Phosphorescence Properties Research Articles

Enhanced solid-state phosphorescence of organoplatinum π-systems by ion-pairing assembly.

Anion binding and ion pairing of dipyrrolyldiketone PtII complexes as anion-responsive π-electronic molecules resulted in photophysical modulations, as observed in solid-state phosphorescence properties. Modifications to arylpyridine ligands in the PtII complexes significantly impacted the assembling behaviour and photophysical properties of anion-free and anion-binding (ion-pairing) forms. The PtII complexes, in the presence of guest anions and their countercations, formed various anion-binding modes and ion-pairing assembled structures depending on constituents and forms (solutions and crystals). The PtII complexes emitted strong phosphorescence in deoxygenated solutions but showed extremely weak phosphorescence in the solid state owing to self-association. In contrast, the solid-state ion-pairing assemblies with tetraalkylammonium cations exhibited enhanced phosphorescence owing to the formation of hydrogen-bonding 1D-chain PtII complexes dispersed by stacking with aliphatic cations. Theoretical studies revealed that the enhanced phosphorescence in the solid-state ion-pairing assembly was attributed to preventing the delocalisation of the electron wavefunction over PtII complexes.

Employing racemization strategies to simultaneously enhance the quantum yield, lifetime, and water stability of room-temperature phosphorescent materials.

Room temperature phosphorescence (RTP) materials are increasingly recognized for their superior luminescent properties, which are pivotal in applications such as anti-counterfeiting, information storage, and optoelectronics. Despite this, the sensitivity of most RTP systems to humidity presents a significant challenge in achieving durable RTP performance in aqueous environments. This study proposes a strategy to enhance organic room-temperature phosphorescence through racemization. By incorporating external racemates of various chiral phosphors-NDBD-Ph, NDBD-Ph-Ph, NDBD-CH3, and NDBD-O-CH3-into a polyacrylonitrile (PAN) matrix, we significantly enhance the RTP properties (quantum yield, lifetime, and afterglow-time) of the resultant films. This enhancement can be attributed to the increased density of racemic molecules in the matrix and the increased spin-orbit coupling (SOC), facilitating the development of a long-lasting polymer RTP system in water. Notably, the racemic rac-NDBD-Ph@PAN film exhibits a persistent bright turquoise afterglow, even after immersion in water for a month. Furthermore, for the first time, we achieved an enhanced green to cyan RTP response to pH variations under both acidic and alkaline conditions (pH = 2-12), with the maximum phosphorescence emission intensity increasing up to threefold. The remarkable water stability, reversible response characteristics, and enhanced phosphorescence properties of this system offer promising potential for dynamic information encryption in aqueous environments.

Lysosome-targeted cyclometalated Ir(III) complexes as photosensitizers/photoredox catalysts for cancer therapy.

A novel lysosome-targeted photosensitizer/photoredox catalyst based on cyclometalated Ir(III) complex IrL has been designed and synthesized, which exhibited excellent phosphorescence properties and the ability to generate single oxygen (1O2) and photocatalytically oxidize 1,4-dihydronicotinamide adenine dinucleotide (NADH) under light irradiation. Most importantly, the aforementioned activities are significantly enhanced due to protonation under acidic conditions, which makes them highly attractive in light-activated tumor therapy, especially for acidic lysosomes and tumor microenvironments. The photocytotoxicity of IrL and the mechanism of cell death have been investigated. Additionally, the tumor-killing ability of IrL under light irradiation was evaluated using a 4T1 tumor-bearing mouse model. This work provides a strategy for the development of lysosome-targeted photosensitizers/photoredox catalysts to overcome hypoxic tumors.

Coordination-induced and tunable layered rare-earth hydroxide-complex intercalated nanohybrid phosphorescent photosensitizer and therapy.

