Regioselective ring-opening reactions of unsymmetric azetidines are systematically summarized and reviewed in this paper. Ring-opening reactions of unsymmetric azetidines include nucleophilic ring opening, Stevens rearrangement and ring expansion, and elimination reactions. Nucleophilic ring-opening reactions are major ring opening reactions of azetidines. The regioselectivity in ring-opening reactions is closely related to the structure of substituents of azetidines. Azetidines are relatively stable and often require Lewis acid catalysis or converted into their quaternary ammonium salts when they undergo ring-opening reactions. Thus, their ring-opening reactions are more susceptible to electronic effects. Azetidines and azetidiniums with 2-unsaturated substituents often undergo cleavage of the C-N bond between the nitrogen atom and carbon atom with the unsaturated groups, because the unsaturated groups such as aryl, 1-alkenyl, cyano, carboxylate, and carboxamide groups possess the conjugative effects with their adjacent carbon atom, stabilizing the generated transition states or intermediates in the ring-opening reactions. So that their C-N bond is more easily broken. In nucleophilic ring opening reactions of azetidines, nucleophiles generally attack arylmethylic, allylic, cyano, acyl, carboxylate, and carboxamide-attached nitrogen-adjacent carbon atoms, controlled by the electronic effect. However, sterically bulky or strong nucleophiles usually attack the less substituted nitrogen adjacent carbon atom of 2-alkylazetidines and azetidiniums in their ring opening reactions, controlled by steric hindrance. The structure of products in intramolecular nucleophilic ring opening reactions of azetidines is controlled by the ring size in the reaction processes, the ring-opening reactions favorably undergo through three-membered ring, five-membered ring, six-membered ring and seven-membered ring processes. Azetidines are a class of very important nitrogen-containing heterocyclic compounds. We can better understand and utilize this kind of reactions by summarizing and analyzing the ring-opening reactions and their regioselectivity of unsymmetric azetidines. The desired compounds can be prepared efficiently after predicting and controlling the regioselectivity in ring-opening reactions of azetidines. We hope that the summarized conclusions can promote the development and application of ring-opening reactions of azetidines in organic synthesis.

Contents
1 Nucleophilic ring-opening reactions of azetidines
1.1 Nucleophiles in group C
1.2 Nucleophiles in group N
1.3 Nucleophiles in group O
1.4 Halogen nucleophiles
1.5 Hydride nucleophiles
2 Stevens rearrangement and ring enlargement of azetidines
2.1 Base-catalyzed Stevens rearrangement and ring enlargment
2.2 Stevens rearrangement and ring enlargement of azetidines and carbenes
3 Eliminating ring-opening reactions
3.1 Transition metal-catalyzed eliminating ring-opening reactions
3.2 Sterically hindered strong base-promoted eliminating ring-opening reactions
3.3 Thermal elimination of azetidines
4 Miscellaneous ring-opening reactions of azetidines
4.1 Reductive ring-opening reactions
4.2 Cleaving ring-opening reactions
5 Conclusion

"With the development of mobile communication equipment and electric cars, there is an increasing demand for high capacity lithium-ion batteries. It is difficult for the present commercialized lithium-ion power batteries to meet the requirement of one charge to travel above 500 km, because of low discharge capacity, like lithium iron phosphate and ternary cathode material, possessing the discharge capacity lower than 180 mAh/g. Therefore, the specific capacity of cathode materials has become a bottleneck to increase the energy density of lithium-ion batteries. Lithium-rich cathode materials with large specific capacity (≥250 mAh/g), high discharge voltage (3.8 V), and high theory energy density (900 Wh/kg) are thought as ideal cathode material of power batteries for electric cars in the future, so, it is of great realistic significance to study the lithium-rich cathode materials with high specific capacity. This paper reviews the development of cathode materials for lithium-ion batteries as well as the situation of recent commercial cathode materials with low specific capacity. Structures and electrochemical properties of lithium-rich cathode materials as a new next-generation higher capacity are summarized, and the discharge mechanism and the latest progress in modifications are presented. Moreover, some problems related with lithium-rich materials for high energy-density lithium-ion batteries are presented, followed by the corresponding ideas and approaches of solution.

