Red Mechanoluminescence and Photoluminescence from Novel Europium Complexes

IntroductionMechanoluminescence(ML)islightemissioncausedbymechanicalforcesuchasgrinding,cuttingandsoon.AlthoughsomeofinorganicandorganicmolecularsolidsshowML,theMLmechanismhasnotbeenclearlyelucidatedyetl-4.The'compound,whichshowsallofML,photoluminescence(PL)andelectroluminescence(EL)properties,hasneverbeenreported.Recently,organiceuropium-compIexeshaveattractedsignificantinterestforthedevelopmentofELdevices5-'.ItisconsideredthateuropiumcomplexesareoneofthebestredELmaterialsduetotheirgo…     

Aggregation and Tunable Color Emission Behaviors of l-Glutamine-Derived Platinum(II) Bipyridine Complexes by Hydrogen-Bonding, π–π Stacking and Metal–Metal Interactions

A n l -glutamine-derived functional group was introduced to the bis(arylalkynyl)platinum(II) bipyridine complexes 1 – 4 . The emission could be switched between the ³MLCT excited state and the triplet excimeric state through solvent or temperature changes, which is attributed to the formation and disruption of hydrogen-bonding, π–π stacking, and metal–metal interactions. Different architectures with various morphologies, such as honeycomb nanostructures and nanospheres, were formed upon solvent variations, and these changes were accompanied by ¹H NMR and distinct emission changes. Additionally, yellow and red emissive metallogels were formed at room temperature due to the different aggregation behaviors introduced by the substituent groups on bipyridine. The thermoresponsive metallogel showed emission behavior with tunable colors by controlling the temperature. The negative Gibbs free-energy change (ΔG) and the large association constant for excimer formation have suggested that the molecules undergo aggregation through hydrogen-bonding, π–π, and metal–metal interactions, resulting in triplet excimeric emission.     

Insight into Iron Leaching from an Ascorbate-Oxidase-like Fe−N−C Nanozyme and Oxygen Reduction Selectivity**

Ascorbate (H₂A) is a well-known antioxidant to protect cellular components from free radical damage and has also emerged as a pro-oxidant in cancer therapies. However, such “contradictory” mechanisms underlying H₂A oxidation are not well understood. Herein, we report Fe leaching during catalytic H₂A oxidation using an Fe−N−C nanozyme as a ferritin mimic and its influence on the selectivity of the oxygen reduction reaction (ORR). Owing to the heterogeneity, the Fe-N_x sites in Fe−N−C primarily catalyzed H₂A oxidation and 4 e⁻ ORR via an iron-oxo intermediate. Nonetheless, trace O₂⋅⁻ produced by marginal N−C sites through 2 e⁻ ORR accumulated and attacked Fe-N_x sites, leading to the linear leakage of unstable Fe ions up to 420 ppb when the H₂A concentration increased to 2 mM. As a result, a substantial fraction (ca. 40 %) of the N−C sites on Fe−N−C were activated, and a new 2+2 e⁻ ORR path was finally enabled, along with Fenton-type H₂A oxidation. Consequently, after Fe ions diffused into the bulk solution, the ORR at the N−C sites stopped at H₂O₂ production, which was the origin of the pro-oxidant effect of H₂A.     

Monocyclometalated (C N) Gold(III) Metallacycles: Tunable Emission and Singlet Oxygen (1O2) Generation Properties

The synthesis, characterization and photoluminescent properties of four cyclometalated (C N)-type gold(III) complexes bearing a bidentate diacetylide ligand, tolan-2,2’-diacetylide (tda), are reported. The complexes exhibit highly tunable excited state properties and show photoluminescence (PL) across the entire visible spectrum from sky-blue (λ_PL=493 nm) to red (λ_PL=675 nm) with absolute PL quantum yields (PLQY) of up to 75 % in solution, the highest PLQY found for any monocyclometalated Au(III) complex in solution. As a consequence of the use of the strongly rigidifying diacetylide bidentate ligand, a significant increase in the excited state lifetimes (τ₀=16–258 μs) was found in solution and in thin films. The complexes showed remarkable singlet oxygen generation in aerated solution with absolute singlet oxygen quantum yield (ϕ^1Δ) values reaching up to 7.5×10⁻⁵ and singlet oxygen lifetimes (τ₀^1Δ) in the range of 66–95 μs. Furthermore, the radiative and non-radiative rates of singlet oxygen were determined using the ϕ^1Δ and τ₀^1Δ values and correlations are drawn between the formation of singlet oxygen and its interaction with cyclometalated (C N) gold(III) complexes.     

