Aqueous zinc ion batteries possess the characteristics of cost-effectiveness, environmental benignancy, intrinsic safety, and relatively high energy density, and are promising to be used in large-scale electrochemical energy storage devices. However, the current commercial zinc foil anode is considerably excessive compared with cathode active materials, which significantly decreases the energy density of the battery. And there are serious problems of anode perforation, tab falling off and so on. Loading zinc on current collector as anode is effective to improve depth of discharge and avoid the electrode perforation. Nevertheless, the zinc dendrites and side reactions are prone to generate at the current collector interface, and they seriously affect the cycle life of the battery. In this review, the causes of zinc dendrites and side reactions and their influence on the electrochemical performance of zinc anode are analyzed, and the design ideas of the zinc anode current collectors are summarized from two aspects of composition selection and structure construction, including the selection of zincophilic materials, the design of preferred-orientation substrates and the construction of three-dimensional current collector structures. Designing an appropriate current collector can effectively regulate the plating and stripping behavior of zinc metal and promote the practical application of aqueous zinc ion batteries.

Thioesters play a very important role in biosynthesis and organic synthesis. Due to smaller orbital overlap of the C(2p) and S(3p) orbitals, the α-proton acidity of thioesters is higher than that of the related oxoesters, making thioesters useful enolate precursors in nature as well as in the laboratory. Meanwhile, thioesters are also efficient acylation reagents which can be used for the construction of ester bond and amide bond. Organocatalysis, a biomimetic catalysis usually with metal- free small organic molecules, is an emerging research field that has been booming since the beginning of the 21st century. In the past decade, many important achievements have been made in the organocatalytic asymmetric reactions involving thioester substrates, which have greatly broadened the reaction types of organocatalytic reactions with ester substrates and realized some reactions that cannot be achieved by using their oxoester analogues. The advances in organocatalytic asymmetric reactions involving thioesters are summarized in this review. According to the types of thioester substrates, these advances are classified to two types. One type is the organocatalytic asymmetric reactions with enolizable thioesters such as trifluoroethyl thioesters, malonic acid half-thioesters (MAHTs), monothiomalonates (MTMs) and dithiomalonates (DTMs). For these reactions, noncovalent interactions between catalysts and thioesters, including hydrogen bonding and ion pair interaction, have been used to promote the reaction and to achieve the high enantioselectivity. Another type is the catalytic asymmetric reactions with α,β-unsaturated thioesters. For the reaction of this type, various chiral organocatalysts, including chiral amines, ureas, NHC (N-heterocyclic carbene), isothiourea, amidine and others, not only activate the thioester substrates, but also control the enantioselectivity well through covalent and non-covalent bonds. Meanwhile, the mechanism of representative transformations will be briefly introduced and at last, the perspective in this area will be given.

The emerging metal-organic framework (MOF) glass, that is brand-new comer to the traditional glass and noncrystalline physics world, was viewed as the Holy Grail of future porous chemistry and the key direction of MOF derived functional materials. The known examples of MOF glass are extremely scarce, prepared mainly through the traditional melt-quenching method. As porous framework constructed from metal ions/clusters and organic linkers through coordinative bonds, the majority of MOFs can not reach high-temperature melt state, which prevents MOF glass formation. Facing these challenges, here we summarized the development history and latest advance of MOF glass. A new strategy of sequential perturbation based on dynamic chemistry was presented to widely prepare MOF glass. How to discover more MOF glasses, expand their properties and functions, and clarify their nature, is the new interdisciplinary frontier from dynamic chemistry to material science and noncrystalline physics. This topic also provides a range of new research opportunities, including the design and regulation of MOF glass based on reticular and dynamic chemistry, exploring new functions of MOF glass beyond its crystalline counterpart, and effectively responding to the scientific challenges in noncrystalline physics including the glass nature, based on the solid-solid structure transformation and relevance between crystalline and glassy MOFs.

In recent years, the multiple resonance thermally activated delayed fluorescence (MR-TADF) has become a hot topic due to the high fluorescence quantum yield and small Stokes shift. In traditional TADF molecules, the lowest triplet excited state (T₁) can convert into the lowest singlet excited state (S₁) through the reverse intersystem crossing (RISC), and then return to the ground state (S₀) by the radiative fluorescence emission. However, recent studies found that in MR-TADF molecules, the higher triplet excited state (T₂) might play an important role. Thus, the detailed mechanism for the luminescence in MR-TADF molecules, especially for the effect of higher triplet excited state, has still been an indefinite problem. In this work, the luminescence mechanism of four newly reported MR-TADF molecules (BCz-BN, 2PTZ-BN, CZ-PTZ-BN and 2Cz-PTZ-BN) which are substituted by tert-butyl-carbazole and phenothiazine groups has been systematically investigated by the first-principle calculation and kinetic time evolution. The results showed that the phenothiazine group can significantly increase the spin-orbit coupling (SOC) and increase the fluorescence quantum yield. More importantly, by computing the rate constants for the TADF process, we found that the internal conversion (IC) rate between two triplet excited states (T₁ and T₂) is much faster than the radiative and non-radiative rates, and meanwhile the rate of the reverse intersystem crossing of T₂→S₁ is also faster than the one of T₁→S₁. Therefore, the TADF process of the above molecules should follow the T₁→T₂→S₁→S₀ process. The above findings were also confirmed by the further kinetic time evolution. In the early stage, the system was mainly dominated by the internal conversion between T₁ and T₂. With the time evolution, the energy gradually transferred from T₂ to S₁, and finally emitted fluorescence on S₁. However, if T₂ is not involved in the time evolution, the TADF process will be significantly slowed down, which could further confirm the importance of T₂ in the TADF process. This work reveals the nature of the TADF process which could be of great importance for designing and synthesizing new TADF molecules.

The new material industry is the foundation of technological change in many related fields, and also the forerunner of the development of new energy, aerospace, electronic information and other high-tech industries. Traditional means cannot meet the development needs of modern society because of disadvantages such as high cost, low efficiency and long commercial cycle. In recent years, with the application of big data combined with artificial intelligence in a deeper degree, data-driven machine learning has made great progress in the design, screening and performance prediction of new materials, which has greatly promoted the development and application of new materials. In this review, the basic process of machine learning, the algorithms commonly used in materials science and the relevant materials database are summarized. This review focuses on the application of machine learning in different functions, as well as the performance prediction in the fields of catalyst materials, lithium-ion batteries, semiconductor materials and alloy materials, presenting the latest progress in materials development. Finally, machine learning in the application of new materials are analyzed and prospected.

Holographic optical waveguide is the most practical waveguide coupling technology for head-mounted augmented reality displays (HMD-AR) due to its advantages of small size, lightweight, clear imaging, flexible design, and a large eye-movement range for users. To enhance the imaging capability of the HMD-AR system and expand its field of view, the volume holographic gratings (VHG) used as the coupling-in and coupling-out elements must have a high refractive index modulation (Δn). Photopolymer is one of the most promising recording media for manufacturing high-performance transparent VHG. The working principle of holographic optical waveguide in HMD-AR and the preparation principle of photopolymer VHG are introduced, the recent research progress of photopolymers in this field is reviewed, the influence of different components in photopolymer formulations and the post-treatment methods of the recording media on their holographic optical properties are summarized, mainly including: (1) the composition of the photoinitiator systems; (2) the crosslink density, molecular weight and refractive index of the film-forming resins; (3) the refractive index, addition and size of the writing monomers; (4) the additive of nanoparticles, chain transfer agents, free radical scavengers and plasticisers; (5) post-treatment methods such as heating and/or light. It is expected to provide guidance for designing new components, developing recording media with higher Δn, and fabricating HMD-AR with better performance.

