Blue Fluorescence Emission Research Articles

Plasmon-enhanced fluorescence of CaF2:Eu2+ nanocrystals by Ag nanoparticles

We report plasmon-enhanced fluorescence in Eu2+ doped CaF2 (CaF2:Eu2+) nanocrystals assembled with Ag nanoparticles (NPs) using a simple hydrothermal method. The structure, morphology and composition of the nanocrystals are confirmed by X-ray diffraction (XRD), transmission electron Microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and UV–vis absorption spectrum. Ag nanoparticles are ideal building blocks for plasmonic materials that can exhibit a wide range of unique and potentially useful optical phenomena. Surface plasmon enhancement makes significant contribution to enhance the blue fluorescence emission of CaF2:Eu2+. The enhancement on the Eu emission in visible regions is up to a factor of 12.3-fold. As shown in time-resolved measurements, surface Plasmon Resonance (SPR) can reduce the fluorescence lifetime and increase the quantum yield. Furthermore, with increasing Ag concentration, the fluorescence intensity increases to its maximum and then decreases.

An ABX3 organic–inorganic perovskite-type material with the formula (C5N2H9)CdCl3: Application for detection of volatile organic solvent molecules

ABX3 organic–inorganic hybrid perovskite materials, particularly CH3NH3PbI3, have been widely investigated in recent years. However, organic–inorganic hybrid perovskite materials containing N-heterocyclic are still rarely reported. Herein, we discover a new material, namely, (C5N2H9)CdCl3(1) by slow evaporation method. The structure of compound 1 was determinated by single crystal X-ray diffraction patterns, and it exhibits 1D chain based edge-sharing CdCl5 tetragonal pyramid. FT-IR and powder X-ray diffraction patterns (PXRD) were performed to confirm the purity of the prepared crystals. The optical diffuse-reflectance spectra indicate that (C5N2H9)CdCl3 is a wide band-gap semiconductor with optical band gap of 3.50eV. Thermogravimetric analysis (TGA) indicates that 1 is thermally stable up to around 226°C. In addition, based on the measurement of luminescence properties of 1 at room temperature, the emission spectra of 1 shows a blue fluorescent emission peak at 420nm (λex=315nm). And the fluorescence quenching of 1 by acetonitrile has been studied at room temperature.

Optically transparent polyamides bearing phenoxyl, diphenylamine and fluorene units with high-contrast of electrochromic and electrofluorescent behaviors

Two kinds of new electroactive polyamides were synthesized from a novel diphenylamine-fluorene skeleton bis(ether amine) monomer “N,N-bis((4-aminophenoxy)phenyl)-2-amino-9,9-dimethylfluorene” with cycloaliphatic and aromatic dicarboxylic acids, respectively. These polyamides were highly soluble in many organic solvents and could be solution-cast into transparent and flexible films. These films were nearly colorless with the optical transmittance over 90% at 450 nm and the cut-off wavelengths in the range of 385–390 nm. These polyamides revealed reversible redox with a strong color changing from colorless (neutral state) to green (oxidation state), and the electrochromic contrast of transmittance was up to 86% at 410 nm. Especially, the polyamide derived from cycloaliphatic acid exhibited strong blue fluorescence emission with the quantum yield up to 14.5% and 58.9% in solid state and solution state, respectively. Furthermore, the fluorescence of the polyamide film could be reversibly and readily modulated by electrochemical redox exhibiting a high contrast of 83.

Novel distorted donor-acceptor type deep blue fluorescent emitter for high efficiency in non-doped blue and cool white organic light-emitting diodes

Distorted donor-acceptor type blue fluorescent emitter, 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1,8-dimethyl-9H-carbazole (DmCzTrz), was developed for use as a high efficiency and non-doped deep blue fluorescent emitter and a deep blue emitter in hybrid white organic light-emitting diodes. The novel distorted donor-acceptor based non-doped DmCzTrz blue fluorescent organic light-emitting diodes achieved high quantum efficiency of 6.8% with a deep blue color coordinate of (0.15,0.10). The DmCzTrz blue emitter was doped with green and red triplet emitters to develop the hybrid white organic light-emitting diodes, and high quantum efficiency of 19.4% in cool white device and 20.8% in warm white device were demonstrated.

