Phosphorescent Color Research Articles

Pyrolysis of Al-Based Metal-Organic Frameworks to Carbon Dot-Porous Al2 O3 Composites With Time-Dependent Phosphorescence Colors for Advanced Information Encryption.

Phosphorescent materials with time-dependent phosphorescence colors (TDPCs) have great potential in advanced optical applications. Synthesis of such materials is attractive but challenging. Here, a series of carbon dot-porous Al2 O3 composites exhibiting distinctive TDPC characteristics is prepared by high-temperature pyrolysis of Al-based metal-organic frameworks NH2 -MIL-101(Al). The composite synthesized at 700 °C (CDs@Al2 O3 -700) shows an obvious change in phosphorescence color from blue to green after removing the excitation light of 280nm. Photophysical analysis reveals that two emission centers in CDs, namely carbon core and surface states, are responsible for the short-lived blue phosphorescence (96ms) and long-lived green phosphorescence (911ms), respectively. The combination of blue and green phosphorescence with different decay rates triggering the interesting TDPC phenomenon. CDs@Al2 O3 -700 has a significantly high phosphorescence quantum yield of up to 41.7% and possesses an excellent optical stability against water, organic solvents, and strong oxidants, which benefits from the multi-confinement of CDs by the porous Al2 O3 matrix through rigid network, strong space constraint, and stable covalent bonding. Based on the TDPC property, multilevel coding patterns composed of CDs@Al2 O3 are successfully fabricated for advanced dynamic information encryption.

Multi-Color Room temperature phosphorescent Silicon-Nanodot-Based nanocomposites with silane tuning and applications to 5D information encryption

Multi-color phosphorescent materials have received considerable attention owing to their wide range of applications. However, a standardized strategy for producing tunable phosphorescent colors has rarely been developed. Herein, we report the preparation of ingeniously designed silicon-nanodot-based nanocomposite materials with multi-color afterglows (cyan, yellow, orange and red) using a simple hydrothermal method that involves combining silane, dyes and urea. Notably, the silane formed silicon nanodots in situ by participating in the hot-melt recrystallization process of urea, accompanied by the formation of new covalent and hydrogen bonds. These nanodots become immobilized in the rigid network structure formed during urea recrystallization to deliver highly efficient phosphorescence. More impressively, orange and red afterglow materials were successfully synthesized based on the phosphorescence Förster resonance energy transfer principle. These properties led to the establishment of the information security systems using single-, multiple-, and 5D information encryption methods. Given the universality of this method, this standardized strategy not only highlights the potential of constructing multifunctional phosphorescent materials from silane, but also provides a novel design principle for the synthesis of full-color afterglow materials.

Carbon dots with full-color-tunable room-temperature phosphorescence for photo-stimulated responsive application

Advances in polymeric matrices with ultralong and color-tunable phosphorescence were recently made, but their luminescence mechanism was not yet thoroughly understood. The current experimental and theoretical studies show that the red-shift of phosphorescence spectrum is caused by increasing the C–N and C=O of carbon dots in the polymeric matrix. In addition, theoretical calculations explain the charge transfer and spin orbit coupling of carbon dots in a system containing different covalent bonds. The phosphorescence emission color and lifetime can be modulated, which is applied into triple anti-counterfeiting of photo-stimulated-dependent color, time-dependent color, and time-dependent phosphorescence lifetime. In the application, the phosphorescence color of carbon dots in the polymeric matrix can be varied from deep blue (431 nm) to red (620 nm) with a maximal lifetime of 2.02 s and a maximum phosphorescence quantum yield of 20.1%. This work provides a new direction for the development of carbon dots with efficient and color-tunable ultra-long phosphorescence.

Time-dependent Phosphorescence Color of Carbon Dots in Binary Salt Matrices through Activations by Structural Confinement and Defects for Dynamic Information Encryption.

The emergence of time-dependent phosphorescence color (TDPC) materials has taken information encryption to high-security levels. However, due to the only path of exciton transfer, it is almost impossible to obtain TDPC for chromophores with a single emission center. Theoretically, in inorganic-organic composites, the exciton transfer of organic chromophores depends on the inorganic structure. Here, we assign two structural effects to inorganic NaCl by metal (Mg2+ or Ca2+ or Ba2+ ) doping, which triggers the TDPC performance of carbon dots (CDs) with a single emission center. The resulting material is used for multi-level dynamic phosphorescence color 3D coding to achieve information encryption. The structural confinement activates the green phosphorescence of CDs; while the structural defect activates tunneling-related yellow phosphorescence. Such simply doped inorganic matrices can be synthesized using the periodic table of metal cations, endowing chromophores with tremendous control over TDPC properties. This demonstration extends the design view of dynamic luminescent materials.

