Browsing by Author "Cornelio J"

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    Photoinduced Electron Transfer in Multicomponent Truxene-Quinoxaline Metal-Organic Frameworks
    (American Chemical Society, 2022-09-27) Cornelio J; Lee SJ; Zhou T-Y; Alkaş A; Thangavel K; Pöppl A; Telfer SG
    Metal-organic frameworks (MOFs) can respond to light in a number of interesting ways. Photochromism is observed when a structural change to the framework is induced by the absorption of light, which results in a color change. In this work, we show that introducing quinoxaline ligands to MUF-7 and MUF-77 (MUF = Massey University Framework) produces photochromic MOFs that change color from yellow to red upon the absorption of 405 nm light. This photochromism is observed only when the quinoxaline units are incorporated into the framework and not for the standalone ligands in the solid state. Electron paramagnetic resonance (EPR) spectroscopy shows that organic radicals form upon irradiation of the MOFs. The EPR signal intensities and longevity depend on the precise structural details of the ligand and framework. The photogenerated radicals are stable for long periods in the dark but can be switched back to the diamagnetic state by exposure to visible light. Single-crystal X-ray diffraction analysis reveals bond length changes upon irradiation that are consistent with electron transfer. The multicomponent nature of these frameworks allows the photochromism to emerge by allowing through-space electron transfer, precisely positioning the framework building blocks, and tolerating functional group modifications to the ligands.
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    Tuning the Stereoselectivity of an Intramolecular Aldol Reaction by Precisely Modifying a Metal-Organic Framework Catalyst
    (Wiley-VCH GmbH, 2022-06-15) Cornelio J; Telfer SG
    We report the catalysis of an enantioselective, intramolecular aldol reaction accelerated by an organocatalyst embedded in a series of multicomponent metal-organic frameworks. By precisely programming the pore microenvironment around the site of catalysis, we show how important features of an intramolecular aldol reaction can be tuned, such as the substrate consumption, enantioselectivity, and degree of dehydration of the products. This tunability arises from non-covalent interactions between the reaction participants and modulator groups that occupy positions in the framework remote from the catalytic site. Further, the catalytic moiety can be switched form one framework linker to another. Deliberately building up microenvironments that can influence the outcome of reaction processes in this way is not possible in conventional homogenous catalysts but is reminiscent of enzymes.