Anti-counterfeiting Applications Research Articles

Ultra-long room temperature phosphorescent materials based on tetraphenylethylene derivatives for anti-counterfeiting and encryption applications

Stimuli-responsive room temperature phosphorescent materials have been the subject of considerable research activity in recent years. In this study, the tetraphenylethylene group was selected in combination with arylboronic acid (TIPE-BOH) and used to dope a rigid polyvinyl alcohol (PVA) matrix to generate a film material (TIPE-BOH-PVA) that exhibited an aggregation-induced emission (AIE) effect. The prepared film exhibits excellent room temperature phosphorescence (RTP) performance, with an enhanced emission wavelength and an afterglow time of up to 12 s. The triplet-to-singlet Förster resonance energy transfer (TS-FRET) has been utilized to modify the afterglow color by adding butyl rhodamine B (BRhB) and rhodamine 6G (R6G), employing a water phase without the use of organic solvents. The resultant material exhibits stimulus responsiveness; the RTP properties disappear when the material is exposed to water vapor, but are restored following thermal treatment. The material has potential applications in information encryption and erasure, double anti-counterfeiting ink, and fingerprint acquisition systems. This work offers a new strategy for the design of stimuli-responsive ultra-long RTP materials with far-ranging end applications.

A multistimuli-responsive fluorescent polymer gel based on thioctic acid and hyperbranched polymer

Fluorescent gels with fast and reversible responses have attracted extensive attention, but it remains a huge challenge to synthesize high performance multistimuli-responsive fluorescent gel through a facile and versatile approach. In this work, a multistimuli-responsive fluorescent thioctic acid-crosslinked hyperbranched polymer gel (TLHP) was designed and fabricated by copolymerization of acrylic acid, amino-ended hyperbranched polymers (AHP), tetrakis(4-aminophenyl)ethene (TPE-4NH2) and thioctic acid (TA). The structures of the TLHP gel were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). AHP played an important role in the TLHP gel. The terminal amino groups of AHP and TPE-4NH2 in the network served as strong complexing centers with carboxylic groups of TA and acrylic acid by hydrogen bonding interactions, thus a unique toughening and self-healing strategy for the supramolecular network was established. Compared with poly(TA and acrylic acid) (TPAA), TLHP-0.4 % which incorporated 0.4% TPE-4NH2 exhibited excellent mechanical properties, with tensile strength up to 438 kPa and stretchability up to 741 %, increased by 193.3 % and 45.3 %, respectively. In addition, TLHP-0.4 % was crosslinked through the dynamic covalent disulfide bonds and the noncovalent H-bonds between amino or carboxy groups, and exhibited fluorescence responsiveness to temperature, pH, and metal ions, greatly expanding the application of TLHP as rewritable printing ink and temperature-based erasing. The fluorescence of TLHP was also sensitive to Cu2+, and the intensity can be restored by EDTA solution to realize fluorescence “switching”. The multistimuli-responsive fluorescence of TLHP may have broad prospects in reversible patterning displays, multi-level anti-counterfeiting applications for information security, and various potential applications.

Sustainable latent fingerprint enhancement with ink-free printing and shape memory behavior using Parthenium Hysterophorus-derived carbon dots

We developed a method to produce red fluorescent carbon dots from Parthenium hysterophorus leaves (PCDs) through hydrothermal carbonization. These PCDs exhibit consistent photoluminescence, emitting light regardless of excitation, with a 6.01 ns fluorescence lifetime and a 10.2% quantum yield. They possess a fine size of 4.4 nm, excellent hydrophilicity, and stability in a pH range of 4–11. Leveraging their optical properties, these PCDs function as precise nano-probes for detecting Fe3+ ions, demonstrating a linear correlation within 0 to 50 μM concentrations and a low detection limit of approximately 0.14 μM. Emitting light at about 620 nm, these PCDs remain visible even in daylight. When applied to fingerprints on various substrates and dried, they reveal distinct prints under 365 nm UV light, retaining stability for 24 h. This resilience is attributed to preventing fluorescence reduction, achieved through the coffee-ring effect and electrostatic interactions during drying. Employing deep learning with the YoLOv8 algorithm, fluorescence images of these latent fingerprints (LFPs) exceptionally resemble standard controls. These PCDs serve a dual role as fluorescent ink and nanocomposite films within a PVA matrix, demonstrating potential in anti-counterfeiting applications. This study presents a straightforward method for synthesizing PCDs with intense red luminescence, establishing them as a versatile platform for Fe3+ sensing, flexible fluorescent films, latent fingerprints, and anti-counterfeiting pursuits.