Contents
1 Introduction
2 Structural research of lithium-rich materials
3 Investigation on electrochemical behaviors of lithium-rich materials
3.1 Interpretation on the first charge/discharge
3.2 Interpretation on capacity and voltage fade
4 Modified research on lithium-rich materials
4.1 Surface coating
4.2 Bulk doping
4.3 Nanosizing
4.4 Hierarchical structure
4.5 Concentration-gradient distribution
4.6 Layered/Spinel heterostructure
4.7 Other methods
5 Conclusion

Transient electrochemical technologies have been widely applied in electrochemistry for providing time dependent information of the electrode kinetics. This review aims to show the time-frequency response behavior of an electrochemical system under periodical sine current/voltage excitations. Manifestations, numerical simulation scheme and experimental characterization methods of the nonlinear frequency response spectroscopy as well as its application in electrochemistry are addressed as the key issues. It is suggested that comparative studies between simulation and experimental data is the main way to utilize the nonlinear spectroscopy. Regulations to select current/voltage amplitude are concluded from its experimental characterization. Furthermore, it is indicated that nonlinearity of the electrochemical system arises from the electrode kinetics, which enables the nonlinear spectroscopy to own its advantages in the mechanism study and some aspects of the electrochemical system diagnosis.

Contents
1 Introduction
2 Linearity and nonlinearity of an electrochemical system
3 Manifestations of the frequency response behaviors of an electrochemical system
4 Numerical simulation and experimental characterization of the frequency response spectroscopy
5 Application of the nonlinear spectroscopy analysis in electrochemistry
6 Conclusion

Perylene diimide and its derivatives (PDIs) have been widely used as organic field-effect transistor (OFET), organic photovoltaic cell (OPV), dye laser and organic light emitting diode (OLED) in the field of optoelectronic materials due to their photo, thermal, chemical stability and high fluorescence quantum yields. However, because of their inherent structure, PDIs have poor water-solubility and easily form aggregates, which has limited their applications in biological fields. So, it's essential to synthesize water-soluble PDIs. This paper systematically presents the synthetic methods for obtaining water-soluble PDIs by introducing anionic substituent, cationic substituent or non-ionic substituent into the imide-position or bay-region of PDIs. Some of these substituents are water-soluble, and the others will achieve the water-solubility of PDIs through electrostatic repulsion or steric hindrance. In addition, several novel biological applications have been listed, such as chemotherapy,photodynamic therapy and fluorescence imaging.PDIs can also be used as a promising photo-acoustic contrast agents due to their good light absorption and photostability.

Contents
1 Introduction
2 Modification of PDIs
3 Modification of water-soluble PDIs
3.1 Anionic substituent
3.2 Cationic substituent
3.3 Non-ionic substituent
4 Biological application of water-soluble PDIs
4.1 Fluorescence probe
4.2 Contrast agent of photo-acoustic imaging
4.3 Chemotherapy
4.4 Photo-sensitizer of photodynamic therapy
5 Conclusion

Lithium is a very important metal resource for lithium-ion batteries and nuclear industries. With the fast-growing market demand for lithium, the focus of lithium extraction technologies has shifted to aqueous lithium resources, such as seawater and salt lake brine. Adsorption method has been recognized as one of the most suitable technologies for recovery of lithium from aqueous resources. The present paper reviews the development of the adsorption materials of lithium ion comprehensively, including the inorganic adsorbents (the natural ores, carbon materials, Mn or Ti lithium ion-sieves and their forming techniques) and organic composite adsorbents. The organic ligand functional groups (crown ether, calixarene and phosphate) for lithium ion adsorption, and their bonded matrixs are also summarized. The adsorption mechanism, adsorption capacity and selectivity of dififferent adsorption materials are compared. This paper provides a reference for developing of novel adsorption materials and separation systems to extract lithium ion from aqueous brine resources.