With the appearance of second harmonic generation (SHG) and two-photon absorption (TPA), organic nonlinear optical (NLO) materials have played an increasingly important role in laser frequency conversion, biological imaging, micro- nano processing, optical limiting, terahertz wave (THz) and other fields in the past decades, arousing widespread interest. So far, most of the organic nonlinear optical active materials reported are single component which chemical synthesis is cumbersome, experimental conditions are rigorous and it is difficult to break the limit of the inherent properties of the single component. While organic composite material can rapidly broaden the variety of materials through simple forms such as blending, doping and cocrystallization, organic cocrystals based on intermolecular non-covalent interactions through more than one molecule have been developed to a large extent towards tuning and modifying the physicochemical properties of molecular solids. However, there is no systematic introduction of organic cocrystals in nonlinear optics at home and abroad. Firstly, the second-order and third-order nonlinear optical performance parameters and their testing methods are introduced; then, the latest research progress of molecular cocrystals materials in this field is introduced, including the types of materials, preparation methods, and the mechanism of optical nonlinearity effect; next, the possible applications of cocrystals nonlinear optical materials are discussed. Finally, some prospects for the development of this field are provided, and it is believed that this review can provide some reference for researchers in the field of organic cocrystals and nonlinear optics.

Since the outbreak of COVID-19, it is becoming important to screen SARS-CoV-2 with high accuracy, high efficiency, and rapidness, for epidemic prevention and control. Conventional detection technologies can not satisfy the requirements of examining massive people in a very short time. Biosensor technology, with the advantages of high sensitivity, good selectivity, low cost, easy miniaturization, and short detection time, is being used to develop real-time detection equipment, thus as a potential alternative for real-time detection of SARS-CoV-2 in clinical diagnosis. In the present study, the authors summarized the construction methods and principles for optical biosensors, electrochemical biosensors, wearable biosensors, magnetic biosensors, gold nanoparticle biosensors, and aptamer biosensors, followed by the introduction of the current application of multiple biosensors in SARS-CoV-2 detection. Conclusively, the technical bottlenecks and future development trends of biosensors in SARS-CoV-2 detection are proposed.

Unnatural α-amino acid derivatives are greatly important in pharmaceuticals and biochemicals owing to their diverse biological activities, and usually serve as versatile building blocks in organic synthesis as well. A variety of approaches have been developed to prepare α-amino acid derivatives, among which N—H insertion reactions of diazo compounds are considered to be one of the most direct methods. These N—H insertion reactions typically proceed through carbene active intermediates that derived from diazo compounds by UV-induction or metal catalysis. As a green and powerful avenue to organic synthesis, visible-light-mediated methodology has also been applied to N—H insertion of diazo compounds principally through carbene intermediates. Due to the single reaction mechanism of these reactions, however, the scope of diazo compounds were limited to α-aryl diazoacetates that can directly absorb the visible-light. Therefore, exploring new activation modes is conducive to expanding the applicable scope and reaction type of diazo compounds in visible- light-mediated reactions. Herein we report visible-light-promoted N-alkylation reactions of (aza)aromatic amines with ethyl diazoacetate based on the mechanism of proton-coupled electron transfer (PCET). A series of α-amino acid derivatives were synthesized by the combination of photocatalyst and Lewis-acid catalyst. This method featured in mild reaction conditions, good functional group tolerance and wide range of substrate scope. Mechanism experiments indicated the reaction involved in radical intermediate rather than carbene that engaged in conventional N—H insertion reactions. According to the fluorescence quenching experiment, the alkyl radical intermediate was formed by the PCET step between ethyl diazoacetate and excited photocatalyst. And then radicals cross-coupling occurred under the coordination of Lewis-acid to produce the final N-alkylation products. This new catalytic strategy expands the applications of diazo compounds in visible-light chemical reactions. The general procedure for the visible-light-promoted N-alkylation reactions of (aza)aromatic amines with ethyl diazoacetate is as following: Aniline 1a (0.1 mmol), ethyl diazoacetate 2 (0.2 mmol), Fe(OTf)₂ (0.02 mmol) and photocatalyst [Ir(ppy)₂(NCMe)₂]PF₆ (0.005 mmol) were dissolved in MeOH (2 mL). Then the mixture was degassed via a “freeze-pump-thaw” procedure (3 times). After that, the resulting mixture was stirred under irradiation of 30 W blue LEDs at room temperature. Upon reaction completion, the crude product was purified by flash chromatograph on silica gel to give the final product.

Titanium-based metal organic frameworks (Ti-MOFs) have become a hot topic in current materials research due to their excellent photocatalytic activity. However, due to the extremely high reactivity and oxygenophilic properties of Ti ions, oxides and other competing by-products are easily formed during the reaction process, making the synthesis of Ti-MOFs extremely challenging. The research on Ti-MOFs was carried out simultaneously at the early stage of MOFs development, however, after more than two decades of development, only tens of Ti-MOFs have been reported, accounting for an extremely limited proportion of the tens of thousands of MOFs. In order to avoid or reduce the occurrence of titanium ion side reactions, Ti-MOFs are usually synthesized by introducing metal Ti ions into the framework of known MOFs to orientate the synthesis of Ti-MOFs, which is called post-synthetic method (PSM) and is also an effective method to construct Ti-MOF framework. The examples of PSM for constructing Ti-MOFs are systematically investigated and summarized in a timely manner. Firstly, based on the different ways and positions of titanium ion introduction, three routes are classified as ion exchange, ion insertion (introduction of titanium ion at the position of metal nodes or cluster units) and ligand modification (introduction of titanium ion at the position of organic ligands), and the Ti-MOFs constructed by each route are introduced by examples. Subsequently, the design and application of Ti-MOFs constructed by PSM and their composites are discussed. Finally, the current status of PSM-constructed Ti-MOFs is summarized and the future development direction is foreseen.

Dye wastewater with high toxicity and poor biodegradability poses a considerable threat to human health and the ecosystem. Although the adsorption effectively removes organic pollutants from wastewater, the pollutants are merely transferred from liquid phase to solid adsorbents. Destroying the adsorbed pollutants and regenerating adsorbents require additional treatments, which may cause secondary harm to the environment. In addition to the removal of organic pollutants by adsorption, the pollutants can be oxidatively degraded by oxidative radicals that are generated in peroxymonosulfate (PMS)-based advanced oxidation technology. However, the degradation efficiency of organic pollutants treated by advanced oxidation technology may be affected by complex components of dye wastewater. Herein, Fe-doped cellulose nanofiber/reduced graphene oxide aerogel (CNFs/RGO/Fe) was prepared and served as both adsorbent and catalyst in advanced oxidation process for dyes wastewater treatment. The morphology and chemical composition of the composite aerogel were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was proved that CNFs/RGO/Fe possessed layered porous structures, which are beneficial for the transport, diffusion, and adsorption of pollutants. The uniform loading of Fe⁰ and Fe₃O₄ particles on the aerogel skeleton contributed to the efficient activation of PMS. The results of the adsorption experiment showed that the CNFs/RGO/Fe exhibited excellent selective adsorption for cationic dyes. The maximum adsorption capacity of methylene blue (MB), rhodamine B (RhB), and crystal violet (CV) on CNFs/RGO/Fe were 655.1 mg/g, 696.5 mg/g, and 962.1 mg/g, respectively. The pseudo-second-order kinetic model and Langmuir isothermal model fitted well with the adsorption process of CNFs/RGO/Fe for cationic dyes. After adsorption, the CNFs/RGO/Fe was immersed in PMS solution separately to study the degradation performance for the adsorbate. The results showed that CNFs/RGO/Fe could promote the activation of PMS to generate a large amount of •OH, leading to the degradation of adsorbate and the regeneration of adsorbent. In addition, the synergistic adsorption-degradation process established by CNFs/RGO/Fe achieved over 75% removal of dyes even after 5 cycles, indicating CNFs/RGO/Fe had good repeatability. The study on the synergistic treatment of dye wastewater by adsorption-degradation is expected to provide a new perspective for the removal of organic pollutants in complex water.