Hydrothermally synthesized fluorescent nitrogen-doped carbon dots for catalytic efficiency and anti-counterfeiting application

Here, Tylophora indica plant extract was utilized to create nitrogen-doped carbon dots by hydrothermal method. The synthesized NDCDs was employed to anti-counterfeiting and enhancing the catalytic activity of Malachite Green dye. The ultraviolet–visible spectroscopy and FT-IR measurements was used to analyze the optical properties and the development of NDCDs as well as the source of Tylophora indica. Using HR-TEM, XRD, and XPS, the structure and elemental contents of the produced NDCDs was investigated. The HRTEM images showed that the NDCDs had a d-spacing of 0.37 nm and an average particle size of 4.3 ± 1 nm. After being subjected to UV light at 365 nm, the produced NDCDs began to glow blue, with a quantum yield (QY) of 16.1 %. The ID and IG ratio values for NDCDs were found to be 0.86. With rate constant values calculated at 0.1830 min−1, respectively, the synthesized NDCDs were found to be a viable catalyst for the Malachite Green (MG) dye reduction process utilizing freshly prepared NaBH4. In addition, the NDCDs solution is used as fluorescent ink. The printed patterns retain their anti-counterfeiting properties even after being heated and stored in an environment for an extended period, indicating the NDCDs stability for prospective anti-counterfeiting applications.

Ultraviolet-B and Near-Infrared Dual-Band Luminescence in Bi3+/Bi2+ Codoped Persistent Phosphor for Optical Storage Application.

Discovering multifunctional luminescent materials to meet the demands of modern spectroscopy is of great significance. However, it is a standing challenge to enable multiple luminescence properties in a single material system via single metal ion doping. Here, we report the inherently Bi3+/Bi2+ codoped Ca3Ga2Ge3O12 persistent phosphor where Bi3+ is in situ reduced to Bi2+. This phosphor can act as an efficient multimodal luminescence material, which simultaneously exhibits long-lasting (>12 h) ultraviolet-B (UVB) and near-infrared (NIR) dual-band persistent luminescence after irradiation by 254 nm ultraviolet (UV) light. UVB and NIR afterglow are ascribed to the distinct Bi3+ and Bi2+ emitters, respectively, proven by comprehensive spectroscopic investigations including X-ray absorption near-edge structure spectra and X-ray photoelectron spectroscopy. Besides, this phosphor also exhibits exceptional photochromic features, accompanied by a rapid body color transformation from white to brown in response to 254 nm UV light within 60 s and excellent recovery capacity upon thermal or blue/white light stimulation. The combination of UVB persistent luminescence of Bi3+ and NIR afterglow of Bi2+ coupled with reversible white-to-brown photochromism phenomenon offers one type of promising multifunctional luminescence material, showing potential to be used for optical storage and anti-counterfeiting applications.

Anti-counterfeiting applications of antimony-doped zero-dimensional indium halide with temperature-responsive broad emission

While spatial-resolved luminescent anti-counterfeiting technology has reached maturity, achieving rapid responsiveness and exceptional fatigue resistance remains a challenge for high-security-level applications. Temperature-based multi-stimuli-responsive luminescent solid-state materials offer a promising solution to meet these requirements. In this study, we present a dual stimuli-responsive photoluminescence (PL) switching system that depends on both temperature and excitation wavelength, utilizing a Zero-Dimensional (0D) (PMA)4In0.98Sb0.02Cl7·H2O (PMA = benzylamine). Notably, (PMA)4In0.98Sb0.02Cl7·H2O exhibits orange broad-band emission at room temperature under both low-energy (365 nm) and high-energy (254 nm) irradiation. At 80 K, green light emission is observed under high-energy irradiation (254 nm), transforming into red emission when excited with low-energy wavelength (365 nm) at the same temperature. Moreover, the (PMA)4In0.98Sb0.02Cl7·H2O both in powder and film states demonstrate excellent stimuli-responsive performance, including short response times and superior cyclic reversibility. Therefore, this 0D (PMA)4In0.98Sb0.02Cl7·H2O can serve as a novel quarter-fold turn-on and tuning luminescent switch for encryption/decryption under the stimuli of temperature and excitation with rapid response and excellent fatigue resistance.

