Authors: Yingmu Zhang
Source: OakTrust (Texas A&M University Libraries) (article, 2019-05-29)
Field: Chemistry — Inorganic Chemistry

Tuning the Structure and Functionality of Metal-Organic Frameworks via Linker Design Metal-organic frameworks (MOFs) are a fascinating class of porous materials that have shown great promise in numerous applications. As one of the building components, organic linkers play an important role in dictating MOF synthesis. The geometry and connectivity of a linker determine the MOF structure, while linkers with desired functional groups lead to the application-orientated MOFs. In this dissertation, we will focus on MOF synthesis via linker design, discussing building MOFs with unique properties for targeted applications, especially for heterogeneous catalysis and chemo-sensing.\n \nMOFs prove to be an ideal platform to bear catalytic-active sites for heterogeneous catalysis. These active sites can be directly functionalized onto the organic linkers. In one of my projects, through topology-guided synthesis, a terpyridine-containing mesoporous MOF was successfully constructed, adopting a β-cristobalite-type structure. The MOF incorporates well-arranged terpyridine coordination sites for facile post-synthetic metalation, which can be effectively applied as a general scaffold for the preparation of noble-metal-free catalysts.\n \nMOFs have also been enacted in solar-energy conversion for photochemical synthesis by means of converting molecular oxygen to reactive oxygen species (ROS). However, visible-light responsive MOFs for oxygen activation remains scarce. To achieve this goal, we synthesized two visible-light responsive MOFs, namely, PCN-822(M) (M= Zr, Hf), which are constructed from a 4,5,9,10-(k-region) substituted pyrene-based ligand. With a broad-band adsorption from 225 nm to 650 nm, these MOFs can be applied as efficient ROS generators under visible-light excitation, while the hafnium-based MOF, PCN-822(Hf), can promote the oxidation of amines to imines by synergistic photoinduced energy and charge transfer to active molecular oxygen.\n\nFunctionalization with π-conjugated fluorescent moieties on the linkers, MOFs can serve as efficient luminescent sensors for molecular recognition. A new luminescent mesoporous MOF, PCN-604, was synthesized from a pyridyl-based linker. Due to the extra open metal site on the pyridyl group, PCN-604 shows a fast fluorescence-quenching response towards trace amounts of Fe³⁺ ions. Moreover, this material has exceptional stability in water, enabling performance in aqueous systems.\n \nThe photoluminescent properties of an organic linker can also be tuned by the MOF structure. A novel metal-organic framework, PCN-811, was constructed by an AIEE-featured triphenylene-based hexatopic linker. The rigidifiying effect of the framework enhances the absolute quantum yield of the linker 4-fold in comparison with that of free-state linker. Moreover, with its electron-rich triphenylene core, PCN-811 exhibits an record-high sensing capability towards electron-deficient 2,4,6-trinitrophenol (TNP) in aqueous media. Linker ; Metal-organic framework ; Computer science ; Chemistry ; Nanotechnology ; Materials science ; Organic chemistry ; Programming language Metal-Organic Frameworks: Synthesis and Applications ; X-ray Diffraction in Crystallography