Thioesters with intriguing chemistry and reactivity are widely used in pharmaceuticals, pesticides, perfume & flavors and materials. Thioesters are versatile building blocks in organic synthesis and are also often employed as electrophilic acylating reagents in substitution reactions, such as Corey-Nicolaou macrolactonizations and native chemical ligation for peptide connection. Thioesters can be easily obtained from direct thioesterification of carboxylic acids with various thiol sources. Whereas more efforts have been made to develop new reactions employing thioesters, their application in organic synthesis is rare compared with other carboxylic acid derivatives. Transition-metal-catalyzed C—S bond activation paves a new avenue to exploit thioester. Many new transformations have been developed, including reduction to aldehydes, decarbonylation to thioethers, addition to unsaturated bonds, and cross-coupling of thioesters with organometallic reagents. Compared with other carboxylic acid derivatives, thioesters are stable but reactive and could undergo the oxidative addition of C(O)—S to low-valent transition-metal species, generating the C(O)—M—S. Transition-metal-catalyzed cross-coupling reaction of thioesters have been extensively studied in the last two decades, and providing alternative and efficient ways to construct C—C bonds. Despite the reaction between thioester and selected organometallic reagents to furnish ketones, thioesters could also be employed as decarbonylative coupling electrophiles. The advances in transition-metal-catalyzed cross-coupling reaction of thioesters are summarized in this review, which is presented by the categories of transition metals including Pd, Ni, Cu and Rh. Simultaneously, synthetic applications of transition-metal-catalyzed cross-coupling reaction of thioesters in nature products and pharmaceuticals are discussed. Attention is also paid to the asymmetric cross-coupling reaction of thioesters reported in recent years, the application of cross-coupling reaction of thioesters in tandem reactions and functional group transformations.

Single molecule magnets is a kind of magnetic materials composed of a single molecule. Its magnetism stems from the magnetic moment of a single molecule. It is expected to be applied in ultra-high density storage, quantum computer, spintronics and other fields. Actinide single molecule magnets have attracted more and more attention due to the great spin-orbit coupling effect of actinides and large radial extension of 5f electrons, and demonstrate promise for exceeding the magnetism performance of transition metal and lanthanide complexes. However, the relaxation mechanism of actinide single molecule magnets and the factors of slow magnetic behavior remain unclear. In this review, the reported actinide single molecule magnets in the last ten years are summarized. It is found that the experimental values of blocking barrier are absolutely inconsistent with the theoretical values, which limited the development of actinide single molecule magnets to some extent. Finally, the future research directions of actinide single molecule magnets are prospected.

The synthesis of organosilicon compounds has attracted considerable interest, especially the allyl silanes, which are regarded as ideal building blocks in the synthesis of small molecules and polymers. The traditional synthetic method for allyl silanes relies on the cross-coupling of Grignard reagent and chlorosilane (Silyl-Kumada reaction), transition metal catalyzed silylation of allylic alcohols with disilanes or silylboranes, and regioselective silylation of conjugated alkenes or allenes. Although some other methods were also developed, the using of transition metal catalysts has resulted in disadvantages such as contamination of desired allyl silanes and high production costs. Therefore, a mild and metal-free practical method is highly desired. We herein describe a metal-free difluoroallylation of silanes with α-trifluoromethyl alkenes in the presence of quinuclidine as hydrogen atom transfer (HAT) reagent under the irradiation of 30 W blue light-emitting diode (LED) (460~470 nm) at room temperature. To an oven dried Schlenk-tube, trifluoromethylpropene (0.1 mmol), silane (0.3 mmol), KHCO₃ (0.1 mmol), 4-CzIPN (1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) (0.002 mmol) and MeCN (1 mL) were added under argon atmosphere. The reaction mixture was stirred under the irradiation of 30 W blue LED (460~470 nm) at room temperature. After completion of the reaction, the reaction solution was removed by reduced pressure and the residue was purified by silica gel chromatographic column to obtain gem-difluoroallylation products. A wide range of aromatic and heterocyclic α-trifluoromethyl alkenes were successfully applied in the difluoroallylation of silanes to afford difluoroallylsilanes. And all of the tested silanes, including trimethylsilane, sterically more demanding silanes as well as dimethylphenylsilane all participated in the present transformation readily to afford the corresponding difluoroallylsilanes in excellent yields. The present methodology has provided an efficient and cost-effective gram scale synthetic method for the preparation of difluoroallylsilanes under blue light irradiation in the presence of 4-CzIPN as organic photosensitizer. The scalability in large scale and excellent functional group compatibility of this transformation ensures broad applicability to a variety of difluoroallylsilanes. The proposed reaction mechanism showed that the reaction proceeded through the radical addition of α-trifluoromethyl alkene with silane free radical and subsequent β-fluoride elimination.

As an emerging high-efficiency solar cell, organic solar cells (OSCs) have been developed rapidly in recent years. The power conversion efficiency (PCE) of OSCs has reached more than 19%, which is the dawn of commercial application. However, the stability of OSCs is not yet satisfied, especially high processing and operation temperature may be applied to the cells, which requires a high thermal stability of the cells. The ternary strategy, where a third component is introduced into the photoactive layer of donor-acceptor based binary OSCs, was found to be able to simultaneously improve device performance and stability by regulating the intermolecular interactions, showing a great potential for application. In this review, we firstly summarized the mechanisms involved in the thermal decay process of OSCs, including thermally induced morphology changes of the photoactive layer, interfacial aging/chemical reactions, and interdiffusion behavior between the layers. Following this, the research progress of the ternary strategies in improving thermal stability are highlighted, and the mechanism for the stabilization effect is reviewed. By the end, the perspective of the ternary strategies in OSCs is given, pointing out that the selection of the proper third component and the understanding on the mechanism of the stabilization effect are the key issues and challenges.

Catalysts play a pivotal role in promoting the development of polyolefin industry, especially, the design and synthesis of metal-catalysts is the key to the metal-organic chemistry. Surprisingly, rare-earth metal harness the unique orbital structure, reactivity and coordination criteria, so rare-earth metal complexes have been one of the efficient catalysts and show the special advantages in the preparation of polyolefin materials by introducing steric hindrance around the metal center, notably, their structure, chemical activity and stability are determined by ligands. The development of rare-earth metal catalysts with cyclopentadienyl ligands (alkyl-substituted, aryl-substituted, indenyl and fluorenyl ligands) and non-cyclopentadienyl ligands (macrocyclic tetradentate, tridentate, didentate, mondentate ligands), and their applications in the preparation of polyolefins are described in this review. This work aims to promote the research of rare-earth metal catalysts in the field of polyolefin synthesis and metal-organic catalysis, as well provide new design ideas and research methods for the synthesis of high-quality and functionalized polyolefin catalysts.

