Supramolecular self-assembly and application of metal clusters

Metal nanoclusters (NCs) are relatively stable aggregates composed of several to several thousand metal atoms through physical or chemical bonding, and their size is generally less than 3 nm. It has excellent quantum size effect and has outstanding applications in many fields such as optics, electricity, magnetism, catalysis, chirality, etc. However, NCs have poor optical properties at room temperature, which limits their further applications in the optical field. Therefore, the assembly of metal clusters with different types of molecular materials is driven by non-covalent bonds inspired by the concepts of "aggregation-induced emission" (AIE) and "supramolecular chemistry", which can not only regulate the optical properties of metal clusters, but also can realize multi-functional coordination. As an important category of supramolecular chemistry, self-assembly provides a way to construct ordered structures from the bottom up. Self-assembly mainly uses non-covalent interactions to precisely control the specific structure of the building element to obtain functionalized micro-nano materials. Supramolecular self-assembly is one of the hot research fields in the chemical industry. It has been widely used in biomedicine, environment, sensing, optoelectronic devices and catalysis due to its simple operation and easy availability of raw materials. Herein, firstly, this paper introduces the effect of self-assembly on the assembly structure in detail combining the research work of this research group and related research on the self-assembly of design metal clusters at home and abroad. The research involving the aggregation morphology and morphology of metal nanoclusters is currently in its infancy in the world, and is a relatively popular research topic. Therefore, the self-assembly strategy to achieve the control of the aggregation morphology and morphology of metal nanoclusters can enrich the research field of self-assembly and realize the functionalization of metal nanoclusters. Secondly, fluorescence is one of the most important properties of metal clusters. Compared with traditional PL materials, the quantum yield (QY) of metal nanoclusters is relatively low. In addition, the proportion of fluorescent metal nanoclusters is also very low. Therefore, precise control of the metal composition and clearly defined surface chemistry factors not only provide a basis for a firm understanding of the structure and fluorescence, but also provide a method for the design and preparation of new nanoclusters with PL enhancement and adjustable emission wavelength. Hence, the vibration and rotation of the ligands around the metal core can be effectively restricted, and non-radiative transitions can be reduced, thereby achieving enhanced fluorescence through self-assembly. The fluorescence intensity and emission wavelength of the metal clusters can be controlled by controlling the assembly conditions of the metal clusters. The effect of self-assembly on the luminescence of metal clusters is commonly regulated by solvent regulation, pH, and co-assembly of other molecules to obtain highly stable luminescent clusters. In addition, the research progress in the application of metal cluster assembly and other aspects are summarized. Although precious metal nanoclusters have been used in chemical sensing, biological fields, catalysis and light conversion materials, the stability of the metal nanoclusters itself is relatively poor and the fluorescence is relatively weak. The assembly of nanoclusters can well solve the above shortcomings. The cluster aggregates have strong PL intensity, good light stability, and wide emission wavelength, which makes it a new type of fluorophore used in chemical sensing, biological fields, catalysis and light conversion materials. Finally, the improved scope and future prospects of the new nanoclusters are summarized and emphasized. Our review is expected to open up new horizons for these scientists to effectively control the functional properties of nanoclusters.