Rebirth of microcrystalline hybrid inorganic and organic crystals – new optical properties, new applications

Over the last twenty years, porous coordination polymers 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. Coordination polymers are usually made out of metal centres or metal-oxo units which can be coordinated via manifold ways with organic electron-donating ligands. Coordination polymers 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 coordination polymers 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.

Nevertheless, determination of the structure of coordination polymers that meet the specifications for specific light emission sensors 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 d10 metal building units were usually embraced as luminescent cations in the production of fluorescent coordination polymers.

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.