamond particles into polydimethylsiloxane (PDMS) and strategically depositing them onto the surface of objects. The resulting PUF codes exhibit essentially perfect uniformity, uniqueness, reproducibility, and substantial encoding capacity, making them applicable as a private key to fulfill the customization demands of circulating commodities. Through integration of a digitized "challenge-response" protocol, a traceable and highly secure PUF system can be established, which is seamlessly compatible with contemporary digital information technology. Thus, the GeV-PUF system holds significant promise for applications in data security and blockchain anticounterfeiting, providing robust and adaptive solutions to address the dynamic demands of these domains.

Uncovering the Recent Progress of CNC-Derived Chirality Nanomaterials: Structure and Functions

Cellulose nanocrystal (CNC), as a renewable resource, with excellent mechanical performance, low thermal expansion coefficient, and unique optical performance, is becoming a novel candidate for the development of smart material. Herein, the recent progress of CNC-based chirality nanomaterials is uncovered, mainly covering structure regulations and function design. Undergoing a simple evaporation process, the cellulose nanorods can spontaneously assemble into chiral nematic films, accompanied by a vivid structural color. Various film structure-controlling strategies, including assembly means, physical modulation, additive engineering, surface modification, geometric structure regulation, and external field optimization, are summarized in this work. The intrinsic correlation between structure and performance is emphasized. Next, the applications of CNC-based nanomaterials is systematically reviewed. Layer-by-layer stacking structure and unique optical activity endow the nanomaterials with wide applications in the mineralization, bone regeneration, and synthesis of mesoporous materials. Besides, the vivid structural color broadens the functions in anti-counterfeiting engineering, synthesis of the shape-memory and self-healing materials. Finally, the challenges for the CNC-based nanomaterials are proposed.

Dual-Mode Hydrogels with Structural and Fluorescent Colors toward Multistage Secure Information Encryption

Constructing an anti-counterfeiting material with non-interference dual optical modes is an effective way to improve information security. However, it remains challenging to achieve multistage secure information encryption due to the limited stimulus responsiveness and color tunability of the current dual-mode materials. Herein, a dual-mode hydrogel with both independently tunable structural and fluorescent colors toward multistage information encryption, is reported. In this hydrogel system, the rigid lamellar structure of poly(dodecylglyceryl itaconate) (pDGI) formed by shear flow-induced self-assembly provides the restricted domains wherein monomers undergo polymerization to form a hydrogel network, producing structural color. The introduction of fluorescent monomer 6-acrylamidopicolinate (6APA) as a complexation site provides the possibility of fluorescent color formation. The hydrogel's angle-dependent structural color can be controlled by adjusting the crosslinking density and water content. Additionally, the fluorescence color can be modulated by adjusting the ratio of lanthanide ions. Information of dual-mode can be displayed separately in different channels and synergistically overlayed to read the ultimate message. Thus, a multistage information encryption system based on this hydrogel is devised through the programed decryption process. This strategy holds tremendous potential as a platform for encrypting and safeguarding valuable and authentic information in the field of anti-counterfeiting.

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

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.

Multicolor Photochemical Printing Inside Polymer Matrices for Advanced Photonic Anticounterfeiting

Conventional security inks, generally directly printed on the data page surface, are vulnerable to counterfeiters, thereby raising the risk of chemical structural deciphering. In fact, polymer film-based data pages with customized patterns embedded within polymer matrix, rather than printed on the surface, emerge as a promising solution. Therefore, the key lies in developing fluorophores offering light dose-controlled fluorescent color inside polymer matrices. Though conventional fluorophores often suffer from photobleaching and uncontrolled photoreactions, disqualifying them for this purpose. Herein a diphenanthridinylfumaronitrile-based phototransformers (trans-D5) that undergoes photoisomerization and subsequent photocyclization during photopolymerization of the precursor, successively producing cis- and cyclo-D5 with stepwise redshifted solid-state emissions is developed. The resulting cyclo-D5 exhibits up to 172 nm emission redshift in rigidifying polymer matrices, while trans-D5 experiences a slightly blueshifted emission (≈28 nm), cis-D5 undergoes a modest redshift (≈14 nm). The markedly different rigidochromic behaviors of three D5 molecules within polymer matrices enable multicolor photochemical printing with a broad hue ranging from 38 to 10 via an anticlockwise direction in Munsell color space, yielding indecipherable fluorescent patterns in polymer films. This work provides a new method for document protection and implements advanced security features that are unattainable with conventional inks.