Contents
1 Introduction
2 Inorganic materials for adsorption of lithium
2.1 Natural ores and carbon materials
2.2 Lithium ion sieves
2.3 Lithium ion sieves composite materials
3 Composite materials for adsorption of lithium
3.1 Organo-functional groups of composite materials
3.2 Matrixes of composite materials
3.3 Composite materials with lithium ion imprinting technology
4 Conclusion

Semiconductor photocatalytic technology has been proved as an effective way to solve the problems of both environmental pollution and energy shortage. It can be applied for the degradation, transformation and mineralization of pollutants in the environment, and for the conversion of solar energy as well. Graphite phase carbon nitride (g-C₃N₄) and bismuth based composite materials have become the hot research topic because of their excellent photocatalytic performance. This paper reviews the preparation methods of g-C₃N₄ and its composites with different bismuth compounds. We also reviews the recent advances of the application of g-C₃N₄ and Bi composites in the environmental purification, including the elimination of pollutants in water, the light induced bacterial inactivation, and the photoinduced hydrolysis for hydrogen production. Taking the elimination of organic contaminants in water as an example, this paper elaborate detailedly their mechanisms of photocatalytic degradation. Finally, we prospect the new development and application potential of the g-C₃N₄ and Bi based composite photocatalytic materials in the environmental field.

Contents
1 Introduction
2 Synthesis of g-C₃N₄
2.1 Thermal polymerization method
2.2 Solvothermal synthesis
2.3 Electrochemical deposition
2.4 Solid phase synthesis
3 Preparation of g-C₃N₄ and bismuth based composites
3.1 Preparation of g-C₃N₄/Bi based halide oxides composites
3.2 Preparation of g-C₃N₄ and bismuth metal salts composites
3.3 Preparation of g-C₃N₄ and other bismuth compounds
4 Application of composites in the environment
4.1 Removal of organic pollutants in water environment
4.2 Photocatalytic hydrogen production by water splitting
4.3 Application of composite materials in other areas
5 Reaction mechanisms
6 Conclusion

Featuring speed, selectivity and flexibility, Rapid Visual Detection (RVD) prevails widely in fields associated with analytical chemistry. RVD relies on reasonable sensors fabricating, which is designed to detect molecules of interest by following three steps:recognition, indication and processing. Among those with great effects, organic photochromic-based sensors advances fast in RVD related fields recently, for tunable recognizing units, chromic/fluorescent bi-stable indication and feasible quality/quantity dual-processing. This paper reviews the recent development and prospects the future potential of organic photochromic-based sensors.

Contents
1 Introduction
2 Applications of organic photochromic materials in rapid visual detection
2.1 Applications of coordination-based photochromic materials
2.2 Applications of reaction-based photochromic materials
2.3 [JP3]Applications of ‘gate-effect’-based photochromic materials
2.4 Applications of undefined-based photochromic materials
3 Conclusion

Naturally occurring chlorophylls are important substances in the photosynthesis of higher plants. Their asymmetric carbon skeleton structures, the aromatic macrocyclic chromophores and the various active substituted groups attached to the periphery form a class of special natural products. The different chlorophullous degradation products have also been applied as photosensitizers in the area of photodynamic therapy (PDT), dye-sensitized solar cells (DSSCs) and artificial photosynthetic reaction centers. The diverse types of aromatic π-systems, the multi-region active reaction sites and the complicated tautomeric structures of the chlorophyllous macrocyclic molecules form their characteristic chemical properties. The close-relevance of the pyrrol subring with the aza-annulene in chlorophyll and the efficient conjugation of peripheric functional groups with mother cyclic delocalized system lead to that the different rearrangements frequently occur in chlorophyllous chlorins. The reaction scopes involve each pyrrol subring, the bridged meso-position and the combined exocyclic ring. The rearrangements, either including common name reaction or revealing unique transannular rearrangement, adequately reflect the universality in rearranged form and the novelty in reaction process. These special chemical conversions have been efficient approaches for designing and establishing macrocyclic compounds with novel carbon framework and practical application prospect, and are also an important entry point to deeply explore the basic theory, chemical synthesis and applications research of chlorophyll. Therefore, the recent rearrangement reactions about chlorophyllous tetrapyrrol molecules, based on their chemical modifications and structural conversions are reviewed.