Graphene nanoribbons (GNRs) are the ribbons of graphene with a width of nanoscale. According to the different edge configurations, the GNRs can be classified into Zigzag-edge graphene nanoribbons (ZGNRs) and Armchair-edge graphene nanoribbons (AGNRs), strongly affecting electronic structure and properties of GNRs. The triggered quantum confinement and edge effects by rationalizing the structural design can open the bandgap of GNRs. Besides, GNRs have huge length-to-width ratio and proportion of edge atoms, which provide infinite possibilities for realizing functional customization through structure tailoring. These geometric and electronic structural properties make graphene nanoribbons have more application potential than graphene in many fields such as electronic devices. Therefore, the related research of graphene nanoribbons has been a hot spot in the field of nanomaterials. This review introduces the structures and properties of graphene nanoribbons firstly, and then provides a comprehensive picture of the preparation approaches of GNRs, and the corresponding preparation methods can be divided into two parts: (1) Top-down categories: The GNRs are obtained by the etching and cutting of graphene, as well as carbon nanotubes (CNTs), with utilizing the plasma, ion beam, scanning tunneling microscope and metal nanoparticles. However, these methods are still in the stage of laboratory research, and fabrication of high quality GNRs is difficult because of lacking the processing accuracy. (2) Bottom-up categories: The GNRs can be synthesized using carbon containing precursors, e.g. organic compounds, hydrocarbon gas and SiC. The bottom-up method facilitates to prepare several nanometers-width GNRs with a certain degree of controllability, among which ultra-narrow GNRs can be fabricated using organic synthesis, and the chemical vapor deposition (CVD) method is expected to achieve the industrial production of high-quality GNRs with low-cost preparation. Finally, we discuss the challenges and prospects of the research of GNRs. We believe that GNRs will become a new structural and functional material with great application potential in numerous fields, as is catalyzed by innovative development of materials and techniques.

Copper(I)-catalyzed cycloaddition reactions, such as [3+2] cycloaddition of organic azides with terminal alkynes (CuAAC), unsaturated compounds with isocyanides, and nitrones with alkynes (Kinugasa reaction), are important methods for the constructions of different types of nitrogen-containing heterocycles. Great progresses have been achieved in such transformations and widely applied in various fields of organic syntheses. In these cycloaddition reactions, similar organocopper(I) intermediates are generated in situ, and can be trapped with additional electrophiles for further tandem or one-pot transformations. The development of the strategy to trap organocopper(I) intermediates in these reactions provides practical and efficient methods for the construction of multisubstituted or fused nitrogen-containing heterocycles. The advances in this area are summarized in this review: (1) trapping organocopper(I) intermediates in CuAAC reaction; (2) trapping organocopper(I) intermediates in the [3+2] cycloaddition of isocyanides with electron-deficient alkynes; (3) trapping enolate organocopper(I) intermediates in Kinugasa reaction. The review may be helpful for researchers to better understand the development and limitations for the trapping of organocopper(I) intermediates.

The Pd₂L₄ type coordination cage has been extensively studied and widely applied in catalysis, drug delivery, molecular recognition and other research fields since the seminal report in 1998. In this work, a gourd-shaped Pd₂L₄ type coordination cage (C1) was synthesized and characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR) and high resolution mass spectrum (HR-MS). The host-guest chemistry of C1 was studied by ¹H NMR with two drug molecules, sulfaguanidine (G1) and cisplatin (G2). ¹H NMR results show that G1 and G2 can be selectively combined in two different cavities of C1. The same host-guest complex could be obtained, whether G1 and G2 were added at the same time or in a stepwise fashion. This work laid a foundation for drug delivery and provided a new inspiration for concomitant drugs.

As one of the most important solid catalysts in chemical industry, zeolites are widely used in different fields. How to prepare zeolites greenly and efficiently has become a research hot issue with the increase of consumption year by year. Hydroxyl free radical is a highly active species, which can promote the depolymerization and repolymerization of aluminosilicates in the zeolite initial gel, and then accelerating the zeolite crystallization process. Besides accelerating the crystallization of zeolite, many studies have shown hydroxyl free radicals have other functions in zeolite synthesis. In this review, the role of hydroxyl free radicals in the synthesis of zeolites is systematically introduced via different generation methods. The challenges of the hydroxyl free radical assisted strategy are put forward, and its development directions are prospected.

Radial conjugated carbon nanohoops, as nanofragments of carbon nanotubes, have attracted great attention in the fields of synthetic chemistry, stereochemistry, supramolecular chemistry and materials science. The structure of nanohoops can be divided into monocyclic and multicyclic nanohoops according to the geometric angle. The main building blocks of monocyclic nanohoops are benzene, polycyclic aromatic hydrocarbons and macrocycles, the monocyclic nanohoops with macrocycle as the building blocks and multicyclic nanohoops not only have special topological structure but also have the characteristics of high fluorescence quantum yield and large cavity. At present, such nanohoops with topological structure have important research value in the fields of host-guest doping, energy storage materials, porous and organic optoelectronic materials. Therefore, this review will focus on the synthetic methods of porphyrin monocyclic nanohoops with macrocycle as building blocks, figure-of-eight nanohoops and nanogrids, and more complex carbon nanocages.

Polynuclear transition metal complexes are widely used as homogeneous catalysts, and the polymetallic active sites of enzymes also play an important role in the mechanism of biochemical reactions under ambient conditions. As the efficient polymetallic catalysts for the activation of small molecules, trinuclear metal complexes have been attracted extensive attention. In order to understand the role of trinuclear transition metal complexes in catalytic reactions, we have classified the trinuclear transition metal complexes according to metal centers, and summarized the characteristics of their ligands, as well as their catalytic applications. Based on the metal centers, the geometric structure and electronic characteristics of the complexes are discussed. Based on the peripheral ligands, the characteristics of the coordination environment, which enable the aggregation of three independent metal sites, are highlighted. In terms of catalytic applications of trinuclear transition metal complexes, the catalytic mechanisms involving specific chemical bonds activation are focused on. Finally, we outlook the crucial potential application in this emerging field.

Throughout the history of transition-metal catalysis, almost every breakthrough is closely related to the development of ligands. Therefore, the history of transition-metal catalysis roughly parallels the development history of ligands. Therefore, ligand development lies in the heart of transition metal catalysis. Since the beginning of homogeneous catalysis, transition metals have been accompanied by phosphine ligands (Wilkinson's catalyst). Till now, phosphine ligands are one of the most widely used ligand types. There are several key factors for the popularity of phosphine ligands, among which the backbone of ligand plays a decisive role in supporting their stability, activity and selectivity. Many privileged phosphine ligands contain five- or six-membered rings in their core structures, possibly due to their ready-availability, low ring strain, and high stability. Seven- and above membered cyclic structures have flexible frameworks, many stable conformations, and are difficult to synthesize, making them unsuitable as ligand backbones. The cyclobutane structure has relatively strong ring strain, but its conformation can be flipped, and it is difficult to synthesize, making it inappropriate to be used as a ligand skeleton, too. As the smallest all-carbon ring, the three carbon atoms of cyclopropane are located in the same plane. Because of the unique electronic structure and rigidity of cyclopropane, changing a substituent on any one of the carbon atoms of the ring will affect the conformation of the substituents on the other two carbons. And cyclopropane structure is relatively simple to synthesize and modify, making it a promising ligand skeleton. However, it is surprising that phosphine ligands with cyclopropane as the core structure have been rarely studied so far, and their applications need to be further explored, too. Based on types of ligands, this perspective systematically summarizes reported phosphine-containing ligands (including monophosphines, diphosphines, phosphine-heteroatoms and triphosphines) with cyclopropane backbone, and their applications in transition metal catalysis. We hope to draw researchers' attention to the cyclopropane-based phosphine ligands and thus promote the development of transition metal catalysis.