Hydro-Photo-Thermo-Responsive Multicolor Luminescence Switching of a Ternary MOF Hybrid for Advanced Information Anticounterfeiting

Developing smart materials capable of solid-state multicolor photoluminescence (PL) switching in response to multistimuli is highly desirable for advanced anticounterfeiting. Here, a ternary MOF hybrid showing hydro-photo-thermo-responsive multicolor PL switching in the solid state is presented. This hybrid is constructed by co-immobilizing Eu3+ and methyl viologen (MV) cations within an anionic MOF via the cation-exchange approach. The confined guest cations are well arranged in the framework channels, facilitating the synergistic realization of stimuli-responsive multiple PL color-switching through intermolecular coupling. The hybrid undergoes a rapid and reversible PL color-switching from red to blue upon water simulation, which is achieved by activating the blue emission of the framework linker while simultaneously quenching the Eu3+ emission. Furthermore, the hybrid displays photo-thermo-responsive PL switching from red to dark. UV-light irradiation or heating triggers the chromic conversion of MV to its colored radical form, which exhibits perfect spectral overlap with Eu3+, thus activating Förster resonance energy transfer (FRET) from Eu3+ to MV radicals and quenching the Eu3+ emission. Inspired by these results, PL morse patterns are designed and fabricated using a novel triple-level encryption strategy, showcasing the exciting potential of this hybrid in advanced anticounterfeiting applications.

Multilevel Information Encryption Based on Thermochromic Perovskite Microcapsules via Orthogonal Photic and Thermal Stimuli Responses

Increasing modal variations of stimulus-responsive materials ensure the high capacity and confidentiality of information storage and encryption systems that are crucial to information security. Herein, thermochromic perovskite microcapsules (TPMs) with dual-variable and quadruple-modal reversible properties are designed and prepared on the original oil-in-fluorine (O/F) emulsion system. The TPMs respond to the orthogonal variations of external UV and thermal stimuli in four reversible switchable modes and exhibit excellent thermal, air, and water stability due to the protection of perovskites by the core-shell structure. Benefiting from the high-density information storage TPMs, multiple information encryptions and decryptions are demonstrated. Moreover, a set of devices are assembled for a multilevel information encryption system. By taking advantage of TPMs as a "private key" for decryption, the signal can be identified as the corresponding binary ASCII code and converted to the real message. The results demonstrate a breakthrough in high-density information storage materials as well as a multilevel information encryption system based on switchable quadruple-modal TPMs.

Efficient Multi-stimulus-Responsive Luminescent Eu(III)-Modified HOFs Materials: Detecting Thiram and Caffeic Acid and Constructing a Flexible Substrate Anti-counterfeiting Platform

The powerful capability of multi-stimulus-responsive luminescent hydrogen-bonded organic frameworks (HOFs) to respond to external chemical or physical stimuli in various manners makes them appealing in the luminescence anti-counterfeiting field. Herein, a novel Eu3+-functionalized HOF (Eu@GC-2) that combines the emission of HOFs with the characteristic emission of Eu3+ ions has been successfully synthesized, which can generate various fluorescence at different excitation wavelengths. Eu@GC-2 has enormous potential as a raw material for a paper-based sensor that is designed for detecting the pesticides thiram and caffeic acid in crops with favorable selectivity, anti-interference, and high efficiency. Based on the above excellent properties, Ln3+-functionalized HOFs (Ln@GC-2) were then employed to produce four luminescent anti-counterfeiting inks. With the incorporation of back-propagation neural network and Gray code conversion functions, a multi-stimulus-responsive luminescent anti-counterfeiting platform, coregulated by the excitation light and the chemical reagent, has been constructed. This approach can not only achieve multiple encryptions and fast information identification but also enhance the code-breaking complexity, making it an efficient strategy for information encryption and decryption.

Direct in Situ Fabrication of Multicolor Afterglow Carbon Dot Patterns with Transparent and Traceless Features via Laser Direct Writing

Multicolor afterglow patterns with transparent and traceless features are important for the exploration of new functionalities and applications. Herein, we report a direct in situ patterning technique for fabricating afterglow carbon dots (CDs) based on laser direct writing (LDW) for the first time. We explore a facile step-scanning method that reduces the heat-affected zone and avoids uneven heating, thus producing a fine-resolution afterglow CD pattern with a minimum line width of 80 μm. Unlike previous LDW-induced luminescence patterns, the patterned CD films are traceless and transparent, which is mainly attributed to a uniform heat distribution and gentle temperature rise process. Interestingly, by regulating the laser parameters and CD precursors, an increased carbonization and oxidation degree of CDs could be obtained, thus enabling time-dependent, tunable afterglow colors from blue to red. In addition, we demonstrate their potential applications in the in situ fabrication of flexible and stretchable optoelectronics.

Tristate Photonic Crystal Film with Structural, Fluorescent, and Up-Conversion Luminescent Color for Multilevel Anticounterfeiting

Counterfeit items are growing worldwide, affecting the global economy and human health. Anticounterfeiting tags based on a physical microstructure or chemical materials have enjoyed long-term commercial success due to their visualization and inexpensive production. However, conventional anticounterfeiting tags can be readily imitated. Herein, we have overcome this limitation by assembling colloidal nanospheres and two luminescent micromaterials into a composited photonic crystal (PhC) and achieved massive scale-up fabrication of multilevel anticounterfeiting PhC films in just several minutes of thermal rolling. The fabricated PhC film exhibits three optical states, including angle-dependent structural color (reflectivity = 66%) under white light, emits green light under 980 nm light, and emits red light under ultraviolet light. Multilevel anticounterfeiting colorful images were obtained by further use of masking templates, which integrate colors from both physically colored microstructures and chemical luminescent materials. Besides, the thermal-rolling process also shows excellent feasibility for assembling microunits with different sizes into high-quality functional PhC films.

