Facile Synthesis of Quinoline-Substituted 3-Hydroxy-2-oxindoles and 3-Amino-2-oxindoles via a Palladium-Catalyzed Cascade Intramolecular Cyclization/Intermolecular Nucleophilic Addition Reaction.

An efficient cascade intramolecular cyclization/intermolecular nucleophilic addition reaction of allenyl benzoxazinone with isatin or isatin-derived ketimine has been established by using Pd0-π-Lewis base catalysis. A series of 3-hydroxy-2-oxindoles and 3-amino-2-oxindoles with quaternary carbon atoms at the C3 position were synthesized in good yields under mild conditions through this protocol.

Visible-light Excited and Highly Photostable Organic Fluorophore with dual-state Emission.

Organic fluorophores with dual-state emission (DSE) are rare or difficult to observe because most of them display either aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ). Amazing works have been accomplished, yet most of the DSE compounds were excited by UV light which limits their wide application in bioimaging. In this work, we achieved a visible-light excited DSE fluorophore and realized its imaging in SKOV-3 cells and zebrafish. The naphtho[2',3':4,5]imidazo[1,2-a]pyridine (NIP) core ensures its emission in dilute solution. Meanwhile, the twisted phenyl ring blocks fluorescence quenching induced by the π-π stacking and leads to the emission of the solid. The fluorescence intensity is steady even after 6 h of continuous intense sunlight. More importantly, photostability of NIP in cells is much better than commercial dye (mitochondrial green).

Simple and Commercially Available 6-chloroimidazo[1,2-a]pyridine-2-carboxylic Acid-based Fluorescent Probe for Monitoring pH Changes.

Commercially available compounds that can be directly used as fluorescent probes will greatly promote the development of fluorescent imaging. Based on our previously work related to nitrogen bridgehead heterocycles, herein, a commercially available compound, 6-chloroimidazo[1,2-a]pyridine-2-carboxylic acid, has been detected for monitoring pH value (3.0-7.0). The probe proves to have high selectivity and sensitivity, brilliant reversibility, and extremely short response time. The real-time imaging of pH changes in yeast was also conducted.

Exogenous tannic acid relieves imidacloprid-induced oxidative stress in tea tree by activating antioxidant responses and the flavonoid biosynthetic pathway.

Pesticide stress on plants is receiving increased scrutiny due to its effect on plant secondary metabolism and nutritional quality. Tannic acid (TA) is a natural polyphenolic compound showing excellent antioxidant properties and is involved in alleviating stress. The present study thoroughly investigated the effects and mechanism of exogenous TA on relieving imidacloprid (IMI) stress in tea plants. Our research found that TA(10 mg/L) activated the antioxidant defense system, enhanced the antioxidant ability, reduced the accumulation of ROS and membrane peroxidation, and notably promoted tea plant tolerance to imidacloprid stress. Additionally, TA boosted photosynthetic capacity, strengthened the accumulation of nutrients. regulated detoxification metabolism, and accelerated the digestion and metabolism of imidacloprid in tea plants. Furthermore, TA induced significant changes in 90 important metabolites in tea, targeting 17 metabolic pathways through extensively targeted metabolomics. Specifically, TA activated the flavonoid biosynthetic pathway, resulting in a 1.3- to 3.1-fold increase in the levels of 17 compounds and a 1.5- to 63.8-fold increase in the transcript level of related genes, such as ANR, LAR and CHS in this pathway. As a potential tea health activator, TA alleviates the oxidative damage caused by imidacloprid and improves the yield and quality of tea under pesticide stress.

An Imidazo[1,5-a]pyridine Benzopyrylium-Based NIR Fluorescent Probe with Ultra-Large Stokes Shifts for Monitoring SO2.

A mitochondria-targeted NIR probe based on the FRET mechanism was developed. It shows ultra-large Stokes shifts (460 nm) and emission shifts (285 nm). Furthermore, we also realized the imaging of SO2 in living SKOV-3 cells, zebrafish and living mice which may be useful for understanding the biological roles of SO2 in mitochondria and in vivo.

Improved photocatalytic activity and stability of black phosphorus/multi-walled carbon nanotube hybrid for RhB degradation.

Black phosphorus (BP) is a two-dimensional (2D) semiconductor that has recently attracted much interest due to its unique characteristics. However, BP is susceptible to oxidization under ambient conditions. In this work, a facile one-step route is presented, in which stable P-C bonds were formed by ball milling bulk BP and multi-walled carbon nanotubes (MWCNTs) mixture without any additives. The BP-MWCNTs hybrid and the milled BP (m-BP) were both dispersed in water under ambient conditions, and their optical absorbances were monitored. The resulting data showed that the absorbance value of the BP-MWCNTs hybrid decreased by 10.87% after 5 d, whereas the m-BP decreased by 59.21%. Surprisingly, the BP-MWCNTs hybrid also exhibited ultrahigh photocatalytic activity in the visible light range. Within 60 min of irradiation, the removal efficiency of rhodamine B (RhB) by the BP-MWCNTs hybrid reached 88.42%, which is four times higher than that of the bare m-BP. This improvement can be attributed to the formation of the P-C bond and the enhanced surface adsorption capacity resulting from the introduction of the MWCNTs, indicating that the utilization of the charges on the surface of the photocatalyst is further improved. In short, this study not only provides an easy method to synthesize the stable BP-based material for practical applications but also represents a new approach to enhance the photocatalytic activity of BP.

