Unique Emission Properties Research Articles

Sensing of Pb (II) ion by micro and nanocarbon materials- influence of functionality and pi-electron density

In the aspect of pollution due to heavy metal ions, especially Pb (II) ions, there is an urgent need for simple, effective materials and processes for sensing the ions. The present study approaches the sensing of Pb (II) ions by non-metal (O, N and S) doped micro and nanoscale Carbon materials. The unique emission (Fluorescence) properties of the as-prepared doped samples of graphene oxides and Carbon Microspheres were tapped in the selective sensing process of nanomolar to the micromolar concentration of Pb (II) ions. The role-play of Carbon dimensionality, functionality and sp2 Carbon density (pi electron density) in the sensing mechanism was evaluated. The study provided an overview of fundamental aspects of heavy metal ion sensing by Carbon-based nanomaterials (CBNs).

Chinese food seasoning derived carbon dots for highly selective detection of Fe3+ and smartphone-based dual-color fluorescence ratiometric visualization sensing

Carbon dots were obtained from Tangshai, a Chinese food seasoning, using a simple and green method through dialysis. Tangshai-derived carbon dots (TSCD) exhibited unique fluorescent emission properties that can be selectively suppressed by Fe3+ over other heavy metal ions including Fe2+. Based on the Benesi-Hildebrand equations study, a ten times larger coordination constant of Fe3+-TSCD than that of Fe2+-TSCD was obtained, which proved the highly selective superiority. Therefore, a fluorescence quenching method for sensitive detection of Fe3+ was established with two linear ranges of 1–80 µmol L−1 and 200–500 µmol L−1 and the limit of detection (LOD) was 0.41 µmol L−1 (3σ). The real sample detection was performed with satisfactory and validated results. Besides, coupled with orange emissive carbon dots (OCD) whose fluorescence can be enhanced by Fe3+, a dual-color fluorescence ratiometric sensor for Fe3+ was established from the opposite fluorescence responses, and visualization sensing was actuated by a smartphone. This work facilely extracted CDs from Chinese food seasoning and revealed the mechanism of selective sensing for Fe3+, facilitating the green synthesis of CDs and heavy metal ions sensing.

Peri-Alkylated Terrylenes and Ternaphthalenes Building-Blocks Towards Multi-Edge Nanographenes.

Since its first synthesis by Clar in 1948, terrylene - a fully connected ternaphthalene oligomer via naphthalene's peri-positions - has gained special focus within the rylene family, drawing interest for its unique chemical, structural, optoelectronic and single photon emission properties. In this study, we introduce a novel synthetic pathway that enhances the solubility of terrylene derivatives through complete peri-alkylation, while also facilitating extensions at the bay-positions. This approach not only broadens the scope of terrylene's chemical versatility but also opens new avenues for developing solution processable novel multi-edge nanographenes and tailoring electronic energy levels through topological edge structures. Our findings include a comprehensive structural and spectroscopic characterization along with transient absorption spectroscopy and photophysics of both the synthesized peri-alkylated terrylene and its phenylene-fused derivative.

Direct generation of a 635 nm red random laser based on praseodymium (Pr)-doped ZBLAN fiber.

Visible random fiber lasers have garnered significant attention due to their unique emission properties and potential applications in various fields. We first, to the best of our knowledge, demonstrateda compact all-fiber structure, red wavelength, and random fiber laser (RFL) based on a double-clad Pr-doped ZBLAN fiber. The simple half-open cavity consists of a high-reflectivity fiber pigtail mirror and the Pr-doped ZBLAN fiber. The Pr-doped ZBLAN fiber not only served as a gain medium but also offered random backward scattering. We investigated the effects of different lengths on output power and slope efficiency of the RFL. For 21 m Pr-doped fiber, the RFL emitted a maximum output power of 208.50 mW with a slope efficiency of 11.09%. For 15 m Pr-doped fiber, the maximum power decreased to 120.18 mW with the slope efficiency of 7.27%. We are also numerically simulating the output power versus the pump power at different fiber lengths based on power steady-state light propagation equations. This novel RFL has the potential for broad applications in fields such as display technology, spectroscopy, biomedical imaging, and optical sensing due to its unique properties and simple all-fiber structure.

Lead-free Perovskite with Distorted [InX6]3- Octahedron Induced by Organic Cation and Enhanced PLQY by Sb Doping.