Light-Responsive Supramolecular Liquid-Crystalline Metallacycle for Orthogonal Multimode Photopatterning

The development of multimode photopatterning systems based on supramolecular coordination complexes (SCCs) is considerably attractive in supramolecular chemistry and materials science, because SCCs can serve as promising platforms for the incorporation of multiple functional building blocks. Herein, we report a light-responsive liquid-crystalline metallacycle that is constructed by coordination-driven self-assembly. By exploiting its fascinating liquid crystal features, bright emission properties, and facile photocyclization capability, a unique system with spatially-controlled fluorescence-resonance energy transfer (FRET) is built through the introduction of a photochromic spiropyran derivative, which led to the realization of the first example of a liquid-crystalline metallacycle for orthogonal photopatterning in three-modes, namely holography, fluorescence, and photochromism.

Enabling Carbonized Polymer Dots with Color-tunable Time-dependent Room Temperature Phosphorescence through Confining Carboxyl Dimer Association

Developing a facile strategy to realize fine-tuning of phosphorescence color in time-dependent room temperature phosphorescence (RTP) materials is essential but both theoretically and practically rarely exploited. Through simultaneously confining carboxyl dimer association and isolated carboxyl into the particle via a simple hydrothermal treatment of polyacrylic acid, a dual-peak emission of red phosphorescence (645 nm) and green phosphorescence (550 nm) was observed from carbonized polymer dots (CPDs). The ratio of the two luminescent species can be well regulated by hydrochloric acid inhibiting the dissociation of carboxyl to promote hydrogen bond. Due to comparable but different lifetimes, color-tunable time-dependent RTP with color changing from yellow to green or orange to green were obtained. Based on the crosslinking enhanced emission effect, the phosphorescence visible time was even extended to 7 s through introducing polyethylenimide. This study not only proposes a novel and facile method for developing CPDs with color-tunable time-dependent RTP, but also provides a bran-new non-conjugated red phosphorescence unit and its definite structure.

Coordination-assembled phosphorescent microstructure from RTP HOF and Eu3+-doping ZGO:Mn phosphors for cancer biomarker amplification detection and information encryption

The ultra-long room temperature phosphorescent hydrogen-bonded organic framework (RTP HOF) materials can achieve long afterglow via ligand hydrogen bond interaction and water implement to suppress the non-radiative decays by matrices rigidification, and its electron donor conjugated structure is first developed as a phosphorescent quencher. The Eu3+/Mn2+ co-doped Zn2GeO4 phosphors (ZGO:Mn, Eu) with abundant metal sites and enhanced phosphorescence were synthesized as response factors and electron acceptors, combined with RTP HOFs to form microstructures featuring multi-color modulation, as an high-level anti-counterfeiting platform and lysophosphatidic acid (LPA) detection unit. LPA is an ideal plasma biomarker for early diagnosis of ovarian and other gynecologic cancers. This detection strategy relies on the differential coordination substitution to restore ZGO:Mn, Eu phosphorescence through synergistic coordination of LPA and the hydrophobic assistance of LPA, and dual functional groups identification of LPA achieve specific detection at the nanomolar level. The anti-counterfeiting platform can fetch specific information by controlling the afterglow distinction and excited light from ZGO:Mn, Eu and RTP HOF. This study not only provides a typical case of the preparation of two phosphors with heterogeneous optical properties, but also expands the application field of combined phosphors as intelligent luminescent materials.

Chameleon-like Photoluminescent Janus Nanoparticles as Full-Color Multicomponent Organic Nanoinks: Combination of Förster Resonance Energy Transfer and Photochromism for Encryption and Anticounterfeiting with Multilevel Authentication

Increasing the security by the multilevel authentication mechanism was the most significant challenge in recent years for the development of anticounterfeiting inks based on photoluminescent nanomaterials. For this purpose, the greatest strategy is the use of multicomponent organic materials and a combination of Förster resonance energy transfer (FRET) with the intelligent behavior of photochromic compounds like spiropyran. Here, the hydroxyl-functionalized polymer nanoparticles were synthesized by emulsion copolymerization of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) in different compositions (0-30 wt % of HEMA). Results illustrated that the size of the nanoparticles changed from 64 to 204 nm, and a morphology evolution from spherical to Janus shape was observed by increasing the concentration of HEMA. Photoluminescent inks with red, green, and blue (RGB) fluorescence emissions were prepared by modification of nanoparticles containing 15 wt % of HEMA with spiropyran, fluorescein, and coumarin, respectively. To develop dual-color and multicolor photoluminescent inks that display static and dynamic emission, RGB latex samples were mixed together in different ratios and printed on cellulosic paper. Results display that the fluorescence emission of developed inks can be photoswitched between different statuses, including white to blue, green to blue, green to red/orange, purple to pink, and white to pink, utilizing the FRET phenomenon, photochromism, and a combination of both phenomena. Samples containing spiropyran displayed dynamic color changes in the emission to red, orange, and pink depending on the composition. Hence, developed dual-color and multicolor photoluminescent inks were used for printing of security tags and also painting of some hand-drawn artworks, which obtained results indicating high printability, maximum fluorescence intensity, high resolution, and fast responsivity upon UV-light irradiations of 254 nm (for static mode) and 365 nm (for dynamic mode). In addition, the multilevel authentication mechanism by a static emission under UV-light irradiation of 254 nm, a dynamic emission under UV-light irradiation of 365 nm, and photochromic color change was observed, resulting in increasing the security of developed inks. Actually, developed multicolor photoluminescent inks are the most efficient candidates for developing a new category of chameleon-like high-security anticounterfeiting inks that have tunable optical properties and complex multilevel authentication mechanisms.