Impact of Intermolecular Non-Covalent Interactions in a CuI8PdII1 Discrete Assembly: Conformers’ Geometries and Stimuli-Sensitive Luminescence Properties

A new highly solid-state luminescent phase of a previously reported weakly luminescent Cu^I₈Pd^II₁ dicationic assembly is reported revealing the high geometrical versatility of this moiety that importantly alters its luminescent properties. This very minor new species B_c is based on a different conformer scaffold than the one encountered in the previously reported B_o form and, essentially differs from B_o by displaying shorter Cu^I-Cu^I intermetallic distances. DFT calculations allow concluding that the predominance in the solid-state of the weakly luminescent and less stable B_o phase is due to the extra stability induced by a larger number of intermolecular non-covalent π-CH interactions in its crystalline packing and not by the intrinsic stability of the Cu^I₈Pd^II₁ dicationic moiety. Calculations also revealed that a more stable conformation B_calc is expected in vacuum, which bears a different distribution of Cu^I-Cu^I intermetallic distances than the dications in B_o and B_c phases. Taking into account that the geometrical alterations are associated to drastic changes of luminescence properties, this confer to the Cu^I₈Pd^II₁ assembly high potentiality as stimuli-sensitive luminescent materials. Indeed, by applying mechanical or thermal stress to samples of B_o phase, new phases B_g and B_m , respectively, were obtained. Alterations of the solid-state photophysical properties of these new species compared to those recorded for B_o are reported together with a combined experimental and computed study of the structures/properties relationships observed in these phases.     

About the Secondary Electron Emission Yield, δ, from e−-Irradiated Insulators

 To account for the published yield curves, δ = f ( E ₀), of some insulators such as diamond, an elementary theory of secondary electron emission (s.e.e) is used. This theory permits the estimation of the effective attenuation lengths of the emitted electrons during their transport and to explain the significant differences between the s.e.e. from metals and that from insulators. Some practical consequences related for instance to the lack of topographic contrast in LVSEM and to charging mechanisms in electron beam techniques are then deduced.     

Photocatalytic Hydrogen and Oxygen Formation from Water over Ga-modified Zeolite

Water could be decomposed into hydrogen and oxygen over Ga-modified ZSM-5 zeolite under UV irradiation. The photocatalytic activity was elevated significantly by supporting the gallium species and was sensitive to the loading amount of gallium species on the ZSM-5 zeolites.     

AIE Ligand Constructed Zn(Ⅱ)Complex with Reversible Photo-induced Color and Emission Changes

Fluoran salicylaldehyde hydrazone metal complex(FSHMC)is a kind of recently reported photo-responsive system,which has the advantages of simple synthesis,multiple colors as well as distinct color change before and after UV light irradiation.However,the emission property of FSHMC is relatively unitary.In solid state,especially,only fluorescence quench is induced after UV light irradiation,which limits their applications.In this work,a typical aggregation-induced emission(AIE)moiety of tetraphenylethene(TPE)was introduced to the design of FSHMC.The obtained FSHMC,2-Zn,exhibited reversible color and fluorescence changes upon UV light irradiation.Due to the AIE feature of compound 2,2-Zn exhibited different emission changes upon UV light irradiation in THF and in solid matrix,because of the fluorescence resonance energy transfer(FRET)process from TPE moiety to rhodamine B moiety.     

Photo-excited Oxygen Reduction and Oxygen Evolution Reactions Enable a High-Performance Zn–Air Battery

The storage of solar energy in battery systems is pivotal for a sustainable society, which faces many challenges. Herein, a Zn–air battery is constructed with two cathodes of poly(1,4-di(2-thienyl))benzene (PDTB) and TiO₂ grown on carbon papers to sandwich a Zn anode. The PDTB cathode is illuminated in a discharging process, in which photoelectrons are excited into the conduction band of PDTB to promote oxygen reduction reaction (ORR) and raise the output voltage. In a reverse process, holes in the valence band of the illuminated TiO₂ cathode are driven for the oxygen evolution reaction (OER) by an applied voltage. A record-high discharge voltage of 1.90 V and an unprecedented low charge voltage of 0.59 V are achieved in the photo-involved Zn–air battery, regardless of the equilibrium voltage. This work offers an innovative pathway for photo-energy utilization in rechargeable batteries.     

Unravelling the Synergy between Oxygen Vacancies and Oxygen Substitution in BiO2−x for Efficient Molecular-Oxygen Activation

Defects in nanomaterials often lead to properties that are absent in their pristine counterparts. To date, most studies have focused on the effect of single defects, while ignoring the synergy of multiple defects. In this study, a model of photocatalytic O₂ activation was selected to unravel the role of dual defects by decorating bismuth oxide with surface O vacancies and bulk O substitution simultaneously. The introduction of dual defects led to a spatial and electronic synergistic process: i) O substitution induced a local electric field in the bulk of BiO_2−x, which promoted bulk separation of electrons and holes immediately after their generation; ii) O vacancies efficiently lowered the conduction band, served as the capture center for electrons, and thus facilitated the adsorption and activation of O₂. This effect was greatly promoted by the coexistence of bulk O substitution, and DFT calculations showed that only O substitution near an O vacancy could have this effect.     

