High-contrast reversible multiple color-tunable solid luminescent ionic polymers for dynamic multilevel anti-counterfeiting

Anion-π interaction guided switchable TADF and low-temperature phosphorescence in phosphonium salts for multiplexed anti-counterfeiting

Anion-π+ interactions have gained continuous attention in diverse organic aggregates, as they can effectively alter emission behavior. Herein, the anion-π+ interaction is introduced to phosphonium salts, which exhibit tunable thermally activated delayed fluorescence and phosphorescence emission. Intriguingly, the emission spectra evolve from deep-blue to yellow emission by regulation of the anion-π+ interaction strength through varying the anions, such as BF4 -, CF3SO3 -, PF6 -, and NO3, accompanied by adjustable luminescent decay times from milliseconds to several seconds. Notably, bright blue emission with a high photoluminescence quantum yield near 100% is achieved when substituting the iodide ions with larger counter anions. The phosphonium iodide with strong anion-π+ interaction and heavy atom effect shows a high inter-system crossing rate, which inhibits the direct and prompt fluorescence emission. The anion-π+ interaction and twisted structure strongly suppress π-π stacking and afford ultra-high photoluminescence yields. Furthermore, the participation of polar solvent molecules results in the solvation and bathochromic-shift phenomenon of the solid-state phosphonium iodide due to the ionic polarized host-guest structure. This work provides new insights into the anion-π+ interaction in luminescent phosphonium aggregates.

Exploring chiral and achiral properties of novel multilayer 3D polymers: synthesis and characterization

This study reports the novel synthesis of multilayered 3D polymers via the 1,3,5-position coupling of 1,3,5-tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene with 1,8-dibronaphthalene, a previously unreported method. The resulting polymers exhibit both achiral and chiral characteristics, offering a unique platform for structural and functional exploration. Comprehensive characterization using gel permeation chromatography, UV-vis spectroscopy, fluorescence measurements, circular dichroism, and scanning electron microscopy revealed intriguing optical properties and morphological features, promoting potential applications in photonics, sensors, and materials science.

Strategic engineering of cationic systems for spatial & temporal anti-counterfeiting applications in zero-dimensional Mn(II) halides

While spatial and time-resolved anti-counterfeiting technologies have gained increasing attention owing to their excellent tunable photoluminescence, achieving high-security-level anti-counterfeiting remains a challenge. Herein, we developed a spatial-time-dual-resolved anti-counterfeiting system using zero-dimensional (0D) organic-inorganic Mn(II) metal halides: (EMMZ)2MnBr4 (named M-1, EMMZ=1-Ethyl-3-Methylimidazolium Bromide) and (EDMMZ)2MnBr4 (named M-2, EDMMZ=1-Ethyl-2,3-Dimethylimidazolium Bromide). M-1 shows a bright green emission with a quantum yield of 78 %. It undergoes a phase transformation from the crystalline to molten state with phosphorescence quenching at 350 K. Reversible phase and luminescent conversion was observed after cooling down for 15 s. Notably, M-2 exhibits green light emission similar to M-1 but undergoes phase conversion and phosphorescence quenching at 390 K, with reversible conversion observed after cooling down for 5 s. The photoluminescence switching mode of on(green)-off-on(green) can be achieved by temperature control, demonstrating excellent performance with short response times and ultra-high cyclic reversibility. By leveraging the different quenching temperatures and reversible PL conversion times of M-1 and M-2, we propose a spatial-time-dual-resolved photoluminescence (PL) switching system that combines M-1 and M-2. This system enables multi-fold tuning of the PL switch for encryption and decryption through cationic engineering strategies by modulating temperature and cooling time. This work presents a novel and feasible design strategy for advanced-level anti-counterfeiting technology based on a spatial-time-dual-resolved system.

Patterned Lead-Free Double Perovskite/Polymer Fluorescent Piezoelectric Composite Films for Advanced Anti-Counterfeiting

The limitations of single fluorescent anti-counterfeiting technologies necessitate the development of more sophisticated encryption methods to protect information and data. Traditional optical anti-counterfeiting encryption techniques, which rely on light sources with varying wavelengths to identify information, are now insufficient to meet contemporary security demands due to their restricted response to a narrow range of wavelengths. In this study, the fabrication of patterned, lead-free double perovskite (DP)/poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) fluorescent piezoelectric composite films (CFs) is reported. These CFs integrate the up-conversion and down-conversion photoluminescent properties of Cs2Na0.8Ag0.2BiCl6:Yb3+/Er3+ DP crystals with the piezoelectric properties of P(VDF-TrFE) film, facilitating multi-modal information protection. The fluorescent signals of different concealed information in CFs are observable under the excitation of 365 nm UV light and 980 nm infrared (IR) light. Additionally, external pressure applied at various locations on the CFs generates corresponding electrical signals, thereby providing triple-layer encryption for protected information. A multifunctional anti-counterfeiting device has been further developed by integrating patterned optical and electrical responses onto flexible CFs, achieving synergistic protection of information security in cross fields and bringing a significant advancement to the high-level anti-counterfeiting market.

