Two coumarin formhydrazide compounds as chemosensors for copper ions

Two coumarin formhydrazide compounds as chemosensors for copper ions have been synthesized. The compounds can recognize copper ion with obvious absorption spectral change and fluorescence decrease in aqueous solution. The detection limit of the compound with terminal diethylamino group to Cu^2 + in aq.-HEPES buffer acetonitrile (3:7, v/v, pH = 7.4) with fluorescence spectra as detected signal is 0.00041 μM. One carbonyl and amine group in one sensor molecule may complex with one copper ion to form 1:1 complex.     

Tetrapyrazinoporphyrazines with different number of peripheral pyridyl rings: Synthesis,photophysical and photochemical properties

Zinc tetrapyrazinoporphyrazines comprising different numbers of pyridin-2-yl and tert-butylsulfanyl substituents were prepared by the statistical condensation of two precursors – 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile (A) and 5,6-dipyridin-2-yl-pyrazine-2,3-dicarbonitrile (B). The ensuing zinc tetrapyrazinoporphyrazines were chromatographically separated on silica column and characterized. Adjacent (AABB) and opposite (ABAB) isomers were not separated. The prepared zinc tetrapyrazinoporphyrazines did not differ in their Q-band position but the B-band position was shifted hypsochromically for compounds bearing more pyridyl units; in addition, a weak band at 450–520 nm decreased with increasing number of pyridyl substituents. Singlet oxygen quantum yields (Φ_Δ in the range 0.69–0.53) decreased with increasing number of pyridyl units on the macrocyclic core, while fluorescence quantum yields showed the reverse tendency (Φ_F in the range 0.22–0.26).     

Y2O3:Yb,Tm and Y2O3:Yb,Ho powders for low-temperature thermometry based on up-conversion fluorescence

Recently, trivalent rare earth doped materials have received significant attention due to the strong temperature dependence of the fluorescence emission of these materials, which can be useful in temperature sensing. Here, we investigated Y₂O₃ ceramic powders doped with Yb³⁺ and co-doped with either Tm³⁺ or Ho³⁺. The powders were obtained via spray pyrolysis at 900 °C and additionally thermally treated at 1100 °C for 24 h. Structural characterization using X-ray powder diffraction confirmed the cubic bixbyte structure. Scanning electron microscopy (SEM) revealed that the particles exhibit a uniform spherical morphology. The up-conversion emissions were measured using laser excitation at 978 nm, resulting in the following transitions: blue emission in the range of 450–500 nm, weak red emission in the range of 650–680 nm and near infrared emission in the range of 765–840 nm for Tm³⁺, as well as green emission centered at 550 nm and weak near infrared emission at 755 nm for the Ho³⁺ ions. In addition, the temperature dependence of the fluorescence intensity ratios of different Stark components was analyzed in the range of 10–300 K. Significant temperature sensitivity was detected for several components, with the largest value of 0.097 K^?1 related to the intensity ratio of I₅₃₆ and I₇₇₂ emissions observed for the Y₂O₃:Yb,Ho powder.     

The synthesis,photophysical and electrochemical properties of a series of novel 3,8,13-substituted triindole derivatives

The synthesis and properties of a series of new 3,8,13-substituted triindole derivatives 1a–1e are reported. The 3,8,13-substituted triindoles were thermally robust with high decomposition temperatures (≥405 °C) and high melt transitions (219 °C–373 °C). Compound 5e was crystallized in the monoclinic system with the space group P2₁/n. These compounds showed UV–Vis absorption (λ_max^Abs) in the range of 311–345 nm in DCM solution and 371–391 nm in solid state, and fluorescence maxima (λ_max^Em) in the range of 394–412 nm in DCM solution and 416–461 nm in solid state. The fluorescence quantum yields ranged from 0.27 to 0.58. The estimated electron affinities (LUMO levels) and estimated ionization potential (HOMO levels) of compounds 1a–1e are 3.54–3.71 eV and 5.12–5.48 eV, respectively. Quantum chemical calculations using DFT B3LYP/6-31G showed nearly identical LUMO (−0.72 to −1.10 eV) and HOMO (−4.65 to −4.84 eV) values. These results demonstrated that the new 3,8,13-substituted triindoles are promising thermally stable host materials for organic light-emitting diodes with reasonable hole mobility.     