Coassembly Behavior and Rheological Properties of a ß-Hairpin Peptide with Dicarboxylates.

To understand the molecular interaction mechanism and develop peptide-based hydrogels, a ß-hairpin peptide CBHH was used as the model peptide, and its coassembly performance with succinic, malic, and tartaric dicarboxylates has been investigated with circular dichroism spectroscopy (CD) and atomic force microscopy (AFM). The rheological properties and cell culture performance of the coassembled hydrogels have also been assessed. The results showed that the dicarboxylates could induce the folding and self-assembly of the ß-hairpin peptide and promote its gelation at low pH. The effects of the dicarboxylates on peptide self-assembly and hydrogel properties were correlated to their hydroxyl group number. The toxicity of the hydrogel has been assessed with NIH-3T3 cells by MTT and Calcein-AM/PI experiments, and it was confirmed that the hydrogel was biocompatible and could be used as cell culture scaffolds. We hope that this study would provide a novel way for biomaterial fabrication in cell and tissue engineering.

Preparation of a Novel pH-responsive Fluorescent Probe Based on an Imidazo[1,2-a]indole Fluorophore and its Application in Detecting Extremely Low pH in Saccharomyces cerevisiae.

A novel pH-responsive probe based on an imidazo[1,2-a]indole fluorophore architecture is reported. The probe was highly selective to strongly acidic pH (pKa = 3.56) with high sensitivity and a fast response time (within 30 s). The probe did not demonstrate any fluorescence changes in the presence of interfering metal ions, and it featured excellent reversibility under strongly acidic conditions. The mechanism of detection of the probe was determined to be based on intramolecular charge transfer (ICT) at different pH. The probe was also able to be used for imaging for detecting acidic pH in Saccharomyces cerevisiae.

Confined growth of ordered organic frameworks at an interface.

Given their modular synthesis, unique structural features and rich functionality, structurally ordered covalent organic frameworks (COFs) and covalent monolayers have shown great potential in a broad range of applications, such as catalysis, molecular separation, energy storage, light harvesting, etc. The synthesis of COF thin films and covalent monolayers mainly utilizes dynamic covalent chemistry (DCvC), which relies on the reversible formation and breaking of rather strong covalent bonds within molecules under certain external stimuli. Such reversible reaction conditions enable a self-correction mechanism, which can selectively resolve defect sites leading to the formation of highly ordered COF films under thermodynamic control. Novel techniques to obtain single-layer covalent nanosheets have spread throughout recent literature. Emerging interfacial polymerization techniques (e.g., air-water, liquid-liquid, liquid-solid, etc.) have been employed to successfully synthesize crystalline COF thin films from a variety of starting building blocks. Although the growth of ordered frameworks at the interface represents a rapidly developing field, the reversible reactions suitable for the synthesis of thin films or monolayers are still very limited. The identification and development of new dynamic reactions and interfacial polymerization conditions would be critical for the further development of COF thin films and covalent monolayer materials. This review covers the recent design and synthesis of COF thin films and covalent monolayers as well as their property study. The fundamental working mechanisms of different surface and interfacial polymerization and the current challenges and opportunities in this rapidly growing field are presented.

Aromatic Hydrocarbon Based and Space Interactions Induced Color-tunable Single-component Organic Phosphorescence.

Construction of new system and exploration of new approach are of great importance for the improvement of their photophysical properties to meet the growing various uses of phosphorescent materials. Triphenylmethane (TPM), composed only of carbon and hydrogen, exhibits excellent color tunable phosphorescence in air, with ultralong lifetime (836 ms), and wide color-tunable range (from cyan to green, then to yellow and finally to orange, 525 nm-616 nm). Through careful comparison with the single crystal diffraction structure of tetraphenylmethane (TTPM) and theoretical calculation analysis, we believe that various clusters formed through space interactions are crucial for color-tunable phosphorescence.

TiO2/BP/g-C3N4 heterojunction photocatalyst for the enhanced photocatalytic degradation of RhB.