Long-Persistent Circularly Polarized Luminescence from a Host-Guest System Regulated by the Multiple Roles of a Gold(I)-Carbene Motif

The promotion of intersystem crossing (ISC) is critical for achieving a high-efficiency long-persistent luminescence (LPL) from organic materials. However, the use of a transition-metal complex for LPL materials has not been explored because it can also shorten the emission lifetime by accelerating the phosphorescence decay. Here, we report a new class of LPL materials by doping a monovalent Au-carbene complex into a boron-embedded molecular host. The donor-acceptor systems exhibit photoluminescence with both high efficiencies (>57 %) and long lifetimes (ca. 40 ms) at room temperature. It is revealed that the Au atom promotes the population of low-lying triplet excited states of the host aggregate (T1 *) which can be converted into the charge-transfer (CT) state, thereby resulting in afterglow luminescence. Moreover, the use of a chirality unit on the guest molecule results in the LPL being circularly polarized. This work illustrates that transition-metal complexes can be used for developing organic afterglow systems by exquisite control over the excited state mechanism.

Thermal annealing promoted room temperature phosphorescence: motion models and internal mechanism

Thermal annealing has been proven to be an efficient method to optimize the device performance of organic and polymeric opto-electronic materials. However, no detailed information of aggregate structures was obtained for a deeper understanding of what happens during thermal annealing. Herein, through modulation of molecular configurations by tunable linkage positions, and the amplified amplitudes of molecular motions by incorporation of additional methylene units, accurate changes of aggregated structures upon thermal annealing have been achieved, accompanying with the 'turn-on' room temperature phosphorescence (RTP) response by about 4800- and 177-fold increase of lifetimes. The stretching and swing motion models have been proposed, which afforded an efficient way to investigate the science of dynamic aggregation in depth.

Conventional Non-Fluorescent Polymers: Unconventional Security Inks for Data Storage and Multidimensional Photonic Cryptography

Traditional security inks relying on fluorescent/phosphorescent molecules are facing increasing risks of forgery or tampering due to their simple readout scheme (i.e., UV-light irradiation) and the advancement of counterfeiting technologies. In this work, a multidimensional data-encryption method based on non-fluorescent polymers via a "lock-key" mechanism is developed. The non-fluorescent invisible polymer inks serve as the "lock" for data-encryption, while the anti-rigidochromic fluorophores that can distinctively light up the polymer inks with programed emissions are "keys" for decryption. The emission of decrypted data is prescribed by polymer chemical structure, molecular weight, topology, copolymer sequence, and phase structure, and shows distinct intensity, wavelength, and chirality compared with the intrinsic emission of fluorophores. Therefore, the data is triply encrypted and naturally gains a high-security level, e.g., only one out of 20 000 keys can access the only correct readout from 40 000 000 possible outputs in a three-polymers-based data-encryption matrix. Note that fluorophores lacking anti-rigidochrimism cannot selectively light up the inks and fail in data-decryption. Further, the diverse topologies, less well-defined structures, and random-coiled shapes of polymers make it impossible for them to be imitated. This work offers a new design for security inks and boosts data security levels beyond the reach of conventional fluorescent inks.

Bio-Inspired Electro-Thermal-Hygro Responsive Rewritable Systems with Temporal/Spatial Control for Environment-Interactive Information Display

Utilization of rewritable luminescent materials for secure information storage and delivery has long been envisaged to reduce the cost and environmental wastes. However, it remains challenging to realize a temporally/spatially controlled display of the written information, which is crucial for secure information encryption. Here, inspired by bioelectricity-triggered skin pattern switching in cephalopods, an ideal rewritable system consisting of conductive graphene film and carbon dots (CDs) gel with blue-to-red fluorescence-color changes via water-triggered CDs aggregation and re-dispersion is presented. Its rewritability is guaranteed by using water ink to write on the CDs-gel and employing Joule heat of graphene film to evaporate water. Due to the highly controlled electrical stimulus, temporally/spatially controlled display is achieved, enabling on-demand delivery and duration time regulation of the written information. Furthermore, new-concept environment-interactive rewritable system is obtained by integrating sensitive acoustic/optical sensors and multichannel electronic time-delay devices. This work opens unprecedented avenues of rewritable systems and expands potential uses for information encryption/delivery.