Protein nanoparticles (NPs), biocompatible and biodegradable, can be easily surface modified. In particular, amphiphilic proteins act as “surfactants” that help form microparticles while undergoing molecular chain rearrangement. These NPs have been successfully used as drug delivery systems, improving bioavailability and reducing the toxic effects of drug molecules. The use of regenerated silk protein (RSF) with m-acrylamidophenylboronic acid (APBA) composites as drug carriers for loading anti-inflammatory herbal extracts was reported. Firstly, a simple and rapid method was used to prepare silk protein/polyphenylboronic acid nanospheres, in brief, RSF solution and a certain amount of initiator were added to APBA solution, and the pH was adjusted by NaOH, and the polymerization was initiated by heating at 90 ℃ under nitrogen protection with stirring at 500 r/min. After 2 h of reaction, a milky solution was obtained, which formed silk protein/benzeneboronic acid nanospheres with hydrophobic interior and hydrophilic surface. The drug-loaded silk protein/polyphenylboronic acid nanospheres with an average size of 550 to 600 nm were prepared by mixing with the drug solution after dialysis and stirring at room temperature for 12 h to load the drug by adsorption. By the same method, drug-loaded albumin/polyphenylboronic acid microspheres and collagen/polyphenylboronic acid microspheres with sizes around 260 nm and 100 nm, respectively, could be prepared. The results observed by scanning and projection electron microscopy and dynamic light scattering showed that the drug-loaded silk protein/polyphenylboronic acid nanomicrospheres displayed regular spherical shape indicating smoothness and good dispersion with no obvious aggregation. The highest drug loading rate was about 13.4%, and the encapsulation rate was over 90%. Also, such drug-loaded nanospheres could achieve controlled release for about seven days and their slow release behavior was pH-responsive, with faster drug release in buffer solution at pH=5.5 than in buffer solution at pH=7.4. In addition, the synergistic interaction of the silk protein/polyphenylboronic acid nanomicrospheres with the subject drug improved its free radical scavenging rate and scavenging efficiency, which was superior to that of the direct drug delivery group. Thus, three protein/polyphenylboronic acid nanomicrospheres with different sizes, electrical properties and drug release rates may be adaptable to a wide range of intravenous and subcutaneous or intraperitoneal drug delivery needs and have great potential for clinical applications.

A large number of chiral drug molecules have a chiral structure containing both D- and L-enantiomers, leading to the mirror image arrangements of the two forms eliciting quite different physiological responses. Penicillamine (Pen) is a common chiral drug that is obtained from penicillin, and researchers have been making continuous efforts to achieve rigorous analysis and discrimination of the two enantiomers. Based on chiral Schiff base macrocycles containing NH functionalities have the advantages of mild synthesis conditions and convergence of structural arrangement. Here we report two enantiomers of the mono-Schiff base macrocycle containing chiral NH moiety in the cyclic structure (C_R and C_S), and the binding affinity and enantioselectivity of the cyclic enantiomers toward small molecules penicillamine (D-Pen and L-Pen). The crystal structures of the mono-Schiff base cyclic enantiomers were determined by X-ray diffraction analysis, and the results show that the two cyclic enantiomers exhibit twisted non-planar conformation, in which the chiral NH proton points to the inside of the ring cavity. The interactions between different enantiomers of the chiral macrocycle and penicillamine were investigated by ultraviolet visible (UV-Vis) and hydrogen nuclear magnetic resonance (¹H NMR) titration, and the results show that the chiral macrocycle binds with the enantiomers of penicillamine with a bonding ratio of 1∶1, binding constants around 10⁷ L•mol^-1, and the complexes of [C-Pen+H]⁺ can be easily formed and detected by electrospray ionization-mass spectrometry (ESI-MS). The interactions between different enantiomers of the chiral macrocycle and penicillamine are attributed to the intermolecular hydrogen bonding of enantiomers by the asymmetrical chiral NH moiety in the mono-Schiff base macrocycle. Comparison of bonding constants based on the chiral macrocycle binds with the enantiomers of penicillamine, the results show that the chiral C_R exhibits higher enantioselectivity for L-Pen, while C_S exhibits the higher enantioselectivity for D-Pen, with a binding constant ratio around 2, respectively. Further, investigation of circular dichroism (CD) spectroscopic titration indicate that the penicillamine with the same chirality as the host macrocycle binds stronger with the host than its enantiomer with the host.

CO₂ emission is a serious global problem. CO₂ capture technology is indispensable to achieve the strategic goals of carbon peaking and carbon neutrality in China. Ionic liquids as new media have attracted much attention in the field of CO₂ capture and separation due to their unique advantages of low volatility, good gas solubility and structure designability. This review focuses on research progresses of amino and non-amino functionalized ionic liquids, ionic liquid hybrid solvents, ionic liquid modified adsorbents and membranes for CO₂ capture and separation reported in the past five years. The influence of amino groups and electronegative functional sites on CO₂ separation performance and mechanism, and the role of functionalized ionic liquids in hybrid solvents, adsorbents and membranes were summarized. Finally, the future development direction and prospect of ionic liquid-based CO₂ capture technologies were also proposed.

As the only natural and sustainable carbon source, biomass shows great potential in solving current environmental and energy problems and creating a carbon-neutral society. Selective hydrogenation is a kind of important reaction. Various unsaturated functional groups in biomass are typical targets of selective hydrogenation. Therefore, selectivity is the key index to measure the efficiency of the hydrogenation reaction. Vanillin is an important platform compound in biomass conversion. In recent years, selective hydrogenation of vanillin to biofuels and other high-value-added chemicals has received widespread attention. Because vanillin has different reducible functional groups (aldehyde group, methoxy group, and hydroxyl group), it is very important to control the selectivity of vanillin hydrogenation. Vanillyl alcohol has long-lasting sweetness and nutty aromas and is used in the food and perfume industries. 2-Methoxy-4-methylphenol (MMP) is also an important biofuel. Therefore, selective hydrogenation of vanillin to vanillyl alcohol or MMP is an important synthesis route. Here, we propose a strategy to introduce the chemical active center of catalytic reaction and the anchoring center of metal nanoparticle deposition by doping nitrogen atoms of graphene, which makes the application of graphene in hydrogenation catalysis obtain better performance. In this work, we report a simple method for in-situ synthesis of nitrogen-doped graphene-supported palladium nanoparticles Pd@N/C-2 catalyst and its application in selective hydrogenation of the C=O bond. The prepared catalyst has good catalytic activity and product selectivity for the hydrogenation of vanillin and has the advantages of simple preparation, high activity and stable performance. It is easy to be separated from organic reaction conditions and can be reused many times. Under relatively mild reaction conditions, Pd@N/C-2 catalyzed the complete conversion of vanillin to vanillyl alcohol and MMP, and the yields were 89% and 99%, respectively. It is worth noting that through the regulation of solvents, we achieved highly selective hydrogenation of vanillin to vanillyl alcohol and MMP, respectively.

