Blue-violet Fluorescence Research Articles

Conjugated Polymers Based on Carbazole and Tridentate Ligands as the "On-Off-On" Fluorescent Probes for Detection of Ni (II) Ion and Lysine.

Two novel conjugated polymers (polymer 1 and polymer 2) containing trisheterocyclic systemsand carbazole as the copolymerization unit were synthesized by the Suzuki coupling reaction and characterized using NMR spectroscopy and other methods. 4'-(3,5-Dibromophenyl)-2,2':6',2''-terpyridine and 2,2'-(4-(3,5-dibromophenyl)pyridine-2,6-diyl)dithiazole were used as the recognizing units of the two polymers respectively. The polymers show blue-violet fluorescence when dissolved in THF. The ability of the polymers to identify anions and metal ions was investigated by fluorescence sensing tests. It was found that I- not only quenched the fluorescence but also undergone some redshift. Ni (II) efficiently quenched the fluorescence of the polymers, and polymer 2 recognized Ni2+ with higher specificity. UV-visible absorption titration experiments showed that Ni2+ formed complexes with the polymers. In addition, the formation of complexes between Ni2+ and polymers were used for the detection of amino acids, and it was found that lysine could regenerate the fluorescence of [polymer 1-Ni2+] and [polymer 2-Ni2+] with 99% fluorescence recovery.

Single and two-photo excited violet-blue fluorescence from aza [6]helicenes and the plannar precursors based-on indole, carbazole, and fluorene

Organic π-conjugated materials exhibiting violet-blue emissions are of great interest for diverse applications. Helicenes and stilbenes hold great potential as compounds capable of achieving violet-blue fluorescence. In this study, aza[6]helicenes THNI and DHNC, along with their planar precursors DFVHI and HHIVC, were successfully synthesized using indole, carbazole, and fluorene units as building blocks. The molecular structures were verified through the utilization of 1H and 13C nuclear magnetic resonance (NMR), high resolution mass spectroscopies (HRMS), and the crystal structure of THNI was further elucidated via X-ray analysis. The synthesized material exhibited exceptional thermal stability with a Td value of ≥350 °C. The HOMO and LUMO energy levels were determined through cyclic voltammetry analysis, while density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at the B3LYP/6-31G(d) level were employed to investigate ground-state geometries and vertical electronic transitions. Optical properties were characterized using UV–vis absorption spectroscopy as well as single- and two-photon excited photoluminescence. The UV–vis absorption spectra indicate that helicenes possess superior light-harvesting capabilities compared to their planar precursors, owing to the former's higher molar extinction coefficients. These compounds exhibit violet-blue emissions in various solvents and solid-state films. In addition, aza[6]helicenes exhibit higher photoluminescence quantum yields (PLQYs) and shorter maximum emission peaks compared to their planar precursors. However, the maximum two-photon absorption (TPA) cross section (δ) values of aza[6]helicenes are lower than those of their planar counterparts. Therefore, THNI and DHNC may be promising candidates for violet-blue emitters in OLEDs due to their curved confined π-electron systems, high thermal and optical stability, and high PLQYs. Meanwhile, DFVHI and HHIVC exhibit potential as two-photon fluorescent probes for bioimaging.

Short-wavelength excitation two-photon intravital microscopy of endogenous fluorophores.

The noninvasive two-photon excitation autofluorescence imaging of cellular and subcellular structure and dynamics in live tissue could provide critical in vivo information for biomedical studies. However, the two-photon microscopy of short-wavelength endogenous fluorophores, such as tryptophan and hemoglobin, is extremely limited due to the lack of suitable imaging techniques. In this study, we developed a short-wavelength excitation time- and spectrum-resolved two-photon microscopy system. A 520-nm femtosecond fiber laser was used as the excitation source, and a time-correlated single-photon counting module connected with a spectrograph was used to provide time- and spectrum-resolved detection capability. The system was specially designed for measuring ultraviolet and violet-blue fluorescence signals and thus was very suitable for imaging short-wavelength endogenous fluorophores. Using the system, we systematically compared the fluorescence spectra and fluorescence lifetimes of short-wavelength endogenous fluorophores, including the fluorescent molecules tyrosine, tryptophan, serotonin (5-HT), niacin (vitamin B3), pyridoxine (vitamin B6), and NADH and the protein group (keratin, elastin, and hemoglobin). Then, high-resolution three-dimensional (3D) label-free imaging of different biological tissues, including rat esophageal tissue, rat oral cheek tissue, and mouse ear skin, was performed in vivo or ex vivo. Finally, we conducted time-lapse imaging of leukocyte migration in the lipopolysaccharide injection immunization model and a mechanical trauma immunization model. The results indicate that the system can specifically characterize short-wavelength endogenous fluorophores and provide noninvasive label-free 3D visualization of fine structures and dynamics in biological systems. The microscopy system developed here can empower more flexible imaging of endogenous fluorophores and provide a novel method for the 3D monitoring of biological events in their native environment.