Recent Progress in High‐Efficiency Blue‐Light‐Emitting Materials for Organic Light‐Emitting Diodes

Organic light‐emitting diodes (OLEDs) are increasingly used in displays replacing traditional flat panel displays; e.g., liquid crystal displays. Especially, the paradigm shifts in displays from rigid to flexible types accelerated the market change from liquid crystal displays to OLEDs. However, some critical issues must be resolved for expansion of OLED use, of which blue device performance is one of the most important. Therefore, recent OLED material development has focused on the design, synthesis and application of high‐efficiency and long‐life blue emitters. Well‐known blue fluorescent emitters have been modified to improve their efficiency and lifetime, and blue phosphorescent emitters are being investigated to overcome the lifetime issue. Recently, thermally activated delayed fluorescent emitters have received attention due to the potential of high‐efficiency and long‐living emitters. Therefore, it is timely to review the recent progress and future prospects of high‐efficiency blue emitters. In this feature article, we summarize recent developments in blue fluorescent, phosphorescent and thermally activated delayed fluorescent emitters, and suggest key issues for each emitter and future development strategies.

Fluorescence Detection of Microcapsule-Type Self-Healing, Based on Aggregation-Induced Emission.

An extrinsic self-healing coating system containing tetraphenylethylene (TPE) in microcapsules was monitored by measuring aggregation-induced emission (AIE). The core healing agent comprised of methacryloxypropyl-terminated polydimethylsiloxane, styrene, benzoin isobutyl ether, and TPE was encapsulated in a urea-formaldehyde shell. The photoluminescence of the healing agent in the microcapsules was measured that the blue emission intensity dramatically increased and the storage modulus also increased up to 105 Pa after the photocuring. These results suggested that this formulation might be useful as a self-healing material and as an indicator of the self-healing process due to the dramatic change in fluorescence during photocuring. To examine the ability of the healing agent to repair damage to a coating, a self-healing coating containing embedded microcapsules was scribed with a razor. As the healing process proceeded, blue light fluorescence emission was observed at the scribed regions. This observation suggested that self-healing could be monitored using the AIE fluorescence.

Highly sensitive fluorescent sensor targeting CuCl2 based on thiophene attached anthracene compound (TA)

A novel thiophene attached anthracene (TA) based fluorescent compound was designed and synthesized. The TA showed a high quantum yield (Qy=0.34) in regard to fluorescence. We applied this TA compound to detect specific metal compound and found that it could identify CuCl2 from other metals through dramatic fluorescence change at λmax=460nm. It showed strong quenching fluorescence property with CuCl2 while with other metal compounds it exhibited strong blue fluorescence emission. UV/Vis absorption spectroscopy clearly demonstrated that the quenching property of TA at λmax=460nm was due to overlapping of the fluorescence peak of TA at λmax=460nm and the absorption band of CuCl2 (from 190nm to 525nm). Binding constant (K′), which was 0.0895mM−2, indicated a complexation ratio between TA and CuCl2 as 1:2 and this interaction induced quenching property.

Bright and sensitive ratiometric fluorescent probe enabling endogenous FA imaging and mechanistic exploration of indirect oxidative damage due to FA in various living systems.

