Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks

Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However, the response of such materials toward laser‐induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)‐based porous COFs—Por‐COF‐HH and its dual metalated congeners Por‐COF‐ZnCu and Por‐COF‐ZnNi—have been prepared and present excellent NLO properties. Notably, intensity‐dependent NLO switching behavior was observed for these Por‐COFs, which is highly desirable for optical switching and optical limiting devices. Moreover, the efficient π‐conjugation and charge‐transfer transition in ZnCu‐Por‐COF enabled a high nonlinear absorption coefficient (β=4470 cm/GW) and figure of merit (FOM=σ₁/σ_o, 3565) value compared to other state‐of‐the‐art materials, including molecular porphyrins (β≈100–400 cm/GW), metal–organic frameworks (MOFs; β≈0.3–0.5 cm/GW), and graphene (β=900 cm/GW).     

Highly emissive coordination polymer derived from tetraphenylethylene-tetrazole chromophore: Synthesis,characterization and piezochromic luminescent behavior

Solid-state materials that exhibit pressure stimulus-response characteristics in a manner of emission signal, known as piezochromic luminescence (PCL), demonstrate great potential in photoelectric devices. The weakened luminescence and insignificant color change in the aggregation state, however, hampers their practical applications. Herein, a highly emissive coordination polymer, [Zn₂(H₄TTPE)(H₂O)₄]·H₂O (CUST-805), is successfully constructed by employing an AIE-active chromophore as the building block. The structural characterization and photophysical properties are systematically studied. Owing to intrinsic twisted conformation and AIE feature of tetraphenylethylene-tetrazole ligand, CUST-805 achieves the visible and reversible PCL from blue to green switched by different external stimuli. The transformation between crystalline and amorphous states is proved to be the origin of present PCL behavior. Moreover, on basis of electron and energy transfer quenching mechanism, the highly selective and sensitive sensor based on CUST-805 is realized, showing the low detection limit of 0.29 ppm towards 2,4,6-trinitrophenol.     

Stable Thiophene-sulfur Covalent Organic Frameworks for Oxygen Reduction Reaction(ORR)

Exploring novel materials deriving from earth resources to substitute for platinum(Pt) electrocatalyst to promote oxygen reduction reaction(ORR) of fuel cell cathode is very important. Herein, we have exploited two crystallographic thiophene-sulfur covalent organic frameworks(COFs), termed JUC-607 and JUC-608, as electrocatalysts that exhibited good ORR performances. These thiophene-sulfur COFs exhibited high stability, and their functional groups acting as active centers in the ORR can be precisely determined. Notably, due to a larger aperture for mass transfer and electrons transport, JUC-608 displayed a growing electrochemical performance, leading to a better ORR activity. Thus, this study will provide a new strategy for designing heteroatom-based COF materials for high-performance electrochemical catalysis.     

偶氮苯功能化的光响应共价有机框架材料

通过后修饰的方法, 在共价有机框架(COFs)材料JUC-500的孔道中引入光敏性的偶氮苯小分子, 合成了具有光热刺激响应的共价有机框架材料JUC-501. 在紫外线和加热作用下, 孔道中的偶氮苯会发生可逆的顺-反异构变化, 对染料污染物甲基橙(MO)表现出优异的可逆吸附与释放性能.     

Porphyrin-based donor–acceptor COFs as efficient and reusable photocatalysts for PET-RAFT polymerization under broad spectrum excitation

Covalent organic frameworks (COFs) are crystalline and porous organic materials attractive for photocatalysis applications due to their structural versatility and tunable optical and electronic properties. The use of photocatalysts (PCs) for polymerizations enables the preparation of well-defined polymeric materials under mild reaction conditions. Herein, we report two porphyrin-based donor–acceptor COFs that are effective heterogeneous PCs for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT). Using density functional theory (DFT) calculations, we designed porphyrin COFs with strong donor–acceptor characteristics and delocalized conduction bands. The COFs were effective PCs for PET-RAFT, successfully polymerizing a variety of monomers in both organic and aqueous media using visible light (λ_max from 460 to 635 nm) to produce polymers with tunable molecular weights (MWs), low molecular weight dispersity, and good chain-end fidelity. The heterogeneous COF PCs could also be reused for PET-RAFT polymerization at least 5 times without losing photocatalytic performance. This work demonstrates porphyrin-based COFs that are effective catalysts for photo-RDRP and establishes design principles for the development of highly active COF PCs for a variety of applications.