Time‐dependent Phosphorescence Color of Carbon Dots in Binary Salt Matrices through Activations by Structural Confinement and Defects for Dynamic Information Encryption

AbstractThe emergence of time‐dependent phosphorescence color (TDPC) materials has taken information encryption to high‐security levels. However, due to the only path of exciton transfer, it is almost impossible to obtain TDPC for chromophores with a single emission center. Theoretically, in inorganic‐organic composites, the exciton transfer of organic chromophores depends on the inorganic structure. Here, we assign two structural effects to inorganic NaCl by metal (Mg2+ or Ca2+ or Ba2+) doping, which triggers the TDPC performance of carbon dots (CDs) with a single emission center. The resulting material is used for multi‐level dynamic phosphorescence color 3D coding to achieve information encryption. The structural confinement activates the green phosphorescence of CDs; while the structural defect activates tunneling‐related yellow phosphorescence. Such simply doped inorganic matrices can be synthesized using the periodic table of metal cations, endowing chromophores with tremendous control over TDPC properties. This demonstration extends the design view of dynamic luminescent materials.

Efficient Solid‐State Emission Control by Positional Isomerism for Platinum(II) Complex with Donor–π–Acceptor Ligand

AbstractSquare‐planar platinum (Pt)(II) complexes have attracted considerable attention owing to their unique luminescent properties, and the development of facile methods to control them is very important. A series of Pt(II) complexes containing a donor–π–acceptor (D–π–A) isomer ligand (ortho‐, meta‐, and para‐position; Pt‐O, Pt‐M, and Pt‐P) is prepared to investigate the positional isomerism on the Pt(II) complex. In particular, the metal‐to‐ligand charge transfer and ligand intramolecular charge transfer characteristics are examined depending on the positional isomer and compared with the donor‐free Pt(II) complex. All Pt(II) complexes observe slightly red‐shifted emission within 10 nm in the order of Pt‐O < Pt‐M < Pt‐P. Experimental data and theoretical calculations show that the Pt(II) complex lowest unoccupied molecular orbital energy level is controlled systematically by the donor position dependency. In particular, the small perturbation of the electronic state by positional isomerism in the single molecule induces significant phosphorescence color disparities of more than 82 nm in the solid‐state emission spectra and aggregation‐induced emission. The intriguing phosphorescent behavior is explained by the ligand‐dependent macroscopic molecular array with the Hirshfeld analysis. Consequentially, this paper reports a facile emission control method by the D–π–A ligand positional isomerism in the Pt(II) complex.

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 10s 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.

Aggregation-induced color fine-tunable carbon dot phosphorescence covering from green to near-infrared for advanced information encryption

Multi-color phosphorescence carbon dots (CDs) show enormous potential in advanced information encryption, yet the achievement of wide-range, fine-tunable phosphorescence CDs, especially with near-infrared (NIR) phosphorescence emission, confront numerous challenges. Herein, for the first time, the phosphorescence CD-based composites with fine-color tunable property ranging from green to NIR are obtained via regulating CDs contents in annealed boric acid (BA). The synthesized CDs are fully passivated by BA molecular and form uniform surface state, which avoids aggregation-induced quenching to some extent. By increasing the CDs contents in BA during thermal treatment, the aggregation degree of CDs is gradually increased, causing substantial electronic interactions. This leads to energy splitting and form low-energy aggregation states, resulting in phosphorescence continuously shifts from 530 to 555, 585, 625, 645 and 750 nm. Based on aggregation-induced discoloration, we further explore solvent-triggered evolutionary discoloration property of CDs, that is, trace methanol could induce phosphorescence color change from green to red, and illustrate their potential applications in advanced anti-counterfeiting and information encryption.

Phosphorescent and Test Strips Detection Properties of ClO− Probes Based on Iridium(III) Complexes with Pivaloyl Unit as Recognition Site

AbstractThree green phosphorescent Iridium(III) complex‐based probes with different ligands (Cl− (Ir‐1), NCS− (Ir‐2) and NCO− (Ir‐3)) had been developed to detect hypochlorite (ClO−) using pivaloyl group as recognition site. The introduction of strong field ligand NCS and NCO caused an increase of quantum yields and phosphorescent lifetime both in solid and solution states. All the three probes could selectively and rapidly detect ClO− through the changes in UV‐visible and phosphorescence spectra. Upon addition of ClO− to the solution of probes, green phosphorescent color of probes displayed obvious quench. Meanwhile, using a portable UV lamp, test strips which were pre‐immersed with the above‐mentioned probes could achieve easy detection of ClO−. The sensing process was confirmed by NMR, IR and ESI‐MS.

