Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

Efficient removal of organic pollutants from wastewater has become a hot research topic due to its ecological and environmental importance. Traditional water treatment methods such as adsorption, coagulation, and membrane separation suffer from high operating costs, and even generate secondary pollutants. Photocatalysis on semiconductor catalysts (TiO2, ZnO, Fe2O3, CdS, GaP, and ZnS) has demonstrated efficiency in degrading a wide range of organic pollutants into biodegradable or less toxic organic compounds, as well as inorganic CO2, H2O, NO3−, PO43−, and halide ions. However, the difficult post-separation, easy agglomeration, and low solar energy conversion efficiency of these inorganic catalysts limit their large scale applications. Exploitation of new catalysts has been attracting great attention in the related research communities. In the past two decades, a class of newly-developed inorganic–organic hybrid porous materials, namely metal–organic frameworks (MOFs) has generated rapid development due to their versatile applications such as in catalysis and separation. Recent research has showed that these materials, acting as catalysts, are quite effective in the photocatalytic degradation of organic pollutants. This review highlights research progress in the application of MOFs in this area. The reported examples are collected and analyzed; and the reaction mechanism, the influence of various factors on the catalytic performance, the involved challenges, and the prospect are discussed and estimated. It is clear that MOFs have a bright future in photocatalysis for pollutant degradation.

Photocatalytic organic pollutants degradation in metal–organic frameworks

The possibility to change the molecular assembled structures of organic and organometallic materials through mechanical stimulation is emerging as a general and powerful concept for the design of functional materials. In particular, the photophysical properties such as photoluminescence color, quantum yield, and emission lifetime of organic and organometallic fluorophores can significantly depend on the molecular packing, enabling the development of molecular materials with mechanoresponsive luminescence characteristics. Indeed, an increasing number of studies have shown in recent years that mechanical force can be utilized to change the molecular arrangement, and thereby the optical response, of luminescent molecular assemblies of π-conjugated organic or organometallic molecules. Here, the development of such mechanoresponsive luminescent (MRL) molecular assemblies consisting of organic or organometallic molecules is reviewed and emerging trends in this research field are summarized. After a brief introduction of mechanoresponsive luminescence observed in molecular assemblies, the concept of "luminescent molecular domino" is introduced, before molecular materials that show turn-on/off of photoluminescence in response to mechanical stimulation are reviewed. Mechanically stimulated multicolor changes and water-soluble MRL materials are also highlighted and approaches that combine the concept of MRL molecular assemblies with other materials types are presented in the last part of this progress report.

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Mechanoresponsive Luminescent Molecular Assemblies: An Emerging Class of Materials

Nitroarene reduction: a trusted model reaction to test nanoparticle catalysts

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Metal-Organic Framework-Based Catalysts with Single Metal Sites.

A multifunctional helical Cu(I) coordination polymer with mechanochromic, sensing and photocatalytic properties.

Two isomeric two-dimensional copper(I) coordination polymer materials based on an in situ generated 5-(3-pyridyl)tetrazole ligand show similar layer structures but distinct photoluminescent and photocatalytic properties, which present an interesting comparative study on the structure–property correlation between isomeric materials.

Two-dimensional copper(I) coordination polymer materials as photocatalysts for the degradation of organic dyes.

Synthetic design of functional boron imidazolate frameworks

Two copper(I) halide-based coordination polymers, namely, [Cu3Cl2(Tipa)2]Cl (1, (Tipa = tris(4-(1H-imidazol-1-yl)phenyl)amine) and [Cu3I3(CuI)2(Tipa)3] (2), were obatined under the solvothermal reactions, respectively. Compound 1 with the chain structure shows unique Cu···Cu interactions, C–H···Cl halogen hydrogen bonds, and π···π stacking interactions. It also exhibits unusual mechanochromic and photocatalytic properties on degradation of methylene blue (MB).

Tian Wen

Papers

A multifunctional helical Cu(I) coordination polymer with mechanochromic, sensing and photocatalytic properties.

Two-dimensional copper(I) coordination polymer materials as photocatalysts for the degradation of organic dyes.

Synthetic design of functional boron imidazolate frameworks

Synthesis of Halide-Modulated Cuprous(I) Coordination Polymers with Mechanochromic and Photocatalytic Properties.

Redox-active Cu(I) boron imidazolate framework for mechanochromic and catalytic applications