Synthetic breakthrough to control the assembly of functional groups versus chaotic mixing
Multifunctional porous solids with various functionalized binders have been used as promising materials for various energy, environmental and biomedical applications. Although their emerging properties are attributed to different types of pores resulting from combinations of functional groups, the chemical environment of the pores remains an open question. Of great interest to materials science is a novel synthetic platform where the pore population can be identified and further controlled.
A research team, led by Professor Wonyoung Choe and Professor Tae-Hyuk Kwon from the Department of Chemistry at the National Institute of Science and Technology in Ulsan (UNIST), South Korea, recently unveiled a new synthetic approach to control assemblies of functional groups in porous solids using a cage-based framework, also known as organometallic polyhedra (MOP). Their findings are expected to have gained attention as a useful synthetic strategy for catalysis, gas storage, and molecular separation.
MOPs are the three-dimensional assembly of discrete cages. While MOPs share compositional similarities (i.e., metal clusters and organic binders) with their solid state counterparts, metal-organic frameworks (MOFs), the discrete and soluble nature of MOP offers a unique advantage. In their study, the research team developed a two-step self-assembly where functionalized cages are mixed. The authors call the new synthetic strategy the “mixed cage”, which is radically different from the conventional mixing strategy, called “mixed linker”. While the mixed-linker strategy results in a random distribution of organic linkers functionalized on the frame, the mixed-cage strategy produces identical functional groups on each cage unit.
In addition, the research team demonstrated a distinct solvatochromic behavior between two multifunctional solids produced by mixed binding and mixed cage strategies. They studied the color changes of fluorescence emissions as a function of the polarity of the solvent. While the mixed linker sample showed pronounced color changes, the mixed cage sample was only slightly affected by solvent types. The authors further discovered detailed photophysical properties using films. Attributed to the radiative decay kinetics of the mixed-cage sample, higher than that of the mixed linker sample, a higher emission intensity was observed for the mixed-cage sample.
“Structure determines function and solids are no exception,” said Professor Wonyoung Choe. “Yet what is more interesting here is that we find a new way to control the assembly of the gaskets, using organometallic polyhedra.” He adds, “Such a breakthrough may change the way we control molecular-based solids.”
The results of this research were published in Material on May 26, 2021. This study was supported by the National Research Foundation (NRF) of Korea through the Mid-Career Researcher Program, the Science Research Center (SRC), the Technology Development Program to Solve Climate Changes and the Global Ph.D . Fellowship (GPF), as well as the Korea Institute of Environmental Industry and Technology (KEITI) under the public technology program based on the environmental policy program, funded by the Korean Ministry of environment (MOE).
Dongsik Nam, Jiyeon Kim, Eunhye Hwang, Joohan Nam, Hyein Jeong, Tae-Hyuk Kwon and Wonyoung Choe, “Multivariate Porous Platform Based on Metal-Organic Polyhedra with Controllable Functionality Assembly”, Material, (2021).
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