PHOTO-ACTIVE AND REDOX-ACTIVE METAL-ORGANIC FRAMEWORKS FOR SOLAR ENERGY UTILIZATION Public Deposited

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  • March 22, 2019
Creator
  • Kent, Caleb
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Isomorphous metal-organic frameworks (MOFs) based on photo-active Ru(II) or Os(II) polypyridal complex building blocks with characteristic strong visible light absorption, and long-lived, high-energy excited states were designed and synthesized to study the classic Ru to Os energy transfer process for applications in light-harvesting with supramolecular assemblies. The crystalline nature of MOFs allows for determination of the distances between metal centers by X-ray diffraction. The Os doping level was systematically varied to experimentally determine relative rates of energy migration. Several structures demonstrated rapid excited state energy transfer and nano/microscale MOFs were synthesized for light harvesting experiments. Suspensions of the particles were quenched by both oxidative and reductive electron transfer reagents at the crystal-solution interface. In a remarkable case, greater than 98% steady-state emission quenching is observed by energy migration over hundreds of nanometers and interfacial electron-transfer. A quantitative Stern-Volmer analysis was developed to distinguish between static and dynamic quenching mechanisms and determine the rates of electron transfer. The light harvesting characteristics of the MOFs allow them to be utilized as highly responsive sensors by an amplified quenching mechanism with the highest triplet excited state amplification in the literature. Strong noncovalent interactions between the MOF microcrystal surface and cationic quencher molecules coupled with rapid energy transfer through the MOF microcrystal facilitates amplified quenching with an enhancement of 7000-fold in the Stern-Völmer quenching constant compared to a model complex. Additional work has investigated a surprising ligand based singlet-triplet equilibrium in the stable complex [Ru(bpy)2(phendione)]2+. A singlet ground state is observed in low temperature SQUID experiments while a thermally populated triplet is observable at room temperature in acetonitrile as confirmed by variable temperature NMR and EPR experiments. DFT calculations confirm that the lowest energy triplet is ligand based and the energy gap can be tuned by substituent effects of the bpy ligands. Incorporation of photo-active Ru polypyridal complexes into MOFs has led to a new class of materials that show promise in light harvesting and amplified quenching. Future work will attempt to exploit the antenna like behavior of these materials for use in photocatalytic systems and by integration into photovoltaic devices.
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  • In Copyright
Advisor
  • Lin, Wenbin
Degree
  • Doctor of Philosophy
Graduation year
  • 2012
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