A light-fueled dissipative aggregation-induced emission system for time-dependent information encryption

A light-fueled dissipative aggregation-induced emission (LDAIE) system is successfully fabricated based on reversible electrostatic interactions between cationic AIE luminogens (AIEgens) and anionic spiropyran (ASP) transformed from sulfonato-merocyanine photoacid (SMEH) upon 420 nm light irradiation. The novel LDAIE system can exhibit reversible and spontaneous AIE fluorescence on/off, showing potential in time-dependent information encryption with self-erasing ability. This work opens new opportunities to fabricate a unique fluorescent anti-counterfeiting platform with high-level security.

Intelligent Colorimetric Indicators for Quality Monitoring and Multilevel Anticounterfeiting with Kinetics-Tunable Fluorescence

The spoilage and forgery of perishable products such as food, drugs, and vaccines cause serious health hazards and economic loss every year. Developing highly efficient and convenient time-temperature indicators (TTIs) to realize quality monitoring and anticounterfeiting simultaneously is urgent but remains a challenge. To this end, a kind of colorimetric fluorescent TTI, based on CsPbBr₃@SiO₂ nanoparticles with tunable quenching kinetics, is developed. The kinetics rate of the CsPbBr₃-based TTIs is easily regulated by adjusting temperature, concentration of the nanoparticles, and addition of salts, stemming from the cation exchange effect, common-ion effect, and structural damage by water. Typically, when combined with europium complexes, the developed TTIs show an irreversible dynamic change in fluorescent colors from green to red upon increasing temperature and time. Furthermore, a locking encryption system with multiple logics is also realized by combining TTIs with different kinetics. The correct information only appears at specific ranges of time and temperature under UV light and is irreversibly self-erased afterward. The simple and low-cost composition and the ingenious design of kinetics-tunable fluorescence in this work stimulate more insights and inspiration toward intelligent TTIs, especially for high-security anticounterfeiting and quality monitoring, which is really conducive to ensuring food and medicine safety.

Butterfly-Inspired Tri-State Photonic Crystal Composite Film for Multilevel Information Encryption and Anti-Counterfeiting

Counterfeiting is a worldwide issue and has long troubled legitimate businesses, while nowadays anti-counterfeiting materials and technology are still insufficient to combat the escalating counterfeit behaviors. Inspired by hindwing structure of Troides magellanus, a new kind of anti-counterfeiting material taking advantage of both physical and chemical structures to display multiple optical states is prepared. The chemical units (luminescent lanthanide) are blended with physical units (monodispersed colloidal particles) and mediating molecules, which are then assembled into a photonic crystal structure at room temperature in less than 10 s through a new assembly technique called molecule-mediated shear-induced assembly technique (MSAT). The as-prepared photonic crystal films feature three unique optical states, each displaying structural, fluorescent, and phosphorescent color under different lighting conditions, which integrates colors from both physical and chemical origins. Furthermore, by incorporating different luminescent materials into different parts of the photonic crystal pattern, a high-level information encryption system is designed to be capable of carrying three distinct types of information. Thanks to this powerful tool of MSAT, it is now possible to assemble different-sized, even irregular non-spherical units with monodispersed spherical units into high-quality photonic crystal films, which provides easy access to incorporating new features into photonic crystal systems.

Engineering Multi-Scale Organization for Biotic and Organic Abiotic Electroactive Systems

Multi-scale organization of molecular and living components is one of the most critical parameters that regulate charge transport in electroactive systems-whether abiotic, biotic, or hybrid interfaces. In this article, an overview of the current state-of-the-art for controlling molecular order, nanoscale assembly, microstructure domains, and macroscale architectures of electroactive organic interfaces used for biomedical applications is provided. Discussed herein are the leading strategies and challenges to date for engineering the multi-scale organization of electroactive organic materials, including biomolecule-based materials, synthetic conjugated molecules, polymers, and their biohybrid analogs. Importantly, this review provides a unique discussion on how the dependence of conduction phenomena on structural organization is observed for electroactive organic materials, as well as for their living counterparts in electrogenic tissues and biotic-abiotic interfaces. Expansion of fabrication capabilities that enable higher resolution and throughput for the engineering of ordered, patterned, and architecture electroactive systems will significantly impact the future of bioelectronic technologies for medical devices, bioinspired harvesting platforms, and in vitro models of electroactive tissues. In summary, this article presents how ordering at multiple scales is important for modulating transport in both the electroactive organic, abiotic, and living components of bioelectronic systems.

Brightening Blue Photoluminescence in Nonemission MOF-2 by Pressure Treatment Engineering

As equally essential as the synthesis of new materials, maneuvering new structure configurations can endow the brand-new functional properties to existing materials, which is also one of the core goals in the synthesis community. In this respect, pressure-induced emission (PIE) that triggers photoluminescence (PL) in nonemission materials is an emerging stimuli-responsive smart materials technology. In the PIE paradigms, harvesting bright PL at ambient conditions, however, has remained elusive. Herein, a remarkable PIE phenomenon is reported in initially nonemission Zn(BDC)(DMF)(H₂ O) (MOF-2), which shows bright blue-emission at 455 nm under pressure. Intriguingly, the bright blue PL with an excellent photoluminescence quantum yield up to 70.4% is unprecedentedly retained to ambient conditions upon decompression from 16.2 GPa. The detailed structural analyses combined with density functional theory calculations reveal that hydrogen bonding cooperativity effect elevates powerfully the rotational barrier of the linker rotor to 3.87 eV mol^-1 from initial 0.91 eV mol^-1 through pressure treatment. The downgrade rotational freedom turns on PL of MOF-2 after releasing pressure completely. This is the first case of harvesting PIE to ambient conditions. These findings offer a new platform for the creation of promising alternatives to high-performance PL materials based on initially nonemission counterparts.

