Luminescence Switching Research Articles

Remarkable Off-On Tunable Solid-State Luminescence by the Regulation of Pyrene Dimer.

It is always a challenge to achieve "off-on" luminescent switch by regulating non-covalent interactions. Herein, we report a unique strategy for constructing high performance "off-on" tunable luminescent materials utilizing a novel molecule (TFPA) consist of pyrene and cyanostilbene. The pristine crystal of TFPA is almost non-emissive. Upon grinding/UV irradiation, an obvious luminescence enhancement is observed. Theoretical and experimental results revealed the underlying mechanism of this intriguing "off-on" switching behavior. The non-emissive crystal consists of ordered H-aggregates, with adjacent two molecules stacked in an anti-parallel manner and no overlapped area in pyrene moieties. When external force is applied by grinding or internal force is introduced through the photoisomerization, the dimer structures are facilitated with shorter intermolecular distances and better overlapping of pyrene moieties. In addition, the "on" state can recover to "off" state under thermal annealing, showing good reversibility and applicability in intelligence material. The present results promote an in-depth insight between packing structure and photophysical property, and offer an effective strategy for the construction of luminescence "off-on" switching materials, toward the development of stimuli-responsive luminescent materials for anti-counterfeiting.

Heat-Set Supramolecular Hydrogelation by Regulating the Hydrophilic-Lipophilic Balance for a Tunable Circularly Polarized Luminescent Switch.

Heat-set supramolecular gels exhibited totally opposite phase behaviors of dissolution upon cooling and gelation on heating. They are commonly discovered by chance and their rational design remains a great challenge. Herein, a rational design strategy is proposed to realize heat-set supramolecular hydrogelation through regulation of the hydrophilic-lipophilic balance of the system. A newly synthesized amphiphile hydrogelator with pyrene embedded in its lipophilic terminal can self-assemble into a hydrogel through a heating and cooling cycle. However, the host-guest complex of the gelator and hydrophilic γ-cyclodextrin (γ-CyD) results in a sol at room temperature. Thus, heat-set hydrogelation is realized from the sol state in a controllable manner. Heat-set gelation mechanism is revealed by exploring critical heat-set supramolecular gelation and the related findings provide a general strategy for developing new functional molecular gels with tunable hydrophilic-lipophilic balance.

Synthesis, structure and tri-stimuli-responsive luminescent switching properties of a bis(σ-acetylide) platinum(II) complex

A square-planar bis(σ-acetylide) platinum(II) complex, Pt(PhenCCTES)(CCC6H42Cl)2 (1) (PhenCCTES = 3-(2-triethylsilylethynyl)-1,10-phenanthroline) was synthesized. Three species with different stacking structures, including two solvated yellow-green samples 1·Cl2CHCHCl2 and 1·ClCH2CH2Cl, and one red solvent-free species 1, were obtained by exposure 1 into the different VOC vapors. 1·Cl2CHCHCl2 and 1·ClCH2CH2Cl emit a green luminescence peaked at 513 (548, sh) nm and 545 (517, sh) nm, respectively and exhibit the vapor-, thermo-, and mechanical grinding triggered tri-stimuli-responsive luminescent switching properties. Once exposure to CH2Cl2 vapor or heating at 110 °C, both 1·Cl2CHCHCl2 and 1·ClCH2CH2Cl will lose their solvated molecule and converted to the red solvent-free species 1. Upon mechanical grinding, 1·Cl2CHCHCl2 and 1·ClCH2CH2Cl will be changed to an amorphous species 1G with red color and red luminescence peaked at 675 nm. Meanwhile, the heating and ground samples could be converted back to the original crystalline 1·Cl2CHCHCl2 and 1·ClCH2CH2Cl by absorbing Cl2CHCHCl2 or ClCH2CH2Cl vapor. Systematic studies on the crystal structure, luminescence spectrum, PXRD patterns as well as TD-DFT calculations demonstrate that the mechanism of the reversible tri-stimuli-responsive luminescent switching properties of complex 1 is due to the interconversion of the lowest-energy excited states of metastable species between ligand to ligand/metal to ligand charge transfer (LLCT/MLCT) and ligand to ligand/metal-metal to ligand charge transfer (LLCT/MMLCT) caused by the formation/destruction of intermolecular Pt-Pt interactions and/or aromatic π-π stacking interactions under external stimuli.