Ultra-stable dual-color phosphorescence Carbon-Dot@Silica material for advanced anti-counterfeiting

Room temperature phosphorescence (RTP) materials have motivated massive attention due to their great advantages in anti-counterfeiting and optical encryption. However, the commonly used carbon-based RTP materials suffer from drawbacks of photobleaching, quenching and single phosphorescence color outputs, which obstruct their performance in high-level anti-counterfeiting techniques. Herein, we present a universal method for the fabrication of a carbon-dot@silica (CDs@SiO2) composite that possesses ultralong lifetime, high phosphorescence quantum efficiency (PQE), excellent luminescence stability, and dual-color phosphorescence emission. Taking advantage of the restriction by rigid network of SiO2 and stable covalent bonding between CDs and SiO2, the triplet excited states of CDs are stabilized. As a result, the CDs@SiO2 exhibit ultralong lifetime of 1.33 s and 0.38 s under excitation at 254 nm and 365 nm, respectively. Furthermore, the phosphorescence color of CDs@SiO2 can change from cyan to yellow when the exciting wavelength switches from 254 nm to 365 nm. The obtained CDs@SiO2 also exhibit outstanding characteristics of anti-photobleaching and phosphorescence stability in an aqueous solution. Based on the unique phosphorescent properties of the CDs@SiO2, a stable and dual-color phosphorescence security label is designed for advanced information encryption.

Multistimuli-Responsive Properties of Aggregated Isocyanide Cycloplatinated(II) Complexes

Here, we describe the neutral cyclometalated tert-butylisocyanide PtII complexes, [Pt(C∧N)Cl(CNBut)] 1, the double salts [Pt(C∧N)(CNBut)2][Pt(C∧N)Cl2] 2, and the cationic complexes [Pt(C∧N)(CNBut)2]ClO43 [C∧N = difluorophenylpyridine (dfppy, a), 4-(2-pyridyl)benzaldehyde (ppy-CHO, b)]. A comparative study of the pseudopolymorphs 1a, 1a·CHCl3, 1b, 1b·0.5Toluene, 1b·0.5PhF, and 3a·0.25CH2Cl2 reveals strong aggregation through Pt···Pt and/or π···π stacking interactions to give a variety of distinctive one-dimensional (1D) infinite chains, which modulate the photoluminescent properties. This intermolecular long-range aggregate formation is the main origin of the photoluminescent behavior of 1a and 1b complexes, which exhibit highly sensitive and reversible responses to multiple external stimuli including different volatile organic compounds (VOCs), solvents, temperatures, and pressures, with distinct color and phosphorescent color switching from green to red. Furthermore, complex 1b undergoes supramolecular self-assembly via Pt···Pt and/or π···π interactions into a polymer thin polystyrene (PS) film 10 wt % in response to toluene vapors, and 3a exhibits vapochromic and vapoluminescent behavior. Theoretical simulations on the dimer, trimer, and tetramer models of 1a and 1b have been carried out to get insight into the photophysical properties in the aggregated solid state.

Structurally Resemblant Dopants Enhance Organic Room-Temperature Phosphorescence.

Doping has shown very promising potential in endowing room-temperature phosphorescence (RTP) properties of organic phosphors with minimal effort. Here, a new isomer design and doping strategy is reported that is applicable to dibenzothiophene (DBT) and its derivatives. Three isomers are synthesized to study the dopant effect on enhancing RTP of DBT derivatives. It is found that isomer dopants bearing close resemblance to the host with matched highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and small energy difference between singlet- and triplet-excited states can yield efficient RTP for the doped system. Meanwhile, phosphorescence color from yellow to red is achieved by varying isomer dopants used for doping the DBT derivatives. This work represents an RTP enhancement strategy based on isomer design and doping to construct luminescent organic phosphors.