Hydrotalcite intercalated nanohybrid has served as a vital phosphorescent photosensitizer owing to remarkable 1O2 quantum yield and high cell mortality performance. However, it is rather difficult for potential large or complex guest phosphors to directly intercalate into the hydrotalcite gallery. Hence, it is necessary to regulate the interlayer microenvironment of hydrotalcites firstly for outstanding photosensitive properties. Herein, two isomers, 5,5'BDA and 4,4'BDA, with distinctive dual coordinative features were selected to modify the layer microenvironment of the LGdH gallery and induce the introduction of prospective Gd(HPhN)3 phosphorescent complexes into hydrotalcite through two different coordination effects successively. A LGdH-BDA-Gd(HPhN)3 intercalated nanohybrid phosphorescent photosensitizer was successfully obtained. The results indicated that the more efficient improvement was observed from 5,5'BDA due to offering a more spacious and stable space. Specifically, LGdH-5,5'BDA-Gd(HPhN)3 showed significantly better room temperature phosphorescence properties than LGdH-4,4'BDA-Gd(HPhN)3, whose lifetime was nearly 15 times longer than the latter. Additionally, the LGdH-5,5'BDA-Gd(HPhN)3 system displayed superior singlet oxygen generation in vitro under 460 nm irradiation (the quantum yield Φ = 0.48) and outstanding photodynamic therapy performance in tumor cells. LGdH presented more remarkable enhancement performance on the RTP properties of the luminescent molecules. This work provides a novel platform for designing a high-performance hydrotalcite intercalated nanohybrid phosphorescent photosensitizer through coordination induction to regulate the layer microenvironment.

Recent progress in ion-regulated organic room-temperature phosphorescence.

Organic room-temperature phosphorescence (RTP) materials have attracted considerable attention for their extended afterglow at ambient conditions, eco-friendliness, and wide-ranging applications in bio-imaging, data storage, security inks, and emergency illumination. Significant advancements have been achieved in recent years in developing highly efficient RTP materials by manipulating the intermolecular interactions. In this perspective, we have summarized recent advances in ion-regulated organic RTP materials based on the roles and interactions of ions, including the ion-π interactions, electrostatic interactions, and coordinate interactions. Subsequently, the current challenges and prospects of utilizing ionic interactions for inducing and modulating the phosphorescent properties are presented. It is anticipated that this perspective will provide basic guidelines for fabricating novel ionic RTP materials and further extend their application potential.

Layered rare-earth hydroxides as multi-modal medical imaging probes: particle size optimisation and compositional exploration.

Recently, layered rare-earth hydroxides (LRHs) have received growing attention in the field of theranostics. We have previously reported the hydrothermal synthesis of layered terbium hydroxide (LTbH), which exhibited high biocompatibility, reversible uptake of a range of model drugs, and release-sensitive phosphorescence. Despite these favourable properties, LTbH particles produced by the reported method suffered from poor size-uniformity (670 ± 564 nm), and are thus not suitable for therapeutic applications. To ameliorate this issue, we first derive an optimised hydrothermal synthesis method to generate LTbH particles with a high degree of homogeneity and reproducibility, within a size range appropriate for in vivo applications (152 ± 59 nm, n = 6). Subsequently, we apply this optimised method to synthesise a selected range of LRH materials (R = Pr, Nd, Gd, Dy, Er, Yb), four of which produced particles with an average size under 200 nm (Pr, Nd, Gd, and Dy) without the need for further optimisation. Finally, we incorporate Gd and Tb into LRHs in varying molar ratios (1 : 3, 1 : 1, and 3 : 1) and assess the combined magnetic relaxivity and phosphorescence properties of the resultant LRH materials. The lead formulation, LGd1.41Tb0.59H, was demonstrated to significantly shorten the T2 relaxation time of water (r2 = 52.06 mM-1 s-1), in addition to exhibiting a strong phosphorescence signal (over twice that of the other LRH formulations, including previously reported LTbH), therefore holding great promise as a potential multi-modal medical imaging probe.

Fused-Ring Pyrrole-Based Near-Infrared Emissive Organic RTP Material for Persistent Afterglow Bioimaging.