Photoluminescence investigation of novel red emitting NaLa(1-x)MgTeO6: XSm3+ phosphor with high color purity for n-UV based warm WLEDS and anti-counterfeiting applications

Recently, red phosphors are extensively developed to find applications in phosphor converted white LEDs (pc-WLEDs) and anti-counterfeiting. In this work, samarium doped sodium lanthanum magnesium tellurate (NaLaMgTeO6:Sm3+) red emitting phosphors have been synthesized for the first time via solid state reaction method. Rietveld refinement of XRD pattern reveals monoclinic crystal structure of NaLaMgTeO6. Under 404 nm (6H5/2 → 4F7/2) n-UV excitation, NLMT:Sm3+ phosphor shows red emission at 643 nm (45/2 → 69/2) with color purity 100 % and the obtained CCT value corresponds to warm light source. Temperature-dependent PL analysis of NLMT:Sm3+ exhibits good thermal stability. The anti-counterfeiting security ink was developed using optimized phosphor and the information was encrypted on different surfaces using the prepared security ink. The encrypted data was decoded only by n-UV light. The aforementioned results revealed that NLMT:Sm3+ is a highly effective phosphor as a red component for pc-WLEDs and luminescent dye for anti-counterfeiting applications.

Fluorescence-enhanced Cs2Ag0.3-xNaxZn0.35In1-yCl6:yM double perovskites for multimodal optical anti-counterfeiting

The excellent optical properties of lead-free halide double perovskites (LHDPs) Cs2AgInCl6 are of great importance in the field of anti-counterfeiting encryption. However, the fluorescence quantum yield of the existing Cs2AgInCl6-based materials is relatively low, and the fluorescence color is monochromatic, making it difficult to use in advanced multi-mode anti-counterfeiting applications. In this study, we synthesized Cs2Ag0.3-xNaxZn0.35In1-yCl6:yM (M = Cr/Bi) series LHDPs using an anti-solvent assisted co-precipitation method, improving the optical properties of Cs2AgInCl6-based materials by optimizing their composition. The fluorescence quantum yield of Zn–Na substituted Cr-doped Cs2Ag0.3-xNaxZn0.35In1-yCl6 LHDPs increased from 1.53 % to 82.57 % on the basis of Cs2AgInCl6. The Zn–Na substituted Bi-doped Cs2Ag0.3-xNaxZn0.35In1-yCl6 LHDPs exhibited dual-wavelength fluorescence emission at 407 and 650 nm, and the relative intensity between the two emission wavelengths changed via a change in the Bi doping amount, resulting in a change in the material's luminescence color. The as-synthesized LHDPs could be applied to multi-mode anti-counterfeiting, optical coding information storage, and art decoration applications.

Dynamic multicolor emissions of multimodal phosphors by Mn2+ trace doping in self-activated CaGa4O7

The manipulation of excitation modes and resultant emission colors in luminescent materials holds pivotal importance for encrypting information in anti-counterfeiting applications. Despite considerable achievements in multimodal and multicolor luminescent materials, existing options generally suffer from static monocolor emission under fixed external stimulation, rendering them vulnerability to replication. Achieving dynamic multimodal luminescence within a single material presents a promising yet challenging solution. Here, we report the development of a phosphor exhibiting dynamic multicolor photoluminescence (PL) and photo-thermo-mechanically responsive multimodal emissions through the incorporation of trace Mn2+ ions into a self-activated CaGa4O7 host. The resulting phosphor offers adjustable emission-color changing rates, controllable via re-excitation intervals and photoexcitation powers. Additionally, it demonstrates temperature-induced color reversal and anti-thermal-quenched emission, alongside reproducible elastic mechanoluminescence (ML) characterized by high mechanical durability. Theoretical calculations elucidate electron transfer pathways dominated by intrinsic interstitial defects and vacancies for dynamic multicolor emission. Mn2+ dopants serve a dual role in stabilizing nearby defects and introducing additional defect levels, enabling flexible multi-responsive luminescence. This developed phosphor facilitates evolutionary color/pattern displays in both temporal and spatial dimensions using readily available tools, offering significant promise for dynamic anticounterfeiting displays and multimode sensing applications.

Photo-Curable 3D Printing of Circularly Polarized Afterglow Metal-Organic Framework Monoliths.