Surface ionization-induced tunable dynamic phosphorescence colors from carbon dots on paper for dynamic multimode encryption

Stimuli-responsive phosphorescence materials with dynamic color-changing properties are highly promising for advanced information security. Herein, we demonstrate a novel strategy that effectively induces tunable dynamic phosphorescence color from carbon dots (CDs) on papers via surface ionization engineering for multimode encryption and information storage. Alkali-induced phenolic hydroxyl ionization on CDs can boost intersystem crossing rates, while surface-ionized groups with negative charges significantly passivate the surface defects and reduce non-radiative transitions, which can activate surface state-related blue phosphorescence emission. Combined with the carbon core state-related yellow-green phosphorescence, excitation/time-dependent phosphorescence color-changing from yellow-green to blue are realized from alkali (Na2CO3) treated CDs on paper. Furthermore, benefiting from the transition from NaHCO3 to Na2CO3 under thermal treatment, dynamic color-changing phosphorescence can also be activated by thermally stimulating NaHCO3-treated CDs on paper. Finally, multi-stimuli (alkali or thermal) and multi-modal dynamic phosphorescent colors from a single CDs system are realized for the first time. Based on these unique features, multimode encryption and smart 3D codes with anti-counterfeiting and monitoring functions for medicine during transport or storage are demonstrated by combining an inkjet printing technique using CD inks.

Heteroleptic cuprous complexes of a diimine MePBO ligand and their structure influence on phosphorescent color: Syntheses, structure characterizations, properties and TD‐DFT calculations

AbstractThree new heteroleptic [Cu(NN)P2]+ type cuprous complexes 1–3 were designed and synthesized by utilizing a diimine ligand 5‐methyl‐2‐(2′‐pyridyl)‐benzoxazole (MePBO) and different phosphine ligands PPh3 (1), m‐Tol3P (2) and POP (3), (PPh3=triphenylphosphine, m‐Tol3P=tris(3‐methylphenyl)phosphine, POP=bis[2‐(diphenylphosphino)phenyl]ether), respectively. All complexes were characterized by single‐crystal X‐ray diffraction, spectroscopic analysis (IR, UV‐Vis), elemental analysis, and photoluminescence study. Single‐crystal X‐ray diffraction revealed that complexes 1–3 all adopt discrete cation complex structure with a tetrahedral CuN2P2 coordination geometry with diverse P−Cu−P angles. Their UV‐Vis absorption spectra exhibit a blue‐shift sequence under the enlarging of P−Cu−P angle from 3 to 2 then to 1. The PL emission peak wavelengths of 1–3 also present similar blue‐shift sequence (3→1/2). Their microsecond PL lifetime indicates that their PL behavior belongs to phosphorescence. TD‐DFT calculation and wavefunction analysis illuminate that the S1 and T1 states of 1–3 should all be assigned as (ML+L′L)CT states. Their UV‐Vis absorption and phosphorescence should be attributed to the charge transfer from the P−Cu−P segment to the MePBO ligand. Therefore, as P−Cu−P angle increases (lower HOMO), the energy of S1 and T1 states also increase, following the change of PL color. Additionally, the steric hindrance from substituents of phosphine ligand, as well as extra strong intra‐molecular π−π stacking interactions should effectively inhibit nonradiative decay so that an abnormal PL emission blue‐shift is observed from 1 to 2.

Time-Dependent Phosphorescence Colors from Carbon Dots for Advanced Dynamic Information Encryption.

The development of phosphorescent materials with time-dependent phosphorescence colors (TDPCs) is of considerable interest for application in advanced dynamic information encryption. In this study, TDPC is realized in carbon dots (CDs) synthesized by the one-pot hydrothermal treatment of levofloxacin. CD ink printed on paper (CD@paper) exhibits a change in phosphorescence color from orange to green, 1 s after irradiation with 395 nm light. However, when irradiated with wavelengths shorter or longer than 395 nm, the CD@paper exhibits only green or red phosphorescence, respectively. The red and green phosphorescence originates from the low-energy surface oxide triplet state and high-energy N-related triplet state, respectively. When irradiated with a suitable light energy (around 395 nm wavelength), the two phosphorescent centers can be simultaneously activated, emitting red and green phosphorescence with different decay rates. The red and green phosphorescence merge into an orange phosphorescence initially, exhibiting the TDPC phenomenon. Based on the unusual phosphorescent properties of the CDs, a kind of multilevel, dynamic phosphorescence colored 3D code is designed for advanced dynamic information encryption.

Bright and Robust Phosphorescence Achieved by Non-Covalent Clipping.