As a notorious toxin, formaldehyde (FA) poses an immense threat to human health. Aberrantly elevated FA levels lead to serious pathologies, including organ damage, neurodegeneration, and cancer. Unfortunately, current techniques limit FA imaging to general comparative studies, instead of a mechanistic exploration of its biological role, and this is presumably due to the lack of robust molecular tools for reporting FA in living systems. More importantly, despite being reductive, FA, however, can induce oxidative damage to organisms, thus providing a challenge to the mechanistic study of FA using fluorescence imaging. Herein, we presented the design and multi-application of a bright sensitive ratiometric fluorescent probe 1-(4-(1H-phenanthro[9,10-d]imidazol-2-yl)phenyl) but-3-en-1-amine (PIPBA). With a π-extended phenylphenanthroimidazole fluorophore and an allylamine group, PIPBA exhibited high quantum yield (φ = 0.62) in blue fluorescent emission and selective reactivity toward FA. When sensing FA, PIPBA transformed to PIBE, which is a product capable of releasing bright green fluorescence (φ = 0.51) with its enhanced intramolecular charge transfer (ICT). Transformation of PIPBA to PIBE contributed to 80 nm of red shift in emission wavelength and a highly sensitive ratiometric response (92.2-fold), as well as a quite low detection limit (0.84 μM). PIPBA was successfully applied to various living systems, realizing, for the first time, ratiometric quantification (in cells), in vivo imaging (zebrafish), and living tissue imaging (vivisectional mouse under anaesthetic) of endogenous FA that was spontaneously generated by biological systems. Furthermore, with the aid of PIPBA, we obtained visual evidence for the oxidative damage of FA in both HeLa cells and renal tissue of a living mouse. The results demonstrated that FA exerted indirect oxidative damage by interacting with free radicals, thus producing more oxidizing species, which eventually caused aggravated oxidative damage to the organism. The indirect oxidative damage due to FA could be alleviated by an exogenous or endogenous antioxidant. The excellent behaviors of PIPBA demonstrate that a chemical probe can detect endogenous FA in cells/tissue/vivo, promising to be an effective tool for further exploration of the biological mechanism of FA in living systems.

Two intensified fluorescence colors' switching achieved by branched dye nanoaggregates.

In this study, a variety of branched target dyes containing double internal proton transfer segments were synthesized. For comparison, some linear analogs including a single internal proton transfer part were synthesized. The corresponding reference molecules lacking proton transfer segments were also prepared. The properties and aggregation modes of these dye aggregates were investigated on the basis of scanning electron microscopy images, transmission electron microscopy images, dynamic light scattering, X-ray diffraction, UV/visible absorption spectra and fluorescence emission spectra. The results showed that molecular aggregates with the morphologies of nano-scaled rounded or cubic particles of the target branched dyes could be yielded in mixed organic solvent/H2O solution. A remarkable emission enhancement and fluorescence switching process (from bright yellow to luminous pure blue) under 365 nm lamp irradiation was observed for these target branched dye nanoaggregates. However, no aggregates of the reference branched dyes free of hydroxyl groups were formed and no obvious spectral variations were found. In contrast, all the studied linear dyes yielded molecular nanoaggregates in mixed organic solvent/H2O solution, and only intensified single normal blue fluorescence emission was presented. This study provided real examples of some branched organic dye aggregates which were capable of displaying naked-eye enhanced fluorescence color switching under an UV lamp.

Substitution effect of super hydrophobic units: A new strategy to design deep blue fluorescent emitters

Fluorescent deep-blue emitters consisting of arylamine chrysene have attracted immense commercial interest in organic light-emitting devices (OLEDs). Herein, we endeavor to design emitters with super hydrophobic groups, namely trifluoromethoxy (OCF3) or trifluoromethylsufanyl (SCF3) substituted on 6,12-diarylamine chrysene. Surprisingly, the new materials show highly efficient and substantial blue shift in fluorescence spectra with more pure color quality, higher thermostability and better moisture resistant properties. Astonishing electroluminescence performance is envisioned by promoting the molecular design based on experience and theoretical calculations along with the single crystal X-Ray analysis. The CIE coordinate values for 6, 12-diamine-N,N,N′,N′-tetra(p-trifluoromethoxyphenyl)chrysene (DATPC-OCF3) and 6,12-diamine-N,N,N′,N′-tetra(p-trifluoromethylsulfanylphenyl)chrysene (DATPC-SCF3) are (0.14, 0.09) and (0.15, 0.06), respectively, which exactly match with the National Television System Committee (NTSC) and High-Definition Television requirements for unprecedented deep-blue emission.