Developing coordination complexes (such as metal-organic frameworks, MOFs) with circularly polarized luminescence (CPL) is currently attracting tremendous attention and remains a significant challenge in achieving MOF with circularly polarized afterglow. Herein, MOFs-based circularly polarized afterglow is first reported by combining the chiral induction approach and tuning the afterglow times by using the auxiliary ligands regulation strategy. The obtained chiral R/S-ZnIDC, R/S-ZnIDC(bpy), and R/S-ZnIDC(bpe)(IDC = 1H-Imidazole-4,5-dicarboxylate, bpy = 4,4'-Bipyridine, bpe = trans-1,2-Bis(4-pyridyl) ethylene) containing a similar structure unit display different afterglow times with 3, 1, and <0.1s respectively which attribute to that the longer auxiliary ligand hinders the energy transfer through the hydrogen bonding. The obtained chiral complexes reveal a strong chiral signal, obvious photoluminescence afterglow feature, and strong CPL performance (glum up to 3.7×10-2). Furthermore, the photo-curing 3D printing method is first proposed to prepare various chiral MOFs based monoliths from 2D patterns to 3D scaffolds for anti-counterfeiting and information encryption applications. This work not only develops chiral complexes monoliths by photo-curing 3D printing technique but opens a new strategy to achieve tunable CPL afterglow in optical applications.

Crystal structural effects on up/down-conversion luminescence properties of GdInO3:Tm,Yb perovskite phosphors for effective dual-mode anti-counterfeit applications

Developing advanced luminescent materials that are recognizable under specified conditions provides better opportunity for reliable optical anti-counterfeiting techniques. In this work, to the best of our knowledge, novel GdInO3:Tm,Yb perovskite phosphors with ultrafine sizes and rounded morphologies were successfully synthesized by a facile chemical precipitation route. Two-type perovskites with orthorhombic and hexagonal structures could be obtained by calcining the precursor at 850 and 1100 °C, respectively. Under 980 nm excitation, the two phosphors exhibited cyan-bluish emission at ∼460−565 nm, red emission at 645−680 nm, and near-infrared emission at 770−825 nm arising from 1G4 + 1D2→3H5,6, 3F2,3→3H6, and 3H4→3H6 transitions of Tm3+, respectively, where the hexagonal perovskite phosphor had relatively strong and sharp red emission as well as red-shifted cyan-bluish emission via successive cross relaxations. The Yb3+ sensitizer enhanced the upconversion luminescence via effective Yb3+→Tm3+ energy transfer and the optimal Yb3+ concentrations were 10 at.% for orthorhombic perovskite and 5 at.% for hexagonal one. The upconversion mechanism mainly ascribed to two-photon processes while three-photon was also present. Upon excitation at 254 nm, their down-conversion spectra exhibited broad multibands in the wavelength range of 400−500 nm deriving from combined effects of the defect-induced emission of GdInO3 and the 1D2→3F4 + 4G4→3H6 emissions of Tm3+. The energy transfer from GdInO3 defect level to Tm3+ excitation state was observed for the first time. The unclonable security codes prepared by screen printing from those dual-mode emitting perovskite phosphors were almost invisible under natural light, which had promising potential for anti-counterfeiting application.

Responsive organic room-temperature phosphorescence materials for spatial-time-resolved anti-counterfeiting

Stimulus-responsive room-temperature phosphorescence (RTP) materials have gained significant attention for their important optoelectronic application prospects. However, the fabrication strategy and underlying mechanism of stimulus-responsive RTP materials remain less explored. Herein, we present a reliable strategy for achieving pH-responsive RTP materials by integrating poly(vinyl alcohol) (PVA) with carboxylic acid or amino group functionalized terpyridine (Tpy) derivatives. The resulting Tpy derivatives-based RTP materials displayed reversible changes in emission color, intensity, and lifetime of both prompt and delayed emission. Notably, the RTP emission undergoes a significant diminish upon exposure to acid due to the protonation of Tpy units. Taking advantage of the decent RTP emission and pH-responsiveness of these RTP films, a spatial-time-resolved anti-counterfeiting application is demonstrated as a proof-of-concept for largely enhancing the security level. This study not only provides new prospects for developing smart RTP materials but also promotes the advancement of optical anti-counterfeiting applications.