Dual stimuli-responsive phosphorescence of a Pb(II) coordination polymer to acidic vapors and thermal treatment

We present a new intensely phosphorescent Pb(II) coordination polymer (1) containing a heteroatomic ligand. It has a quantum yield of 21.62% and a lifetime of 25.46 μs. The naked-eye solid-state photoluminescence of 1 significantly changes in response to acidic vapors and thermal treatment, indicating the coexistence of acidochromic and thermochromic luminescence.

Dual-Color Photoluminescent Functionalized Nanoparticles for Static-Dynamic Anticounterfeiting and Encryption: First Collaboration of Spiropyran and Coumarin

Increasing the security of anticounterfeiting materials has been the most important challenge in recent years, and the development of dual-color photoluminescent inks with multi-level security, static/dynamic emission, and dynamic color change is an important solution to overcome this problem. In this study, the multi-functionalized copolymer nanoparticles containing different functional groups (with a concentration of 20 wt %), including ester, carboxylic acid, hydroxyl, epoxide, amide, and amine groups were synthesized successfully by the emulsion polymerization method. The results showed that the particle size and morphology of nanoparticles are affected by the polarity of functional groups. The prepared multi-functionalized copolymer nanoparticles were modified physically with spiropyran (photochromic and red fluorescence emission) and coumarin (cyan emission) derivatives to develop dual-color photoluminescent polymer nanoparticles with application in static-dynamic photoluminescent anticounterfeiting inks, which have multi-level security. The investigation of optical properties indicates that the kinetics of photochromism and photoluminescence properties of samples containing spiropyran is dependent on the local polarity on the surface of polymer nanoparticles. Hence, an increase in the polarity (functionalization with amide, carboxylic acid, and hydroxyl groups) has resulted in fast photochromism, high-intensity photoluminescence emission and increased the efficiency of the photoswitchable color change of emission from cyan to pink. Dual-color photoluminescent anticounterfeiting inks were prepared by mixing polymer nanoparticles containing spiropyran with polymer nanoparticles containing coumarin, in different ratios (1:1, 1:3, 1:5, 1:8, and 1:10). Obtained results showed that prepared samples have cyan emission under UV light of 254 nm (static mode), and a dynamic photoswitching of fluorescence emission from cyan to pink (as a function of irradiation time) was also observed under UV-light irradiation of 365 nm, which is well known as a dynamic mode of emission. The responsivity and intensity of dynamic photoluminescence emission are dependent on the local polarity of the surface functional groups, in which the samples based on amide functionalized copolymer nanoparticles displayed high-intensity emission in the static mode and high-intensity photoswitchable dual-color emission in the dynamic mode, in the case of all ratios of colloid solution mixtures. Printing security tags on cellulose paper by dual-color photoluminescent inks indicates advantages such as maximum printability, resolution, brightness, and static-dynamic photoluminescence emission with high intensity for inks based on amide functionalized nanoparticles. The static-dynamic dual-color photoluminescent anticounterfeiting ink with unique properties and multi-level security was reported for the first time by the collaboration of spiropyran and coumarin. This study can open a new approach and window to the future of advanced and high-security anticounterfeiting technologies.

The Effect of Molecular Conformations and Simulated "Self-Doping" in Phenothiazine Derivatives on Room-Temperature Phosphorescence

The research of purely organic room-temperature phosphorescence (RTP) materials has drawn great attention for their wide potential applications. Besides single-component and host-guest doping systems, the self-doping with same molecule but different conformations in one state is also a possible way to construct RTP materials, regardless of its rare investigation. In this work, twenty-four phenothiazine derivatives with two distinct molecular conformations were designed and their RTP behaviors in different states were systematically studied, with the aim to deeply understand the self-doping effect on the corresponding RTP property. While the phenothiazine derivatives with quasi-axial (ax) conformation presented better RTP performance in aggregated state, the quasi-equatorial (eq) ones were better in isolated state. Accordingly, the much promoted RTP performance was achieved in the stimulated self-doping state with ax-conformer as host and eq-one as guest, demonstrating the significant influence of self-doping on RTP effect.

