Multi-F-Structured MOF Materials Enhance Nanogenerator Output Performance for Corrosion Protection of Metallic Materials.

MOF (metal organic framework) materials have been used as functional materials in a number of fields due to their diverse spatial tunability, which produces rich porous structures with stable and continuous pores and a high specific surface area. A triboelectric nanogenerator can convert trace mechanical energy into electrical energy, and the application of MOF materials to triboelectric nanogenerators has been intensively studied. In this work, we report on two MOFs with similar spatial structures, and the modulation of the end microstructures was achieved using the difference in F content. The output performance of friction power generation increases with the increase in F content, and the obtained polyacidic ligand materials can be used to construct self-powered corrosion protection systems, which can effectively protect metallic materials from corrosion.

Directional design of carboxylic acid coordination number fine-tuned space structure to improve the output performance of nanogenerators.

The emergence of nanogenerators, which provide a way to obtain mechanical energy from the environment and to collect and transmit tiny amounts of energy, has attracted a lot of attention. MOFs, because of their diverse structures as well as stable pores and large specific surface area, have very significant advantages to be used as nanogenerator materials. In this paper, two MOFs with similar spatial structures are designed to take advantage of the different coordination numbers of carboxylic acids to achieve the regulation of their microstructures. The output performance of friction power generation was found to be affected significantly by their microstructures. The friction power generation performance improved with the increase of carboxylic acids, and the obtained polyacid ligand materials can be used for light bulb illumination, which is a step forward for the practical exploration.

Fluorinated covalent organic frameworks for efficient drug delivery.

In this study, two novel fluorine-functionalized crystalline covalent organic frameworks (COFs), namely DF-TAPB-COF and DF-TATB-COF, were synthesized, and their ordered structure, porosity, suitable pore size, and abundant fluorine groups were expected to serve as effective carriers in drug delivery. The excellent cell viability of DF-TAPB-COF and DF-TATB-COF was verified using MTT assays. Both COFs exhibited very high loading capacities in terms of drug loading performance, in particular the drug loading rate of DF-TAPB-COF for 5-fluorouracil (5-FU) was up to 69%. They also exhibited efficient drug release performance in a simulated body fluid environment. Cell endocytosis experiments demonstrated that DF-TAPB-COF and DF-TATB-COF could be effectively endocytosed by cells. Hence, this study offers new insight into the design and development of COF-based drug carrier systems.

Directed molecular structure design of coordination polymers with different ligands for regulating output performance of triboelectric nanogenerators.

A triboelectric nanogenerator (TENG) provides an effective method to harvest mechanical energy from the environment. The morphology and structure of frictional electrode materials of this type of device affect the output performance significantly. Metal-organic coordination polymers (CPs) with special structure advantages offer a vast pool of materials enabling high performances. Two Co-CPs based on terephthalic acid and 2,5-dihydroxyterephthalic acid ligands, respectively, were used to fabricate TENGs. Detailed electrical characterizations of the TENG devices revealed that the introduction of the substituent groups in the organic ligands leads to the structural changes of CPs, which ultimately leads to significant differences in the output performance.

Fluorescent porous organic polymers for detection and adsorption of nitroaromatic compounds.

A fluorescent porous organic polymer (FPOP) with strong fluorescence and tunable emission colors, was synthesized through a simple cost-effective method via Scholl coupling reaction. Experiments proved the stability and excellent detection and adsorption ability, and microporous nature of the material. Luminescence of FPOP was quenched when addition of nitroaromatic compounds. The properties along with large-scale and low-cost preparation make these FPOP potential candidates for fluorescence detection of nitroaromatic compounds. Additionally, FPOP shows higher adsorption capacity and rate than other reported adsorbents, and has the possibility of being an effective adsorbent for industrial usage. Moreover, a fluorescent test paper was further developed and is found to be sensitive to 10-8 M level, complete with a rapid response time and visual detection. This newly developed strategy may open up an avenue for exploring porous polymers, particularly those with a strong fluorescence, for the large-scale fabrication of FPOP for various advanced applications.

A novel AIE-active imidazolium macrocyclic ratiometric fluorescence sensor for pyrophosphate anion.

An imidazolium bridged macrocyclophane was synthesized as a ratiometric fluorescence sensor with aggregation-induced emission (AIE) characteristic to detect pyrophosphate anion with high selectivity among various anions. In the presence of zinc ion, macrocyclophane can form aggregates through complexation with pyrophosphate anion and emit ratiometric fluorescence, resulting from an enhancement in its aggregate-state emission and a reduction in its monomer emission. This AIE-active macrocycle showed great potential as a ratiometric fluorescence receptor.