Edge-Confined Excitons in Monolayer Black Phosphorus.

Quantum confinement of two-dimensional excitons in van der Waals materials via electrostatic trapping, lithographic patterning, Moiré potentials, and chemical implantation has enabled significant advances in tailoring light emission from nanostructures. While such approaches rely on complex preparation of materials, natural edges are a ubiquitous feature in layered materials and provide a different approach for investigating quantum-confined excitons. Here, we observe that certain edge sites of monolayer black phosphorus (BP) strongly localize the intrinsic quasi-one-dimensional excitons, yielding sharp spectral lines in photoluminescence, with nearly an order of magnitude line width reduction. Through structural characterization of BP edges using transmission electron microscopy and first-principles GW plus Bethe-Salpeter equation (GW-BSE) calculations of exemplary BP nanoribbons, we find that certain atomic reconstructions can strongly quantum-confine excitons resulting in distinct emission features, mediated by local strain and screening. We observe linearly polarized luminescence emission from edge reconstructions that preserve the mirror symmetry of the parent BP lattice, in agreement with calculations. Furthermore, we demonstrate efficient electrical switching of localized edge excitonic luminescence, whose sites act as excitonic transistors for emission. Localized emission from BP edges motivates exploration of nanoribbons and quantum dots as hosts for tunable narrowband light generation, with future potential to create atomic-like structures for quantum information processing applications as well as exploration of exotic phases that may reside in atomic edge structures.

Stimuli-Responsive Properties on a Bisbenzofuropyrazine Core: Mechanochromism and Concentration-Controlled Vapochromism.

Stimulus-responsive organic materials with luminescence switching properties have attracted considerable attention for their practical applications in sensing, security, and display devices. In this paper, bent-type bisbenzofuropyrazine derivatives, Bent-H and Bent-sBu, with good solubilities were synthesized, and their physical and optical properties were investigated in detail. Bent-H gave three crystalline polymorphs, and they showed different luminescence properties depending on their crystal packing structures. In addition, Bent-H exhibited mechanochromic luminescence in spite of its rigid skeleton. Bent-sBu exhibited unique concentration-dependent vapochromic luminescence. Ground Bent-sBu was converted to blue-emissive, green-emissive, and green-emissive high-viscosity solution states at low, moderate, and high concentrations of CHCl3 vapor, respectively. This finding represents a concentration-dependent multi-phase transition with an organic solvent, which is of potent interest for application in sensing systems.

Fabrication and luminescence switching of Pt-loaded macro-porous Y2WO6:Eu3+ phosphor thin films for hydrogen-gas detection

A luminescence-switching phenomenon of Pt/Y2WO6:Eu3+ phosphor thin films was examined under redox conditions using hydrogen gas and air as a reductant and an oxidant, respectively. Macro-porous Y2WO6:Eu3+ thin films were initially synthesized by a Pechini-type sol–gel dip-coating method on silica glass substrates. Attempts were then made to load Pt nanoparticles (NPs) on the surface of the Y2WO6:Eu3+ thin films immersed in aqueous K2PtCl4 solutions through a method of self-regulated reduction of surfactants using a nonionic triblock copolymer (P-123). The amount of P-123, the concentration of the K2PtCl4 solutions, and the immersion duration were set as three parameters influencing the deposition of the Pt NPs. The number and size of the Pt NPs were found to be dependent on all the three parameters and their excessive deposition led to inevitable quenching of the Eu3+ emission from thin films. In contrast, the lightly loaded Pt NPs were effective to induce turn-off luminescence upon exposure of the thin films to hydrogen gas at a low temperature of 150 °C probably through their catalytic action. The recovery of luminescence was also possible simply by treating the reduced thin films at 200 °C in air. Thus the Pt/Y2WO6:Eu3+ phosphor thin films are promising as a facile hydrogen-gas detector.