Formation Mechanism and Emission Spectrum of AlO Radicals in Reaction of Laser－ablated Al Atom and Oxygen

IntroductionLaser ablation has been applied broadly toplasma production,cluster formation,nanometermaterial and thin film material preparation[1,2 ] .Us-ing spectroscopic technique and mass spectrometryto identify the transient species formed in the pro-cess could provide much useful information aboutthe prosperity ofplasma,the mechanism of materi-al growth[3 ,4] .Aluminum is an important metal material andwidely used in industry and daily life. To study thereaction mechanism of Al atoms with…     

Red Electroluminescence and Photoluminescence from Novel Binuclear Europium Complex with Squaric Acid Ligand

Organic electroluminescent devices (OELDs) have attracted much attention for several years because of their potential application in large area, multi-colored flat panel displays1-5. The green organic EL display using Alq3 as emitter was commercialized in 19976. However, red-emitting OELD with excellent properties has not been well developed. In order to realize practical full-color OELDs, it is considered very important to develop red and blue emitting materials with excellent propert…     

Alternately π-Stacked Systems Assisted by o-Carborane: Dual Excimer Emission and Color Modulation by Bcage-Methylation

Herein, we report the unique solid-state excimer emission of three types of acridine-tethered o-carboranes with variable degrees of methylation at the o-carborane unit. They all showed columnar packing structures based on dimer formation, and two types of π-overlapping motifs were alternately stacked. From the photoluminescence (PL) measurements on the crystalline samples, it was found that three types of luminescence bands can simultaneously appear: monomer emission, excimer emission from the moderately π-stacked intra-dimer unit, and excimer emission from the widely π-stacked inter-dimer unit. Consequently, the PL colors were drastically changed by the steric effect of the methyl groups, with a strong correlation found between the π-overlapping and excimer character. In addition, variable-temperature PL measurements revealed that these PL species should be in thermal equilibrium at room temperature, with the intensity ratios sensitive toward temperature changes.     

Helical β-isoindigo-Based Chromophores with B−O−B Bridge: Facile Synthesis and Tunable Near-Infrared Circularly Polarized Luminescence

It is essential to create organic compounds that exhibit circularly polarized luminescence (CPL) in the near-infrared (NIR) range. Helicene-type emitters possess appealing chiroptical features, however, such NIR molecules are scarce due to a paucity of synthetic strategies. Herein, we developed a series of helical β-isoindigo-based B−O−B bridged aza-BODIPY analogs that were synthesized conveniently. The reaction of diimino-β-isoindigo with a heteroaromatic amine produced a restricted ligand cavity, which triggered off the generation of a B−O−B bridge. The B−O−B bridge led to distorted conformations that satisfy the helical requirements, resulting in excellent spectroscopic and chiroptical properties. Tunable CPL with the highest luminescence dissymmetry factor (g_lum) of 1.3×10⁻³ and a CPL brightness (B_CPL=11.5 M⁻¹ cm⁻¹) in the NIR region was achieved. This synthetic approach is expected to offer a new opportunity to chiral chemistry and increase flexibility for chiroptical tuning.     

Crystal Structure and Fluorescent Study of a Binuclear Europium（Ⅲ） Complex

A novel binuclear Eu（Ⅲ） complex [Eu2（dpa dioxide）2（NO3）4（bpdioxide）-（EtOH）] （dpa dioxide = di-2-pyridylamine N,N＇-dioxide, bpdioxide = 2,2＇-bipyridine N,N＇-dioxide） has been synthesized and it exhibits strong and sharp fluorescent emission at 614 nm under UV radiation of 245 nm at room temperature. X-ray structural determination indicates two independent Eu（Ⅲ） ions in the structure with different EuO8N and EuOgN environments. The compound crystallizes in the triclinic system, space group P1, with a = 10.8089（7）, b = 11.4670（8）, c = 17.1440（12） A, α = 92.834（2）, β = 93.854（3）, γ = 95.433（2）°, Z = 2, Dc = 1.876 g/cm3, V= 2107.3（2） A3, F（000） = 1168.0, the final R = 0.032 and wR = 0.086 for 6331 observed reflections with I 〉 2σ（I）.     