Fluorescence Emission Is Highly Structure-Dependent in Hybrid Lead Halides.

Hybrid lead halide perovskites have received extensive scientific attention owing to their great potential in the field of fluorescent displays and light-emitting diodes. Currently, most luminescent materials contain functional molecular and rare-earth metal ion parts. However, the mechanism of photoluminescence property in two-dimensional hybrid lead halide perovskites with different layered inorganic skeletons has been reported rarely. To better understand the effect of an inorganic skeleton on the fluorescence property, here, we report three organic-inorganic hybrid materials with different layered inorganic frameworks: (MACH)2·PbBr4 (Prv-1, MACH = cyclohexylmethylammonium), (2-MPQ)·PbBr4 (Prv-2, 2-MPQ = 2-methylpiperazinium), and (TMBA)4·Pb3Br10 (Prv-3, TMBA = N'N'N'-trimethylbenzylammonium). Among them, Prv-1 is a (100)-oriented perovskite, Prv-2 belongs to the (110)-oriented perovskite, and the inorganic framework of Prv-3 possesses [Pb3Br10] units. Interestingly, Prv-1 has a strong blue-violet fluorescence emission, while the luminescence effect of Prv-2 is very weak; notably, Prv-3 emits a charming bright-orange light. Meanwhile, results of theoretical computational studies also reveal that the electronic structure of all three compounds is highly dependent on structurally distorted [PbBr6] octahedra, and the frontier molecular orbital (FMO) analysis further suggests that HOMO and LUMO of Prv-3 are contributed by inorganic and organic components, respectively. In addition, all three materials belong to direct band gap semiconductors, and the band gaps are 2.79, 2.97, and 2.76 eV, respectively. Significantly, there are obvious differences in conduction bands. Based on the above analysis, the photoluminescence mechanism of three hybrid materials is explained from the electronic levels. Consequentially, this work might provide practical strategies and perspectives for exploring novel structure-related properties.

Solid-state silica gel-catalyzed synthesis of fluorescent polysubstituted 1,4- and 1,2-dihydropyridines.

We present the green, highly atom-economical, solid-state silica gel-catalyzed synthesis of polysubstituted 1,4- and 1,2-dihydropyridines (DHPs) from commercially available materials, amines and ethyl propiolate. The DHP skeleton was assembled by heating the reactants and silica gel in a closed vessel. Aliphatic amines provided 1,4-isomers as the main or only DHP products, but the reactions of aromatic amines yielded a mixture of 1,4- and 1,2-isomers. To the best of our knowledge, this is the first example of the formation of a 1,2-DHP structure by the reaction of an amine with propiolic ester. Addition of 1 mass percent of H2SO4 to silica gel shifted the product distribution to 1,4-DHP as the main or the only isomer obtained. Experimental and theoretical analyses led to the identification of two key intermediates en route to DHPs and the explanation of the observed regioisomeric ratios. 1,2-DHPs show blue-cyan fluorescence in MeOH with the quantum yield Φ = 0.10-0.22 relative to quinine sulfate Φ = 0.58 and 1,4-DHPs show blue-violet fluorescence with Φ = 0.09-0.81.

