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.

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.

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.

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.

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.

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.

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.

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.

Enhanced Energy Density for P-Doped Hierarchically Porous Carbon-Based Symmetric Supercapacitor with High Operation Potential in Aqueous H2SO4 Electrolyte.

Phosphorus-doped hierarchically porous carbon (HPC) is prepared with the assistance of freeze-drying using colloid silica and phytic acid dipotassium salt as a hard template and phosphorus source, respectively. Intensive material characterizations show that the freeze-drying process can effectively promote the porosity of HPC. The specific surface area and P content for HPC can reach up to 892 m2 g-1 and 2.78 at%, respectively. Electrochemical measurements in aqueous KOH and H2SO4 electrolytes reveal that K+ of a smaller size can more easily penetrate the inner pores compared with SO42-, while the developed microporosity in HPC is conducive to the penetration of SO42-. Moreover, P-doping leads to a high operation potential of 1.5 V for an HPC-based symmetric supercapacitor, resulting in an enhanced energy density of 16.4 Wh kg-1. Our work provides a feasible strategy to prepare P-doped HPC with a low dosage of phosphorus source and a guide to construct a pore structure suitable for aqueous H2SO4 electrolyte.

Functional thiophene-diketopyrrolopyrrole-based polymer derivatives as organic anode materials for lithium-ion batteries.

In this study, four thiophene-diketopyrrolopyrrole-based (TDPP-based) polymer derivatives modified by different groups and alkyl chains were synthesized. The effects of various functional groups on the electrochemical properties of the polymers for application in lithium-ion batteries were compared, where the carbazole (C) and tert-butyl acetate (TA) groups improved the capacity performance of the polymer electrodes, while hexane (H) and fluorene (F) groups enhanced the cycle stability of the polymer electrodes. The P(C-TDPP-TA) polymer electrode, i.e., the TDPP-based polymer composed of carbazole and tert-butyl acetate groups, exhibited the best capacity performance among the four polymer electrodes, where its discharge specific capacity and capacity retention were up to 357 mA h g-1 and 82% and its energy density and power density were 213 W h kg-1 and 149 W kg-1 at 100 mA g-1 after 500 cycles, respectively. The P(F-TDPP-H) polymer electrode, i.e., the TDPP-based polymer composed of fluorene and hexane groups, possessed the best cycle stability and conductivity, where its capacity retention was up to 92% at 100 mA g-1 for 500 cycles and its electronic conductivity and ionic conductivity were 4.80 × 10-3 and 6.68 × 10-3 S m-1, respectively. For application in lithium-ion batteries, the P(C-TDPP-TA) electrode exhibited the best comprehensive performance. When the current density reached up to 1000 mA g-1, after 1000 cycles, the P(C-TDPP-TA) electrode still exhibited a high discharge specific capacity (203.6 mA h g-1) and excellent capacity retention (88.8%), and its energy density and power density were 116 W h kg-1 and 376 W kg-1 (1000 mA g-1, after 1000 cycles), respectively. Therefore, the P(C-TDPP-TA) electrode has potential as a promising anode material for lithium-ion batteries.

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.

Three-dimensional thiophene-diketopyrrolopyrrole-based molecules/graphene aerogel as high-performance anode material for lithium-ion batteries.

Herein, 3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (TDPP) and di-tert-butyl 2,2'-(1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)diacetate (TDPPA) were synthesized, which were then loaded in graphene aerogels. The as-prepared thiophene-diketopyrrolopyrrole-based molecules/reduced graphene oxide composites for lithium-ion battery (LIB) anode composites consist of DPPs nanorods on a graphene network. In relation to the DPPs part, embedding DPPs nanorods into graphene aerogels can effectively reduce the dissolution of DPPs in the electrolyte. It can serve to prevent electrode rupture and improve electron transport and lithium-ion diffusion rate, by partially connecting DPPs nanorods through graphene. The composite not only has a high reversible capacity, but also shows excellent cycling stability and performance, due to the densely distributed graphene nanosheets forming a three-dimensional conductive network. The TDPP60 electrode exhibits high reversible capacity and excellent performance, showing an initial discharge capacity of 835 mA h g-1 at a current density of 100 mA g-1. Even at a current density of 1000 mA g-1, after 500 cycles, it still demonstrates a discharge capacity of 303 mA h g-1 with a capacity retention of 80.7%.

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.

Nickel-Embedded Carbon Materials Derived from Wheat Flour for Li-Ion Storage.

The biomass-based carbons anode materials have drawn significant attention because of admirable electrochemical performance on account of their nontoxicity and abundance resources. Herein, a novel type of nickel-embedded carbon material (nickel@carbon) is prepared by carbonizing the dough which is synthesized by mixing wheat flour and nickel nitrate as anode material in lithium-ion batteries. In the course of the carbonization process, the wheat flour is employed as a carbon precursor, while the nickel nitrate is introduced as both a graphitization catalyst and a pore-forming agent. The in situ formed Ni nanoparticles play a crucial role in catalyzing graphitization and regulating the carbon nanocrystalline structure. Mainly owing to the graphite-like carbon microcrystalline structure and the microporosity structure, the NC-600 sample exhibits a favorable reversible capacity (700.8 mAh g-1 at 0.1 A g-1 after 200 cycles), good rate performance (51.3 mAh g-1 at 20 A g-1), and long-cycling durability (257.25 mAh g-1 at 1 A g-1 after 800 cycles). Hence, this work proposes a promising inexpensive and highly sustainable biomass-based carbon anode material with superior electrochemical properties in LIBs.

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.

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-).

Two-photon fluorescence visualization of lysosomal pH changes during mitophagy and cell apoptosis.

We herein develop a novel two-photon fluorescent probe termed L-pH for visualization of lysosomal pH within live cells. L-pH is composed of three moieties, including naphthalimide fluorophore as a fluorescence off-on response moiety, piperazine and morpholine groups as lysosomal targeting and pH responsive sites, as well as a reactive benzyl chloride segment for further lysosomal anchoring. The experimental results demonstrate that L-pH can instantaneously respond to various pH values with high sensitivity and selectivity, and has low cytotoxicity and excellent photostability. The one-photon and two-photon fluorescence imaging data indicate L-pH can preferably accumulate into lysosome and monitor the rise of lysosomal pH changes during myriad cell stress conditions, including heat shock, cell apoptosis and mitophagy. Moreover, L-pH was applied for imaging of pH difference in abdominal tissues of mice. L-pH will be a potential tool for monitoring lysosomal pH variation during lysosome-associated physiological and pathological states.