Regulation of Multiple Resonance Delayed Fluorescence via Through-Space Charge Transfer Excited State towards High-Efficiency and Stable Narrowband Electroluminescence

B- and N-embedded multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters usually suffer from slow reverse intersystem crossing (RISC) process and aggregation-caused emission quenching. Here, we report the design of a sandwich structure by placing the B−N MR core between two electron-donating moieties, inducing through-space charge transfer (TSCT) states. The proper adjusting of the energy levels brings about a 10-fold higher RISC rate in comparison with the parent B−N molecule. In the meantime, a high photoluminescence quantum yield of 91 % and a good color purity were maintained. Organic light-emitting diodes based on the new MR emitter achieved a maximum external quantum efficiency of 31.7 % and small roll-offs at high brightness. High device efficiencies were also obtained for a wide range of doping concentrations of up to 20 wt % thanks to the steric shielding of the B−N core. A good operational stability with LT₉₅ of 85.2 h has also been revealed. The dual steric and electronic effects resulting from the introduction of a TSCT state offer an effective molecular design to address the critical challenges of MR-TADF emitters.     

Separate and Concentrate Lactic Acid Using Combination of Nanofiltration and Reverse Osmosis Membranes

The processes of lactic acid production include two key stages, which are (a) fermentation and (b) product recovery. In this study, free cell of Bifidobacterium longum was used to produce lactic acid from cheese whey. The produced lactic acid was then separated and purified from the fermentation broth using combination of nanofiltration and reverse osmosis membranes. Nanofiltration membrane with a molecular weight cutoff of 100–400 Da was used to separate lactic acid from lactose and cells in the cheese whey fermentation broth in the first step. The obtained permeate from the above nanofiltration is mainly composed of lactic acid and water, which was then concentrated with a reverse osmosis membrane in the second step. Among the tested nanofiltration membranes, HL membrane from GE Osmonics has the highest lactose retention (97 ± 1%). In the reverse osmosis process, the ADF membrane could retain 100% of lactic acid to obtain permeate with water only. The effect of membrane and pressure on permeate flux and retention of lactose/lactic acid was also reported in this paper.     

Syntheses, crystal structures, and properties of two salts based on Ni(mnt)2 (mnt2− = maleonitriledithiolate) anion and substituted triphenylphosphonium cation

Two new salts, [oClBzTPP]₂⁺[Ni(mnt)₂]²⁻(1) and [oClBzTPP]⁺[Ni(mnt)₂]⁻(2) ([oClBzTPP]⁺ = 1-(2′-chlorobenzyl)triphenylphosphonium and mnt²⁻ = maleonitriledithiolate) have been prepared and characterized by elemental analyses, UV, IR, MS spectra, single crystal X-ray diffraction, and magnetic susceptibility. The Ni ions of the Ni(mnt)₂ anions for 1 and 2 exhibit the square-planar coordination geometry. The Ni(III) ions of 2 form a 1D zigzag alternating magnetic chain within a Ni(mnt)₂⁻ column through Ni···S, S···S, or Ni···Ni interactions. The C–H···N, C–H···S, C–H···π hydrogen bonds or π···π stacking interactions play important roles in the molecular stabilizing and stacking of 1 and 2. Magnetic susceptibility measurements in the temperature range 1.8−300 K show that 2 exhibits diamagnetic behavior.     

Synthesis and anhydrous proton conductivity of poly(5-vinyltetrazole) prepared by free radical polymerization

5-Vinyltetrazole (VT)-based polymer is mainly produced by ‘click chemistry’ from polyacrylonitrile due to the unavailability of 5-vinyltetrazole monomer, which usually produces copolymers of VT and acrylonitrile rather than pure poly(5-vinyltetrazole) (PVT). In present work, VT was synthesized from 5-(2-chloroethyl)tetrazole via dehydrochlorination. A series of PVT with different molecular weight were synthesized by normal free radical polymerization. The chemical structures of VT and PVT were characterized by ¹H NMR and FTIR. PVT without any doped acid exhibits certain proton conductivity at higher temperature and anhydrous state. The proton conductivity of PVT decreases at least 2 orders of magnitude after methylation of tetrazole. PVT and PVT/H₃PO₄ composite membranes are thermally stable up to 200 °C. The glass transition temperature (T_g) of PVT/xH₃PO₄ composite membranes is shifted from 90 °C for x = 0.5 to 55 °C for x = 1. The temperature dependence of DC conductivity for pure PVT exhibits a simple Arrhenius behavior in the temperature range of 90–160 °C, while PVT/xH₃PO₄ composite membranes with higher H₃PO₄ concentration can be fitted by Vogel–Tamman–Fulcher (VTF) equation. PVT/1.0H₃PO₄ exhibits an anhydrous proton conductivity of 3.05 × 10⁻³ at 110 °C. The transmission of the PVT/xH₃PO₄ composite membrane is above 85% in the wavelength of visible light and changes little with acid contents. Thus, PVT/xH₃PO₄ composite membranes have potential applications not only in intermediate temperature fuel cells but also in solid electrochromic device.     