Triangle Cl−Ag1−Cl Sites for Superior Photocatalytic Molecular Oxygen Activation and NO Oxidation of BiOCl

BiOCl photocatalysis shows great promise for molecular oxygen activation and NO oxidation, but its selective transformation of NO to immobilized nitrate without toxic NO₂ emission is still a great challenge, because of uncontrollable reaction intermediates and pathways. In this study, we demonstrate that the introduction of triangle Cl−Ag₁−Cl sites on a Cl-terminated, (001) facet-exposed BiOCl can selectively promote one-electron activation of reactant molecular oxygen to intermediate superoxide radicals (⋅O₂⁻), and also shift the adsorption configuration of product NO₃⁻ from the weak monodentate binding mode to a strong bidentate mode to avoid unfavorable photolysis. By simultaneously tuning intermediates and products, the Cl−Ag₁−Cl-landen BiOCl achieved >90 % NO conversion to favorable NO₃⁻ of high selectivity (>97 %) in 10 min under visible light, with the undesired NO₂ concentration below 20 ppb. Both the activity and the selectivity of Cl−Ag₁−Cl sites surpass those of BiOCl surface sites (38 % NO conversion, 67 % NO₃⁻ selectivity) or control O−Ag₁−O sites on a benchmark photocatalyst P25 (67 % NO conversion and 87 % NO₃⁻ selectivity). This study develops new single-atom sites for the performance enhancement of semiconductor photocatalysts, and also provides a facile pathway to manipulate the reactive oxygen species production for efficient pollutant removal.     

Crystal Structure and Luminescence of a Europium Nitrate Complex with Furancarboxylic Acid and 2,2′-Bipyridine

Abstract

A quaternary mixed ligand europium complex, [Eu(FA)₂NO₃bipy]₂, has been synthesized, where FA = α-furancarboxylic acid anion and bipy=2,2′-bipyridine. The europium complex crystallizes in the triclinic system, space group P1. Its structure was determined by X-ray diffraction methods. The two europium ions in the dimer are held together by four carboxylate groups of furancarboxylic acid and each europium ion is further bonded to one chelated bidentate nitrate and one 2,2′-bipyridine molecule. The coordination modes of the four carboxylate groups are divided into two types, bidentate bridging and tridentate bridging, making a coordination number of 9. Excitation and luminescence spectra observed at 77 K show that the europium ion site in the crystal has low symmetry and emission 5D ₁→⁷ F_J of the Eu³⁺ ion disappears after 20 μs.     

Trinuclear Organometallic Pt−Ir−Pt Complexes: Insights into Photophysical Properties,Amino Acid Binding and Protein Sensing

The rational synthesis of trinuclear emissive organometallic complexes with two equivalent platinum(II) centres appended to the ancillary substituted 2,2′-bipyridyl ligand of the cyclometalated iridium(III) centre is reported here. The alkynyl-platinum moiety and cyclometalated iridium(III) centres have been separated through a non-conjugated CH₂−O−CH₂ linkage. The emission titration with amino acids reveals that the complexes sense free amino acids. The luminescence sensing of BSA is thus attributed to the amino acid sensing ability of the complexes and confirmed by emission anisotropy and Far-UV CD spectral study. The decrease in α-helix in the CD spectra signifies the changes in the secondary structure of protein in presence of the complexes.     

Polymers to Selectively Remove Oxidizing Anions from Non-Oxidizing Anions and NO3 − and NO2 − and NO2 − From Polluted Waters

Abstract

A copolymer of 1-phenyl-2-diethylaminoethyl-p-aminobenzoate and polyvinyl-benzyl chloride was found to have a greater capacity for NO₃ ^? and NO₂ ^? than a previously reported nitron polymer but did not react as rapidly. The resin is readily regenerated with NH₄OH or NH₄Cl and is not affected by the pH of the water over the range of 4–10.

A copolymer of 1-(4′-nitrophenyl)-2-diethyl aminoethyl-p-nitrobenzoate and polyvinylbenzyl chloride was found to react nearly as fast as the nitron polymer and have a larger capacity for NO₃ ^? and NO₂ ^?.     

Identiˉcation and Chemistry of Phenylnitrene in Premixed Pyridine/Oxygen/Argon Flame with Tunable Synchrotron Photoionization

The triplet state phenylnitrene (PhN) species generated from the low-pressure (4.0 kPa) premixed laminar pyridine/oxygen/argon °ame was detected and identiˉed using tunable synchrotron vacuum ultraviolet photoionization and molecular-beam mass spectrometry techniques. The ionization energies of PhN were determined experimentally by photoionization e±ciency spectra and theoretically by calculations. The results indicate that PhN has a 3A2 ground state and its ˉrst and second adiabatic ionization energies are 8.04 and9.15§0.05 eV, respectively. Furthermore, the formation and consumption pathways of PhN are proposed according to the species detected in the present work. PhN is the ˉrst nitrogen-containing diradical detected in combustion chemistry, and so it should be added to the kinetic model of pyridine °ames.