Robust two-color physically unclonable patterns from controlled aggregation of a single organic luminophore

This research presents a new approach to create two-color luminescent physically unclonable functions (PUFs) using an organic luminophore with tunable emission colors. These PUFs offer high security and stable performance, significantly enhancing anti-counterfeiting capabilities by exponentially increasing encoding capacity through dual-color integration and complex pattern formation.

Responsive Organic Fluorescent Aggregates Based on Ion-π Interactions Away from Fluorescent Conjugated Groups

Responsive organic luminescent aggregates have a wide range of application fields, but currently there is still a lack of reasonable molecular design strategies. Introducing ion-π interactions into molecules can effectively alter their luminescent properties. However, current research typically focuses on ion localization at luminescent conjugated groups with the strong interaction forces. In this work, we introduce the flexible alkoxy chain spacers between fluorescent conjugated groups and ion-π interaction sites, and then adjust the fluorescence performance of the molecule by changing the strength of ion-π interactions. Bromine ion-based molecules with strong ion-π interactions exhibit high and stable fluorescence quantum yields in crystals and amorphous powders under the external stimuli. Hexafluorophosphate ion-based molecules with weak ion-π interactions have the high fluorescence quantum yield in crystals and very low fluorescence quantum yield in amorphous powders, showing variable fluorescence intensities under external stimuli. This demonstrates a new class of responsive organic luminescent solid-state materials.

Multimode Dynamic Photoluminescence of Bi3+-Activated ZnGa2O4 for Optical Information Encryption

Optical storage technology for information encryption is a popular means of safeguarding information. Herein, a Bi³⁺-activated ZnGa₂O₄ multimode dynamic photoluminescence (PL) material is developed. Upon being irradiated with an ultraviolet lamp at a fixed excitation wavelength of 254 nm, the ZnGa₂O₄: x% Bi³⁺ (x = 0.5-5.0) samples exhibit varying degrees of dynamic PL emission due to a distinct Bi³⁺ doping effect. The mechanism underlying the dynamic PL of ZnGa₂O₄: Bi³⁺ associated with Bi³⁺-activated trap concentration modulation is investigated using thermoluminescence spectra. Additionally, the ZnGa₂O₄: 5% Bi³⁺ sample shows a reversible thermally responsive dynamic PL with a color variation from blue to red upon heating from 283 to 393 K. Predesigned procedures based on single-wavelength-mediated photochromic and thermochromic dynamic PL emissions of ZnGa₂O₄: Bi³⁺ are designed for rewritable optical data storage and high-level information encryption. Also, an enhanced encryption scheme with a mask encoding technique applying a ZnGa₂O₄: Bi³⁺ hybridized polyvinylidene difluoride film is then proposed to increase the security level. Accordingly, this work provides a feasible way to rationally design dynamic PL material offering more creative designs for safeguarding information via encryption.

A 3D multistage information encryption platform with self-erasure function based on a synergistically shape-deformable and AIE fluorescence-tunable hydrogel

The traditional stored information is statically shown on single 2D planes, which leads to low information storage capacity and secondary information leakage without the proper handling of decrypted information. Developing a 3D multistage information encryption platform with self-erasure function is highly desirable. Here, a novel bilayer hydrogel with synergistic deformation and fluorescence color (SDFC) change is designed for 3D multistage information encryption. The bilayer hydrogel consisting of a shape-deformable hydrogel layer and a fluorescence hydrogel layer with aggregation-induced emission (AIE) properties can exhibit pH-responsive SDFC change. Fluorescence information can be ionoprinted on the fluorescent hydrogel layer based on electrostatic interactions and dynamic covalent bonds. The 2D bilayer hydrogel encoded with information can synergistically produce predesigned 3D shape configuration and enhanced background fluorescence to wrap information, which is only readable after sequential shape recovery with the disappearance of background fluorescence. Furthermore, multistage information can be further obtained by stepwise decryption due to information with differential fluorescence fading rates. The displayed information is automatically self-erased in the end, avoiding the information secondary leakage. This study paves an avenue for broadening conventional 2D single-level information encryption platforms to 3D multistage counterparts with self-erasure and multi-decryption capabilities based on SDFC change of the bilayer hydrogel.