The electronic and optical properties of π-conjugated materials are determined by their molecular structures and supramolecular architectures. Discotic liquid crystals consist of π-conjugated aromatic core and peripheral alkyl chains, they self-organize into two-dimensional discotic columnar mesophase, which can be applied as charge carrier transport channel in optical and electronic thin-film devices. Order and dynamics are two unique features of discotic liquid crystalline semiconductors. Three star-shaped 1,3,5-triazine-triphenylene discotic liquid crystals TPPTn (n=6, 8, 12) were synthesized by Suzuki-Miyaura cross-coupling reaction and characterized. Thermogravimetric analysis (TGA) shows that TPPTn have good thermal stability, and their thermal decomposition temperatures were higher than 350 ℃. The ultraviolet-visible (UV-Vis) absorption spectra and fluorescence spectra showed that they have outstanding fluorescence emissions in solution, thin film and even in solid state, and the length of alkoxy chain affects a little the fluorescence properties of the film or solid state by affecting the molecular aggregation. TPPTn have the aggregation-induced emission (AIE) effect: longer the alkoxy chain, more obvious the AIE phenomenon, this AIE effectively overcomes the disadvantage of aggregation caused quenching (ACQ) of π-extended discotic liquid crystalline molecules. Further, TPPT6 exhibits significant solvatochromism from blue to orange with the increasing of solvent polarity, due to the intramolecular charge transfer (ICT), which provides possibility for visual recognition of solvent polarity. The fluorescent emission absolute quantum yield is up to 43%. What is more, TPPT6 exhibits a temperature-responsive fluorescence enhancement with increasing temperature in solution, which is different from the temperature quenching of traditional molecules, and the fluorescence exhibits a reversible switching from green to blue with increasing/decreasing of temperature. TPPT6 also has obvious acid-base stimuli- responsive fluorescent response by CF₃COOH and Et₃N. ¹H NMR titration proves that the protonation of triazine core is the mechanism to acid discoloration. Based on the acid-base stimuli response phenomena, two kinds of fluorescent safety inks have been designed and demonstrated. Differential scanning calorimetry (DSC), polarizing microscope (POM) and X-ray diffraction (XRD) indicate that these star-shaped molecules TPPTn have liquid crystal properties, self-organizing into columnar rectangular (Col_rec) mesophase with mesophase temperature range as wide as 278 ℃. Trifluoroacetic acid (CF₃COOH) modulates successfully the mesomorphic behavior of TPPTn by ionizing the triazine core. In addition, TPPT6 also displays electroluminescent properties, which has been applied to a green organic light-emitting diode (OLED), and the luminous efficiency of OLED reaches 7.41 lm/W. The star-shaped triphenylene-triazine TPPTn have potential applications as liquid crystalline semiconductors, fluorescence sensing, information encryption and organic light-emitting diodes.

Advanced electrocatalytic oxidation technology generally uses plate electrodes, because the hindered mass transfer has disadvantages of incomplete degradation, which limits the application of electrocatalytic degradation of pollutants. As a new type of electrode, porous carbon nanomembranes can effectively improve the mass transfer efficiency, thereby overcoming the shortcomings of traditional technology, it have been widely used in recent years. In this paper, the methods for preparing carbon films are reviewed, including electrospinning technology (EST), chemical vapor deposition (CVD) and template method, the principles and operating methods of the different techniques are introduced separately, and examples of the practical application of each method are given. Among them, electrospinning technology has the advantages of facilitating the modification of carbon films and the preparation of oriented carbon membranes. Secondly, the research on the electrocatalytic degradation of wastewater containing antibiotics, dye molecules and other organic compounds by carbon membrane is summarized, the universality of electrocatalysis is illustrated from the effective degradation results of carbon membranes for different organic compounds, the high efficiency, cleanliness and reproducibility of carbon membranes as electrodes for electrocatalytic degradation of wastewater are further demonstrated by different studies. These studies have further improved the performance of carbon membrane as electrodes by adding metals, metal oxides and metal-organic frameworks to the carbon membranes. Finally, the mechanism of electrochemical advanced oxidation, effect of electrode and main detection methods of free radicals are described, the mechanism of electrochemical advanced oxidation is introduced in terms of direct and indirect oxidation, and specific demonstration is made through equations, the possible electrode effects and their influence on electrocatalytic degradation of wastewater are cited as example. The methods of detecting free radicals are mainly introduced as quenching method and probe method, the principles and controversies are explained, and the development of carbon film electrocatalytic degradation of wastewater is prospected.

o-Hydroxyphenyl substituted p-quinone methides (p-QMs) belong to a class of p-QMs with unique advantages. They not only maintain the high reactivity of p-QMs, but also have more reactive and activation sites owing to the introduction of hydroxyl group. Therefore, o-hydroxyphenyl substituted p-QMs have wide applications in synthetic and medicinal chemistry. The catalytic asymmetric 1,6-conjugate addition and [4＋n] cycloaddition of o-hydroxyphenyl substituted p-QMs have developed very rapidly in recent years, which have become efficient strategies for the synthesis of chiral oxygen-containing heterocycles and arylmethanes with potential bioactivity. This review summarizes the catalytic asymmetric reactions involving o-hydroxyphenyl substituted p-QMs and points out the remaining challenges in this research area, which will open a new window for the design of new type of o-hydroxyphenyl substituted p-QMs and their involved catalytic asymmetric reactions.

Dicarboxylic acid is an important polyester monomer, which is widely used in all aspects of chemical fiber, light industry, electronics and other industrial production. With the development of social industrialization, the production of dicarboxylic acids from a large number of non-renewable petroleum resources has caused the lack of oil resources and environmental pollution of the earth. The preparation of high value-added chemicals dicarboxylic acids by biomass and its derivatives has attracted extensive attention in chemical applications. In the research of synthetic biomass dicarboxylic acid, it is of great significance to design and prepare catalysts with high activity and high stability. In recent years, many works have explored the types of catalysts and made certain research progress. In this review, the catalytic system for the preparation of C₃~C₆ dicarboxylic acid, including malonic acid, succinic acid, 2,5-furandicarboxylic acid and adipic acid, was reviewed from the aspects of biomass raw materials, catalyst performance evaluation and reaction mechanism, and the development of biomass dicarboxylic acid preparation is prospected.

Chiral C—X (X=N, O, P, B, F, etc.) bond fragments are present in a wide variety of natural and pharmaceutically active molecules. Transition metal-catalyzed asymmetric hydrogenation is one of the most attractive strategies for the synthesis of these chiral compounds. Among the many transition metal catalysts, earth-abundant transition metals (iron, cobalt, nickel, and copper) have been used in asymmetric hydrogenation to replace rare metals (rhodium, ruthenium, iridium and palladium) due to their abundant reserves, low toxicity, and environmental friendliness. At present, this method for the construction of chiral C—X bonds has become a prominent trend in modern organic chemistry. Among them, the development of nickel catalysts has been relatively rapid. Based on this, the article will review the latest research in the preparation of compounds with chiral C—X bonds via nickel-catalyzed asymmetric hydrogenation using hydrogen. It is divided into five sections consisting of the construction of chiral C—N, C—O, C—P, C—B and C—F bonds by nickel-catalyzed asymmetric hydrogenation.