Phase evolution,structure, and up-/down-conversion luminescence of Li6CaLa2Nb2O12:Yb3+/RE3+ phosphors (RE = Ho,Er, Tm)

Garnet-type Li₆Ca(La_0.97Yb_0.02RE_0.01)₂Nb₂O₁₂ (RE = Ho, Er, Tm) new phosphors were successfully synthesized via solid reaction at 900°C for 5 hours, whose course of phase evolution, macroscopic/local crystal structure and up-/down-conversion (UC/DC) photoluminescence were clarified. Mechanistic study and materials characterization were attained via XRD, Rietveld refinement, DTA/TG, electron microscopy (FE-SEM/TEM), and Raman/reflectance/fluorescence spectroscopies. The phosphors were shown to exhibit UC luminescence dominated by a ~ 553 nm green band (⁵F₄/⁵S₂ → ⁵I₈ transition) for Ho³⁺, a ~ 568 nm green band (⁴S_3/2 → ⁴I_15/2 transition) for Er³⁺ and a ~ 806 nm near-infrared band (³H₄ → ³H₆ transition) for Tm³⁺ under 978 nm laser excitation, with CIE chromaticity coordinates of around (0.31, 0.68), (0.38, 0.60) and (0.17, 0.24), respectively. Analysis of the pump-power dependence of UC intensity indicated that all the emissions involve a two-photon mechanism except for the ~ 486 nm blue emission of Tm³⁺ (¹G₄ → ³H₆), which requires a three-photon process. The DC luminescence of these phosphors is featured by dominant bands at ~ 553 nm for Ho³⁺ (green, ⁵F₄/⁵S₂ → ⁵I₈ transition), ~568 nm for Er³⁺ (green, ⁴S_3/2 → ⁴I_15/2 transition) and ~ 464 nm for Tm³⁺ (blue, ¹D₂ → ³F₄ transition). The UC and DC properties were also comparatively discussed.     

Synthesis of nano-titanium diboride powders by carbothermal reduction

The nano-sized titanium diboride particles were synthesized by carbothermal reduction process. In this study, carbothermal reduction process was used by controlling reaction rate and duration time. TiO₂, B₂O₃ and carbon resin were used as starting materials with a molar composition; TiO₂:B₂O₃:C = 1:2:5. The mixture was placed in a graphite crucible and pushed into a heating zone maintained at 1500 °C and Ar was flown for a period of 20 min. After reaction, the crucible was pulled out from the heating zone to cooling zone of the furnace for the rapid cooling. The average particle size of the agglomerated product was found to be ∼500 nm, which was composed with small primary particles of <100 nm in size. After milling, the large agglomerate was reduced to primary particles.     

Microwave bottom-up route for size-tunable and switchable photoluminescent graphene quantum dots using acetylacetone: New platform for enzyme-free detection of hydrogen peroxide

We report a microwave sequential bottom-up route to produce green and blue luminescent graphene quantum dots (g-GQDs and b-GQDs) with size-tunable and switchable functionalities by tailoring the diameter size and functional groups via microwave carbonization and aromatization processes from acetylacetone as a starting organic solvent. The b-GQDs as the final product show only one emission peak at 433 nm and pH-independent blue luminescence, because two-step microwave irradiation could reduce the size and the oxygen-functional groups of the g-GQDs as an intermediate product. Also, the b-GQDs provide an exemplar enzyme-free platform for hydrogen peroxide detection through the electrochemical sensing due to much higher electron density and electron donating properties. In contrast, the g-GQDs show two different switchable photoluminescent emissions at ∼460 nm (P1) and ∼500 nm (P2): the P1 emission with sky-blue fluorescence originates from randomly conjugated oxygen-functional groups on the basal plane and/or edge of the g-GQDs and the P2 emission with green fluorescence results from quasi-molecular fluorophores formed by the electronic coupling of carboxylic acid groups.     

Yb3+/Er3+ co-doped Gd2Te4O11 nanosheets with intrinsic polarity: One-step hydrothermal synthesis and upconverted optical temperature measuring ability

The digadolinium tellurite phosphors of Gd₂Te₄O₁₁(GTO):Yb³⁺/Er³⁺ have been successfully synthesized as upconversion luminescence (UCL) materials via one-step hydrothermal method. The crystal structure, morphology, and upconversion luminescence property were systematically characterize by XRD, SEM, and spectroscopy techniques. The Rietveld refinements of crystal structure were carried out on the XRD patterns and the feature of crystal structure was analyzed. Under the 980 nm NIR excitation, these materials showed very bright upconverted emissions. The concentrations of Yb³⁺ and Er³⁺ were optimized and the strongest upconverted emissions were achieved in the GTO:15%Yb³⁺/1%Er³⁺. The possible energy transfer mechanism of UCL was proposed based upon the analysis of power-dependent UCL and fluorescence kinetics. Furthermore, the fluorescence intensity ratio (FIR) derive from the two thermally coupled energy levels (²H_11/2 and ⁴S_3/2) of Er³⁺ was employed as indicator for temperature measurement. The maximum absolute sensitivity can be achieved to be 7.34 × 10^?3 K^?1 at 501 K. This material exhibited good reliability and repeatability in optical temperature measurement, which could be a novel promising candidate for noncontact temperature sensors.     

