Membrane-Organized Chemical Photoredox Systems

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This project has three interrelated goals relevant to solar water photolysis, which are to develop: (1) vesicle-organized assemblies for H2 photoproduction that utilize pyrylium and structurally related compounds as combined photosensitizers and cyclic electroneutral transmembrane electron carriers; (2) transmembrane redox systems whose reaction rates can be modulated by light; and (3) homogeneous catalysts for water oxidation. In area (1), initial efforts to photogenerate H2 from vectorially-organized vesicles containing occluded colloidal Pt and commonly available pyrylium ions as transmembrane redox mediators were unsuccessful. New pyrylium compounds with significantly lower reduction potentials have been synthesized to address this problem and their apparent ... continued below

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Hurst, James K. May 15, 2007.

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Description

This project has three interrelated goals relevant to solar water photolysis, which are to develop: (1) vesicle-organized assemblies for H2 photoproduction that utilize pyrylium and structurally related compounds as combined photosensitizers and cyclic electroneutral transmembrane electron carriers; (2) transmembrane redox systems whose reaction rates can be modulated by light; and (3) homogeneous catalysts for water oxidation. In area (1), initial efforts to photogenerate H2 from vectorially-organized vesicles containing occluded colloidal Pt and commonly available pyrylium ions as transmembrane redox mediators were unsuccessful. New pyrylium compounds with significantly lower reduction potentials have been synthesized to address this problem and their apparent redox potentials in functioning systems have been now evaluated by using a series of occluded viologens. These studies provide an estimate of thermodynamic constraints imposed by these assemblies on hydrogen photoproduction. In area (2), spirooxazine-quinone dyads have been synthesized and their capacity to function as redox mediators across bilayer membranes has been evaluated through continuous photolysis and transient spectrophotometric measurements. These studies provide information on how quinone pools transfer charge in biomimetic systems designed to store solar energy as transmembrane electrochemical gradients. Photoisomerization of the spiro moiety to the ring-open mero form caused net quantum yields to decrease significantly, providing a basis for photoregulation of transmembrane redox; unexpectedly, both electrogenic and electroneutral pathways were observed, which were dependent upon the isomeric state of the chromophore (mero vs. spiro) and quinone substituent groups. Research on water oxidation (area 3) has been directed at understanding mechanisms of catalysis by cis,cis-[(bpy)2Ru(OH2)]2O4+ and related polyimine complexes. Using a variety of physical techniques, we have: (i) identified the redox state of the complex ion that is catalytically active; (ii) shown using 18O isotopic labeling that there are two reaction pathways, both of which involve participation of solvent H2 O; and (iii) detected by EPR and resonance Raman spectroscopies new species which may be key intermediates in the catalytic cycle. Analogs containing substituted bipyridine ligands have been synthesized to probe molecular details of these reactions whose understanding is necessary for rational design of superior catalysts.

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  • Report No.: DOE/ER/14943-3(final)
  • Grant Number: FG03-99ER14943
  • DOI: 10.2172/903348 | External Link
  • Office of Scientific & Technical Information Report Number: 903348
  • Archival Resource Key: ark:/67531/metadc888148

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  • May 15, 2007

Added to The UNT Digital Library

  • Sept. 22, 2016, 2:13 a.m.

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  • Nov. 7, 2016, 3:09 p.m.

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Hurst, James K. Membrane-Organized Chemical Photoredox Systems, report, May 15, 2007; United States. (digital.library.unt.edu/ark:/67531/metadc888148/: accessed January 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.