Photoluminescent Polymer Nanoparticles Based on Oxazolidine Derivatives for Authentication and Security Marking of Confidential Notes

Colloidal materials have widely been used to develop innovative anticounterfeiting nanoinks for information encryption. Latex nanoparticles based on methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) bearing hydroxyl functional groups were synthesized via semicontinuous miniemulsion polymerization. The size determination of the nanoparticles and microscopic results showed mostly spherical nanoparticles with a narrow size distribution and a mean size of about 80 nm. Two oxazolidine derivatives were physically doped at the surface of the nanoparticles to prepare photoluminescent polymer nanoparticles. Hydroxyl functional groups at the surface of the nanoparticles led to their hydrogen bonding interactions with the doped luminescent compounds. Optical analysis of the photoluminescent nanoparticles displayed different fluorescence emission and UV-vis absorbance intensities based on the amount of polar groups located at the surface of colloidal nanoparticles. Reducing the particle size to below 100 nm along with increasing the surface area can assist the decrease of the light reflectance and improvement of the latex nanoparticles' efficiency in the anticounterfeiting industry. This preparation methodology can efficiently provide remarkable photoreversible anticounterfeiting nanoinks used in different applications, such as print marking, security encoded tags, labeling, probing, and handwriting.

Novel Stimuli-Responsive Spiropyran-Based Switch@HOFs Materials Enable Dynamic Anticounterfeiting

Developing smart fluorescent materials having very advanced levels, showing dynamic displays of encrypted messaging, remains a huge challenge. In this paper, we present a unique method based on combining a common photochromic molecule spiropyran (SP) with hydrogen-bonded organic frameworks (HOFs), which allows for reversible switching of SP in solid states and shows dynamic displays of encrypted information. With the irradiation time extended, the fluorescence emission undergo an evident transformation from yellow-green to orange to red, because of the fluorescence resonance energy transfer (FRET) process between the unique HOFs and merocyanine (MC) isomer. By doping with polydimethylsiloxane (PDMS), we obtained free-standing membranes with high flexibility and mechanical strength, which can be reversibly and repeatedly bent and folded at angles of >90°. Notably, the comparison of fatigue resistance between SP2/PDMS (can be used for no more than 5 times) and SP2 ⊂ HOF2/PDMS (can be used for more than 100 times) further proved the importance of HOFs. This composite system has many advantages: (1) it has diverse dynamic fluorescence emission and visible colors regulated by ultraviolet radiation with high contrast and can be reversibly converted; (2) these changes in behavior can be achieved by simple UV illumination; and (3) compared with previous work, this work not only shows the dynamic fluorescence emission, but also shows the dynamic information during the decryption.

Invisible Thermoplasmonic Indium Tin Oxide Nanoparticle Ink for Anti-counterfeiting Applications

In this study, we present a thermoplasmonic transparent ink based on a colloidal dispersion of indium tin oxide (ITO) nanoparticles, which can offer several advantages as anti-counterfeiting technology. The custom ink could be directly printed on several substrates, and it is transparent under visible light but is able to generate heat by absorption of NIR radiation. Dynamic temperature mapping of the printed motifs was performed by using a thermal camera while irradiating the samples with an IR lamp. The printed samples presented fine features (in the order of 75 μm) and high thermal resolution (of about 250 μm). The findings are supported by thermal finite-element simulations, which also allow us to explore the effect of different substrate characteristics on the thermal readout. Finally, we built a demonstrator comprising a QR Code invisible to the naked eye, which became visible in thermal images under NIR radiation. The high transparency of the printed ink and the high speed of the thermal reading (figures appear/disappear in less than 1 s) offer an extremely promising strategy toward low-cost, scalable production of photothermally active invisible labels.

Light-activated photodeformable supramolecular dissipative self-assemblies

Dissipative self-assembly, one of fundamentally important out-of-equilibrium self-assembly systems, can serve as a controllable platform to exhibit temporal processes for various non-stimulus responsive properties. However, construction of light-fueled dissipative self-assembly structures with transformable morphology to modulate non-photoresponsive properties remains a great challenge. Here, we report a light-activated photodeformable dissipative self-assembly system in aqueous solution as metastable fluorescent palette. Zwitterionic sulfonato-merocyanine is employed as a light-induced amphiphile to co-assemble with polyethyleneimine after light irradiation. The formed spherical nanoparticles spontaneously transform into cuboid ones in the dark with simultaneous variation of the particle sizes. Then the two kinds of nanoparticles can reversibly interconvert to each other by periodical light irradiation and thermal relaxation. Furthermore, after loading different fluorophores exhibiting red, green, blue emissions and their mixtures, all these fluorescent dissipative deformable nanoparticles display time-dependent fluorescence variation with wide range of colors. Owing to the excellent performance of photodeformable dissipative assembly platform, the light-controlled fluorescence has achieved a 358-fold enhancement. Therefore, exposing the nanoparticles loaded with fluorophores to light in a spatially controlled manner allows us to draw multicolored fluorescent images that spontaneously disappeared after a specific period of time.

Dissipative self-assembly can serve as a controllable platform to exhibit temporal processes for various non-stimulus responsive properties but construction of light-fueled dissipative self-assembly structures with transformable morphology to modulate non-photoresponsive properties remains a challenge. Here, the authors report a light-activated photodeformable dissipative self-assembly system in aqueous solution as metastable fluorescent platform.