The synthesis and spectroscopic investigation of dichromophoric hemicyanine dyes

Alkane α,γ-bis[4-methylpyridinium] diiodide and alkane α,γ-bis[4-methylquinolinium] diiodide were prepared and used as starting materials in the synthesis of dichromophoric cyanine dyes. Structural confirmation of the synthesized dyes was carried out by ¹H NMR, MS spectroscopy and elemental analysis. The electronic absorption and the emission spectra for all the hemicyanines were measured in four organic solvents of varying polarity. All derivatives absorb in the region of about 500 nm and have molar absorptivity of about 10⁴ M⁻¹ cm⁻¹. The absorption spectra of tested compounds are affected by their structure i.e. the structure of dialkyl(aryl)amino group, the electron acceptor part of the dye and the linker between two identical hemicyanine chromophores. The fluorescence bands' positions, in contrast to the absorption, are strongly affected by the solvent polarity.     

Formation of uniformly and finely dispersed nanoshells by carbonization of cobalt-coordinated oxine–formaldehyde resin and their electrochemical oxygen reduction activity

To obtain uniformly and finely dispersed nanoshell structures in nanoshell carbons (NSCs), we synthesized three oxine–polymer (OFR)/cobalt complexes with different ligand/metal ratios (L/M) (xOFR(Co), x = L/M = 1, 2, and 3) as the starting materials of NSCs by polycondensation of 8-hydroxyquinoline (oxine) and formaldehyde. The formation of polymeric structures and coordination bonds was confirmed by infrared spectroscopy. Thermogravimetry revealed that the thermal decomposition temperature increased with the L/M ratio. Carbonization of xOFR(Co) (x = 2 and 3) at 1000 °C resulted in the uniform formation of nanoshells with diameters of 30 nm, while carbonization of 1OFR(Co) resulted in the formation of nanoshells with a broader size distribution including some with diameters over several hundred nm. The results indicate that the fixation of metal atoms in the starting polymers is an effective method for the preparation of uniformly and finely dispersed nanoshells in NSCs. The carbon from 3OFR(Co), i.e., 3OFR(Co)/C, showed the highest electrocatalytic activity for the oxygen reduction reaction (ORR). The linear shape of the voltammograms were understood in terms of the distribution of active sites for ORR with different activation energies.     

Preparation of γ‐aluminum oxynitride phosphor with Eu doping by direct nitridation in ammonia and postannealing

γ‐aluminum oxynitride (γ‐AlON) with spinel structure has attracted much attention for structural and functional application. γ‐AlON powders were successfully prepared by direct nitridation method of Al/Al(OH)₃ starting mixture in ammonia and then calcined at high temperature. XRD, SEM, TEM, EDX, and photoluminescence were conducted to investigate the detail procedure and the optical properties of AlON: xEu phosphors. Nitrogen was introduced by the nitridation of metallic aluminum, appropriate Al amount and nitridation condition was necessary to obtain phase pure γ‐AlON. The as‐prepared AlON powders exhibited multifaceted grain morphology with fine particle size (1‐5 μm). Eu₂O₃ activator was reduced and transformed to EuAl₁₂O₁₉ by reaction with alumina, which remained in the product when x > 0.25%. Under 331 nm excitation, AlON: xEu phosphors exhibited emission bands of 475 and 410 nm. 475 nm band reached a plateau at x = 0.25% due to the solubility of Eu²⁺ ion in AlON, whereas 410 nm band showed a linear increase in intensity with Eu²⁺ doping amount, which was believed to be the contribution of EuAl₁₂O₁₉. The present approach combination of direct nitridation in ammonia and postcalcination process showed potential application for AlON ceramic and AlON phosphors.     