Tri-channel tubular lanthanide nanocomposites for multimodal anti-counterfeiting

Integrating multiple signals with different excitation wavelength dependence and temperature response properties into a single nanomaterial to construct multimodal anti-counterfeiting materials is still challenging. In this research, an exciting lanthanide hybrid tri-channel tubular anti-counterfeiting nanomaterial was fabricated by fixing NaYF4:Yb3+/Tm3+ up-conversion nanoparticles and Cit-Eu-TC complex on the surface of YHF:Ce/11.4%Tb nanotubes, which can be further used to make anti-counterfeiting fluorescent ink and hydrogel. The hidden three-mode anti-counterfeiting patterns showed bright green, red, and blue-violet fluorescence under 254 nm, 365, and 980 nm excitation, respectively. More importantly, under the co-irradiation of 254 and 365 nm light, the patterns prepared by the anti-counterfeiting ink showed mesmerizing dynamic anti-counterfeiting performance under the stimulation of developer and temperature. With the developer's dosage increase or temperature change, the color of anti-counterfeiting patterns changed obviously. The combination of this dynamic stimulus-responsive anti-counterfeiting feature and the above three-channel static anti-counterfeiting feature might bring about multi-mode static-dynamic anti-counterfeiting performance, significantly improving the difficulty of forgery and was expected to be widely used in the field of confidential information and file anti-counterfeiting.

Highly Emissive Luminogens in Both Solution and Aggregate States

Highly Emissive Luminogens in Both Solution and Aggregate States

Identification Characteristic of Purple Jadeite Treated with Bleaching, Filling and Dyeing

To explore the identification characteristics of purple jadeite that is treated with bleaching, filling and dyeing, the gem microscope, refractometer, UV-Vis-NIR spectropho-tometer, XRF spectrometer, DiamondViewTM, FTIR and Raman spectrometer were used. The results showed that the internal structure of the purple jadeite samples treated with bleaching, filling and dyeing was destroyed, and epoxy resin was detected by infrared spectrometer and Raman spectrometer. Strong Raman peak at 1 596 cm-1 could be the characteristic peak of dyes. Luminescent images showed the characteristic blue-violet fluorescence of the polymers formed by epoxy resin and organic dyes. The UV-Vis spectra of the purple jadeite samples treated with bleaching, filling and dyeing showed the absorption band of 200-350 nm, the absorption peak at 409 nm and the absorption band near 569 nm.The internal structure of the jadeite stained by the purple polishing powder was not damaged, and the purple colour only stained on the surface since the powder particles only remained on the surface. The luminescent images showed pinkish purple fluorescence, which was caused by the purple polishing powder. The strong central absorption band at 558 nm and the weak central absorption band at 611 nm can be seen in the UV-Vis spectra, which are different from the natural purple jadeite.

Molecular Dynamics Simulation of the Excited-State Proton Transfer Mechanism in 3-Hydroxyflavone Using Explicit Hydration Models.

3-Hydroxyflavon (3-HF) represents an interesting paradigmatic compound to study excited-state intramolecular proton transfer (ESIPT) and intermolecular (ESInterPT) processes to explain the experimentally observed dual fluorescence in solvents containing protic contamination (water) as opposed to single fluorescence in highly purified nonpolar solvents. In this work, adiabatic on-the-fly molecular dynamics simulations have been performed for isolated 3-HF in an aqueous solution using a polarizable continuum model and including explicit water molecules to represent adequately hydrogen bonding. For the calculation of the excited state, time-dependent density functional theory and the Becke-3-Lee-Yang-Parr (B3LYP) functional have been used. For the isolated 3-HF, ultrafast ESIPT from the enol group to the neighboring keto group has been observed. The calculated PT time of 48 fs agrees well with the experimental value of 39 fs. Addition of one water molecule quenches this ESIPT process but shows an intermolecular concerted or stepwise tautomerization process via the bridging water molecule. Adding a second or more water molecules inhibits this ESInterPT process to a large degree. Most of the trajectories do not show any PT, preserving the initial excited-state enol structure, which is the origin of the violet-blue fluorescence appearing in the solvents contaminated with protic components.

Ratiometric determination of Cr(VI) based on a dual-emission fluorescent nanoprobe using carbon quantum dots and a smartphone app.