Single-Atom and Dual-Atom Electrocatalysts Derived from Metal Organic Frameworks: Current Progress and Perspectives.

Single-atom catalysts (SACs) have attracted increasing research interests owing to their unique electronic structures, quantum size effects and maximum utilization rate of atoms. Metal organic frameworks (MOFs) are good candidates to prepare SACs owing to the atomically dispersed metal nodes in MOFs and abundant N and C species to stabilize the single atoms. In addition, the distance of adjacent metal atoms can be turned by adjusting the size of ligands and adding volatile metal centers to promote the formation of isolated metal atoms. Moreover, the diverse metal centers in MOFs can promote the preparation of dual-atom catalysts (DACs) to improve the metal loading and optimize the electronic structures of the catalysts. The applications of MOFs derived SACs and DACs for electrocatalysis, including oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, carbon dioxide reduction reaction and nitrogen reduction reaction are systematically summarized in this Review. The corresponding synthesis strategies, atomic structures and electrocatalytic performances of the catalysts are discussed to provide a deep understanding of MOFs-based atomic electrocatalysts. The catalytic mechanisms of the catalysts are presented, and the crucial challenges and perspectives are proposed to promote further design and applications of atomic electrocatalysts.

Hydrangea-like α-Ni1/3Co2/3(OH)2 Reinforced by Ethyl Carbamate "Rivet" for All-Solid-State Supercapacitors with Outstanding Comprehensive Performance.

Improving the self-conductivity and structural stability of electrode materials is a key strategy to improve the energy density, rate performance, and cycle life of supercapacitors. Controlled intercalation of ethyl carbamate (CH3CH2OCONH2) as the rivet between Ni-Co hydroxide layers can be used to obtain sufficient ion transport channels and robust structural stability of hydrangea-like α-Ni1/3Co2/3(OH)2 (NC). Combining the improved electronic conductivity offered by the coexistence of Ni2+ and Co2+ optimizing itself electronic conductivity and the addition of carbon nanotubes (CNTs) as the electron transport bridge between the active material and the current collector and the large specific surface area (296 m2 g-1) reducing the concentration polarization, the capacitance retention ratio of NC-CNT from 0.2 to 20 A g-1 is up to 93.4% and its specific capacitance is as high as 1228.7 F g-1 at 20 A g-1. The large total hole volume (0.40 cm3 g-1) and wide crystal plane spacing (0.71 nm) provide an adequate space to withstand structure deformation during charge/discharge processes and enhance the structural stability of the NC material. The capacitance fading ratio of NC-CNT is only 4.5% at 10 A g-1 for 10 000 cycles. The aqueous supercapacitor (NC-CNT//AC) and all-solid-state supercapacitor (PVA-NC-CNT//PVA-AC) exhibit high energy density (35.2 W h kg-1 at 100.0 W kg-1 and 35.4 W h kg-1 at 100.7 W kg-1), ultrahigh rate performance (the specific capacitances at 20 A g-1 are 92.8 and 87.2% compared to that at 0.5 A g-1), and long cycling life span (the specific capacitances after 100 000 cycles at 10 A g-1 are 91.5 and 90.8% compared with that of their initial specific capacitances), respectively. Therefore, hydrangea-like NC could be a promising material for advanced next-generation supercapacitors.

Macrocycles and cages based on tetraphenylethylene with aggregation-induced emission effect.

Organic molecules with an aggregation-induced emission (AIE) effect have recently been attracting more and more attention due to their colossal potential in solid emitters and chemo/biosensors. The number and variety of AIEgen compounds are expanding very rapidly to obtain better application performance and a wider area of application. Among AIEgen systems, tetraphenylethylene (TPE) and its derivatives are the class that have received the most extensive study and the most rapid development because of their facile synthesis. Due to its C2 symmetry and at least tetratopic reaction positions, the TPE unit is also an ideal building block for constructing macrocycles and cages. The resultant cyclic TPE compounds have exhibited many exceptional performances that are difficult to access in their open chain counterparts, such as AIE enhancement, improvement in selectivity and sensitivity as sensors, emission tuning by guests, supramolecular catalysis, further disclosure of the AIE mechanism, molecular adsorption, storage and release, the propeller-like conformation exploitation of the TPE unit in chiral materials and so on. Recently, therefore, a large variety of studies about the synthesis, properties and application research of TPE macrocycles and cages have been reported. These TPE macrocycles and cages significantly expand the research area for the AIE phenomenon and its applications, and represent a development of the AIE area. However, up to now, no review of TPE macrocycles and cages has been available. Thus, this review serves as a summary of the designs, synthesis, photophysical properties, self-assembly, applications and prospects of TPE macrocycles and cages.