Phosphorescent materials with bright emission in versatile media are important for their practical applications, which require to lower the susceptibility of triplet excitons to surroundings. Herein a non-covalent clipping strategy has been developed to attain this objective, by designing a tweezer receptor to encapsulate PtII -based triplet emitters through two-fold π-stacking interactions. The PtII emitters display robust phosphorescence by virtue of synergistic rigidifying and shielding effects, which are hardly influenced by emitter concentration, oxygen content, and solvent polarity changes. The phosphorescent colors are elaborately modulated by varying ligand substitutes on PtII emitters. Circularly polarized phosphorescence is further amplified for chiral PtII emitters, by taking advantage of dual phosphorescence and chirality enhancement upon non-covalent tweezer complexation. Overall, the clipping approach paves the way for the development of high-performance phosphorescent materials with bright emission, environmental robustness, and facile color tunability.

Bright and Robust Phosphorescence Achieved by Non‐Covalent Clipping

AbstractPhosphorescent materials with bright emission in versatile media are important for their practical applications, which require to lower the susceptibility of triplet excitons to surroundings. Herein a non‐covalent clipping strategy has been developed to attain this objective, by designing a tweezer receptor to encapsulate PtII‐based triplet emitters through two‐fold π‐stacking interactions. The PtII emitters display robust phosphorescence by virtue of synergistic rigidifying and shielding effects, which are hardly influenced by emitter concentration, oxygen content, and solvent polarity changes. The phosphorescent colors are elaborately modulated by varying ligand substitutes on PtII emitters. Circularly polarized phosphorescence is further amplified for chiral PtII emitters, by taking advantage of dual phosphorescence and chirality enhancement upon non‐covalent tweezer complexation. Overall, the clipping approach paves the way for the development of high‐performance phosphorescent materials with bright emission, environmental robustness, and facile color tunability.

A highly sensitive ‘turn-on’ phosphorescence probe based on iridium(III) complex with polyether segment subunits for rapid detection of thiophenol

A red-emitting cyclometalated Ir(III) complex-based phosphorescent probe 1 was designed and synthesized to selectively and sensitively detect thiophenol in 90% DMSO/PBS (0.01 M, pH = 7.4) solution with a low detection limited (LOD = 8.68 × 10−7 mol L−1). For probe 1, cyclometalated [Ir(ppy)2Phen]+ moiety acted as phosphor, 2,4-dinitrobenzenesulfonyl (DNBS) group was regarded as recognition site and phosphorescent quencher, and polyether (1-ethoxy-2-(2-methoxyethoxy)ethane) units in the C^N ligands was introduced to improve the water solubility of complex. Due to strong electro-withdrawing DNBS moiety, probe 1 exhibited very week phosphorescence at 600 nm. Upon addition with thiophenol to probe 1 and DNBS moiety left due to the cleavage of sulfonamide bond though nucleophilic elimination reaction, an obvious phosphorescence at 600 nm belong to complex 2 could be observed and the solution displayed red phosphorescent color. Meanwhile, the probe possessed a large Stokes shift (180 nm) and a relatively larger phosphorescence lifetime (τ = 5.265 μs). At the same time, the probe could be used for quantitative detection of thiophenol in actual water samples with high recovery, and detect thiophenol in human serum (100-fold dilution by PBS).

Wide‐Range Color‐Tunable Organic Phosphorescence Materials for Printable and Writable Security Inks

AbstractOrganic materials with long‐lived, color‐tunable phosphorescence are potentially useful for optical recording, anti‐counterfeiting, and bioimaging. Herein, we develop a series of novel host–guest organic phosphors allowing dynamic color tuning from the cyan (502 nm) to orange red (608 nm). Guest materials are employed to tune the phosphorescent color, while the host materials interact with the guest to activate the phosphorescence emission. These organic phosphors have an ultra‐long lifetime of 0.7 s and a maximum phosphorescence efficiency of 18.2 %. Although color‐tunable inks have already been developed using visible dyes, solution‐processed security inks that are temperature dependent and display time‐resolved printed images are unprecedented. This strategy can provide a crucial step towards the next‐generation of security technologies for information handling.

Wide-Range Color-Tunable Organic Phosphorescence Materials for Printable and Writable Security Inks.

Organic materials with long-lived, color-tunable phosphorescence are potentially useful for optical recording, anti-counterfeiting, and bioimaging. Herein, we develop a series of novel host-guest organic phosphors allowing dynamic color tuning from the cyan (502 nm) to orange red (608 nm). Guest materials are employed to tune the phosphorescent color, while the host materials interact with the guest to activate the phosphorescence emission. These organic phosphors have an ultra-long lifetime of 0.7 s and a maximum phosphorescence efficiency of 18.2 %. Although color-tunable inks have already been developed using visible dyes, solution-processed security inks that are temperature dependent and display time-resolved printed images are unprecedented. This strategy can provide a crucial step towards the next-generation of security technologies for information handling.