The efficiency of graphite carbon nitride (g-C3N4, CN) as a photocatalyst is limited due to its quick recombination of photogenerated carriers and layer re-stacking. To enhance its photocatalytic activity, a multi-heterojunction photocatalyst was developed using TiO2 and black phosphorus (BP) coupled with CN through a liquid-phase ultrasonic method. The composite, TiO2/BP/CN, demonstrated a wider range of light response and higher photo-induced carrier separation efficiency. The presence of TiO2 nanoparticles on CN nanolayers reduced interlayer stacking and increased specific surface area, thereby providing more reactive sites. As a result, the optimized TiO2/BP/CN composite demonstrated enhanced photocatalytic efficiency for the degradation of Rhodamine B (RhB), with a first-order kinetic constant of 2.8, 4.3, and 6.4 times that of CN, TiO2, and BP, respectively. Active substance capture experiments confirmed that superoxide radical (·O2) was the primary reactive species. This study highlights the potential of the developed TiO2/BP/CN composite as a promising photocatalyst for environmental remediation applications.

Color-Tunable Ultralong Organic Phosphorescence: Commercially Available Triphenylmethylamine for UV-Light Response and Anticounterfeiting.

Due to the unclear mechanism and lack of effective design for color-tunable ultralong organic phosphorescence (UOP) in a single-component molecule, the development of new types of single-component UOP materials with color-tunable property remains challenging. Herein, commercially available triphenylmethylamine-based single-component phosphors featuring color-tunablity and ultralong lifetime (0.56 s) are reported. The changed afterglow colors from cyan to orange were observed after different wavelengths of UV excitation. Crystal structure and calculation studies show that multiple emission centers in the aggregated states may be responsible for the color-tunablity. In addition, visual probing of UV light (from 260 to 370 nm) and colorful anti-counterfeiting were conducted. More importantly, UV light ranging from 350 to 370 nm could be detected with the minimal interval of 2 nm. The findings provide a new type of single-component color-tunable UOP materials and shed new light on mechanism and design for such materials.

Bi2 Te3 /Bi2 Se3 /Bi2 S3 Cascade Heterostructure for Fast-Response and High-Photoresponsivity Photodetector and High-Efficiency Water Splitting with a Small Bias Voltage.

Large-scale multi-heterostructure and optimal band alignment are significantly challenging but vital for photoelectrochemical (PEC)-type photodetector and water splitting. Herein, the centimeter-scale bismuth chalcogenides-based cascade heterostructure is successfully synthesized by a sequential vapor phase deposition method. The multi-staggered band alignment of Bi2 Te3 /Bi2 Se3 /Bi2 S3 is optimized and verified by X-ray photoelectron spectroscopy. The PEC photodetectors based on these cascade heterostructures demonstrate the highest photoresponsivity (103 mA W-1 at -0.1 V and 3.5 mAW-1 at 0 V under 475 nm light excitation) among the previous reports based on two-dimensional materials and related heterostructures. Furthermore, the photodetectors display a fast response (≈8 ms), a high detectivity (8.96 × 109 Jones), a high external quantum efficiency (26.17%), and a high incident photon-to-current efficiency (27.04%) at 475 nm. Due to the rapid charge transport and efficient light absorption, the Bi2 Te3 /Bi2 Se3 /Bi2 S3 cascade heterostructure demonstrates a highly efficient hydrogen production rate (≈0.416 mmol cm-2  h-1 and ≈14.320 µmol cm-2  h-1 with or without sacrificial agent, respectively), which is far superior to those of pure bismuth chalcogenides and its type-II heterostructures. The large-scale cascade heterostructure offers an innovative method to improve the performance of optoelectronic devices in the future.

Direct Z-Scheme SnSe2/SnSe Heterostructure Passivated by Al2O3 for Highly Stable and Sensitive Photoelectrochemical Photodetectors.

To mimic the natural photosynthesis system, a Z-scheme heterostructure is proposed as a viable and effective strategy for efficient solar energy utilization such as photocatalysis and photoelectrochemical (PEC) water splitting due to the high carrier separation efficiency, fast charge transport, strong redox, and wide light absorption. However, it remains a huge challenge to form a direct Z-scheme heterostructure due to the internal electric-field restriction and vital band-alignment at the interface. Herein, the van der Waals heterostructure based on the allotrope SnSe2 and SnSe is designed and synthesized by a two-step vapor phase deposition method to overcome the limitation in the formation of the Z-scheme heterostructure for the first time. The Z-scheme heterostructure of SnSe2/SnSe is confirmed by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, PEC measurement, density functional theory calculations, and water splitting. Strikingly, the PEC photodetectors based on the Z-scheme heterostructure show a synergistic effect of superior stability from SnSe and fast photoresponse from SnSe2. As such, the SnSe2/SnSe Z-scheme heterostructure shows a good photodetection performance in the ultraviolet to visible wavelength range. Furthermore, the photodetector shows a faster response/recovery time of 13/14 ms, a higher photosensitivity of 529.13 µA/W, and a higher detectivity of 4.94 × 109 Jones at 475 nm compared with those of single components. Furthermore, the photodetection stability of the SnSe2/SnSe is also greatly improved by a-thin-Al2O3-layer passivation. The results imply the promising rational design of a direct Z-scheme heterostructure with efficient charge transfer for high performance of optoelectronic devices.

Synthesis, characterization, optical properties and theoretical studies of novel substituted imidazo[1,5-a]pyridinyl 1,3,4-oxadiazole derivatives.

Novel imidazo[1,5-a]pyridinyl 1,3,4-Oxadiazole derivatives were synthesized and characterised by IR, (1)H NMR and HRMS.UV-vis absorption and fluorescence properties of these compounds in different solutions showed that the maximal emission wavelength was not significantly changed in different solvents; however, maximum absorption wavelength was blue-shifted with the increase of solvent polarity. Absorption λ(max) and emission λ(max) was less correlated with substituent groups on benzene rings. The calculated molecular orbital correlates well with their absorption.

Synthesis, X-ray crystal structure and optical properties of novel 2-aryl-3-ethoxycarbonyl-4-phenylpyrido[1,2-a]benzimidazoles.

A series of novel 2-aryl-3-ethoxycarbonyl-4-phenylpyrido[1,2-a]benzimidazole derivatives were synthesized by the tandem reaction of 2-benzoyl benzimidazole and (Z)-ethyl 4-bromo-3-arylbut-2-enoate in the presence of potassium carbonate. The compounds were characterized using IR, 1H-NMR, 13C-NMR, HRMS and the structure of 6f was further determined by X-ray crystallography. Both absorption and fluorescence spectra characteristics of the compounds were investigated in acetonitrile and dichloromethane. The results showed that the absorption maxima of the compounds varied from 220 to 284 nm, depending on the structure of 2-aryl group. The fluorescence results revealed that these compounds exhibited blue-green fluorescence (463-475 nm) in dilute solutions and showed acceptable fluorescence quantum yields (Ф(PL) = 0.13-0.73) in dichloromethane.

1-(1-Benzyl-1H-benzimidazol-2-yl)ethanone.

In the title compound, C16H14N2O, the benzimidazole ring system is essentially planar. The planes of the benzene rings make a dihedral angle of 85.92 (8)°. In the crystal, neighbouring molecule are connected into paris along the c axis by weak C-H⋯O interactions and the connected pairs are expanded through C-H⋯N hydrogen bonds and C-H⋯π interactions along the b axis.

4-Acetyl-1H-pyrrole-2-carbaldehyde.

The title compound, C(7)H(7)NO(2), was synthesized via a one-pot Vilsmeier-Haack and subsequent Friedel-Crafts reaction. The pyrazole ring makes dihedral angles of 4.50 (9) and 2.06 (8)°, respectively, with the aldehyde and acetyl groups. In the crystal, classical N-H⋯O hydrogen bonds and weak C-H⋯O inter-actions assemble the mol-ecules into a chain along the b axis.

3-(4-Bromo-phen-yl)-1-(4-chloro-benz-yl)-1H-pyrazole-5-carbaldehyde.

The title compound, C(17)H(12)BrClN(2)O, was synthesized by oxidation of [3-(4-bromo-phen-yl)-1-(4-chloro-benz-yl)-1H-pyrazol-5-yl]methanol under mild conditions. The pyrazole ring makes dihedral angles of 3.29 (9) and 74.91 (4)°, respectively, with the bromo-phenyl and chloro-phenyl rings.

Layer-Dependent Nonlinear Optical Properties of WS2, MoS2, and Bi2S3 Films Synthesized by Chemical Vapor Deposition.

Two-dimensional (2D) layered materials have shown layer-dependent optical properties in both linear optical and nonlinear optical (NLO) regimes due to prominent interlayer coupling and quantum confinement in an atomic scale. However, the NLO properties become more complicated as both saturable absorption (SA) and reverse saturable absorption (RSA) easily happen in 2D materials, which results in a significant challenge to understand the evolution of nonlinear absorption with layers. Motivated by this, chemical vapor-deposited chalcogenide compounds (WS2, MoS2, and Bi2S3) are used to investigate the pump intensity and layer number-dependent NLO properties. The values of nonlinear absorption coefficients of these chalcogenide compounds increase with the pump intensity by an 800 nm femtosecond laser, which can be described by an empirical power law function. The SA process due to the large transition probability of the ground state readily takes place in thick samples, while RSA occurs easily in thin samples due to the two-photon absorption (TPA). The transition from TPA to SA is deduced to occur at 13L-WS2, 15L-MoS2, and 5L-Bi2S3, which is related to the layer-dependent band gaps. Our results provide an efficient way to tune optical nonlinearities with a controlled layer number and to design corresponding NLO devices such as optical switches and saturable absorbers.