Raman inks based on triple-bond-containing polymeric nanoparticles for security

Developing security inks with spectral outputs/multiple colors, which have unique identification characteristics, is of great importance in enhancing the anti-counterfeiting strength of ink anti-counterfeiting technology. Herein, a print-driven triple-bond coding mode is proposed for the first time. Two kinds of triple-bond-containing polymeric nanoparticles (NPs) with Raman shifts at 2227 and 2241 cm^-1 have been designed into printable ink, and the decimal coding output can be easily obtained by reasonably adjusting the proportions of the two polymeric NPs. Single Raman scattering inks can be used as invisible inks to print monochromatic patterns and words that the decoder can read out. According to the two-dimensional pixels of the graphics decoder, invisible colorful graphics can be printed with mixed inks under different polymer proportions. More interestingly, three-dimensional invisible patterns with stronger anti-counterfeiting strength can also be obtained in the double-layer anti-counterfeiting patterns with different proportions of ink by the spatial complementary coding mode. It is predicted that more security inks associated with triple-bond Raman signals will spur the application of the anti-counterfeiting field.

Cyclodextrin-Confined Supramolecular Lanthanide Photoswitch

The utilization of azobenzene-based photoisomerization cannot only control the morphology of supramolecular assemblies, but can also regulate many biological processes. However, the design of azobenzene-involved nanoconstructs with switchable photoluminescence remains challenging because of the light-quenching ability of azobenzene. Herein, an azobenzene-derived multicomponent nanosystem is reported and its function as a supramolecular lanthanide photoswitch is explored. The metal chelation between lanthanide ions (Ln³⁺  = Eu³⁺ and Tb³⁺ ) and 2,6-pyridinedicarboxylic acid is utilized as the light-emitting center but its inherent fluorescence emission is completely suppressed via the disordered motion of the adjoining azophenyl unit. Interestingly, the hydrophobic cavity of α-cyclodextrin can provide a confined microenvironment to immobilize the molecular conformation of trans-azobenzene, thus leading to the recovery of characteristic lanthanide luminescence both in aqueous solution and the hydrogel state. Also, the luminescence can be reversibly turned off when the cis-azobenzene is expelled from the cavity of α-cyclodextrin upon alternating light irradiation. This mutual cooperation arising from host-guest complexation and metal-ligand coordination confers the desired photoswitchable luminescence abilities on the commonly used azobenzenes, which may hold great promise in the creation of more advanced light-responsive smart materials.

Critical Size/Viscosity for Coffee-Ring-Free Printing of Perovskite Micro/Nanopatterns

Inkjet printing is the most encouraging method for patterning and integrating perovskite materials into microminiature application scenarios. However, it is still challenging to achieve high-resolution, coffee-ring-free, and perfect crystallized patterns. Here, a strategy based on powerful electrohydrodynamic printing and droplet viscosity-size coordinate regulation is developed to solve the above problems. By adding a long-chain polymer poly(vinylpyrrolidone) (PVP) into perovskite precursor to tune ink viscosity and introducing electrohydrodynamic printing to print the high-viscosity ink into droplets of different sizes, we can manipulate the inside flowing resistance and outside evaporation rate of a droplet, thus revealing a critical size/viscosity under which the coffee ring effect is inhibited, showing immense potential and significance for high-quality patterning. In addition, the long-chain polymer benefits droplet spatial limitation and uniform crystallization. The as-printed luminous patterns demonstrate high resolution (structure size ∼1 μm), excellent brightness, pleasant uniformity, and fascinating compatibility with flexible substrates, which is promising for future perovskite optoelectronic device applications.

Wide-Range Time-Dependent Color-Tunable Light-Response Afterglow Materials via Absorption Compensation for Advanced Information Encryption

Stimuli-responsive luminescent materials with time-dependent color are highly desirable in optical information encryption. In this study, multiple time-dependent color processes are achieved by light-responsive afterglow materials through the strategy of absorption compensation. Based on the single-emission band of light-responsive afterglow materials, the color of samples could show a time-dependent change from colored to colorless over several seconds. The strategy possesses high flexibility such that the stimulus light and emission color of light-responsive afterglow materials can be adjusted conveniently to adapt to various scenes. It is also beneficial to expand the capacity and complexity of information encryption. A three-color, time-resolved anticounterfeiting, and data encryption mode is demonstrated. This facile absorption compensation method based on light-response afterglow materials may promote the development of advanced dynamic information encryption.

Bioinspired Perovskite Nanocrystals-Integrated Photonic Crystal Microsphere Arrays for Information Security

Information security occupies an important position in the era of big data. Attempts to improve the security performance tend to impart them with more additional encryption strategies. Herein, inspired by the wettability feature of Stenocara beetle elytra and signal model of traffic light, a novel array of perovskite nanocrystals (PNs)-integrated PhC microsphere for information security is presented. The photoluminescent PNs are encapsulated in angle-independent PhC microspheres to impart them with binary optical signals as coding information. Through the multimask superposition approach, PNs-integrated PhC microspheres with different codes are placed into fluorosilane-treated PDMS substrate to form different arrays. These arrays could converge moisture on PhC microspheres in wet environment, which avoids the ions loss of the PNs and effectively prevented mutual contamination. In addition, the fluorescence of the PNs inside PhC microspheres could reversibly quench or recover in response to the environmental moisture. Based on these features, it is demonstrated that the PNs-integrated PhC microsphere arrays could realize various information encryption modes, which indicate their excellent values in information security fields.