Fluorescent carbon dots for glyphosate determination based on fluorescence resonance energy transfer and logic gate operation

Herein, a novel method based on fluorescence resonance energy transfer (FRET) between carbon dots (CDs) and glyphosate (Gly) was designed for Gly detection. CDs were synthesized via a facile and one-step hydrothermal method using citric acid and Tris. The CDs possessed strong blue fluorescence and excitation wavelength-dependent emission behavior with the maximum excitation and emission wavelength at 340nm and 410nm, respectively. However, the presence of glyphosate could effectively quench the fluorescence intensity of the CDs through FRET and this phenomenon has been exploited to design an “AND” logic gate for sensitively sensing Gly for the first time. Furthermore, the proposed method has been successfully utilized to detect glyphosate in water samples with satisfactory results. The detection limit for glyphosate was 0.6μmolL−1(3σ/k), with the linear range of 0.02–2.0μmolL−1. This is a promising approach for rapid screening of glyphosate in environmental water samples without using any costly instruments.

Chemical Etching of Bovine Serum Albumin-Protected Au25 Nanoclusters for Label-Free and Separation-Free Ratiometric Fluorescent Detection of Tris(2-carboxyethyl)phosphine.

This study describes a novel ratiometric fluorescent sensor based on chemical etching of gold nanocluster (GNCs) for label-free, separation-free determination of tris(2-carboxyethyl)phosphine (TCEP). TCEP was discovered to exhibit unusual chemical behavior toward fluorescent gold nanoclusters: it quenched the red fluorescent emission of the bovine serum album (BSA)-protected GNCs (GNCs@BSA) and simultaneously restored the blue fluorescent emission of the dityrosine (diTyr) residues of the BSA ligand. The TCEP-induced quenching of the fluorescent GNCs@BSA was investigated with the UV-vis adsorption spectrum, the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), inductively coupled plasma-mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy (XPS), revealing the chemical etching of the gold(0) core of the GNCs@BSA by TCEP. Furthermore, the ratio of the blue fluorescence intensity of the diTyr to the red fluorescence intensity of the GNCs@BSA was found to be dependent on TCEP concentration and showed a linear relationship in the TCEP concentration range of 500 nM to 50, 000 nM (R2 = 0.9943) with a limit of detection (LOD) of 130 nM, achieving the higher sensitivity over previous reports. This ratiometric sensor also showed superior selectivity for TCEP over certain common interferences including glutathione, 20 kinds of natural amino acids, and the oxidized form of TCEP. With the developed ratiometric method, the deproteinized human serum samples spiked with TCEP were analyzed with satisfactory results. In addition, it is worth noting that compared with conventional ratiometric fluorescent sensors, the ratiometric sensor developed in this study does not require external fluorophores, avoiding the additional derivation procedures.

Brightly near-infrared to blue emission tunable silver-carbon dot nanohybrid for sensing of ascorbic acid and construction of logic gate

Recently, carbon dots (CDs) have drawn extensive attention owing to their unique properties. While more and more research had been focusing on the exploration of CDs as fluorescence sensors, the blue or green fluorescence emission of CDs restricts further applications of CDs, particularly in the biology-relevant fields due to the commonly blue auto-fluorescence of biological matrix. Therefore, the preparation of CDs with strong emission at long wavelengths is highly desirable. For these situations, a facile, straightforward and extra-reductant needless method was established to fabricate silver-carbon dot nanohybrid with enhanced near-infrared fluorescence through metal-enhanced fluorescence (MEF). We applied the Ag-CD nanohybrid as a probe to detect antioxidants such as ascorbic acid in near-infrared window, and the probe possesses a linear range of 0.2–60μM. More importantly, this sensor could not only function in aqueous solution, but also display well selective response in intricate biological fluids. In addition, an IMPLICATION logic gate was constructed based on the unique characteristics of Ag-CD nanohybrid which presages more opportunities for application in single and multiple biological sensing.