A simple dual-colour fluorescent nanoprobe has been designed composed of blue and yellow emission carbon quantum dots (CQDs). This system isinexpensive and easy to operate and was successfully employed for on-site measurements based on a smartphone app. The designed nanoprobe exhibited increased selectivity for Cr(VI), leading to a double stable response of the two CQDs. The dual-emission nanoprobe showed blue-violet fluorescence upon UV irradiation, and the fluorescent emission peaks were located at 418nm and 552nm. The blue light emission of CQDs was quenched with increasing Cr(VI) concentration due to the inner filter effect, whereas the yellow light emission was enhanced due to the aggregation-induced emission effect. The different responses of the dual emissions to Cr(VI) resulted in a fluorescent colour variation, thus enabling facile macroscopic visualization. With a smartphone, the change in the fluorescence colour could be observed more apparently than that of a single fluorescence nanoprobe, and the response increased linearly so that the nanoprobe could be applied toinstantaneous measurements. Furthermore, the dual-emission nanoprobe was successfully employed for analysing food and water samples. Accurate concentrations were obtained by constructing a calibration plot using a fluorescence spectrometer and a smartphone app; the recoveries were 81.6% to 107.7%, and the relative standard deviation was below 3.6%. Therefore, this smartphone-integrated dual-emission detection system is promising as a new portable method for the on-site measurement of Cr(VI) ions. * Y-CQDs: yellow emission carbon quantum dots. B-CQDs: blue emission carbon quantum dots. B/Y-CQDs: a mixture of B-CQDs and Y-CQDs.

A portable logic detector based on Eu-MOF for multi-target, on-site, visual detection of Eu3+ and fluoride in groundwater

Developing a portable analytical device for rapid and visual detection of multiple targeted pollutants in groundwater is very important. In this paper, a novel Eu-MOF was prepared and applied for the highly sensitive and selective detection of Eu3+ and fluoride in groundwater. In the presence of Eu3+, the blue-violet fluorescence at 425 nm of Eu-MOF is greatly quenched because of the aggregation effect caused by Eu3+ combined with the amino functional groups exposed on Eu-MOF. The detection limit of Eu3+ has been determined as (2.481 ± 0.014) ×10−7 M according to the 3σ rule. Furthermore, the addition of fluoride would replace Eu3+ bound to amino group to induce the fluorescence recovery, and the detection limit of fluoride was calculated to be (1.145 ± 0.009) ×10-6 M. The common interfering ions have no influences on the selective detection of Eu3+ and fluoride by Eu-MOF. In addition, the spiked and recovery test indicated that Eu-MOF can be used for detection of Eu3+ and fluoride in real water samples and possess efficient and favorable practicability. More importantly, the logic detectors and paper sensors based on Eu-MOF were designed and fabricated as the portable analytical devices for the visual detection of Eu3+ and fluoride in groundwater. Our research would be beneficial and helpful for the water quality safety and human health guarantee.

Sensitive and selective detection of phosgene with a bis-(1H-benzimidazol-2-yl)-based turn-on fluorescent probe in the solution and gas phase.

As one of the chemical weapons in World War I, phosgene (COCl2) is an extremely toxic gas. Due to wide applications in industrial production, phosgene can easily leak inadvertently and poses a serious threat to the environment and human health and safety. In this study, we report for the first time a new fluorescent probe (bis-(1H-benzimidazol-2-yl)-methanone) for the rapid detection of phosgene. The probe is based on the easily prepared bis-(1H-benzimidazol-2-yl), which can quickly combine with phosgene to obtain a six-membered cyclic carbamylation product showing fluorescence turn-on. The combination of phosgene caused the maximum absorption of the probe shifting from 361 nm to 373 nm, which showed a color change from colorless to yellow under visible light. Meanwhile, a strong fluorescence emission peak appeared at 428 nm, which showed change from no fluorescence to blue-violet fluorescence under a UV lamp (365 nm). The response of the probe towards phosgene is fast (within 30 s), highly selective and sensitive (the detection limit in solution being 3.3 nM). Furthermore, the portable test strips manufactured using the probe can conveniently perform visual and fluorescence detection of phosgene in the gas phase.

4-Azafluorenone and α-Carboline Fluorophores with Green and Violet/Blue Emission.