In-based halide perovskites have attracted a lot of attention because of their unique broadband emission properties. Herein, a series of In-based hybrid perovskites of (H2MP)2InCl7·H2O (1), (H2EP)2InCl7·H2O (2), (H2MP)2InBr7·H2O (3), and (H2EP)2InBr7·H2O (4) were synthesized under the control of halogen ions and organic cations. 1, 2, and 4 exhibit obvious photoluminescence properties with peaks at 392, 442, and 652 nm, respectively. The effects of the different components on the crystal structure and photoluminescence properties are discussed by calculating the structural distortion of the [InX6]3- octahedron. The photoluminescence properties of 1 and 4 were significantly improved after Sb3+ doping with PLQY values of 57.12 and 41.53%. Finally, a white LED was successfully fabricated with the two doped compounds coated onto the 365 nm blue LED chip.

Photorewriting, Time-Resolved Encryption, and Unclonable Anticounterfeiting with Artificial Intelligence Authentication via a Reversible Photoswitchable System.

In the fields of photolithographic patterning, optical anticounterfeiting, and information encryption, reversible photochromic materials with solid-state fluorescence are emerging as a potential class of systems. A design strategy for reversible photochromic materials has been proposed and synthesized through the introduction of photoactive thiophene groups into the molecular backbone of aryl vinyls, compounds with unique aggregation-induced emission properties, and solid-state reversible photocontrollable fluorescence and color-changing properties. This work develops novel photochromic inks, films, and cellulose hydrogels for enhancing the security of information encryption and anticounterfeiting technologies. They achieve rapid and reversible color change under ultraviolet light irradiation. Dependent upon the rate of color change, higher levels of time-resolved security can be achieved. This feature is important for enhancing the confidentiality of encrypted information and the reliability of security labels. Color-changing cellulose hydrogels, inks, and films consisting of three photochromic fluorescent molecules have quick photoactivity, great photoreversibility and photostability, and good processability, making them ideal for time-delayed anticounterfeiting and smart encryption. Furthermore, specialized algorithms are used to construct convolutional neural networks, and image analysis is performed on these systems, thus solving the current problem of the time-consuming information decryption process. This artificial intelligence method offers new opportunities for enhanced data encryption.

Atomic insights into the optoelectronic properties of vacancy-ordered double perovskite halide semiconductors

Vacancy-ordered halide perovskite Cs2BX6 semiconductors are attracting an increasing level of interest for optoelectronic applications due to their high chemical stability and unique light emission properties. Here, we performed first-principles calculations to determine the energy positions and atomic orbital hybridization features of band edge states in Cs2BX6 (B = Ge, Sn, Te, Ti, Zr, Hf; X = Cl, Br, I). Our results revealed that all the Cs2BX6 perovskites, except for Cs2TeX6, have direct bandgaps at the Γ point. The indirect bandgaps of Cs2TeX6 originate from the symmetry-forbidden Te p–X p coupling at the Γ point. Both energy positions and dispersions of the band edge states of Cs2BX6 can be well modulated by varying X- and B-site ions. Our work provides a comprehensive understanding of electronic structures and optoelectronic properties of Cs2BX6 perovskites, shedding light on the design rules for high-performance perovskite optoelectronics.

Observation of Multi-Phonon Emission in Monolayer WS2 on Various Substrates.

Transition metal dichalcogenides (TMDs) have unique absorption and emission properties that stem from their large excitonic binding energies, reduced-dielectric screening, and strong spin-orbit coupling. However, the role of substrates, phonons, and material defects in the excitonic scattering processes remains elusive. In tungsten-based TMDs, it is known that the excitons formed from electrons in the lower-energy conduction bands are dark in nature, whereas low-energy emissions in the photoluminescence spectrum have been linked to the brightening of these transitions, either via defect scattering or via phonon scattering with first-order phonon replicas. Through temperature and incident-power-dependent studies of WS2 grown by CVD or exfoliated from high-purity bulk crystal on different substrates, we demonstrate that the strong exciton-phonon coupling yields brightening of dark transitions up to sixth-order phonon replicas. We discuss the critical role of defects in the brightening pathways of dark excitons and their phonon replicas, and we elucidate that these emissions are intrinsic to the material and independent of substrate, encapsulation, growth method, and transfer approach.