Efficient triplet harvesting of hybrid white organic light-emitting diodes using thermally activated delayed fluorescence green emitter

Hybrid white organic light-emitting diodes (WOLEDs) were fabricated by applying triplet harvesting (TH) using a green thermally activated delayed fluorescence (TADF) emitter. The triplet exciton of the green TADF emitter can be upconverted to its singlet state. The TH involved energy transfer of triplet exciton from a blue fluorescent emitter to a green TADF and red phosphorescent emitters, where they can decay radiatively. In addition, the triplet exciton of the green TADF emitter was energy transferred to its singlet state for a reverse intersystem crossing by green emission. Enhanced hybrid WOLEDs were demonstrated using an efficient green TADF emitter combined with red phosphorescent and blue fluorescent emitters. Hybrid WOLEDs were fabricated with various hole-electron recombination zones as changing blue emitting layer thicknesses. Among these, hybrid WOLEDs showed a maximum external quantum efficiency of 11.23%, luminous efficiency of 29.20 cd/A, and a power efficiency of 26.21 lm/W. Moreover, the WOLED exhibited electroluminescence spectra with Commission International de L’Eclairage chromaticity of (0.38, 0.36) at 1000 cd/m2 and a color rendering index of 82 at a practical brightness of 20,000 cd/m2.

A Method to Identify and Isolate Pluripotent Human Stem Cells and Mouse Epiblast Stem Cells Using Lipid Body-Associated Retinyl Ester Fluorescence

We describe the use of a characteristic blue fluorescence to identify and isolate pluripotent human embryonic stem cells and human-induced pluripotent stem cells. The blue fluorescence emission (450–500 nm) is readily observed by fluorescence microscopy and correlates with the expression of pluripotency markers (OCT4, SOX2, and NANOG). It allows easy identification and isolation of undifferentiated human pluripotent stem cells, high-throughput fluorescence sorting and subsequent propagation. The fluorescence appears early during somatic reprogramming. We show that the blue fluorescence arises from the sequestration of retinyl esters in cytoplasmic lipid bodies. The retinoid-sequestering lipid bodies are specific to human and mouse pluripotent stem cells of the primed or epiblast-like state and absent in naive mouse embryonic stem cells. Retinol, present in widely used stem cell culture media, is sequestered as retinyl ester specifically by primed pluripotent cells and also can induce the formation of these lipid bodies.

Synthesis of ZnS:Ag,Co water-soluble blue afterglow nanoparticles and application in photodynamic activation

Silver and cobalt co-doped ZnS (ZnS:Ag,Co) water-soluble afterglow nanoparticles were synthesized using a wet chemistry method followed by aging at room temperature. The nanoparticles had a cubic zinc blende structure with average sizes of approximately 4 nm and emitted a blue fluorescence emission centered at 441 nm due to radiative transitions from surface defects to Ag+ luminescent centers. Intense afterglow emission peaking at 475 nm from the obtained nanoparticles was observed and was red-shifted compared to the fluorescence emission peak. X-ray photoelectron spectroscopy revealed a large increase of O/S ratio, indicating a surface oxidation process during aging. The S vacancies produced accordingly may contribute to form more electron traps and enhance afterglow. The ZnS:Ag,Co afterglow nanoparticles have a very low dark-toxicity and are applied as a light source for photodynamic therapy activation by conjugating with protoporphyrin together. Our preliminary study has shown that the ZnS:Ag,Co afterglow nanoparticles can significantly reduce the x-ray dosage used in activation and thus may be a very promising candidate for future x-ray excited photodynamic therapy in deep cancer treatment.