The emission properties of three 4-azafluorenone and five new α-carboline fluorophores in both solution and thin solid films were investigated. Fluorescence of the azafluorenone is clearly enhanced in thin solid films due to the presence of phenyl/biphenyl rotors, and these derivatives can be classified as green Aggregation-Induced Emission luminogens (AIEgens) with a non-emissive heteroaromatic core structure. Compared to azafluorenones, emission of α-carbolines is hypsochromically shifted to the blue region of the electromagnetic spectrum, and most of these derivatives exhibit strong violet-blue fluorescence in both solution and thin solid film layers. Further, the effective mobility and electroluminescence of new α-carbolines were investigated in prepared organic field-effect transistors and organic light-emitting diodes, respectively.

Synthesis, crystal structure, vibrational spectra, optical and DFT study of N-(3-ammonium propyl)-1, 3 diaminopropane tris iodate dehydrate [(C6H20N3) (IO3)3·2H2O

The new inorganic-organic iodate hybrid compound N-(3-ammonium propyl)-1, 3 diaminopropane tris iodate dehydrate [(C6H20N3) (IO3)3·2H2O] denoted as BATID was synthesized and characterized by single X-ray diffraction. This iodate salt crystallizes in the orthorhombic system with acentric space group Aba2. The crystal structure consists of discrete ionic entities of (C6H20N3)3+cations, (IO3)- iodate anions and neutral water molecules linked via simple and bifurcated NH ⋯OI and O(W)H⋯OI hydrogen bonds. TG analysis agrees well with the XRD data showing that the crystal structure of BATID is hydrated. DSC measurement shows that BATID compound exhibits a single phase transition around 361 K. DFT calculation were performed to optimize the molecular geometry and to calculate harmonic vibrational frequencies, electric dipole moments (μ), first Hyperpolarizability (βTot), atomic Mulliken charges and HOMO-LUMO properties using B3LYP method with (6-311 + G*, LanLD2Z (ECP)) mixed basis sets.The calculated structural parameters (bond lengths and angles) are in good agreement with the experimental XRD data. An optical analysis was also undertaken using reflectance diffuse UV–visible and fluorescence spectroscopy showing that BATID has wide transparent windows as well as two strong blue–violet fluorescence emissions at room temperature.

Gold‐Catalyzed Regiospecific C−H Annulation of o‐Ethynylbiaryls with Anthranils: π‐Extension by Ring‐Expansion En Route to N‐Doped PAHs

We describe a novel, short, and flexible approach to diverse N-doped polycyclic aromatic hydrocarbons (PAHs) through gold-catalyzed π-extension of anthranils with o-ethynylbiaryls as reagents. This strategy uses easily accessible starting materials, is simple due to high step and atom economy, and shows good functional-group compatibility as well as scale-up potential. Mechanistically, the tandem reaction is proposed to involve a nucleophilic addition/ring opening/regiospecific C-H annulation/protodeauration sequence terminated by a Friedel-Crafts-type cyclization. Photophysical studies of the products indicated violet-blue fluorescence emission with quantum yields up to 0.45.

Size-dependent magnetic properties of cubic-phase MnSe nanospheres emitting blue-violet fluorescence

We report a facile controlled synthesis of non-iron based cubic phase MnSe magnetic nanocrystals with well-defined spherical shape of different size (7–16 nm, TEM data) by hot injection method without need for special conditions. It was found that the size and its polydispersity could be easily controlled by controlling the reaction temperature. The highly crystalline (confirmed by XRD) synthesized nanoparticles showed blue-violet fluorescence emission and were antiferromagnet in nature. The observed size dependent weak ferromagnetism, resulting hysteresis loop in antiferromagnet was attributed to the surface spins. Strengthening of antiferromagnetism with increasing size could be the reason for shifting of the freezing temperature towards higher side.

Transition Metal-Free trans-Selective Alkynylboration of Alkynes.

We report the first transition metal-free and trans-selective alkynylboration reaction of alkynes. This unprecedented carboboration reaction is enabled by pseudo-intramolecular activation of alkynylboronates using propargylic alcohols. The carboboration affords 4-alkynyl-1,2-oxaborol-2(5H)-ols, which are not only versatile building blocks but also exhibit strong violet-blue fluorescence emission.