Contents 1 Introduction 2 The basic carbon skeleton structures and chemical reactivities of natural products related to chlorophyll 3 Rearrangement reactions of pyrrol subring in chlotophyll derivatives 3.1 Rearrangement reactions of A-Pyrrol subring 3.2 Rearrangement reactions of B-Pyrrol subring 3.3 Rearrangement reactions of C-Pyrrol subring 3.4 Rearrangement reactions of D-Pyrrol subring 4 Rearrangement reactions at meso-position of chlorophyll derivatives 4.1 Rearrangement reaction at 5- and 10-meso-position 4.2 Rearrangement reaction at 5-meso-position and on the exocyclic ring 4.3 Rearrangement reactions at 20-meso-position 5 Conclusion

The polar monomer is an olefin monomer with polar group. It includes polar monomer with halogen, polar monomer with oxygen atom, polar monomer with nitrogen atom, and polar monomer with phosphorus atom. The polar vinyl monomer is monomer with conjugated vinyl group and polar group. The polymerization of polar vinyl monomer produces a polymer with polar group. This polymer has obvious advantages over the traditional non-polar polyolefin materials in terms of viscosity, toughness, interfacial properties (dyeing and printing), and compatibility with solvents or other polymers. In order to obtain polymer with good physical properties, it is a hot spot to get a polymer with certain degree of regularity. The structure of the polymer has a significant impact on its physical properties, such as melting point, glass transition temperature and mechanical properties. The most effective way to obtain the stereoregular polymer is the development of the stereoselective catalysts for polar vinyl polymeization. This paper reviews the recent research progress in stereoselective catalysts for the polar vinyl monomer polymerization, the polar vinyl monomers involved include:methacrylate, methacrylamide, vinylphosphonate, vinyl pyridine, 2-isopropenyl-2-oxazoline and heteo-atom substituted styrene. The polymerization system includes the coordination polymerization, the Lewis pair, and the anionic polymerization system.

Contents
1 Introduction
2 Methacrylate and methylene-butyrolactone polymerization
2.1 Methyl methacrylate polymerization
2.2 Methylene-butyrolactone polymerization
2.3 Polar divinyl monomer polymerization
3 Methacrylamide and vinylphosphonate polymerization
4 Vinylpyridine and 2-isopropenyl-2-oxazoline polymerization
5 Hetero-atom substituted styrene polymerization
6 Copolymerization of ethylene and polar vinyl monomer
7 Conclusion

Azide compounds have displayed wide applications in biological chemistry and pharmaceutical chemistry. However, the classic methods to prepare these compounds usually involve long synthesis steps, harsh reaction conditions and low reaction yields. Recent chemical approaches for direct azidation via C-H activation have drawn more attention due to its high efficiency, high conversion rate and good selectivity. This review intends to explore advances for direct azidation via C-H functionalization in the last five years and discuss the proposed mechanisms. These results are applicable to the development of synthetic methodology, natural product synthesis, and protein research.