Porphyrin-based donor–acceptor COFs are effective heterogeneous photocatalysts for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT), including for aqueous polymerizations and under red-light excitation.     

室温离子液体法合成新型三维共价有机骨架材料

采用室温离子热法合成了一种氟取代的具有五重贯穿金刚石拓扑结构的三维共价有机骨架材料(COFs), 记为JUC-515. 与高温溶剂热法不同的是, 室温离子液体法具有反应温度和压力低、 反应时间短、 操作简单、 无需催化剂和不产生有机蒸汽污染等优势. 制备的材料具有高度结晶性、 较大的孔隙率和良好的CO₂选择性吸附性能.     

Recent Advances in Mechanism of AIE Mechanochromic Materials

Organic mechanochromic materials(also known as piezochromic materials),whose color or emission changes under mechanical force,have attracted great interest owing to their potential applications in pressure sensors,rewritable materials,optical storage,and security ink.Organic mechanochromic materials with aggregation-induced emission(AIE)features have better development prospects and research value owing to their excellent optical properties.To date,mechanochromism has mostly been realized by means of mechanical grinding.Nevertheless,the magnitude of the grinding force is usually uncontrollable and its direction is anisotropic,making it awkward to study the mechanism of mechanochromic materials.On the contrary,hydrostatic pressure,whose magnitude and direction are controllable,is a more valid and governable method to investigate the mechanism of mechanochromic materials,which can help us to construct a meaningful structure-property relationship and understand the latent origin of the mechanochromism.Furthermore,it is conducive to developing other mechanochromic material systems with desired chemical and physical properties.In this review,we focus on the recent progress in the mechanism of organic mechanochromic materials with AIE features under hydrostatic pressure.Four types of mechanisms are included:intermolecular interaction change,intramolecular conformation change,transformation from locally excited state to intramolecular charge-transfer state,and intra-and inter-molecular effects induced by hydrostatic pressure,respectively.     

卟啉-硫醚基共价有机框架材料用于氧还原反应电催化剂

氧还原反应（ORR）是能进行能量存储的核心电化学过程。由于它的动力学速率缓慢,因此亟需制备出高活性的电催化剂来促进这一反应的速率。二维共价有机框架材料（2D COFs）的π-π堆积结构可赋予骨架高导电率,并且一维有序的孔道有利于促进中间反应体传输。因此,其在可再生能源领域中具有良好的应用前景,并有望作为能量存储与转化的强大催化平台。本文通过向2D COFs中引入金属卟啉单元及硫醚单元成功制备了两个2D COFs （JUC-600和JUC-601）。通过多种表征手段证明,这两个2D COFs均具有AA堆积的sql拓扑结构。通过电化学测试表明,Co²⁺配位的JUC-601具有更正的ORR起始电势（0.825 V）和半波电势（0.7 V）、更高的活性表面积（7.8 mF/cm²）,更低的Tafel斜率（58 mV/dec）。这主要是由于JUC-601的高比表面积和高孔隙率使得中间产物能更易在COFs的表面和孔道中接触和传输。此外,Co²⁺-卟啉单元以及硫醚单元的存在使其骨架整体的电子结构发生了变化,更有利于电子转移。这一工作不仅开发了新的二维卟啉-硫醚基COFs材料,同时也拓展了2D COFs材料在电催化领域的应用。     

Photoactivated Fluorescence Enhancement in F,N‐Doped Carbon Dots with Piezochromic Behavior

Photoactivation in CdSe/ZnS quantum dots (QDs) on UV/Vis light exposure improves photoluminescence (PL) and photostability. However, it was not observed in fluorescent carbon quantum dots (CDs). Now, photoactivated fluorescence enhancement in fluorine and nitrogen co‐doped carbon dots (F,N‐doped CDs) is presented. At 1.0 atm, the fluorescence intensity of F,N‐doped CDs increases with UV light irradiation (5 s–30 min), accompanied with a blue‐shift of the fluorescence emission from 586 nm to 550 nm. F,N‐doped CDs exhibit photoactivated fluorescence enhancement when exposed to UV under high pressure (0.1 GPa). F,N‐doped CDs show reversible piezochromic behavior while applying increasing pressure (1.0 atm to 9.98 GPa), showing a pressure‐triggered aggregation‐induced emission in the range 1.0 atm–0.65 GPa. The photoactivated CDs with piezochromic fluorescence enhancement broadens the versatility of CDs from ambient to high‐pressure conditions and enhances their anti‐photobleaching.     

基于四硫富瓦烯的无金属共价有机框架材料用于高效电催化析氧反应

共价有机框架(COFs)在电催化析氧反应(OER)中的应用得到了广泛的关注。然而,大多数无金属共价有机框架(COFs)的导电性较差,不利于OER反应。四硫富瓦烯(TTF)是一种良好的电子供体,具有快速的电子转移能力,将TTF整合到共价有机框架骨架中将有助于电子的转移。在此,我们报道了一种基于四硫富瓦烯的二维无金属共价有机框架材料,JUC-630。与不含四硫富瓦烯的同类材料(Etta-Td COF)相比,JUC-630具有较低的过电位(400 mV)和塔菲尔斜率(104 mV∙dec⁻¹)。本研究提出了合理设计功能基元的策略,这有助于大大提高COF材料的OER催化活性。     

Atomistic Simulation of Structural and Mechanical Properties of the AMgF3 (A = K,Rb, and Cs) Compounds Under Hydrostatic Pressure

Structural, mechanical, elastic, and dielectric properties of the AMgF₃ (A = K, Rb, and Cs) compounds were investigated using classical atomistic simulation. A new set of interatomic potentials was developed for these compounds. Lattice parameters and interatomic distances have shown to accurately reproduce all structures, with very close agreement to the experimental data. In all cases, the relative error is below 0.5%. Effect of hydrostatic pressure in the structural, mechanical, elastic, and dielectric properties of these materials were studied from 0 up to 50 GPa. Compounds behavior and stability under pressure were analyzed. KMgF₃ and RbMgF₃ changed from brittle to ductile at approximately 2 GPa. These calculations play an important role in understanding the properties of the AMgF₃ (A = K, Rb, and Cs) compounds under pressure, and open up a new opportunity to study defects in this class of materials. © 2019 Wiley Periodicals, Inc.     

Photoactivated Fluorescence Enhancement in F,N-Doped Carbon Dots with Piezochromic Behavior

Photoactivation in CdSe/ZnS quantum dots (QDs) on UV/Vis light exposure improves photoluminescence (PL) and photostability. However, it was not observed in fluorescent carbon quantum dots (CDs). Now, photoactivated fluorescence enhancement in fluorine and nitrogen co-doped carbon dots (F,N-doped CDs) is presented. At 1.0 atm, the fluorescence intensity of F,N-doped CDs increases with UV light irradiation (5 s–30 min), accompanied with a blue-shift of the fluorescence emission from 586 nm to 550 nm. F,N-doped CDs exhibit photoactivated fluorescence enhancement when exposed to UV under high pressure (0.1 GPa). F,N-doped CDs show reversible piezochromic behavior while applying increasing pressure (1.0 atm to 9.98 GPa), showing a pressure-triggered aggregation-induced emission in the range 1.0 atm–0.65 GPa. The photoactivated CDs with piezochromic fluorescence enhancement broadens the versatility of CDs from ambient to high-pressure conditions and enhances their anti-photobleaching.     

Hierarchical Microtubular Covalent Organic Frameworks Achieved by COF-to-COF Transformation

Pore environment and aggregated structure play a vital role in determining the properties of porous materials, especially regarding the mass transfer. Reticular chemistry imparts covalent organic frameworks (COFs) with well-aligned micro/mesopores, yet constructing hierarchical architectures remains a great challenge. Herein, we reported a COF-to-COF transformation methodology to prepare microtubular COFs. In this process, the C₃-symmetric guanidine units decomposed into C₂-symmetric hydrazine units, leading to the crystal transformation of COFs. Moreover, the aggregated structure and conversion degree varied with the reaction time, where the hollow tubular aggregates composed of mixed COF crystals could be obtained. Such hierarchical architecture leads to enhanced mass transfer properties, as proved by the adsorption measurement and chemical catalytic reactions. This self-template strategy was successfully applied to another four COFs with different building units.     

Mechanical Properties of Dense Zeolitic Imidazolate Frameworks (ZIFs): A High‐Pressure X‐ray Diffraction,Nanoindentation and Computational Study of the Zinc Framework Zn(Im)2, and its Lithium?Boron Analogue,LiB(Im)4

The dense, anhydrous zeolitic imidazolate frameworks (ZIFs), Zn(Im)₂ ( 1 ) and LiB(Im)₄ ( 2 ), adopt the same zni topology and differ only in terms of the inorganic species present in their structures. Their mechanical properties (specifically the Young’s and bulk moduli, along with the hardness) have been elucidated by using high pressure, synchrotron X‐ray diffraction, density functional calculations and nanoindentation studies. Under hydrostatic pressure, framework 2 undergoes a phase transition at 1.69 GPa, which is somewhat higher than the transition previously reported in 1 . The Young’s modulus (E) and hardness (H) of 1 (E≈8.5, H≈1 GPa) is substantially higher than that of 2 (E≈3, H≈0.1 GPa), whilst its bulk modulus is relatively lower (≈14 GPa cf. ≈16.6 GPa). The heavier, zinc‐containing material was also found to be significantly harder than its light analogue. The differential behaviour of the two materials is discussed in terms of the smaller pore volume of 2 and the greater flexibility of the LiN₄ tetrathedron compared with the ZnN₄ and BN₄ units.     

Pressure-induced phosphorescence enhancement and piezochromism of a carbazole-based cyclic trinuclear Cu(i) complex

Interest in piezochromic luminescence has increased in recent decades, even though it is mostly limited to pure organic compounds and fluorescence. In this work, a Cu₃Pz₃ (Cu3, Pz: pyrazolate) cyclic trinuclear complex (CTC) with two different crystalline polymorphs, namely 1a and 1b, was synthesized. The CTC consists of two functional moieties: carbazole (Cz) chromophore and Cu3 units. In crystals of 1a, discrete Cz–Cu3–Cu3–Cz stacking was found, showing abnormal pressure-induced phosphorescence enhancement (PIPE), which was 12 times stronger at 2.23 GPa compared to under ambient conditions. This novel observation is ascribed to cooperation between heavy-atom effects (i.e., from Cu atoms) and metal–ligand charge-transfer promotion. The infinite π–π stacking of Cz motifs was observed in 1b and it exhibited good piezochromism as the pressure increased. This work demonstrates a new concept in the design of piezochromic materials to achieve PIPE via combining organic chromophores and metal–organic phosphorescence emitters.

One molecule, two response mechanisms: a pair of newly-designed cyclic trinuclear Cu(i) complex crystalline polymorphs are engineered, which show excellent luminescent piezochromism and pressure-induced phosphorescence enhancement, respectively.     

Super‐Hydrated Zeolites: Pressure‐Induced Hydration in Natrolites

High‐pressure synchrotron X‐ray powder diffraction studies of a series of alkali‐metal‐exchanged natrolites, A₁₆Al₁₆Si₂₄O₈₀ ? n H₂O (A=Li, K, Na, Rb, and Cs and n=14, 16, 22, 24, 32), in the presence of water, reveal structural changes that far exceed what can be achieved by varying temperature and chemical composition. The degree of volume expansion caused by pressure‐induced hydration (PIH) is inversely proportional to the non‐framework cation radius. The expansion of the unit‐cell volume through PIH is as large as 20.6 % in Li‐natrolite at 1.0 GPa and decreases to 6.7, 3.8, and 0.3 % in Na‐, K‐, and Rb‐natrolites, respectively. On the other hand, the onset pressure of PIH appears to increase with non‐framework cation radius up to 2.0 GPa in Rb‐natrolite. In Cs‐natrolite, no PIH is observed but a new phase forms at 0.3 GPa with a 4.8 % contracted unit cell and different cation–water configuration in the pores. In K‐natrolite, the elliptical channel undergoes a unique overturn upon the formation of super‐hydrated natrolite K₁₆Al₁₆Si₂₄O₈₀ ? 32 H₂O at 1.0 GPa, a species that reverts back above 2.5 GPa as the potassium ions interchange their locations with those of water and migrate from the hinge to the center of the pores. Super‐hydrated zeolites are new materials that offer numerous opportunities to expand and modify known chemical and physical properties by reversibly changing the composition and structure using pressure in the presence of water.     

Molecular design of a new family of bridged bis(multinitro-triazole) with outstanding oxygen balance as high-density energy compounds

A new family of bridged bis(multinitro-triazole) was designed and investigated using the density functional theory method. The density, oxygen balance, heat of formation, detonation performance, and impact sensitivity were calculated systematically. The results show that the multinitromethyl groups play an important role in increasing densities. At the same time, different bridged groups present diverse performances with high density (1.86-1.96 g·cm⁻³), excellent detonation properties (V = 8.72 km·s⁻¹-9.20 km·s⁻¹; P = 34.54 GPa-39.49 GPa), outstanding oxygen balance (0%-11.59%), and acceptably impact sensitivity. Especially, tetrazine (M7)-bridged and diaminofurazan (M9)-bridged groups are very helpful for enhancing their detonation performance (V_(M7) = 9.12 km·s⁻¹, P_(M7) = 38.51 GPa; V_(M9) = 9.20 km·s⁻¹, P_(M9) = 39.49 GPa), respectively, which are better than RDX. They could be seen as the potential candidates of high energy density materials (HEDMs).     

Piezochromic luminescent (PCL) behavior and aggregation-induced emission (AIE) property of a new cationic iridium(III) complex

A new cationic Ir(III) complex based on a dendritic ancillary ligand has been designed and synthesized, which simultaneously exhibits piezochromic luminescent (PCL) behavior and aggregation-induced emission (AIE) property for the first time.     

Syntheses,Structures, Fluorescence and Magnetism of Six Lanthanide Metal-organic Frameworks Based on Silicon-centered Tetrahedral Ligand

Multifunctional lanthanide metal-organic frameworks(MOFs), M(H₄TCPS)(H₂O)_1.5[M=Tb(JUC-95a), Er(JUC-95b), Dy(JUC-95c), Tm(JUC-95d), Y(JUC-95e) and Pr(JUC-95f); H₄TCPS=tetrakis(4-carboxyphenyl)silane] were synthesized via the reaction of the lanthanide metal ions(Ln₃?) with a rigid silicon-centered tetrahedral carbo- xylate ligand H₄TCPS via a hydrothermal synthesis method. X-Ray diffraction(XRD) analyses reveal that they are extremely similar in structure and crystallized in a monoclinic system with space group C2/c. Two eight-coordinated metal centers and four tetrahedral H₄TCPS groups constructed a paddle-wheel building block. The paddle-wheel buil- ding blocks assembled with each other via one oxygen bridge from a water molecule to lead to a 1D infinite inorganic rod-shaped chain, -Y-O-C-O-Y-, along the [001] direction. These 1D inorganic rod-shaped chains linked with the phenyl groups of the tetrahedral H₄TCPS ligand to form a 3D framework. In addition, the luminescent and magnetic properties of these compounds show that they could be potential antiferromagnetic and fluorescent materials.     

具有高气态碘吸附的二维介孔共价有机框架

合成了一种新型的二维介孔共价有机框架(COF)材料JUC-573. 粉末X射线衍射、 氮气吸附-脱附和热重等表征结果表明合成的COF材料具有高结晶度、 高比表面积以及良好的热稳定性. 在333 K、 常压条件下, 该材料表现出优异的碘吸附能力, 且吸附量高达4.15 g/g. 这是由于在JUC-573中规则定向的垂直一维介孔孔道能够有效地避免碘吸附后的堵塞, 从而优化了材料的吸附能力. JUC-573可多次循环用于气态碘的捕获且保持几乎不变的吸附量.