Functionalized Mesoporous SBA-15 with CeF<Subscript>3</Subscript>: Eu<Superscript>3+</Superscript> Nanoparticle by Three Different Methods: Synthesis,Characterization, and Photoluminescence

Luminescence functionalization of the ordered mesoporous SBA-15 silica is realized by depositing a CeF₃: Eu³⁺ phosphor layer on its surface (denoted as CeF₃: Eu³⁺/SBA-15/IS, CeF₃: Eu³⁺/SBA-15/SI and CeF₃: Eu³⁺/SBA-15/SS) using three different methods, which are reaction in situ (I-S), solution impregnation (S-I) and solid phase grinding synthesis (S-S), respectively. The structure, morphology, porosity, and optical properties of the materials are well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, N₂ adsorption, and photoluminescence spectra. These materials all have high surface area, uniformity in the mesostructure and crystallinity. As expected, the pore volume, surface area, and pore size of SBA-15 decrease in sequence after deposition of the CeF₃: Eu³⁺ nanophosphors. Furthermore, the efficient energy transfer in mesoporous material mainly occurs between the Ce³⁺ and the central Eu³⁺ ion. They show the characteristic emission of Ce³⁺ 5d → 4f (200–320 nm) and Eu^{3+ 5}D₀ → ⁷F _J (J = 1–4, with ⁵D₀ → ⁷F₁ orange emission at 588 nm as the strongest one) transitions, respectively. In addition, for comparison, the mesoporous material CeF₃: Eu³⁺/SBA-15/SS exhibits the characteristic emission of Eu³⁺ ion under UV irradiation with higher luminescence intensity than the other materials.     

Solvent-dependent selective fluorescence sensing of Al3 + and Zn2 + using a single Schiff base

The selective assay of Al^3 + and Zn^2 + ions is reported using fluorescence enhancement of a simple Schiff base receptor 1 (1 = 1-((E)-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)naphthalen-2-ol) in aqueous solvents. The Schiff base receptor 1 showed a turn-on fluorescence in the presence of Al^3 + in a mixture of methanol–water, as a result of a restricted CN isomerization mechanism. The ion selectivity of 1 could be switched for Zn^2 + by swapping the solvent from methanol–water to DMF–water mixture. In particular, this chemosensor could clearly distinguish Zn^2 + from Cd^2 +. The binding properties of 1 with the metal ions were investigated by UV–vis, fluorescence, electrospray ionization mass spectroscopy and ¹H NMR titration.     

Synthesis,X-ray crystal structure and optical properties of novel 2,5-diaryl-1,3,4-oxadiazole derivatives containing substituted pyrazolo[1,5-a]pyridine units

A series of pyrazolo[1,5-a]pyridine-containing 2,5-diaryl-1,3,4-oxadiazole derivatives were synthesized and their structures were characterized by IR, ¹H NMR and HRMS spectra. The crystal structure of 3a was determined using single crystal X-ray crystallography. Its spatial structure was found to be monoclinic, and all aromatic rings were approximately coplanar, which allowed conjugation. The absorption results showed that compounds 1a–f presented their absorption peaks ranging from 264 nm to 290 nm, while compounds 3a–f with a larger conjugation system exhibited red-shifted absorption character (absorption maxima between 283 nm and 303 nm) compared to the corresponding absorption of 1a–f. Fluorescence spectra revealed that these compounds exhibited blue fluorescence (421–444 nm) in dilute solutions and showed quantum yields of fluorescence between 0.32 and 0.83 in dichloromethane.     

Synthesis, X-ray crystal structure and optical properties of novel 2,5-diaryl-1,3,4-oxadiazole derivatives containing substituted pyrazolo[1,5-a]pyridine units

A series of pyrazolo[1,5-a]pyridine-containing 2,5-diaryl-1,3,4-oxadiazole derivatives were synthesized and their structures were characterized by IR, ¹H NMR and HRMS spectra. The crystal structure of 3a was determined using single crystal X-ray crystallography. Its spatial structure was found to be monoclinic, and all aromatic rings were approximately coplanar, which allowed conjugation. The absorption results showed that compounds 1a-f presented their absorption peaks ranging from 264 nm to 290 nm, while compounds 3a-f with a larger conjugation system exhibited red-shifted absorption character (absorption maxima between 283 nm and 303 nm) compared to the corresponding absorption of 1a-f. Fluorescence spectra revealed that these compounds exhibited blue fluorescence (421-444 nm) in dilute solutions and showed quantum yields of fluorescence between 0.32 and 0.83 in dichloromethane.     