Covalent organic framework enhanced aggregation-induced emission of berberine and the application for detection

In this work, we prepared TaTp-COF, a covalent organic framework material with porous and uniform spheres, by hydrothermally reacting 1,3,5-tris (4-aminophenyl) benzene (TaPb) with terephthalaldehyde (TpTa). TaTp-COF could significantly enhance the aggregation-induced emission (AIE) of berberine (BBR), a natural plant medicine, which was related to the porous structure, the suitable voids, and the hydrogen bonding between TaTp-COF and BBR that could limit the free movement of BBR. The unique emission properties of BBR on TaTp-COF were investigated and used for the sensitive detection of BBR based on the fluorescence intensity of AIE, with a linear range of 10–100 μ mol/L (R2 = 0.9991) and a detection limit of 0.0453 μ;mol/L. Finally, the TaTp-COF was successfully applied to the detection of BBR in real samples, achieving good recoveries and satisfactory relative standard deviations.

Innovative Real-Time Flow Sensor Using Detergent-Free Complex Emulsions with Dual-Emissive Semi-Perfluoroalkyl Substituted Α-Cyanostilbene.

In this study, the potential of complex emulsions is investigated as transducers in sensing applications. Complex emulsions are stabilized without external detergents by developing a novel α-cyanostilbene substituted with PEG and semi-perfluoroalkyl chain (CNFCPEG). CNFCPEG exhibits unique variable emission properties depending on its aggregation state, allowing dual blue and green emissions in complex emulsions with hydrocarbon-in-fluorocarbon-in-water (H/F/W) morphology. The green excimer emissions result from the self-assembly of CNFCPEG at the fluorocarbon/waterinterface, while the blue emission observed is due to aggregation in the organic phase. A novel flow-injection method is developed by incorporating complex emulsions with CNFCPEG into multiple-well flow chips (MWFC). Iodine is successfully detected in a mobile aqueous solution by monitoring morphology changes. The findings demonstrate that self-stabilized complex emulsions with MWFC hold great promise for real-time sensing without costly instruments.

In-situ fabricated amorphous silicon quantum dots embedded in silicon nitride matrix: Photoluminescence control and electroluminescence device fabrication

Herein, we report that high-quality SiN:H films embedded with Si QDs were in-situ fabricated and prepared by the reactive facing target sputtering, which relies on tuning N2 and Ar mixture gas flow ratio. The size of Si QDs in SiN:H films can be tuned from 3.87 nm to 1.40 nm, which exhibit color-tunable photoluminescence from red to blue in the visible region. The microstructure evolution and optical properties of SiN:H films embedded with Si QDs were analyzed by FTIR, Raman, PL, and TRPL measurements, respectively. Considering their unique emission properties, SiN:H films embedded with Si QDs were especially utilized as the emitting layer for fabricating high-performance EL SiN-based LEDs. The broad EL emission properties of the devices were explored by both experimental observations and a theoretical model. This work offers a novel idea to prepare high-quality SiN:H films embedded with Si QDs and a deep understanding of their optoelectronic properties.

Architectures and Mechanisms of Perylene Diimide-Based Optical Chemosensors for pH Probing

The precise control and monitoring of pH values remain critical for many chemical, physiological and biological processes. Perylene diimide (PDI)-based molecules and materials exhibit excellent thermal, chemical and photochemical stability, unique UV-vis absorption and fluorescent emission properties, low cytotoxicity, as well as intrinsic electron-withdrawing (n-type semiconductor) nature and impressive molecular assembly capability. These features combined enable promising applications of PDIs in chemosensors via optical signal modulations (e.g., fluorescent or colorimetric). One of the typical applications lies in the probing of pH under various conditions, which in turn helps monitor the extracellular (environmental) and intracellular pH change and pH-relying molecular recognition of inorganic or organic ions, as well as biological species, and so on. In this review, we give a special overview of the recent progress in PDI-based optical chemosensors for pH probing in various aqueous and binary water–organic media. Specific emphasis will be given to the key design roles of sensing materials regarding the architectures and the corresponding sensing mechanisms for a sensitive and selective pH response. The molecular design of PDIs and structural optimization of their assemblies in order to be suitable for sensing various pH ranges as applied in diverse scenarios will be discussed in detail. Moreover, the future perspective will be discussed, focusing on the current key challenges of PDI-based chemosensors in pH monitoring and the potential approach of new research, which may help address the challenges.