Photochromic molecules show great potential in biological imaging, logic gates, super-resolution imaging and other fields due to the sensitivity, accuracy and penetrability of light. By utilizing their variations on physical properties upon light irradiation, the fluorescence signal of photochromic dyes can be turned on or off accurately by specific wavelength. As an important luminescent dye, organic room-temperature phosphorescence (RTP) materials have attracted great research interest of scientists by the triplet state radiation process, and have potential in sensing, anticounterfeiting, photo-dynamic therapy, and so forth. In this work, we combine the phosphorescence and photochromic properties together by connecting a classic photochromic dye (bithienylethene) with an efficient phosphor (thiochroman-4-one) via sp² and sp³ linker (BTE1oand BTE2o). These compounds show typical photochromic phenomenon in solution and polymer matrix and have good fatigue resistance. During the irradiation, a clear isosbestic point can be observed, indicating the quantified transition between two isomers. The emission quenching of derivatives is considered as the radiative energy transfer between fluorescent open form and non-fluorescent closed form. It’s interesting that the fluorescence lifetime of BTE1oand BTE2oincreases after ultraviolet (UV) irradiation, which rules out the possibility of non-radiative energy transfer mechanism of the fluorescence quenching phenomena. In the poly(vinyl alcohol) (PVA) matrix, these compounds show decent RTP emission and millisecond level lifetime. And the RTP emission can also be reversibly turned “ON” or “OFF” via irradiation of different wavelengths. It’s very interesting that the phosphorescence lifetime also increases (from 16.1 to 19.4 ms) with the irradiation of UV light, which is identified with the variation of fluorescence lifetime in solution and PVA matrix. The increase of lifetime can rule out the non-radiative energy transfer mechanism for the phosphorescence quenching phenomena. Considering the fluorescence quenching phenomena in tetrahydrofuran (THF) solution, the fluorescence and phosphorescence quenching in PVA matrix should also be attributed to the form conversion and the radiative energy transfer process between open and closed isomers.

At present, the development of efficient (high quantum efficiency and high thermal stability) narrow-band emitting phosphors is a crucial problem in the application of white light emitting diodes (WLED) for high-performance liquid crystal display (LCD) backlights. In this work, an efficient narrow-band blue emitting phosphor Ba₃Y₂B₆O₁₅:Bi³⁺ was prepared by high temperature solid state method, and its structure and properties were characterized and calculated. By using the density functional theory (DFT), Ba₃Y₂B₆O₁₅ is calculated to be a direct band gap material with a high band gap value of 4.67 eV, which is a necessary condition for achieving high quantum efficiency phosphors. The experiment results show that Ba₃Y₂B₆O₁₅:0.5%Bi³⁺ has a narrow-band blue-emitting spectrum with a full width at half maximum (FWHM) of 2168 cm⁻¹ (36.2 nm) at 409 nm, which is owing to the ³P₁→¹S₀ transition of Bi³⁺ ions. The emission spectra of Ba₃Y₂B₆O₁₅:0.5%Bi³⁺ can be split into two peaks at 406 and 422 nm, respectively, because there are two kinds of Y ions (Y1 and Y2) in the crystal cell of Ba₃Y₂B₆O₁₅. Under the 365 nm UV radiation, the Ba₃Y₂B₆O₁₅:0.5%Bi³⁺ exhibits high internal quantum efficiency (IQE=93.8%), and ultra-high color purity (98.9%). The high quantum efficiency and narrow-band emission spectrum are mainly due to the compact and highly symmetric crystal structure of Ba₃Y₂B₆O₁₅ matrix. The photoluminescence (PL) intensity of Ba₃Y₂B₆O₁₅:0.5%Bi³⁺ remains 73.9% of the initial intensity at 150 ℃, and there is almost no color drift. The thermal quenching activation energy (E_a) of Ba₃Y₂B₆O₁₅:0.5%Bi³⁺ was calculated to be 0.290 eV by the Arrhenius Equation, which indicates that Ba₃Y₂B₆O₁₅:0.5%Bi³⁺ has high thermal stability. When Y³⁺ is partially substituted by Sc³⁺, the emission spectrum of Ba₃Sc_xY_2-xB₆O₁₅:Bi³⁺ (0≤x≤1.6) is redshifted with the increase of x. Finally, the blue phosphor Ba₃Y₂B₆O₁₅:0.5%Bi³⁺ was mixed with commecial green and red phosphors and then coated them on a 365 nm chip to fabricate a WLED device. Under a driven current of 20 mA, the correlated color temperature of the obtained WLED is 5679 K and the color gamut can reach 95.3% NTSC. Above results indicate that Ba₃Y₂B₆O₁₅:Bi³⁺ is a promising phosphor for high-performance LCD backlights.

Layered double hydroxides (LDHs) have attracted wide attention in the fields of environment, energy and biomedicine owing to their tunable chemical composition, large specific surface area and good biocompatibility. However, the agglomeration of LDHs caused by the intermolecular forces during their synthesis process may lead to their uneven dispersion in the matrix, thereby limiting their further practical application. In this review, the organic modification methods of LDHs in recent years are summarized from the perspectives of surface modification and intercalation modification. Their emerging applications in diverse fields, such as flame retardancy, adsorption, catalysis, gas barrier, luminescence, energy storage and biomedicine are also described. Finally, future research directions and application fields of modified LDHs are highlighted.

Paper and paper-based cultural relics are of great value as the main carriers for writing and preserving information. Acid-catalyzed hydrolysis is one of the most fatal reactions for paper degradation, and deacidification would effectively slow down the rate of its degradation and prolong the life time of paper. Therefore, the design and application of deacidifying materials with safety and effectiveness is the indispensable requirement for the protection of paper and paper-based cultural relics. Generally, alkaline materials, such as amino/amine compounds, magnesium/calcium hydroxides, oxides, carbonates are the mostly used deacidifying materials for their good paper compatibility, suitable alkalinity, low cost and low toxicity, which exhibit considerable paper deacidification performance. In this review, the recent research progresses of deacidifying materials on liquid phase deacidification process were reviewed, including the categories of deacidifying materials, preparation methods and the relationship between paper deacidification performance and structures of deacidifying materials, finally, the challenges and development of deacidifying materials were also discussed. For classification purpose according to chemical structure, deacidifying materials can be divided into four categories: ionic form, molecular form, micro/nano-scale form and composite form. The deacidifying materials with molecular form can significantly improve the mechanical properties of paper and show a certain deacidification effect, it is necessary to control the improvement of mechanical properties within reasonable ranges while considering the effective deacidification performance. Micro/nano-scale materials with large surface area, good penetration and high efficiency are the widely used deacidifying materials, which can achieve better deacidification effects at lower concentrations. The controlled alkalinity, high dispersion and suspension stability in solvents and uniform distribution in paper fibers of micro/nano-scale materials are highly demanded. Additionally, ionic form materials can interact with paper fibers more evenly through homogeneous deacidification process, but their alkaline reserve is relatively insufficient. And more insight is demanded into the co-existence stability of composite deacidifying materials and its contribution to paper protection.