Contents
1 Introduction
2 Azidation via metal C-H activation
2.1 Guide group-based catalysts
2.2 Free radical reaction
3 Conclusion"

Quantum dots (QDs), as novel fluorescent nanomaterials, have been widely used in fluorescent sensing and visual detection with high sensitivity and specificity analysis of target, owing to their excellent optical and electrical properties. The review addresses the surface functionalization of QDs that able to the use of sensing, and discusses different sensing mechanism including fluorescence resonance energy transfer (FRET), electron transfer (CT), direct fluorescent sensing, bioluminescence resonance energy transfer (BRET), chemiluminescence resonance energy transfer (CRET) and electrochemiluminescence (ECL), being applied in the different sensing systems. The challenges and existing problems of QDs fluorescent sensing application are summarized. Meanwhile fluorescent sensing of QDs will develop in the field of the good biocompatibility, real time visualization of sensing in cells or in vivo, multiplexed detection in complex systems and the function of sensing with logic-gate operations in the future.

Contents
1 Introduction
2 Photo-properties of quantum dots
3 Surface chemistry and conjugates of quantum dots
4 Mechanisms and design strategies of quantum dots fluorescence sensing
4.1 Fluorescence resonance energy transfer
4.2 Electron transfer
4.3 Direct fluorescent sensing
4.4 Bioluminescence resonance energy transfer
4.5 Chemiluminescence resonance energy transfer
4.6 Electrochemiluminescence
5 Conclusion

N-halamine antibacterial materials have aroused scientists' great interest due to their unique properties, such as powerful antibacterial activity, long term stability, effectiveness toward a broad spectrum of microorganisms, regenerability upon exposure to washing cycles, safety to humans and environment. In this review, recent development is summarized by discussing the synthesis and applications of N-halamine antibacterial polymers and N-halamine antibacterial nanomaterials. Three main approaches of preparation of N-halamine polymers are given:polymerization of N-halamine monomers; grafting N-halamine monomers onto polymer surfaces; others (blending, coating, electrospinning, etc.). Antibacterial performance of N-halamine materials strongly depends on their surface area, and thus nano-sized N-halamines exhibit high antibacterial activity due to the large activated surface area. So the research progress and developing trend of N-halamine nanomaterials are emphatically introduced. The subsequent development and application prospect of N-halamine antibacterial materials are also discussed.

Contents
1 Introduction
2 Antibacterial N-halamine polymers
2.1 Preparation of N-halamine polymers from the polymerization of N-halamine monomers
2.2 Preparation of N-halamine polymers by grafting N-halamine monomers onto polymer surfaces
2.3 Others
3 N-halamine nanomaterials
3.1 Preparation of N-halamine nanomaterials
3.2 Application of N-halamine nanomaterials
4 Conclusion

Photothermal therapy (PTT), as a new type of tumor treatment technology, has received intensive attention recently due to its high efficiency for tumor inhibition and low damage to normal tissue. Over the past decade, many photothermal conversion agents have been widely used in the research of PTT, especially inorganic nanomaterials with surface plasmon resonance properties, such as gold based nanoparticles. With the development of nanotechnology and nanomaterials, the types and properties of photothermal agents have been increasingly improved. Spired by the excellent cancer therapy effect of photothermal therapy, people pay more attention to the possibility of its clinical application. In recent years, organic photothermal agents have been developed rapidly, due to their abilities to overcome the non-biodegradable characteristics of inorganic materials. This article summarizes the recently developed research of several typical photothermal nanomaterials, including small molecular dyes, supramolecular complexes and conjugated polymers. Based on these organic agents, various biocompatible materials are developed for clinical photothermal therapy. And the application of the imaging guided photothermal therapy and combined therapy is briefly described. In the end, the primary categories and development direction of organic photothermal agents are summarized. And the problems and challenges of clinical photothermal therapy are pointed out.

Contents
1 Introduction
2 Small molecular dyes
2.1 Indocyanine green
2.2 Prussian blue
2.3 Thiadiazole derivatives
3 Supramolecular complexes
3.1 Porphysomes
3.2 BPDI/(CB[7])₂
4 Conjugated polymers
4.1 Polyaniline
4.2 Polypyrrole
4.3 PEDOT:PSS
4.4 Polydopamine
5 Other applications of photothermal therapy
5.1 Imaging-guided photothermal therapy
5.2 Combined cancer therapy
6 Conclusion and outlook