Carbon dot-based afterglow composite with tunable room temperature phosphorescence and thermally activated delayed fluorescence and their anti-counterfeiting and encryption application

Carbon dots (CDs) based afterglow materials have attracted much attention owing to their low toxicity, environmental protection, stable luminescence, abundant raw materials, and low cost. However, CD-based afterglow materials with both room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) characteristics are rarely reported, which greatly limits their in-depth application in advanced anti-counterfeiting, intelligent sensing, and other fields. In this paper, Cu, N co-doped CDs (Cu, N-CDs) with dual emission centers were synthesized via a simple solvothermal method by heteroatom doping to enhance the spin–orbit coupling of CDs and regulate the luminescence properties of CDs. Then, boric acid (BA) was used as the matrix to synthesize Cu, N-CDs@BA composites by matrix-assisted method, and the electron transfer enhancement afterglow was realized by the inorganic electronic defects of the matrix. Cu, N-CDs@BA can realize the mutual conversion of TADF and RTP by changing the excitation wavelength or increasing the temperature. At the excitation of 285 nm, the room temperature afterglow of Cu, N-CDs@BA exhibit TADF, and the average afterglow lifetime is 94.21 ms. At the excitation of 365 nm, they exhibit RTP, and the average afterglow lifetime is 347.96 ms. Based on three different emission properties (fluorescence, RTP, and TADF), Cu, N-CDs@BA was applied in anti-counterfeiting and encryption, which shows good application potential.

Continuous-Wave Pumped Monolayer WS2 Lasing for Photonic Barcoding.

Micro/nano photonic barcoding has emerged as a promising technology for information security and anti-counterfeiting applications owing to its high security and robust tamper resistance. However, the practical application of conventional micro/nano photonic barcodes is constrained by limitations in encoding capacity and identification verification (e.g., broad emission bandwidth and the expense of pulsed lasers). Herein, we propose high-capacity photonic barcode labels by leveraging continuous-wave (CW) pumped monolayer tungsten disulfide (WS2) lasing. Large-area, high-quality monolayer WS2 films were grown via a vapor deposition method and coupled with external cavities to construct optically pumped microlasers, thus achieving an excellent CW-pumped lasing with a narrow linewidth (~0.39 nm) and a low threshold (~400 W cm-2) at room temperature. Each pixel within the photonic barcode labels consists of closely packed WS2 microlasers of varying sizes, demonstrating high-density and nonuniform multiple-mode lasing signals that facilitate barcode encoding. Notably, CW operation and narrow-linewidth lasing emission could significantly simplify detection. As proof of concept, a 20-pixel label exhibits a high encoding capacity (2.35 × 10108). This work may promote the advancement of two-dimensional materials micro/nanolasers and offer a promising platform for information encoding and security applications.

Highly efficient upconversion luminescence in narrow-bandgap Y2Mo4O15.

Lanthanide-doped upconversion (UC) materials have been extensively investigated for their unique capability to convert low-energy excitation into high-energy emission. Contrary to previous reports suggesting that efficient UC luminescence (UCL) is exclusively observed in materials with a wide bandgap, we have discovered in this study that Y2Mo4O15:Yb3+/Tm3+ microcrystals, a narrowband material, exhibit highly efficient UC emission. Remarkably, these microcrystals do not display any four- or five-photon UC emission bands. This particular optical phenomenon is independent of the variation in doping ion concentration, temperature, phonon energy, and excitation power density. Combining theoretical calculations and experimental results, we attribute the vanishing emission bands to the strong interaction between the bandgap of the Y2Mo4O15 host matrix (3.37 eV) and the high-energy levels (1I6 and 1D2) of Tm3+ ions. This interaction can effectively catalyze the UC emission process of Tm3+ ions, which leads to Y2Mo4O15:Yb3+/Tm3+ microcrystals possessing very strong UCL intensity. The brightness of these microcrystals outshines commercial UC NaYF4:Yb3+,Er3+ green phosphors by a factor of 10 and is 1.4 times greater than that of UC NaYF4:Yb3+,Tm3+ blue phosphors. Ultimately, Y2Mo4O15:Yb3+/Tm3+ microcrystals, with their distinctive optical characteristics, are being tailored for sophisticated anti-counterfeiting and information encryption applications.

Lateral flow assemblies and allied application of carbon quantum dots derived from cigarette tobacco in biosensing, anticounterfeiting and fluorescent films: Theoretical and experimental overview