Thermally responsive flexible self-luminous binary fatty alcohol eutectic-based reversible thermochromic passive energy-saving eucalyptus wood aerogel composites

The development of flexible self-luminous reversible thermochromic passive energy-saving composites (TPCMs) is self-challenge due to the defects of easy leakage, non-visibility, solid phase rigidity, and weak light absorption. So, the emerging TPCMs were cleverly constructed using wood aerogel as support skeleton and different mass ratios of natural latex/long afterglow components as flexible and self-luminescent matrix based on optimal binary fatty alcohol eutectic (C14C20). Among them, C14C20R-TEW-1R and C14C20G-TEW-0.35 P stand out with suitable phase transition temperatures (28.8 °C and 29.7 °C), high latent heat values (100.5 J g−1 and 119.4 J g−1), and low supercooling (0.7 °C and 0 °C). Induced by phase change, they change from rigid to flexible, from red/green to milky white, and can absorb light to achieve self-luminescence in the dark (orange red and blue-green) and enhanced photothermal efficiency. Beyond the traditional thermal/light stability and excellent anti-leakage performance, TPCMs realizes the combination of temperature sensitivity/control and self-luminous, providing broad application prospects in home automation, passive energy-saving in buildings, luminescent response switches, and other fields.

MnOx In Situ Growth-Induced Luminescence and Oxidase-Like Feature Bimodulation of CePO4:Tb Nanorods: Toward Ascorbic Acid-Related Bioanalysis in a "One-Stone-Two-Birds" Manner.

Nanozyme-based multimode detection is a useful means to improve the accuracy and stability of analytical methods. However, both multifunctional nanozymes and related multimodal sensing strategies are still very scarce. Besides, they require complex processes to fabricate and operate. To fill this gap, here we propose a spontaneous interfacial in situ growth strategy to prepare a new bifunctional material (CePO4:Tb@MnOx) featuring good oxidase-like activity and green photoluminescence for the dual-mode colorimetric/luminescence determination of ascorbic acid (AA)-related biomarkers specifically. CePO4:Tb@MnOx was gained through the controllable redox reaction between KMnO4 and CePO4:Tb nanorods. It was interestingly found that MnOx in situ growth not only significantly enhanced the enzyme-like activity but also could reversibly regulate the luminescence of CePO4:Tb via a dual quenching mechanism. More interestingly, CePO4:Tb@MnOx exhibited a distinctive response toward AA against other reducing species. A double-coordination regulation mechanism was further verified to clarify the catalytic activity and luminescence switching behaviors in CePO4:Tb@MnOx. Based on these findings, a dual-mode colorimetric/luminescence approach was established for AA sensing in a "one-stone-two-birds" manner, providing excellent selectivity, sensitivity, and practicability. Furthermore, the determination of AA-related biomarkers, including acid phosphatase activity and organophosphorus residue, was also validated by the sensing principle. Our work not only deepens the understanding of the coordinated regulation of the luminescence and enzyme-like features in lanthanide-based materials but also offers a novel way to design and develop multifunctional nanozymes for advanced bioanalytical applications.

Double‐Key Optical Information Encryption Enabled by Multi‐State Excitation–Emission of Mn‐Doped Metal Chlorides

Given the paramount importance of information security and confidentiality, various optical information encryption (OIE) strategies are developed based on luminescence. However, the protected information usually can be decrypted, and there is a lack of high‐level security because only one protection key can be applied. Herein, a double‐key OIE strategy is developed based on multi‐state excitation–emission of Mn‐doped metal chlorides (MMCs). The information delivered by different MMCs can be encrypted based on the similar orange luminescence of Mn d–d transition. The distinguishable excitation conditions, switchable luminescence, and unique afterglow in MMCs enable new encryption mechanisms with a great potential for high confidentiality multi‐key encryption. It is demonstrated that four information channels can be encrypted into a single luminescent pattern, concealing the true information by three interference messages, which greatly increases the security. As a demo, an encrypted quick response (QR) code is created, which can only be decrypted with both the “excitation wavelength key” and “capture time key.” The double‐key mechanism enhances the level of security and confidentiality without using expensive equipment or external stimuli.

Mechanoresponsive luminescence switching by polymorphs and doped crystals of donor–acceptor-type benzothiadiazoles

Mechanoresponsive luminescence switching by polymorphs and doped crystals of donor–acceptor-type benzothiadiazoles

Dual Monomeric Inorganic Units Constructed Bright Emissive Zero-Dimensional Antimony Chlorides with Solvent-Induced Reversible Structural Transition.

A5M2X11 and A3M2X9 families (A = monovalent organic cation; M = trivalent metal; X = halogen) are receiving increasing attention because of their combination of easy solution processability and superior ferroelectricity properties. However, synthesizing highly efficient A5M2X11 and A3M2X9-type fluorophores with multiple monomeric inorganic units and achieving their structural interconversion remains challenging. Here, we report two novel zero-dimensional (0D) antimony halides, (C10H16N)5Sb2Cl11·C2H3N (1) and (C10H16N)3Sb2Cl9 (2), which not only contain two distinct [SbXn]3-n units but also have excellent orange (590 nm) and yellow-green emission (540 nm) with high PLQY of 17.7% and 31.5%, respectively. Interestingly, a reversible structural conversion could be triggered by acetonitrile steam stimulation, accompanied by luminescence switching properties. This work not only enriches the structure of hybrid Sb-based halides but also provides the possibility of well-known A5M2X11 and A3M2X9 families as structural transformation materials.

Utilizing Energy Transfer in Mn2+/Ho3+/Yb3+ Tri-doped ZnAl2O4 Nanophosphors for Tunable Luminescence and Highly Sensitive Visual Cryogenic Thermometry.

Lanthanide (Ln3+)-doped upconversion (UC) phosphors converting near-infrared (NIR) light to visible light hold very high promise toward biomedical applications. The scientific findings on luminescent thermometers revealed their superiority for noninvasive thermal sensing. However, only few reports showcase their potential for applications in extreme conditions (temperatures below -70 °C) restricted by low thermal sensitivity. Here, we demonstrate the tailoring of luminescence properties via introducing Ho3+-Mn2+ energy transfer (ET) routes with judicious codoping of Mn2+ ions in ZnAl2O4/Ho3+,Yb3+ phosphor. Preferentially, a singular red UC emission is required to improve the bioimaging sensitivity and minimize tissue damage. We could attain UC emission with 94% red component by a two-photon UC process. Higher temperature annealing brings the color coordinates to the green domain, highlighting the potential for color-tunable luminescence switch. Moreover, this work investigates the thermometric properties of ZnAl2O4/Yb3+, Ho3+ in the range of 80-300 K and influence of inducing extra ET pathways by Mn2+ codoping. Interestingly, the luminescence intensities for nonthermally coupled (5F4,5S2) and the 5F5 radiative transitions of Ho3+ ions display opposite behavior at 80 and 300 K, which revealed competition between temperature-sensitive decay pathways. The codoping of Mn2+ ions is fruitful in causing a fourfold increase of absolute sensitivity. Notably, the color tunability from green through yellow to red is helpful in rough temperature estimation by naked eyes. The maximum relative (Sr) and absolute sensitivities (Sa) were estimated to be 1.89% K-1 (140 K) and 0.0734 K-1 (300 K), respectively. Even at 80 K, a Sa of 0.00447 K-1 and Sr of 0.6025% K-1 were achievable in our case, which are higher than most of the other Ln3+-based systems. The above-mentioned results demonstrate the potential of ZnAl2O4/Yb3+,Ho3+ for cryogenic optical thermometry and a strategy to design new Ln3+-based UC thermometers by taking advantage of ET routes.

Circularly polarized luminescence switch based on a photochromic europium(III) helicate derived coordination polymer

Chiroptical switches based on circularly polarized luminescence (CPL) have shown the promising applications in advanced information technologies. Herein, a pair of lanthanide coordination polymer enantiomers [Eu2(LR)3(BTFPO)2]n and [Eu2(LS)3(BTFPO)2]n with light-regulated CPL property are designed, which are assembled by a chiral binuclear triple-stranded Eu3+ helicates [Eu2(LR/S)3] coordinated with two photochromic triphenylphosphine oxides (BTFPO). Upon the alternative UV and 526 nm light irradiation, the complexes show the reversible photochromism, PL and CPL responses. Notably, the luminescence dissymmetry factor, glum of 5D0→7F1 (591 nm) transition shows an obvious increase from 0.19 to 0.29 before and after 275 nm light irradiation. Additionally, the emission from Eu3+ center is not completely quenched in closed-ring state due to the low photocyclization (Фo-c) quantum yield of the polymer. The partial maintenance of emissive intensity is of essential importance for the monitor of CPL signal. More importantly, the CPL photo-switching property of the complexes in solid hybrid film is maintained, and still displays the enhanced CPL emission in photostationary state. Further, the potential applications of the doping film in logic gate and anti-counterfeiting were investigated.

Two crystalline Zn(II)-viologen compounds with photochromism, photomodulated luminescence and water-induced reversible crystal-to-amorphous transformation

In this work, two Zn(II)-viologen compounds, {[Zn(cpbpy)(L)](H2O)5}n (1) and [Zn(H2O)6](cpbpy)2(L)2(H2O)2 (2) (cpbpy = N-(3-carboxypyridin-5-yl)− 4,4′-bipyridinium, H2L = 1,4-benzenedicarboxylic acid) have been constructed via different synthetic routes. Structural analysis exhibits compound 1 features a two-dimension layered structure consisting of one-dimension [Zn(L)]n chains and bridging cpbpy ligands while compound 2 exists as a discrete monomeric structure. In a very short period of time, both compounds display electron-transfer photochromic behaviors. However, the photoproduct of compound 2 is more stable than compound 1 in air, which is attributed to better coplanarity of pyridyl rings of 4,4′-bipyridine moieties in compound 2. Also, both compounds show photomodulated luminescence properties. Strikingly, compound 2 also exhibits interesting water-induced reversible crystal-to-amorphous transformation accompanying with reversible luminescence switch behavior. To our knowledge, this is the first example of a crystalline viologen-based compound that displays water-induced reversible crystal-to-amorphous transformation.

Circularly Polarized Luminescence Switching Driven by Precisely Tuned Supramolecular Interactions: From Hydrogen Bonding to π-π Interaction.

It is highly challenging to achieve circularly polarized luminescence (CPL) switching by precisely tuning supramolecular interactions and unveiling the mechanism of supramolecular chirality inversion. Herein, we demonstrated CPL switching based on diethyl l-glutamate-9-cyanophenanthrene (LGCP) and diethyl l-glutamate-pyrene (LGP) via the precise regulation of supramolecular interactions. LGCP assembly driven by hydrogen bonding showed right CPL, while LGP assembly driven by π-π interaction led to left CPL. Remarkably, significant CPL switching was observed from the assemblies of LGCP/octafluoronaphthalene (OFN), attributed to the alteration of the dominating interaction from weak hydrogen bonding to rather strong π-π interaction, while the assemblies of LGP/OFN exhibited minimum CPL variation because the dominating π-π interaction within the assembly of LGP/OFN illustrated quite limited variations upon arene-perfluoroarene interaction. This work provides a feasible strategy toward the efficient modulation of the chiroptical properties of multiple component supramolecular systems, meanwhile offering possibilities for the mechanism exploration of the chirality inversion of supramolecular assemblies.

Heat-induced ʻparallelʼ to ʻorthogonalʼ switching of fluorophores and reversible luminescence changes in divinylbenzene-benzoxazole crystals

Organic crystals that exhibit reversible solid-state luminescence triggered by heat stimulus have garnered great research interest in recent years. In this work, we demonstrate thermoresponsive, reversible color and photoluminescence switching in divinylbenzene-benzoxazole derivatives. The fluorescence switching is caused by differential chromophore packing and the resulting charge transfer On/Off states induced by heat. It is noteworthy that the reversibility, range of colors, and transition temperature associated with the luminescence switching are dependent on the length of the alkyl chains. Our results suggest that controlling charge-transfer interactions in chromophore assemblies may offer a versatile approach for creating functional organic materials with switchable, high-contrast solid-state luminescence. These findings have implications for the development of sensors, data storage devices, dynamic optical materials, and security inks.