Binding-Directed Energy Transfer of Conjugated Polymer Materials for Dual-Color Imaging of Cell Membrane

Binding of biomolecules or probes to the plasma membrane is of great importance for investigations of cell morphology and various biological processes. Herein, a water-soluble conjugated polymer is designed as a membrane probe. The probe shows a strong affinity toward lipid membranes owing to the high charge density from abundant imidazolium moieties together with the moderate rigidity and hydrophobicity derived from the conjugated backbone. Upon binding with a membrane, the interchain FRET of the probe was substantially enhanced, which resulted in the emission of both blue and red fluorescence. This is favorable for dual-color imaging. Finally, cellular experiments demonstrate the excellent performance of this macromolecular probe on stable binding with cell membranes without the appearance of cell endocytocysis even after a long retention time.

Design of blue fluorescence emitter star-shaped macromolecules based on pyrene and anthracene

Star-shaped macromolecules decorated with fluorescence moieties such as pyrene and anthracene have been developed, which exhibit aggregation enhanced excimer emission (AEEE). The presented star-shaped macromolecules showed only weak emissions in the visible region in dilute solution, due to the predominance of the monomer emission, which has its maximum in the UV-A region of the spectrum. However, the strong blue visible excimer-like emission is generated in the aggregated state, by the use of poorly solubilizing solvents or high concentration. The solution of these macromolecules emitted blue light centred at 475 and 474 nm with pyrene and anthracene moieties respectively. In addition, emission efficiency increases were observed with increasing water fraction. The unique phenomenon of AEEE was verified by determining the excimer-monomer emission intensities ratio (IE/IM). TEM was used to detect the difference between the aggregation states in various THF/water ratios. The molecular structures of the fluorescent star were investigated using (MMFF).

Determination of sunset yellow in soft drinks based on fluorescence quenching of carbon dots

Fluorescent carbon dots was prepared by heating N-(2-hydroxyethyl)ethylene diaminetriacetic acid in air. The carbon dots were not only highly soluble in water but also uniform in size, and possessed strong blue fluorescence and excitation wavelength-dependent emission properties with the maximum excitation and emission wavelength at 366nm and 423nm, respectively. Food colorant sunset yellow whose excitation and emission wavelength at 303nm and 430nm could selectively quench the fluorescence of carbon dots, efficient fluorescent resonance energy transfer between the carbon dots and sunset yellow is achieved. This was exploited to design a method for the determination of sunset yellow in the concentration range from 0.3 to 8.0μmolL−1, with a limit of detection (3σ/k) of 79.6nmolL−1. Furthermore the fluorimetric detection method was established and validated for sunset yellow in soft drinks samples with satisfactory results.

Efficient organic blue fluorescent light-emitting devices with improved carriers' balance on emitter molecules by constructing supplementary light-emitting layer

In this work, we demonstrated an efficient device design strategy in improving the electroluminescent performances of blue fluorescent emitter 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl (BCzVBi) by constructing predominant and supplementary light-emitting layers. 4,4′,4″-tris(carbazole-9-yl)triphenylamine (TcTa) and 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy) were selected as host materials. Experimental results revealed BCzVBi doped TcTa film functions as predominant light-emitting layer, while BCzVBi doped 26DCzPPy film functions as supplementary light-emitting layer, which helps to broaden the recombination zone, improve the trapping of carriers and balance the distribution of holes and electrons on emitter molecules. Finally, the 15 wt% doped device with the Commission Internationale de 1′Eclairage coordinates of (0.143, 0.189) obtained the maximum current efficiency, power efficiency, external quantum efficiency and brightness up to 11.99 cd/A, 10.91 lm/W, 8.0% and 36,060 cd/m2, respectively. Even at the high brightness of 1000 cd/m2, current efficiency as high as 9.76 cd/A can be retained by the same device.