Tetraphenylethene-Based cis/trans Isomers for Targeted Fluorescence Sensing and Biomedical Applications.

Molecular probes which can be modulated, functionalized and used to visualize the processes are highly desirable for understanding and manipulating biological systems. Geometric cis and trans isomers of tetraphenylethene (TPE) emerge as attractive candidates to fulfill these tasks thanks to the unique aggregation-induced emission properties, tailorable structures, and responsiveness to external stimuli. This minireview focuses on cis and trans isomers of TPE derivatives that are functionalized with molecular recognition units for fluorescence detection, bioimaging and cancer therapy. The effects of molecular geometry on fluorescence property, target binding ability and biological activity are summarized. The feasibility to in vitro and in vivo switch molecular configuration and thus bio-activity is discussed. Finally, the future development and challenges are discussed in view of TPE-based stereoisomers for targeted sensing and imaging-guided modulation of biological processes.

Multifaceted Excited State Dynamics of Coumarin Dyes Anchored on Al2O3 Film.

The co-facially stacked dyes on semiconductor films serve as an alternative model to elucidate the photo-driven exciton dynamics occurring in a molecular assembly. In this study, we report the unique emission properties of coumarin dye adsorbed on the surface of the semiconductor film, measured by ultrafast time-resolved fluorescence. When a rigid coumarin derivative, 7-hydroxycoumarin-3-carboxylic acid (OHCCA), is anchored on the Al2O3 film, the dye manifests dual emissions from the two lowest excited states. Various anchoring modes of a carboxylic acid group on the Al2O3 surface are invoked to account for the unusual emission process. Additionally, we identified characteristic transition dipole interactions in the well-stacked dye aggregates, which leads to discernible excitonic splitting in the electronic transitions. Femtosecond time-resolved fluorescence reveals that the excimer formation in the aggregate occurs with the time constant of 550 fs. Picosecond time-resolved emission spectra confirm the subsequent structural relaxations of the nascent excimer. The enhanced transition dipole via the electronic coupling between OHCCA and metal oxide can be responsible for the dual emission and the ultrafast excimer formation.

“One stone, five birds”: Ultrabright and multifaceted carbon dots for precise cell imaging and glutathione detection

Developing a single system capable of realizing bacterial Gram-type identification, fungal cell imaging, endoplasmic reticulum (ER) imaging, glutathione (GSH) detection, and normal/cancer cell discrimination with excellent performance is a huge challenge. Herein, ultrabright green-emitting endoplasmic reticulum-targeting sulfur-doped carbon dots (SCDs) with a quantum yield of ∼ 78 % were synthesized via the hydrothermal treatment of rose bengal (RB) and dl-cysteine (Cys). The obtained SCDs possessed excellent fluorescence stability, unique excitation-independent emission property, and satisfactory biocompatibility. We demonstrated that the SCDs could be used for fast (15 min) identification of Gram-positive bacteria due to their S-containing groups (e.g., sulfate and sulfydryl groups) and high-quality fungal cell imaging. We also demonstrated that the SCDs could realize selective and long-term ER imaging in normal/cancer cells, and achieve the monitoring of the cell behaviors during ER stress caused by starvation or various ER stress inducers in live cells. Further, by mixing SCDs and Cu2+, we prepared Cu/SCD nanocomposites (Cu/SCDs), in which the fluorescence of SCDs was quenched by Cu2+ and could recover upon the addition of GSH, realizing GSH detection with a limit of detection of 0.681 μM. Subsequently, based on the much higher GSH level of cancer cells than that of normal cells, Cu/SCDs were successfully applied for distinguishing normal cells from cancer ones. Overall, this work fabricates ultrabright and multifaceted SCDs for precise and high-quality cell imaging and GSH detection, confirming the great potential of SCDs for versatile biomedical applications.