Organic near-infrared room temperature phosphorescence (RTP) materials offer remarkable advantages in bioimaging due to their characteristic time scales and background noise elimination. However, developing near-infrared RTP materials for deep tissue imaging still faces challenges since the small band gap may increase the non-radiative decay, resulting in weak emission and short phosphorescence lifetime. In this study, fused-ring pyrrole-based structures were employed as the guest molecules for the construction of long wavelength emissive RTP materials. Compared to the decrease of the singlet energy level, the triplet energy level showed a more effectively decrease with the increase of the conjugation of the substituent groups. Moreover, the sufficient conjugation of fused ring structures in the guest molecule suppresses the non-radiative decay of triplet excitons. Therefore, a near-infrared RTP material (764 nm) was achieved for deep penetration bioimaging. Tumor cell membrane is used to coat RTP nanoparticles (NPs) to avoid decreasing the RTP performance compared to traditional coating by amphiphilic surfactants. RTP NPs with tumor-targeting properties show favorable phosphorescent properties, superior stability, and excellent biocompatibility. These NPs are applied for time-resolved luminescence imaging to eliminate background interference with excellent tissue penetration. This study provides a practical solution to prepare long-wavelength and long-lifetime organic RTP materials and their applications in bioimaging.

Fused‐Ring Pyrrole‐Based Near‐Infrared Emissive Organic RTP Material for Persistent Afterglow Bioimaging

AbstractOrganic near‐infrared room temperature phosphorescence (RTP) materials offer remarkable advantages in bioimaging due to their characteristic time scales and background noise elimination. However, developing near‐infrared RTP materials for deep tissue imaging still faces challenges since the small band gap may increase the non‐radiative decay, resulting in weak emission and short phosphorescence lifetime. In this study, fused‐ring pyrrole‐based structures were employed as the guest molecules for the construction of long wavelength emissive RTP materials. Compared to the decrease of the singlet energy level, the triplet energy level showed a more effectively decrease with the increase of the conjugation of the substituent groups. Moreover, the sufficient conjugation of fused ring structures in the guest molecule suppresses the non‐radiative decay of triplet excitons. Therefore, a near‐infrared RTP material (764 nm) was achieved for deep penetration bioimaging. Tumor cell membrane is used to coat RTP nanoparticles (NPs) to avoid decreasing the RTP performance compared to traditional coating by amphiphilic surfactants. RTP NPs with tumor‐targeting properties show favorable phosphorescent properties, superior stability, and excellent biocompatibility. These NPs are applied for time‐resolved luminescence imaging to eliminate background interference with excellent tissue penetration. This study provides a practical solution to prepare long‐wavelength and long‐lifetime organic RTP materials and their applications in bioimaging.

Synthesis, Structural Characterization, and Phosphorescence Properties of Trigonal Zn(II) Carbene Complexes.

The sterically demanding N-heterocyclic carbene ITr (N,N'-bis(triphenylmethyl)imidazolylidene) was employed for the preparation of novel trigonal zinc(II) complexes of the type [ZnX2(ITr)] [X = Cl (1), Br (2), and I (3)], for which the low coordination mode was confirmed in both solution and solid state. Because of the atypical coordination geometry, the reactivity of 1-3 was studied in detail using partial or exhaustive halide exchange and halide abstraction reactions to access [ZnLCl(ITr)] [L = carbazolate (4), 3,6-di-tert-butyl-carbazolate (5), phenoxazine (6), and phenothiazine (7)], [Zn(bdt)(ITr)] (bdt = benzene-1,2-dithiolate) (8), and cationic [Zn(μ2-X)(ITr)]2[B(C6F5)4]2 [X = Cl (9), Br (10), and I (11)], all of which were isolated and structurally characterized. Importantly, for all complexes 4-11, the trigonal coordination environment of the ZnII ion is maintained, demonstrating a highly stabilizing effect due to the steric demand of the ITr ligand, which protects the metal center from further ligand association. In addition, complexes 1-3 and 8-11 show long-lived luminescence from triplet excited states in the solid state at room temperature, according to our photophysical studies. Our quantum chemical density functional theory/multireference configuration interaction (DFT/MRCI) calculations reveal that the phosphorescence of 8 originates from a locally excited triplet state on the bdt ligand. They further suggest that the phenyl substituents of ITr are photochemically not innocent but can coordinate to the electron-deficient metal center of this trigonal complex in the excited state.

Room-temperature phosphorescence of a calcium-based metal-organic framework

A 3D calcium-based metal–organic framework (Ca-MOF) (named CaL-3) is obtained with 2,3-pyrazine-dicarboxylic acid (H2PZDC) and Ca(NO3)2·4H2O. It is the first time that the room-temperature phosphorescence properties of Ca-MOF based on H2PZDC were studied. Notably, CaL-3 exhibits a remarkable afterglow lasting 5 s at room temperature, which is mainly attributed to the unique framework structure of the Ca-MOF.

Polylactic acid film embedded with phosphor nanoparticles: Photochromic and afterglow biodegradable window and concrete

A smart window is a window made of a stimuli-responsive material whose transparency can be switched on and off. However, smart windows are often made of fragile, non-biodegradable and costly glass. Herein, this work presents the preparation of a transparent smart window from the environmentally-friendly polylactic acid (PLA) plastic. The plastic window was prepared by physically immobilizing nanoparticles of lanthanide-doped aluminate (NLdA; 79-112 nm) at different ratios into PLA bulk. The developed plastic showed afterglow emission, photochromism, superhydrophobicity, durability, UV shielding, rigidity, photostability, biodegradability, and excellent optical transmittance. NLdA was produced as nanoparticles to enhance NLdA dispersion in the plastic mass. NLdA must be uniformly disseminated in the PLA matrix without aggregation in order to provide transparent smart PLA window with long-persistent phosphorescence and photochromic properties. Different analytical methods were employed to determine the morphology, chemical composition, photoluminescence and coloration properties of smart films. There was an examination of the hardness characteristics. The transparent PLA window absorbed light at 365 nm and emitted at 435 nm and 517 nm, demonstrating reversible photochromism to green when irradiated with UV and greenish-yellow emission when exposed to darkness. There was a significant improvement in ultraviolet shielding and hydrophobicity upon increasing the phosphor content.

Two calcium-based metal organic frameworks with long afterglow as anticounterfeiting materials

Calcium-based metal–organic frameworks (Ca-MOFs) with room-temperature phosphorescence (RTP) properties are promising for applications. Herein, two 3D Ca-MOFs with robust RTP have been successfully synthesized with scaled-up production. The afterglows of these two Ca-MOFs are visible to the naked eye in darkness that lasts for approximately 13 s once they are excited with 365 nm UV light. It is mainly attributed to the rigid and dense structures of 3D Ca-MOFs via 4,5-Imidazole dicarboxylic acid tugging Ca2+ elucidated by means of single-crystal X-ray diffraction and density functional theory (DFT). Furthermore, a program was designed for dynamic anti-counterfeiting based on the long afterglow properties of Ca-MOFs, which can be extended for all kinds of material with long afterglow.

Decoration of MoO3-x on clay mineral matrix with great phosphorescence properties for oxygen activation, photochemical properties, bactericidal and oxidase-like mimics for prompt detection of pesticide

Decoration of MoO3-x on clay mineral matrix with great phosphorescence properties for oxygen activation, photochemical properties, bactericidal and oxidase-like mimics for prompt detection of pesticide

Multicolor‐Tunable and Time‐Dependent Circularly Polarized Room‐Temperature Phosphorescence from Liquid Crystal Copolymers

AbstractCircularly polarized luminescent (CPL) materials have significant promising applications in organic light‐emitting diodes, asymmetric synthesis, and other fields. However, due to the instability of triplet‐state excitons, how to achieve an effective combination of CPL with room‐temperature phosphorescence (RTP) remains a formidable challenge. Here, a simple and feasible method for constructing polymer‐based CPRTP materials is proposed by preparing chiral phosphorescent liquid crystals through copolymerization. A series of RTP chiral liquid crystal copolymers are successfully synthesized by copolymerizing phosphorescent monomer bearing chiral cholesterol mesogen with phosphorescent monomer bearing dibenzofuran chromophore. Due to the introduction of chiral cholesterol mesogen, copolymers can form chiral smectic C‐phase liquid crystals. Utilizing their selective reflection characteristic, efficient CPRTP is achieved, with a glum value of up to −1.6 × 10−2. In addition, both components in copolymers exhibit RTP properties and show significant differences in phosphorescence color and lifetime. By changing the composition of copolymers, the regulation of their phosphorescence properties is successfully achieved. As a result, multicolor‐tunable and time‐dependent CPRTP materials are successfully prepared.

Room Temperature Phosphorescence in Chiral 0D Zn(II) Metal Halide Crystals for Multiple Anti‐Counterfeiting

AbstractThe development of metal halides that enable multiple information storage and cryptographic security is highly desirable but remains a challenge. Here, a pair of 0D Zn(II) metal halide enantiomers ZnCl2·R/S‐2‐MP with excitation wavelength‐dependent emission and room temperature phosphorescence properties are reported. Organic ligands via N─H···Cl hydrogen bonding induce structural chirality. In order to stabilize the triplet state exciton and achieve excellent photophysical properties, the organic ligands combine with halogens to promote emission. The differences between the photophysical properties of ZnCl2·R‐2‐MP and ZnCl2·S‐2‐MP are analyzed in depth. Furthermore, combined with femtosecond transient absorption (fs‐TA) results, the long phosphorescence lifetimes may originate from the triplet state emission due to the synergistic effect between the organic components and the inorganic metal halides. The design strategy of advanced multiple anticounterfeiting technology is further extended.

A phase transformation–phosphorescence model of europium-doped yttria-stabilized zirconia and its application in two-dimensional thermal history measurement

Phosphorescence thermal history sensors are off-line temperature measurement devices with potential applications in harsh environments. However, changes in phosphorescence after heating at various temperatures or for various durations cannot be precisely quantified based on current theory. In this study, europium-doped yttria-stabilized zirconia (YSZ:Eu) was selected as a potential thermal history sensor and its structural and phosphorescence properties were characterized after heating at various temperatures. It was found that the tetragonal-to-cubic phase transformation of zirconia had a major effect on the phosphorescence intensity ratio (PIR) of YSZ:Eu. Accordingly, theoretical and semi-empirical versions of a novel phase transformation–phosphorescence model were developed based on Judd–Ofelt theory and the Avrami equation, and were used to quantify phosphorescence changes induced by heating YSZ:Eu at various temperatures and for various durations. The results of a calibration experiment showed that the PIR increased from 0.5 to 1.0 as the heating temperature and heating duration increased from 900 °C to 1200 °C and from 10 min to 80 min, respectively. The mean relative fitting errors of the theoretical and semi-empirical model were 2.2 % and 5.6 %, respectively. Finally, thermal history measurement was demonstrated in a flame-impingement experiment that was conducted using a phosphor-coated plate subjected to two different heating durations. The phosphorescence signals collected by an industrial camera were processed to yield two-dimensional (2D) surface-temperature distributions of the plate and compared with those obtained using an infrared camera. The average differences between the 2D surface-temperature distributions obtained by the two methods were 5.9 °C and 6.5 °C for 40 min and 80 min heating durations, respectively. These findings enhance theoretical understanding of thermal history sensing and will facilitate advancement from single-point to 2D thermal history measurement.

Achieving efficient room temperature phosphorescence of 1, 8-naphthalimide by a three-component doping strategy

Yellow phosphorescence emission of 1,8-naphthalimide guest was activated by doping it into m-bromobenzaldehyde host (energy transfer mechanism). With the aim of alleviating the triplet-triplet annihilation of the benzaldehyde itself, m-dibromobenzene was introduced as the third component. As a result, the phosphorescence quantum yields of the doped crystallized materials significantly increase from 1.72 % for NI@mBA to 19.17 % for NI@mBA@mDBB (with 11 times enhancement) due to the cascade activation in the three-component system. The encryption/decryption using these phosphorescent doped materials provides potential application in security field. This study not only expands the scope of organic host molecules capable of activating the phosphorescence properties of NI, but also provides a platform for developing multi-component organic doping systems that can effectively regulate phosphorescence properties.

Phosphorescence and Tarnish Resistance Properties of Copper with Strontium Aluminate Addition

The purpose of this research is to examine the effect of strontium aluminate (SrAl2O4) in copper samples on phosphorescence and tarnish resistance properties. The samples were fabricated by powder metallurgy using the compression moulding technique and then sintered in argon atmosphere. Phosphorescence, hardness, microstructure and tarnish resistance were studied. In the process of the compression moulding, the samples contain 100, 90, 80 and 70 percent of copper powder, by weight, with the addition of 0, 10, 20 and 30 percent of strontium aluminate, by weight, respectively. Polyvinyl alcohol (PVA) was used as a binder and mixed with copper and strontium aluminate powder to produce the green specimens using a hydraulic machine. Then, the green samples were sintered at 900 °C for one hour. After sintering, PVA was eliminated and the samples became denser. It was found that the hardness of the sample without strontium aluminate (30.5 HV) is higher than that of the sample with 10% of strontium aluminate addition (12.84 HV). Furthermore, copper samples containing strontium aluminate were fluorescent under ultraviolet at 517 nm. The sample with the largest amount of strontium aluminate (70Cu-30SrAl2O4) has higher phosphorescence than 90Cu-10SrAl2O4. In sulphur atmosphere, the tarnish resistance was found to be improved when strontium aluminate was added into copper. The colour difference (DE*) of 100Cu, which has no strontium aluminate, was 6.42 and higher than that of 90Cu-10SrAl2O4 (DE*= 3.5), 80Cu-20SrAl2O4 (DE*= 1.37), and 70Cu-30SrAl2O4 (DE*= 0.49), when testing in sulphur atmosphere for 30 min. 70Cu-30SrAl2O4, containing the highest amount of strontium aluminate, has the least colour changing on its surface resulting in the resistance in tarnishing.

Doped Carbon Dots Enable Highly Efficient Multiple‐Color Room Temperature Phosphorescence

AbstractColloidal carbon dots (C‐dots) are considered as promising heavy‐metal‐free materials to achieve room‐temperature phosphorescence (RTP) properties for promising applications, such as photoelectronic devices, information encryption, and bio‐imaging. However, most of the current obtained RTP C‐dots have a short lifetime with a relatively low quantum yield (QY). In this work, the C‐dots large‐scale synthesized via a vacuum heating approach have multiple RTP emissions (blue, green, and yellow), a long RTP lifetime of as high as 1.92 s, and a high QY of 34.4% by selecting different types of precursors, which is superior to most of reported RTP C‐dots. The multiple atoms doping and strong bonding between neighbored C‐dots promoted by vacuum heating contributes to the excellent RTP properties. As a proof‐of‐concept, the as‐obtained RTP C‐dots are used as optical ink for flexible security codes, exhibiting a bright shape with a lifetime of 1.37 s. This work offers an efficient approach for producing large‐scale high‐quality RTP C‐dots, which can be applied to anti‐counterfeiting and information encryption systems.

A carbon dot-based time-dependent color-changing room temperature phosphorescent material

Carbon dots (CDs) based room-temperature phosphorescent materials have received extensive research attention due to their excellent optical properties, low biotoxicity and their great potential for applications in the field of anti-counterfeiting. However, only few CDs-based materials possessing time-dependent color-changing room-temperature phosphorescence (RTP) properties have been reported. In the present work, RTP composite materials with unique time-dependent color-changing properties were synthesized by a one-pot method using ethylenediaminetetraacetic acid (EDTA), boric acid (BA) and phosphoric acid (PA) as raw materials. The phosphorus-doped composites of carbon dots and boric acid (P-CDs@BA) possess yellow and green RTP properties. The coexistence of multiple luminescent centers and the difference in the phosphor lifetime and luminescence intensity of the luminescent centers make the P-CDs@BA composites possess unique time-dependent color change properties. Finally, a specific example of the application of P-CDs@BA composites in the field of anti-counterfeiting is given based on their time-dependent color-changing RTP properties. The present work provides ideas for the preparation of time-dependent color-changing carbon dot-based room temperature phosphorescent materials and their applications in the field of anti-counterfeiting.