Wavelength-shift-based visual fluorescence sensing of aspartic acids using Eu/Gd-MOF through pH triggering

With the increasing demand for on-site detection, the current approach of building dual-emission or multi-emission luminescence sensors based on metal-organic frameworks (MOFs) which possess the capacity of self-reference for numerous non-analyte factors falls short of meeting sensing requirements. Therefore, we have designed a novel strategy for constructing wavelength shift-based luminescence sensor named Eu/Gd(TCPP), which exhibits dual-emitting from metal ions Eu3+ and flexible rotating aggregation-induced emission (AIE) ligands H4TCPP (2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine). This sensor was prepared by a simple, green and fast plasma synthesis method. It's worth noting that the fluorescence emission of Eu/Gd(TCPP) shows a specific wavelength shift from ligand peak, and a visual color change from red to blue within a pH range of 4 to 3. Moreover, various characterization data verified that the luminescence switching mechanism of Eu/Gd(TCPP) was attributed to the H+-induced collapse of the Eu/Gd(TCPP) crystal structure, followed by untwisting of free ligands that lose rigid MOFs confinement. This hindered the antenna effect from H4TCPP to Ln3+ ions and restricted the rotation emission of ligand, resulting in the red-shifting of the ligand emission and corresponding luminescence switching. By tactfully utilizing the short-range pH response property of Eu/Gd(TCPP), highly sensitive and selective on-site visual detection of acidic aspartic acid can be achieved.

Circularly Polarized Luminescence Switching, Chirality Self‐Sorting, and Cell Imaging of Chiral Rhodamine Dyes

AbstractRhodamine dyes, as star molecules of fluorescent dyes, are critical tools in modern analytical and biochemical research. However, switching their chiroptical properties still remains a big challenge because of the absence of a suitable synthesis method to incorporate through conjugation a chiral fragment into the chromophore core of rhodamine. Herein, a simple and straightforward way is utilized to link two rhodamine chromophores by different chiral bridges. The conjugated RRR/SSS birhodamine dyes with one axial chirality, which is constructed directly by two rhodamine chromophores, and two spirocyclic chiralities show the interesting circular dichroism and circularly polarized luminescence switching and lysosome‐targetable properties. On the other hand, the unconjugated RR/SS birhodamine dyes with two chiral carbons do not have such chiroptical switching properties but do have different amazing cellular staining properties. The RR birhodamine dye can stain both lysosomes and mitochondria, but SS birhodamine dye can stain lysosomes only. Moreover, the mechanisms of chiroptical switching and diastereoselectivity are investigated as well, based on single‐crystal structures and density functional theory calculations. Therefore, a new platform is afforded here in designing chiral dyes for chiroptical switching and cell imaging applications.

Lanthanide-hydrogel with reversible dual-stimuli responsive luminescent switching property for data protection

The development of data protection materials with low cost is still challenging in the era of big data and artificial intelligence. Herein, the luminescent hydrogel with luminescent switching property was prepared by the introduction of lanthanide complex into poly(vinyl alcohol) gelation matrix. The developed luminescent hydrogel showed good reversible luminescent switching behavior under the stimulation of HCl/NH3 and Fe3+/EDTA2-, respectively. It enables the hydrogel to be applied as reversible data security storage material with low cost. The results showed that the input and erasure of data was reversible. Moreover, the fabricated data was invisible under daylight whereas it was visible under UV light. It is suitable for data protection. Furthermore, the combination of dual-stimuli was demonstrated to improve the security level of data effectively. The hydrogel also exhibited good stability against UV irradiation. The findings suggested that the stimuli-responsive luminescent hydrogel has potential application in data protection.

Opposite thermal-stimuli fluorescent behavior induced by π-bridge in two carbazole derivatives for high-level information encryption

Organic luminophores that exhibit emission ON-OFF switching under thermal stimulus are prominent candidates for developing high-level information encryption. Herein, the rationally controlled luminescence ON-OFF switching behavior of two carbazole derivatives with identical acceptor by tailoring the π-bridge are demonstrated. CPDI with phenyl π-unit showed aggregation induced emission (AIE) but thermally stimulated emission turn-off, while CTDI with thienyl as π-unit exhibited a totally different aggregation caused quenching (ACQ) and thermally stimulated emission turn-on in the solid-state. Structural characterizations revealed that the difference was derived from the opposite effect that form intermolecular π-π interactions after heating treatment. Based on their opposite thermally stimulated ON-OFF and OFF-ON luminescence switching model, fourth-level information encryption application was achieved.