In recent years, organic reactions involving difluorocyclopropenes have attracted the attention of organic chemists and have made great progress. The reactions mainly include: (1) cyclization: a) transition-metal catalyzed C—H bond activation cyclization with directing groups; b) cyclization reactions with non-directing groups; (2) hydrogenation reduction; (3) fluorination as “F” source reagents. In this paper, the synthesis methods and applications of difluorocyclopropenes in past 10 years are summarized. The conversion reactions of difluorocyclopropenes are emphasized. Additionally, difluorocyclopropenes have aroused considerable interests both from a structural standpoint and their participation in various ring-opening reactions. Given the increasing application of cyclopropyl skeleton in the development of drugs and unarguable importance of fluorinated compounds in medicinal chemistry and agrochemistry, it is no doubt that difluorocyclopropenes are encountered into bioactive molecular and at present lie among “emerging fluorinated motifs”. Although the synthesis and application of structurally diverse difluorocyclopropenes have been witnessed in the past decade, the most widely used methods for the preparation of these compounds include difluoromethylenation of alkynes and difluoromethylation of heteroatom nucleophiles (such as NaF, NaI, ⁿBuN₄X, etc.) with a difluorocarbene reagent, which can be generated from various precursors (such as TMSCF₃, TMSCF₂X, Ph₃P^＋CF₂CO₂^-, TFDA, etc.). For the transition metal-catalyzed cyclization of difluorocyclopropenes, some common metal salts (such as rhodium, ruthenium, copper, palladium, silver) are used as catalysts. Moreover, the metallic hydrogen (M—H) reduction strategy is a simple and efficient method for the hydrogenation reduction of difluorocyclopropenes leading to difluorocyclopropanes, and the asymmetric hydrogenation reduction of difluorocyclopropenes can be achieved in the presence of chiral ligands. In fluorination reactions, difluorocyclopropenes have some advantages that cannot be achieved by traditional fluorination reagents for the direct fluorination and functionalization of hydroxyl groups (such as fluorination of polyhydroxyl alcohols). Of course, the biggest disadvantage of difluorocyclopropene as a fluorine source lies in its poor atomic economy, which has been criticized. Despite the remarkable achievements in the reactions of difluorocyclopropenes, there are still many issues that need to be addressed. For instance, difluorocyclopropenes are rarely applied in traditional radical reactions, photocatalysis, electrocatalysis and flow chemistry. Hopefully, difluorocyclopropenes can gradually appear in photo- and electro-catalyzed radical chemistry, and the related asymmetric reactions will also get more attention and development in the near future.

In this work, a borondipyrromethene (BODIPY)-based activatable photosensitizer FP-IBDP was designed and synthesized, which has absorption and emission wavelengths in the near infrared (NIR) region. The maximum absorption and emission of FP-IBDP are 681 nm and 740 nm in acetonitrile. The fluorescence quantum yield and singlet oxygen yield of FP-IBDP is 0.01 and 0.09, respectively. After activated by H₂O₂, FP-IBDP was transformed to photosensitizer IBDP, which has maximum absorption and emission peak at 661 nm and 701 nm in acetonitrile. Compared with FP-IBDP, the fluorescence quantum yield and singlet oxygen yield of IBDP are much increased, up to 0.11 and 0.48 respectively. It is demonstrated that FP-IBDP can respond H₂O₂ sensitively in cancer cells and has the ability to distinguish cancer cells from normal cells by a fluorescence enhancement way. Reactive oxygen species (ROS) detection indicated that FP-IBDP could be activated by the endogenous H₂O₂ in cancer cells and produce highly toxic singlet oxygen under 660 nm light excitation with dichlorodihydrofluorescein diacetate (DCFH-DA) as ROS indicator. Tetrazolium (MTT) assay indicated that FP-IBDP has good biocompatibility and low dark toxicity to both cancer cells and normal cells, while phototoxicity test and living/dead cell double staining experiment proved that FP-IBDP has higher phototoxicity to cancer cells than to normal cells. Besides, wounding healing assay confirmed its good ability to inhibit cancer cell proliferation. Fluorescence localization and lysosome disruption assays further indicated that FP-IBDP was specifically located in lysosomes of living cells and the produced singlet oxygen could induce cancer cell death in a lysosome disruption associated pathway. These features are expected to lay good foundation for the application of FP-IBDP in imaging guided photodynamic therapy under NIR excitation.

Covalent organic frameworks (COFs) are a class of crystalline organic porous materials formed by molecular building blocks via covalent bonds. According to the dimensions of the framework extended in space, COFs can be divided into two-dimensional and three-dimensional COFs. Owing to their high specific surface area, good stability and strong designability, COFs have broad prospects in the fields of gas adsorption and separation, catalysis, sensing, optoelectronics, and energy storage. In the field of photocatalysis, COFs have the following advantages. First, COFs are highly designable, which can achieve efficient photocatalysis by introducing different functional units to adjust the band gap energy and light absorption range. Secondly, the ordered structure of COFs improves the electron-hole separation efficiency. In addition, the high specific surface area and abundant active sites of COFs can promote the photocatalytic reaction and improve the reaction rate. Finally, COFs are connected by covalent bonds, which make them highly stable and facilitate the maintenance of catalytic activity in the photocatalytic process. Porphyrins are a class of 18 π-electron conjugated macrocyclic compounds formed by the interconnection of four pyrroles, which can be involved in photosynthesis as the core part of chlorophyll and other biomolecules. As a kind of functional units with large π-conjugated structure and good photophysical properties, porphyrins usually have strong absorption in the 400~450 nm (Soret band) and 500~700 nm (Q band) regions, and their photocatalytic properties can be regulated by coordination with metal ions and modification of functional groups, which has unique advantages in the field of photocatalysis. By introducing porphyrins into COFs, combined with their unique advantages, porphyrin-based COFs have been found great potential in the field of photocatalysis due to the exceptional optical absorption in a broad spectral range, multiple active sites and effective electron-hole separation ability. As a new type of photocatalyst, porphyrin-based COFs have attracted much interest and have been rapidly developed in the field of photocatalysis. In this review, we focus on the discussion of porphyrin-based COFs in the photocatalytic CO₂ reduction, photocatalytic water splitting, photocatalytic organic transformation, and photocatalytic reduction of hexavalent uranium. Finally, the prospects and challenges of porphyrin-based COFs in photocatalysis are discussed.

The thermal decomposition characteristics of ammonium perchlorate (AP) have a great influence on the performance of solid propellant. Although a large number of mechanistic studies have been published over the past few decades, there is no unified understanding of the decomposition yet, and the overall mechanism pathway is still unclear. In the present work, the thermal decomposition pathways of AP were studied systematically using broken-symmetry density functional theory method (BS-UB3LYP/6-311＋G(d,p). This method can describe the homo-cleavage process of covalent bond well, and locate the transition state with singlet-diradical characteristics. Compared with typical multireference method, broken- symmetry density functional theory (BS-UDFT) can give good results and is much faster, and therefore is highly convenient for practical application. The results show that, the overall thermal decomposition pathway under the experimental conditions is initiated by the proton transfer between NH₄⁺ cation and ClO₄⁻ anion, leading to neutral NH₃ and HClO₄ molecules, which are absorbed on the AP surface and then escape to the gas phase. The second important step is the homolytic cleavage of the Cl—OH bond in HClO₄. The energy barrier is 67.5 kJ/mol under 620 K. Then, •OH radical and •ClO₃ radical react with NH₃ molecule, yielding •NH₂ radical. Then the •NH₂ radical react with HClO₄, leading to •ClO₄ radical, which reacts with NH₃, leading to the oxidized species H₂NO. The radical species, such as •OH, •NH₂, •ClO and so on, abstract the H atom of H₂NO, yielding NO. NO reacts with •OH radical, leading to NO₂; NO reacts with •NH₂ radical and •OH radical, leading to N₂O. These products are consistent well with the experimental observations. Due to the complexity of the mechanisms, some strategies are used in this study: firstly, we concentrate on the reaction pathways of active species and the NH₃ and HClO₄ molecules, which exist in large amount; secondly, more reaction pathways involving the newly formed active species are considered.