Adsorption behavior of Pb(II) on montmorillonite

The present work investigated the adsorption and desorption behaviors of Pb(II) on montmorillonite. The adsorption experiments were carried out using batch process. The results show that the adsorption is dependent on the pH value of the medium, and the uptake of Pb(II) increases with the pH increasing in the pH range of 2.0–10.0. The adsorption kinetics is in better agreement with pseudo-second order kinetics, and the adsorption data is a good fit with Langmuir isotherm. The presence of EDTA may result in a decrease of the amount of Pb(II) adsorbed. The presence of electrolyte and EDTA may enhance the desorption of Pb(II) ions adsorbed. The adsorption mechanism of Pb(II) on montmorillonite may be explained in two aspects: the chemical binding between Pb(II) ions and surface hydroxyl groups; and the electrostatic binding between Pb(II) ions and the permanent negatively charged sites of montmorillonite.     

Liquid chromatography/mass spectrometry for metabonomics investigation of the biochemical effects induced by aristolochic acid in rats: the use of information-dependent acquisition for biomarker identification

The toxic effects of oral administrations of nephrotoxic and carcinogenic aristolochic acid (AA) to male Sprague-Dawley rats were investigated by using high-performance liquid chromatography coupled with a quadrupole time-of-flight mass spectrometer. Analysis of the urine and plasma samples revealed distinct changes in the biochemical patterns in the AA-dosed rats. After peak finding and alignment, principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) were used for multivariate data analysis. Potential biomarkers were studied by high-resolution mass spectrometry (MS) and tandem mass spectrometry (MS/MS) analyses. The MS/MS spectra of all endogenous metabolites satisfying the pre-defined criteria were acquired in a single information-dependent acquisition (IDA) analysis, demonstrating that IDA was an efficient approach for structural elucidation in metabonomic studies. Citric acid and a glucuronide-containing metabolite were observed as potential biomarkers in rat urine. A significant increase in plasma creatinine concentration was also observed in the AA-dosed rats, which indicated that AA induced an adverse effect on the renal clearance function.     

Oriented organic islands and one-dimensional chains on a Au(111) surface fabricated by electrodeposition: an STM study

Organic islands and oriented one-dimensional (1D) chains are fabricated on a Au(111) surface by electrodeposition. The cyclic voltammograms (CVs) of Au(111) in solutions containing nitrobenzene and picric acid show an electrochemical reaction in a negative potential region, which results in irreversible reductive deposition. The deposition process is monitored by in situ electrochemical scanning tunneling microscopy (ECSTM). At the double layer potential region, for example, nitrobenzene molecules form a well-defined adlayer in a (square root(3) x square root(3)) structure. With potential shifting negative to the reductive region, nitrobenzene is reduced to hydroxyaminobenzene. Organic islands were formed first and then aggregated into ordered 1D chains. The formation of these organic islands and 1D chains is completely potential-dependent. Intriguingly, the so-prepared islands and 1D chains are well-oriented along the reconstructed lines of the underlying Au(111) substrate and stable under ambient conditions even if the sample was removed from electrolyte solution. The results reported here provide a simple and effective method to fabricate oriented organic nanodots and nanowires on a solid surface by an electrochemical technique.     

Identification of the structures of superlong oriented single-walled carbon nanotube arrays by electrodeposition of metal and Raman spectroscopy

In this Communication, we have demonstrated a facile and effective approach to identify the structure of the superlong well-aligned single-walled carbon nanotubes (SWNTs) by the combination of electrodeposition of metal (Ag) with Raman spectroscopy. The suitable density and the visibility of the Ag-deposited long oriented nanotubes make it possible to acquire Raman spectra from isolated individual nanotubes very easily. The results reveal that the well-oriented SWNT arrays on SiO2/Si wafer fabricated by EtOH chemical vapor deposition using Fe/Mo nanoparticles as catalyst exhibit a low percentage of metallic SWNTs (5%). Among other SWNTs about 62.3% are semiconducting SWNTs, and a small amount of nanotubes are quasimetallic. About 32% are a so-called quasi-insulator, which is caused inevitably by the defects during growth. Furthermore, the structural uniformity of the long SWNTs can be also evaluated by the deposition of Ag along the length and Raman spectroscopy. This method also provides an approach to deposit other metals on long SWNTs, which could have various potential applications such as for use as sensors, etc. More importantly, this facile method can be applied to long SWNT arrays fabricated from other different catalytic systems so that the relationship between the growth conditions and the structures of SWNTs are expected to be ruled out.     

Photoswitchable nanoparticles enable high-resolution cell imaging: PULSAR microscopy

Beyond-diffraction-limit optical imaging of cells will reveal biological mechanisms, cellular structures, and physiological processes in nanometer scale. Harnessing the photoswitching properties of spiropyran fluorophores, we achieved nanoresolution fluorescence imaging using photoactuated unimolecular logical switching attained reconstruction (PULSAR) microscopy. The PULSAR microscope successfully resolved nanostructures and subcellular organelles when the photoswitchable nanoparticles containing spiropyran dyes were used as fluorescent probes.     

Enantioselective total syntheses of trichodermamides A and B

Starting from commercially available (-)-quinic acid, the enantioselective total syntheses of trichodermamides A and B were achieved. The key reactions involve the stereoselective construction of the oxazine ring via an intramolecular epoxide ring opening reaction and an EDCI-assisted peptide coupling reaction.