Zinc and Cadmium Diphenate Coordination Polymers with Conformationally Flexible Dipyridylamide Ligands

Zinc and cadmium diphenate (dip, biphenyl-2,2′-dicarboxylate) coordination polymers containing conformationally flexible dipyridylamide ligands show diverse chain and layer topologies as determined by single-crystal X-ray diffraction. [Cd(dipH)2(bdin)]n (1) [bdin = N,N′-(butane-1,3-diyl)diisonicotinamide] shows a simple 1D zigzag chain structure. {[Cd(dip)(pdin)(H2O)]·1.25H2O}n (2) [pdin = N,N′-(propane-1,3-diyl)diisonicotinamide] shows bilayer slabs formed by interleaving of (4,4) rectangular grid layers. {[Zn2(dip)2(3-pna)2]·3H2O}n (3) (3-pna = 3-pyridylnicotinamide) manifests a rare 4-connected 1D ribbon topology. {[Cd(dip)(4-ppbp)]·2H2O}n (4) [4-ppbp = propane-1,3-diylbis(piperidine-4,1-diyl)bis(pyridin-4-ylmethanone)] shows a 3,5-connected layer with (426)(42678) 3,5L2 topology. {[Zn4(dip)4(H2O)2(4-ppbp)2]·12H2O}n (5) exhibits 2D 3,6-connected layers with (43)2(466683) kgd topology featuring embedded R(8)A(2) classification 10-membered water clusters. Compounds 1, 4, and 5 undergo violet or blue-violet fluorescence upon ultraviolet irradiation. Thermal decomposition behavior of the new phases is also discussed.

Rapid Synthesis of C-dots@PGV Nanocomposites Powders for Development of Latent Fingermarks

Abstract Novel fluorescent nanocomposites prepared by microwave irradiation and electrostatic adsorption have been formulated for developing latent fingermarks on various object surfaces. As-synthesized carbon dots@montmorillonite (C-dots@PGV) nanocomposites were characterized using UV–visible absorption spectroscopy, fluorescence spectroscopy, infrared spectroscopy, TEM/HRTEM, SEM and XRD. Due to its photoluminescence and stable chemical properties, C-dots@PGV nanocomposites powders with intense fluorescence produce sharp and clear development of latent fingermarks with good contrast and satisfactory ridge details. It is widely used for painted metal, glass, plastic and stainless steel surfaces, and the small, fine fluorescent nanocomposites demonstrate great advantages. Especially for multicolor surfaces, the fluorescent probe can help us to observe and photograph using UV light as excitation light source to eliminate background effects. After developing by facile powder technique, the prints emit strong violet-blue fluorescence under UV light (365 nm), at the same time, this nontoxic powder without any organic solvent and dyes can reduce harm to the operators.

Preparation of the Water-Soluble Pyrene-Containing Fluorescent Polymer by One-Pot Method

A new water-soluble pyrene-containing fluorescent polymer, 1-{3′-S-[poly(acryloyl ethylene diamine hydrochloride)-2′-methyl propionic acid]}propionyloxy hexyloxy pyrene (P3) with defined structure, was designed and synthesized using the click reaction between thiol and a carbon-carbon double bond. The intermediate products P1 (S-1-dodecyl-S′-[poly(N-Boc-acryloyl ethylene diamine)-2′-methyl propionic acid]trithiocarbonate) and AHP (1-(acryloyloxy hexyloxy)pyrene) were prepared via reversible addition fragmentation chain transfer (RAFT) polymerization and Williamson synthesis, respectively. Conjugating AHP with P1, P2 (1-{3′-S-[poly(N-butoxycarbonyl-acryloyl ethylene diamine)-2″-methyl propionic acid]} propionyloxy hexyloxy pyrene) was synthesized, adopting both the reduction reaction of a trithioester bond of P1 to thiol and the click reaction between thiol and the carbon-carbon double bond of AHP simultaneously. P3 was obtained by the deprotection of the resulting Boc-protected polymer (P2) with aqueous HCl. The experiment results showed that P2 exhibited a bright blue-violet emission band at approximately 387–429 nm. After deprotection, P3 displayed good solubility in water and not only exhibited a blue-violet fluorescence emission band at approximately 387–429 nm in aqueous solution but also had the similar photoluminescent spectra to those of AHP and P2 in dichloromethane. The fluorescence quantum yields of P2 in dilute tetrahydrofuran and P3 in a dilute aqueous solution were 0.44 and 0.39, respectively. This experiment provided a novel insight into the study of water-soluble fluorescent polymers.