Porous Interdigitation Molecular Cage from Tetraphenylethylene Trimeric Macrocycles That Showed Highly Selective Adsorption of CO2 and TNT Vapor in Air.

A new [3 + 3] trimeric macrocycle, based on tetraphenylethylene having an aggregation-induced emission effect, could form a interdigitation molecular cage with a big void by host-guest interactions. The cage could accommodate two TNT molecules and detect TNT at the 1.7 fg level per mL of air. Moreover, the cage could give permanent pores that had a BET surface area of 347 m2/g and could adsorb 7.8 wt % CO2 with high CO2/N2 selectivity up to 32 (273 K, 1 bar).

Evidence for Aggregation-Induced Emission from Free Rotation Restriction of Double Bond at Excited State.

This paper reports that cis-TPE dicycles emit strong fluorescence, while the gem dicycles show almost no emission in solution, demonstrating that the free rotation restriction of the double bond at the excited state is the key factor for AIE effects.

Tetraphenylethylene Foldamers with Double Hairpin-Turn Linkers, TNT-Binding Mode and Detection of Highly Diluted TNT Vapor.

Tetraphenylethylene (TPE) foldamers with double hairpin-turn linkers showing an aggregation-induced emission (AIE) effect have been synthesized for the first time. A crystal structure of a foldamer-TNT complex has been obtained, enabling unprecedented direct observation of the interactions between TNT molecules and the chromophores of the foldamer. Instead of π-π stacking interactions, which have often been considered to be the key mechanism in the binding of TNT by chromophoric receptors, strong n-π interactions between the nitro groups of TNT and the aromatic rings of the foldamer have been found. Exceptionally, by addition of 1 % NaF to a suspension of the foldamer in H2 O/THF (95:5), the fluorescence quenching efficiency by TNT vapor significantly increased from about 20 % to more than 90 %. Even after diluting TNT-saturated air at 25 °C by a factor of 2×104 , an obvious quenching response was observed, indicating that ultratrace TNT vapor (down to 3.4 fg per mL of air) could be detected.

Selective Host-Guest Co-crystallization of Pyridine-Functionalized Tetraphenylethylenes with Phthalic Acids and Multicolor Emission of the Co-crystals.

Tetraphenylethylene (TPE) and its derivatives are the most typical and most widely studied organic compounds showing aggregation-induced emission (AIE). Due to their propeller-like structures, V-like clefts exist between the aryl rings, which make them promising host compounds. However, such a possibility is seldom explored. Herein, it is reported that TPE derivatives bearing two or four pyridine rings at the para positions of the phenyl rings (TPE-Pys) can selectively include triangular (Δ-like) m-phthalic acid from a mixture of o-, m-, and p-phthalic acids due to their shape complementary to form host-guest co-crystals, which showed redder emission than the TPE-Pys themselves. The emission of co-crystals 1-5 could be reversibly switched between yellow and red by alternating exposure to HCl and ammonia vapor. The host-guest co-crystals not only exhibited great potential for selectively recognizing and separating m-phthalic acid and as multicolor emission materials, but are also suitable for use as secret ink due to their reversible color change on varying the host-guest interactions.

The Fixed Propeller-Like Conformation of Tetraphenylethylene that Reveals Aggregation-Induced Emission Effect, Chiral Recognition, and Enhanced Chiroptical Property.

The propeller-like conformation of tetraphenylethylene (TPE) with aggregation-induced emission (AIE) effect was partially and completely fixed by intramolecular cyclization for the first time. The immobilization of propeller-like conformation was found to show great advantages in determining the enantiomer purity, identifying the chiral amines. The completely fixed conformers are resolved into M- and P-enantiomer, which showed mirror imaged CD and almost quantitative fluorescence quantum yield. Furthermore, it also showed a mirror and large circularly polarized luminescence dissymmetric factor, depending on the helicity of the enantiomer. The result provides the most direct and persuasive evidence for AIE via the restriction of intramolecular rotation and finds the new insight of the compounds in chiroptical property.

Enantioselective Recognition for Many Different Kinds of Chiral Guests by One Chiral Receptor Based on Tetraphenylethylene Cyclohexylbisurea.

A neutral chiral receptor based on TPE cyclohexylbisurea was synthesized and could discriminate the enantiomers of many different kinds of chiral reagents, including chiral acidic compounds, basic compounds, amino acids, and even neutral alcohols. The (1)H NMR spectra disclosed that the ability of chiral recognition could be ascribed to the multiple hydrogen bonds and CH-π interactions between the TPE urea receptor and the enantiomer of the chiral guest, which led to the selective aggregation of the receptor with one of the two enantiomers. This result exhibited a great potential in enantiomer discernment and high-throughput analysis of enantiomer composition of these chiral analytes by one chiral AIE molecule.