Rebirth of microcrystalline hybrid inorganic and organic crystals – new optical properties, new applications
Creators: name: Zheng, Min
Publisher: name: figshare
Year: 2022
Subjects: subject: 30301 Chemical Characterisation of Materials
subject: FOS: Chemical sciences
subject: 39999 Chemical Sciences not elsewhere classified
subject: Inorganic Chemistry
subject: 30299 Inorganic Chemistry not elsewhere classified
subject: 30304 Physical Chemistry of Materials
subject: 30206 Solid State Chemistry

description: Over the last twenty years, porous metal-organic frameworks have grown as a new class of hybrid inorganic and organic crystals have demonstrated a wide array of applications such as sensors, light emission devices, nonlinear optical materials because of their huge chemical and structural diversity. Metal-organic frameworks are usually made out of metal centres or metal-oxo units which can be coordinated via manifold ways with organic electron-donating ligands. Metal-organic frameworks can be accessed by design and synthesis with variable high porosities, huge specific surfaces with uniform pore sizes as well as functional structure. These structural characteristics allow them to be excellent luminescent sensing probes. Because of that, the functional pore surface used as chemical sensors may enhance molecular recognition by interactions between host and guest, such as coordination bonds and pi-pi interactions or even simple hydrogen bonding. Moreover, large surface areas can direct analytes directly to pores thereby increasing the limit of detection. Additionally, optical sensors have distinct advantages over traditional methods as well as advanced analytical instruments, such as rapid response, simplicity, selectivity, and they can be used in solid state as well as solution. In the past several years, many microcrystalline metal-organic frameworks have been utilized successfully for nonlinear optical applications as well as luminescent sensors. They have demonstrated superior performance with high sensitivity to explosive compounds such as nitrocompounds, cations, anions and small species and other small molecules. There are two general methods are used to synthesize of SHG-active metal-organic frameworks ( metal-organic frameworks): (i) the use of enantiopure linkers or the induction by chiral sources like catalysts, additives and solvents and template molecules in addition to (ii) spontaneously breaking symmetry process that is derived from achiral ligands without the use the presence of active optical linkers or the use of reagents. The second method is generally more appealing as these compounds are costly. The synthesis of homochiral metal-organic frameworks made from achiral precursors is not well-studied. Typically the flexible and achiral linkers are used to make homochiral metal-organic frameworks due to their diverse structure and coordination modes and homochiral structures made using rigid achiral linkers are not well documented. The spontaneous symmetry breaking crystallization of achiral material to create homochiral metal-organic frameworks is extremely rare due to the existence of racemic twins and especially high-dimensional metal-organic frameworks. A few homochiral crystal structures in the bulk of crystals were found in the past. Thus, the efficient synthesizing of chiral high-dimensional metal-organic frameworks made from an achiral source presents an immense issue in the field materials science. Worth noting is that homochirality brings about one of the most interesting nonlinear optical (NLO) properties of metal-organic frameworks – second harmonic generation. Nevertheless, determination of the structure of metal-organic frameworks that meet the specifications for specific light emission functionalities remains an enormous challenge for scientists working in the field of various chemical sciences. For these materials the right selection of metal center and functional organic ligand that has been predesigned as a linker is a crucial component of their fluorescent properties. It is known that the d<sup>10</sup> metal building units were usually embraced as luminescent cations in the production of fluorescent metal-organic frameworks. Finally, the incorporation of organic functional linkers that have guest-accessible sites on the surface of the pore demonstrated to be an easy and efficient approach to improve molecular detection in future coordination polymer materials.