Gd-based oxyfluoride glass ceramics: Phase transformation,optical spectroscopy and upconverting temperature sensing

A series of precursor glasses with compositions of SiO₂-Al₂O₃-AlF₃-Na₂O- NaF-Gd₂O₃/GdF₃-YbF₃-ErF₃ were prepared and their crystallization behaviors were investigated. For the samples with high F content, meta-stable hexagonal GdF₃ nanocrystals were preferentially precipitated from glass matrix and decreasing F/O ratio induced phase transformation to cubic NaGdF₄ and finally to hexagonal NaGdF₄. Benefited from its multiple active sites, significant enhanced upconversion luminescence was achieved for Yb/Er co-doped glass ceramic containing hexagonal NaGdF₄ nanocrystals. Importantly, significant temperature-sensitive upconversion fluorescence intensity ratio between Er³⁺: ²H_11/2 → ⁴I_15/2 transition (520 nm) and ⁴S_3/2 → ⁴I_15/2 one (540 nm) was detected owing to the competitive radiation transitions from these two thermally coupled emitting-states. Furthermore, linear temperature-dependent fluorescence intensity ratio between Er³⁺: ⁴F_9/2 → ⁴I_15/2 transition (650 nm) to ⁴S_3/2 → ⁴I_15/2 one (540 nm) was achieved, showing the advantages of high sensitivity, superior signal discriminability as well as excellent thermal stability for temperature determination.     

Broadband emission phosphor Sr3Al2O5Cl2:Bi3+: Luminescence modulation and application for a white-light-emitting diode

Bi³⁺ ions can regulate and control the fluorescence of a phosphor by transferring energy to the activating agent or occupying different luminescent centers, which is important for modifying phosphors and revealing fluorescence mechanisms. As a base material, Sr₃Al₂O₅Cl₂ has three types of Sr sites (Sr 1, Sr 2, and Sr 3) that may be occupied by Bi³⁺ ions (Sr²⁺ has a similar radius to Bi³⁺). Herein, we successfully synthesized a series of Sr₃Al₂O₅Cl₂:x%Bi³⁺ phosphors using the high-temperature solid-state method and determined a two-site-occupying emission mechanism. X-ray diffraction patterns indicated that the samples were synthesized well, and Rietveld refinement results provided their structural information. Photoluminescence spectra showed 490 nm (λ_ex = 345 nm) and 556 nm (λ_ex = 376 nm) emission peaks, which might arise from different luminescent centers. The concentration quenching study, peak separation analysis, fluorescence lifetime spectra, and diffuse reflection spectra indicated that the Bi³⁺ ions occupied two of the three Sr sites. Calculations of relative system energies and distortion index proved that the occupation only occurred in the Sr 1 and Sr 3 sites, and crystal splitting analysis determined that Sr 1 site generated 490 nm emission light and Sr 3 site generated 556 nm emission light. The charge compensator and flux were added to enhance the fluorescence intensity of the phosphor, and 5% K⁺ along with 1% BaF₂ is the optimal dosage. Finally, the SrAlSiN₃:Eu²⁺, BaMgAl₁₀O₁₇:Eu²⁺, and optimized Sr₃Al₂O₅Cl₂:5%Bi³⁺ phosphors were combined as a luminous layer and a warm-white light-emitting diode was realized; the color rendering indices were 84.3, 85.8, 86.4, and 86.2 under working currents of 20, 30, 40, and 50 mA, respectively.     

Carbon-containing droplet combustion–carbothermal synthesis of well-distributed AlN nanometer powders

A novel three-step technique was employed to synthesize the well-distributed AlN nanopowders. First, the hollow spherical precursor particles with an average diameter of 2–5 μm, consisting of an amorphous structure mixture of Al₂O₃ and C, was prepared by carbon-containing droplet combustion method by using glucose, urea, and aluminum nitrate as starting materials. The carbothermal reduction and nitridation (CRN) was carried out at 1500°C under N₂ flow for 2 h and subsequently the CRN product was calcined at 700°C in air for 1 h to remove residual carbon and transform the CRN product to high-purity AlN powders consisting of nanostructured hollow spheres. The formation mechanism of precursor and AlN hollow spheres was discussed in detail. The AlN powder exhibited well-distributed spherical particles with a size of 30–50 nm and good sinterability. After additive-free and pressureless sintering at 1800°C for 2 h, the relative density of the sintered AlN sample was measured to be 99.02%.     

Synthesis of a fluorescent gold(I) complex with a thiosemicarbazone, [Au2(3-NO2-Hbtsc)4]Cl2 · 2CH3CN

Direct reaction of gold(I) chloride with 3-nitrobenzaldehyde thiosemicarbazone (3-NO₂-Hbtsc) in the presence of triphenylphosphine in acetonitrile has yielded ionic complex, [Au₂(3-NO₂-Hbtsc)₄]Cl₂ · 2CH₃CN (1). It exhibited an intense fluorescence band (λ_em) at 383 nm (λ_ex = 300 nm), and two bands of medium intensity at 413 and 436 nm (λ_ex = 350 nm). Complex 1 represents first example of ionic gold(I) complex with a thiosemicarbazone.