Deferasirox derivative-based fluorescent probes for the potential diagnosis and therapy of iron overload-induced hepatocellular carcinoma by cellular and zebrafish experiments

The association of excess iron in humans with the incidence and proliferation of hepatocellular carcinoma (HCC) has been confirmed by numerous studies. In this case, developing a fluorescent probe that can both target HCC and eliminates excess iron in HCC is extremely meaningful. To accomplish these goals, a fluorescent probe ExPh2-CNAc2 was designed and synthesized, which can be selectively hydrolyzed by carboxylesterases (CE), one kind of biomarker in HCC. The fluorescent parent ExPh2-CN with unique aggregation-induced emission (AIE) and iron-chelating properties of deferasirox derivatives generated by CE hydrolysis of ExPh2-CNAc2 can further chelate with Fe (III) and target HCC for the treatment of iron excess, and the whole process can be effectively monitored by fluorescence changes. Furthermore, the potential for CE imaging and Fe (III) overload resolution of ExPh2-CNAc2 is demonstrated by experiments in cells and zebrafish at different growth stages. The superior in vivo imaging and chelation properties of the probe ExPh2-CNAc2 may provide a new avenue for the diagnosis and treatment of HCC in iron overloaded patients.

Sensitively Site‐Dependent Enhancement of Emissions from Ge Quantum Dots in SiGe Microdisks

Herein, the unique emission properties of Ge quantum dots (QDs) SiGe microdisk system are reported on Si substrates. Two types of microdisks embedded with random QDs and radial site‐controlled QDs are realized by top–down and bottom–up methods, respectively. Photoluminescence results demonstrate that the maximum enhancement factor (EF) of emissions from radial site‐controlled QDs is ≈5.2 times of that from random QDs in microdisks. Moreover, the EF dramatically depends on the site of QD in a microdisk. For a single QD in a microdisk, the difference of EF can be more than five orders due to radial site‐dependent Purcell effect. For multiple QDs in a microdisk, both the azimuthal site and the number of QDs also substantially affect EF due to the interference effect of QDs’ emissions coupling into the cavity modes of microdisks. These unique features disclose the critical effect of the spatial matching between the QD site and the cavity mode on light–matter interactions in a microdisk. In addition, the microdisk via the bottom–up method can efficiently suppress nonradiative losses at the sidewall of microdisk. A promising strategy to QDs’ microdisk system is provided in the results, which promises strong coupling between QDs and the cavity modes and the realization of innovative light sources.

Star-Shaped ROMP Polymers Coated with Oligothiophenes That Exhibit Unique Emission.

A series of oligo(thiophene)-modified “soluble” star-shaped ring-opening metathesis polymerization (ROMP) polymers were prepared by sequential living ROMP of norbornene and a cross-linking agent using a molybdenum-alkylidene catalyst, followed by Wittig-type coupling for termination with oligo(thiophene) carboxaldehydes. The resultant star-shaped ROMP polymers displayed unique emission properties affected by the core size and arm repeat units as well as the kind of oligothiophene coated. The effects of the thiophene groups on photophysical properties of star-shaped/linear polymers were studied via time-resolved fluorescence spectroscopy. Fluorescence lifetimes were determined in THF as 400, 640, 730, and 820 ps for Star 3TPh, Linear 3TPh, Star 4T, and Linear 4T, respectively. A significant enhancement of the nonradiative rate constants knr in the star-shaped polymers results in relatively lower fluorescence quantum yields and shorter fluorescence lifetimes compared to the corresponding linear polymers.

Bringing out the potential of organoboron compounds by designing the chemical bonds and spaces around boron.

Since the structures, reactivity and properties of organoboron compounds stem from the electron deficiency and low electronegativity of boron, the design of the chemical bonds attached to boron as well as the space provided by substituents around boron leads to particular reactivity and functions of organoboron compounds. Based on the concept of vacant boron p-orbital engineering in combination with peripheral space design for boron, we have developed new organoboron compounds, which exhibit exotic reactivity and properties and boron-mediated organic transformations capable of constructing large π-conjugated systems. Here we describe our recent study by focusing on three topics: (i) the synthesis and its derivatization, small-molecule activation and application to materials science of a two-coordinate boron cation (borinium ion), (ii) a 9-borafluorene-mediated benzannulation reaction of alkyne derivatives and (iii) BN-substituted molecules featuring a 4nπ heterocycle exhibiting unique electronic and emission properties. The molecules and reactions appearing in this article are unprecedented, yet feature very simple systems, and therefore clearly demonstrate intrinsic and new potential of organoboron compounds.

An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging

An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging