Precise Synthesis of Organic Cocrystal Alloys with Full-Spectrum Emission Characteristics for the Stepless Color Changing Display.

Organic luminescent materials are indispensable in optoelectronic displays and solid-state luminescence applications. Compared with single-component, multi-component crystalline materials can improve optoelectronic characteristics. This work forms a series of full-spectrum tunable luminescent charge-transfer (CT) cocrystals ranging from 400 to 800 nm through intermolecular collaborative self-assembly. What is even more interesting is that o-TCP-Cor(x)-Pe(1-x), p-TCP-Cor(x)-Pe(1-x), and o-TCP-AN(x)-TP(1-x) alloys are prepared based on cocrystals by doping strategies, which correspondingly achieve the stepless color change from blue (CIE [0.22, 0.44]) to green (CIE [0.16, 0.14]), from green (CIE [0.27, 0.56]) to orange (CIE [0.58, 0.42]), from yellow (CIE [0.40, 0.57]) to red (CIE [0.65, 0.35]). The work provides an efficient method for precisely synthesizing new luminescent organic semiconductor materials and lays a solid foundation for developing advanced organic solid-state displays.

Oriented Self-Assembly of Hierarchical Branch Organic Crystals for Asymmetric Photonics.

Organic hierarchical branch micro/nanostructures constituted by single crystals with inherent multichannel characteristics exhibit superior potential in regulating photon transmission for photonic circuits. However, organic branch micro/nanostructures with precise branch positions are extremely difficult to achieve due to the randomness of the nucleation process. Herein, by taking advantage of the dislocation stress field-impurity interaction that solute molecules deposit preferentially along the dislocation line, twinning deformation was introduced into microcrystals to induce oriented nucleation sites, and ultimately organic branch microstructures with controllable branch sites were fabricated. The growth mechanism of these controllable single crystals with an angle of 140° between trunk and branch is attributed to the low lattice mismatching ratio (η) of 4.8%. These as-prepared hierarchical branch single crystals with asymmetrical optical waveguide characteristics have been demonstrated as an optical logic gate with multiple input/out channels, which provides a route to command the nucleation sites and offers potential applications in the organic optoelectronics at the micro/nanoscale.

Reactivity and Selectivity of the Diels-Alder Reaction of Anthracene in [Pd6L4]12+ Supramolecular Cages: A Computational Study.

The field of supramolecular metal-organic cage catalysis has grown rapidly in recent years. However, theoretical studies regarding the reaction mechanism and reactivity and selectivity controlling factors for supramolecular catalysis are still underdeveloped. Herein, we demonstrate a detailed density functional theory study on the mechanism, catalytic efficiency, and regioselectivity of the Diels-Alder reaction in bulk solution and within two [Pd6L4]12+ supramolecular cages. Our calculations are consistent with experiments. The origins of the catalytic efficiency of the bowl-shaped cage 1 have been elucidated to be the host-guest stabilization of the transition states and the favorable entropy effect. The reasons for the switch of the regioselectivity from 9,10-addition to 1,4-addition within the octahedral cage 2 were attributed to the confinement effect and the noncovalent interactions. This work would shed light on the understanding of [Pd6L4]12+ metallocage-catalyzed reactions and provide a detailed mechanistic profile otherwise difficult to obtain from experiments. The findings of this study could also aid to the improvement and development of more efficient and selective supramolecular catalysis.

Recent Progress of Small-Molecule Ratiometric Fluorescent Probes for Peroxynitrite in Biological Systems.

Peroxynitrite (ONOO- ) as a major reactive oxygen species plays important roles in cellular signal transduction and homeostatic regulation. Precise detection of ONOO- in biological systems is vital for exploring its physiological and pathological function. Among numerous detection methods, fluorescence imaging technology using fluorescent probes offers some advantages, including simple operation, high sensitivity and selectivity, as well as real-time and nondestructive detection. In particular, ratiometric fluorescent probes, in which the built-in calibration of the two emission bands prevents interference from the biological environment, have been extensively employed to monitor the fluctuation of bioactive species. In this review, we will discuss small-molecule ratiometric fluorescent probes for ONOO- in live cells or in vivo, which involves chemical structures, response mechanisms, and biological applications. Moreover, the challenges and future prospects of ONOO- -responsive ratiometric fluorescent probe are also proposed.

Recent progress in small-molecule fluorescent probes for endoplasmic reticulum imaging in biological systems.

Endoplasmic reticulum (ER) is an indispensable organelle in eukaryotic cells involved in protein synthesis and processing, as well as calcium storage and release. Therefore, maintaining the quality of ER is of great importance for cellular homeostasis. Aberrant fluctuations of bioactive species in the ER will result in homeostasis disequilibrium and further cause ER stress, which has evolved to contribute to the pathogenesis of various diseases. Therefore, the real-time monitoring of various bioactive species in the ER is of high priority to ascertain the mysterious roles of ER, which will contribute to unveiling the corresponding mechanism of organism disturbances. Recently, fluorescence imaging has emerged as a robust technique for the direct visualization of molecular events due to its outstanding sensitivity, high temporal-spatial resolution and noninvasive nature. In this review, we comprehensively summarize the recent progress in design strategies, bioimaging applications, potential directions and challenges of ER-targetable small-molecular fluorescent probes.

Oxidation of Hypophosphorous Acid by a Ruthenium(VI) Nitrido Complex in Aqueous Acidic Solution. Evidence for a Proton-Coupled N-Atom Transfer Mechanism.

The oxidation of hypophosphorous acid (H3PO2) by a ruthenium(VI) nitrido complex, [(L)RuVI(N)(OH2)]+ (RuVIN; L = N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion), has been studied in aqueous acidic solutions at pH 0-2.50. The reaction has the following stoichiometry: 2[(L)RuVI(N)(OH2)]+ + 3H3PO2 + H2O → 2[(L)RuIII(NH2P(OH)2)(OH2)]+ + H3PO3. The pseudo-first-order rate constant, kobs, depends linearly on [H3PO2], and the second-order rate constant k2 depends on [H+] according to the relationship k2 = k[H+]/([H+] + Ka), where k is the rate constant for the oxidation of H3PO2 molecule and Ka is the dissociation constant of H3PO2. At 298.0 K and I = 1.0 M, k = (2.04 ± 0.19) × 10-2 M-1 s-1 and Ka = (6.38 ± 0.63) × 10-2 M. A kinetic isotope effect (KIE) of 2.9 ± 0.1 was obtained when kinetic studies were carried out with D3PO2 at pH 1.16, suggesting P-H bond cleavage in the rate-determining step. On the other hand, when the kinetics were determined in D2O, an inverse KIE of 0.21 ± 0.03 (H3PO2 in H2O vs H3PO2 in D2O) was found. On the basis of experimental results and DFT calculations, the proposed mechanism involves an acid-catalyzed tautomerization of H2P(O)(OH) to HP(OH)2; the latter molecule is the reacting species which reacts with RuVIN via a proton-coupled N-atom transfer pathway.

Mechanistic Study on Palladium-Catalyzed Regioselective Oxidative Amination: Roles of Ammonium Salts.

Anti-Markovnikov selective oxidative amination reaction with simple alkenes is particularly promising but challenging because of the inherent electronic effect of the alkene substrate which is in favor of the Markovnikov product. In a recently reported Pd-catalyzed anti-Markovnikov oxidative amination reaction, the addition of quaternary ammonium salts is shown to be critical. We performed a comprehensive DFT study to elucidate the reaction mechanism and the origin of the regioselectivity, as well as the roles of the ammonium salts. Our results show that without and with the ammonium salts the reaction mechanisms are different. Detailed analyses indicate that the steric effects account for the switch of regioselectivity. The roles of the quaternary ammonium salts have been elucidated: (1) Me4NOAc plays the role of base in deprotonating the phthalimide and allows the reaction to proceed through a trans-aminopalladation mechanism; (2) Me4NCl facilitates the thermodynamically favorable transformation of Pd(OAc)2 to the palladate ([Pd(AcO)2Cl2]2-), which lessens the polarity of the carbon-carbon double bond, minimizes the inherent electronic effects, and leads to a steric-effect-controlled reaction; (3) Me4NCl is essential in decreasing the activation barrier in the rate-determining ligand exchange step by Cl- acting as a better leaving group (compared to AcO-).

The photophysical properties and imaging application of a new polarity-sensitive fluorescent probe.

A new excited-state intramolecular proton transfer (ESIPT) based and polarity-sensitive fluorescent probe M-HA was easily developed by conjugated connection of indole and 2'-hydroxyacetophenone through (E)-2-chloro-3-(hydroxymethylene)cyclohex-1-enecarbaldehyde. M-HA shows near-infrared fluorescence, high molar absorption coefficient and a large Stokes shift in various common solvents. In particular, M-HA exhibits red-shifted maximum emission wavelength, and extraordinarily high fluorescence intensity and quantum yield in high-polarity solvents. The theoretical calculation results indicate that the reduced electron-vibration coupling related to out-of-plane motions of benzene units in more polar solvents is mainly responsible for such unusual photophysical properties. For further application, M-HA was utilized to image live cells. The confocal fluorescence imaging results demonstrate that M-HA possesses excellent membrane permeability and can fluoresce brightly in the cytoplasm. Overall, M-HA, as a polarity-sensitive fluorescent probe, will serve as an excellent tool for quantitative determination of polarity in vitro and in-depth study of the polarity biology in physiopathology in future.

Monitoring mitochondrial pH with a hemicyanine-based ratiometric fluorescent probe.

Mitochondria as essential organelles play critical roles in cellular metabolism. Mitochondrial pH is a vital parameter that directly affects the unique function of mitochondria. Herein, we present a new ratiometric fluorescent probe M-pH for monitoring the pH within the mitochondria. M-pH consists of a stable and large π-electron conjugated merocyanine system. The lipophilic cationic benzyl group will facilitate the accumulation of M-pH in mitochondria. The phenol unit is the recognition moiety, achieving the ratiometric sensing of pH changes. The experimental results indicate that M-pH displays ratiometric fluorescence response to different pH values. Meanwhile, M-pH shows negligible response to common species, and has high stability and low cytotoxicity. In biological experiments, M-pH can solely accumulate in mitochondria and visualize the pH changes during mitophagy and cell apoptosis. We thus believe that M-pH has great potential as a practical tool for real-time monitoring of pH changes of mitochondria, contributing to revealing the pathogenesis of mitochondrial pH associated diseases.

Optical properties of semiconducting zigzag carbon nanotubes with and without defects.

The excited states of a series of semiconducting zigzag (n, 0) tubes are studied using the GW method and the Bethe-Salpeter equation within the ab initio many-body perturbation theory. The optical variation rule of the excitation energy with the tube diameter exhibits a family pattern, which arises from the electronic structure of the pristine tube and depends on the value of n mod 3. The introduction of single vacancy and Stone-Wales defects with different orientations affords an effective route for modulating the band structures and optical spectra, resulting in the variation of the selection rules of the excitons and turning dipole-forbidden excitons into dipole-allowed ones. The new localized impurity states in defected tubes will provide additional optically allowed transitions and give rise to pronounced satellite red-shifted peaks. These findings provide inspiration for the tune of optical properties of carbon nanotubes in the future for applications in optoelectronics.

Three Dimensional Nitrogen-Doped and Nitrogen, Sulfur-Codoped Graphene Hydrogels for Electrode Materials in Supercapacitors.

In present work, reduced graphene oxide hydrogels (RGOHs) with three-dimensional (3D) porous structure are prepared through chemical reduction method by using aminourea (NRGOHs) and aminothiourea (NSRGOHs) as reductants. The as-prepared RGOHs are considered not only as promising electrode materials for supercapacitors, but also the doping of nitrogen (aminourea, NRGOHs) or nitrogen/sulfur (aminothiourea, NSRGOHs) can improve electrochemical performance through faradaic pseudocapacitance. The optimized samples have been prepared by controlling the mass ratios of graphene oxide (GO) to aminourea or aminothiourea to be 1:1, 1:2 and 1:5, respectively. With adding different amounts of aminourea or aminothiourea, the obtained RGOHs exhibited different electrochemical performance in supercapacitors. With increasing the dosage of the reductants, the RGOHs revealed better specific capacitances. Moreover, NSRGOHs with nitrogen, sulfur-codoping exhibited better capacitance performance than that of NRGOHs with only nitrogen-doping. NSRGOHs showed excellent capacitive performance with a very high specific capacitance up to 232.2, 323.3 and 345.6 F g-1 at 0.2 A g-1, while NRGOHs showed capacitive performance with specific capacitance up to 220.6, 306.5 and 332.7 F g-1 at 0.2 A g-1. This provides a strategy to improve the capacitive properties of RGOHs significantly by controlling different doping the materials.

Three-Dimensional Reduced Graphene Hydrogels Using Various Carbohydrates for High Performance Supercapacitors.

In present work, three-dimensional (3D) reduced graphene hydrogels (RGHs) are prepared through an efficient and facile strategy by employing three types of carbohydrates (glucose, fructose and sucrose) as reducing agents in aqueous solution of graphene oxide (GO) with ammonia. The formation of RGHs could be confirmed by X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The structures and porosity were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and N2 sorption experiments. Benefiting from the abundant porous architectures as fast ionic channels for electrochemical energy storage, the prepared RGHs exhibited a high specific capacitance up to 153.5, 145.0 and 150.3 F g−1 at 0.3 A g−1 for FRGHs (fructose), GRGHs (glucose) and SRGHs (sucrose), which can be maintained for 61.4, 61.5 and 46.9% as the discharging current density was increased up to 20 A g−1. Moreover, it also showed that the electrode based on RGHs has good electrochemical stability and high degree of reversibility in the charge/discharge cycling test.

Hierarchical micro/nano-structured cobalt sulfide spindles as low-cost counter electrodes for dye-sensitized solar cells.

Hierarchical micro/nano-structured cobalt sulfide spindles are synthesized via a hydrothermal method and investigated as counter electrodes for dye-sensitized solar cells (DSCs). It is demonstrated that DSCs with hierarchical cobalt sulfide spindle electrodes show an excellent photovoltaic performance competing with that of a device with a Pt counter electrode.

Critical role of small micropores in high CO2 uptake.

Microporous carbon materials with extremely small pore size are prepared by employing polyaniline as a carbon precursor and KOH as an activating agent. CO(2) sorption performance of the materials is systematically investigated at the temperatures of 0, 25 and 75 °C. The prepared carbons show very high CO(2) uptake of up to 1.86 and 1.39 mmol g(-1) under 1 bar, 75 °C and 0.15 bar, 25 °C, respectively. These values are amongst the highest CO(2) capture amounts of the known carbon materials. The relation between CO(2) uptake and pore size at different temperatures is studied. An interesting and innovative point that the micropores with pore size smaller than a critical value play a crucial role in CO(2) adsorption at different temperatures is demonstrated. It is found that the higher the sorption temperature is, the smaller this critical value of pore size is. Pores smaller than 0.54 nm are manifested to determine CO(2) capture capacity at high sorption temperature, e.g. 75 °C. This research proposes a basic principle for designing highly efficient CO(2) carbon adsorbents; that is, the adsorbents should be primarily rich in extremely small micropores.

Cation Vacancies in Feroxyhyte Nanosheets toward Fast Kinetics in Lithium-Sulfur Batteries.

Lithium-sulfur batteries have attracted extensive attention owing to their environmental friendliness, abundant reserves, high specific discharge capacity, and energy density. The shuttling effect and sluggish redox reactions confine the practical application of Li-S batteries. Exploring the new catalyst activation principle plays a key role in restraining polysulfide shuttling and improving conversion kinetics. In this respect, vacancy defects have been demonstrated to enhance the polysulfide adsorption and catalytic ability. However, inducing active defects has been mostly created by anion vacancies. In this work, an advanced polysulfide immobilizer and catalytic accelerator is developed by proposing FeOOH nanosheets with rich Fe vacancies (FeVs). The work provides a new strategy for the rational design and facile fabrication of cation vacancies to improve the performance of Li-S batteries.

Green Catalytic Method for Hydrothiolation of Allylamines: An External Electric Field.

Based on the idea of environmental friendliness, we first studied the hydrothiolation reactions of thiophenol with allylamine using a green catalyst-an external electric field (EEF). The hydrothiolation reactions could occur through Markovnikov addition (path M) and anti-Markovnikov addition (path AM) pathways. The calculation results demonstrated that when the EEF was oriented along F -X , F -Y , and F +Z directions, path M was accelerated. However, it is favorable for path AM only when the EEF is oriented along the +X and -Y-axes. In addition, the introduction of the EEF further increased and lowered the differences of the reaction barrier as the EEF was oriented along F -X , F -Y , and F +X directions. The solvent effects were also considered in this work. Hopefully, this unprecedented and green catalytic method for the hydrothiolation reactions of allylamine may provide guidance in the lab.

Carbon and phosphorus co-doped carbon nitride hollow tube for improved photocatalytic hydrogen evolution.

Graphitic carbon nitride, regarded as a charming conjugated polymer, has been a visible light photocatalyst. Bulk carbon nitride endures the limited light absorption ability, few surface active sites and slow separation of photoinduced charge carriers, leading to the poor catalytic activity. Herein, a new carbon (C) and phosphorus (P) co-doped carbon nitride hollow tube with adjustable optical property (CPCN) was developed by applying melamine and polyacrylic amide as the precursors and phosphoric acid as the P source via a hydrothermal-thermal copolymerization way. The effects of polyacrylic amide content on the morphology and photocatalytic performance were intensively investigated. The special hollow tube favors the improvement of active sites and visible light harvesting ability. Meantime, C and P co-doping results in the narrow band gap and rapid charge transfer, thus enabling an enhanced catalytic activity under visible light irradiation. Particularly, CPCN-50 exhibits a remarkable H2 generation rate of 4485.7 µmol h-1 g-1 under λ > 400 nm, which is higher than pure carbon nitride CN (902.3 µmol h-1 g-1), C doped sample CCN-50 (3741.1 µmol h-1 g-1) and P doped sample CNP (2280.0 µmol h-1 g-1). It implies that C, P co-doping exhibits a synergistic effect on boosting photoinduced charge transfer and hindering the recombination. Moreover, CPCN-50 illustrates a higher H2 generation rate (3024.5 µmol h-1 g-1) than CN (400.8 µmol h-1 g-1) under λ > 420 nm irradiation. This way developed in this work might exhibit utility for synthesizing highly effective photocatalysts for the CO2 reduction, H2 evolution and so on.

Experimental and theoretical study of ZrMo-KIT-6 solid acid catalyst with abundant Brønsted acid sites.

Given their excellent reusability and environmental friendliness, solid acid catalysts have drawn considerable attention in acid-catalyzed reactions. However, the rational design and synthesis of solid acid catalysts with abundant Brønsted acid sites remains a challenge. In this paper, KIT-6, Zr-KIT-6, Mo-KIT-6, and ZrMo-KIT-6 solid acid catalysts are designed and synthesized. The textural properties, chemical bonds, and acidic properties of these catalysts are explored. Theoretical calculations are conducted to explore the formation mechanism of Brønsted acid sites. The theoretical trend of acidity is consistent with the experimental result of acidity and further demonstrates that the synergistic effect of Zr and Mo species improves the formation of Brønsted acid sites. The as-obtained ZrMo-KIT-6 solid acid catalysts are employed in Friedel-Crafts benzylation reaction, and the outstanding catalytic performance of the ZrMo-KIT-6 catalyst indicates that it is an excellent Brønsted solid acid catalyst.

Study and Comparison on Purification Methods of Multicolor Emission Carbon Dots.

Recent years have witnessed a rapid development of carbon dots (CDs), due to their outstanding luminescence properties and excellent biocompatibility. However, the internal structure and photoluminescent (PL) mechanism of CDs are still the subject of considerable debate, which is due to the fact that reaction products usually contain mixtures of several CD fractions as well as molecular intermediate and side products. Therefore, careful purification of the CDs is significant for analysis of structure and luminescence mechanism. Here, multicolor emission CDs were prepared by a one-pot pyrolysis of citric acid in formamide. Then, the precipitation method, dialysis and gel permeation chromatography (GPC) are successively employed to purify the multicolor emission CDs. This post-treatment allowed us to compare the optical properties of CDs obtained by different separation methods and provide a valuable guidance for the purification of CDs.

External electric field: a new catalytic strategy for the anti-Markovnikov hydrohydrazination of parent hydrazine.

The anti-Markovnikov hydroamination reaction is considered to be a particular challenge, and one of the reactants, parent hydrazine, is also regarded as a troubling reagent. In this study, we first studied the hydrohydrazination of parent hydrazine via an effective and green catalyst-external electric field (EEF). The calculation results demonstrated that the anti-Markovnikov and Markovnikov pathways are competitive when there was no catalyst. EEF oriented along the negative direction of the X axis (F x ) accelerated the anti-Markovnikov addition reaction. Moreover, it lowered the barrier height of the first step by 16.0 kcal mol-1 (from 27.8 to 11.8 kcal mol-1) when the field strength was 180 (×10-4) au. Under the same conditions, the Markovnikov reaction pathway was inhibited, which means that EEF achieved the specificity of hydrohydrazination. The solvents are favorable for the first step addition reaction, particularly the synergy between solvents and F x lowered the barrier heights by 8.3 (C6H6) and 10.7 (DMSO) kcal mol-1 for an F x = -60 (×10-4) au. Besides, the introduction of the electron-withdrawing substituent (trifluoromethyl) is also a good strategy to catalyze hydrohydrazination, while the electron-donating group (methoxy) is unfavorable.