The bio-sensing activity of fluorescence based nanoprobes is one of the most significant aspects to scrutinize the analytical pursuance in modern security and lateral flow assays. Herein, potent transmogrification of waste cigarette tobacco into fluorescent carbon quantum dots (CQDs) has been achieved by calcination approach. The waste transformation to CQDs holds diverse benefits, comprising high quantum yield, low toxicity and scale up synthesis. The developed CQDs were able to identify tetracycline with phenomenal selectivity and sensitivity through fluorescence based method. The sensing mechanism was fully explored using Density Functional Theory (DFT) and Molecular docking studies. Governing features comprising tetracycline concentration, interfering studies, and real water analysis on the identification of tetracycline were also investigated. Along with, the prepared CQDs act as colorimetric probe, facilitating the detection of tetracycline with the naked eye. The lateral flow device was constructed for the on-site detection of tetracycline in real water samples. To the best of our knowledge, the present work represents a novel approach to designing CQDs and demonstrates their significant potential for application in anticounterfeiting measures and lateral flow devices. This work holds significant prospective as the prepared CQDs was fully utilized to its maximum usage in developing films and fluorescent anti-counterfeiting applications. Concisely, current work opens up distinctive opportunities for rapid on-site, real-time and visualized surveillance of tetracycline using CQDs prepared with a quite simple green approach.

A triphenylamine derivative with multistimuli responsive behavior and high-contrast vapochromism of its Zn(II) complex

In this work, we designed and synthesized a novel multifunctional molecule, (E)-2-(4-(diphenylamino)styryl)-5-(4-pyridyl)-8-quinolinol (HL), which possessed D-π-A structure and exhibited optical responses to acid-base vapor and Zn(II) ions. Zn(II) complex of HL (W1) was obtained and characterized by SC-XRD. Spectral experiments demonstrated that complex W1 displayed aggregation-induced emission enhancement (AIEE) property, which was exact opposite to the aggregation-caused quenching effect of HL. The quantum yield of W1 (15%) was much higher than that of HL (2.1%) in the solid state. Both HL and complex W1 involved sp2 hybrid N atoms, whose protonation and deprotonation gave rise to reversible acidochromism with high contrast. The mechanism was clarified by XPS, 1H NMR, infrared spectroscopy, elemental analysis, PXRD and thermogravimetry results. Benefiting from excited state intramolecular proton transfer in HL together with AIEE of W1, HL could recognize Zn(II) sensitively in aqueous media. The detection limit of HL for Zn(II) reached as low as 5.02 × 10−8 M. An anti-counterfeiting application was realized using HL-loaded test strip, which exhibited fluorescence response, but no color change upon exposure to Zn(II) solution. In addition, HL and W1 solids were combined to develop a stimuli induced encryption/decryption strategy successfully based on their reversible acidochromic behaviors.

Polymer Network Film with Double Reflection Bands Prepared Using a Thermochromic Cholesteric Liquid Crystal Mixture.

Cholesteric liquid crystal polymer network (CLCN) films with a single reflection band have found applications for decoration and anticounterfeiting. The CLCN films with double reflection bands were more suitable for these applications. Herein, they were prepared by using thermochromic cholesteric liquid crystals (CLCs) through a two-step photopolymerization approach. At the first step, due to oxygen inhibition, the CLC monomers near the substrate surface were polymerized at a certain temperature. At the second step, those near the air were polymerized at another temperature. The wavelengths of these two reflection bands of the CLCN film were dominated by the two polymerization temperatures. Based on this approach, patterns with composite colors were prepared, which were suitably applied for decoration. Moreover, a double-layered CLCN film with a broad reflection band was prepared that could potentially be applied for displays.

Regulated polarization degree of upconversion luminescence and multiple anti-counterfeit applications

Regulated polarization degree of upconversion luminescence and multiple anti-counterfeit applications

A novel group of N,N-diaryl-1,2-benzenediamine room temperature phosphors based on structural engineering

Room temperature phosphorescence (RTP) has gained new momentum as a long-term topic along with the appearance of novel phosphors with versatile application potentials. Compared to traditional RTP materials, innovative pure organic phosphors have become promising alternatives due to their superiority in cost and processibility. However, the development of single-component organic phosphors with ultralong emission lifetimes and simple structures is still ongoing. Despite several kinds of organic phosphors being developed, the ones utilizing arylamine skeletons are barely reported. In this paper, we present a novel family of N,N-diaryl-1,2-benzenediamine phosphors with varying numbers of methyl substituents on terminal phenyl rings based on structural engineering. These molecules exhibited bright phosphorescence in the region of green to yellow light with a remarkably long lifetime up to 684 ms in crystalline states under ambient conditions. Comprehensive experimental and theoretical studies revealed that diverse intermolecular interactions and weak intramolecular hydrogen bonds co-contribute to the long-lived RTP emission. An encryption QR code was constructed, which displayed great potential in anti-counterfeiting applications. This work offered a novel structural motif for ultralong RTP material design and is constructive for material pool expansion.