Zwitterion mediator/quenchers. Coulombic minimization of the back-reaction in photocatalysis

Journal Article · Thu Mar 18 04:00:00 EST 1982 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100395a021· OSTI ID:5678727

Brugger, P A ^[1]; Graetzel, M; Guarr, T; McLendon, G

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1. Ecole Polytechnique Federale, Lausanne, Switzerland

Zwitterionic analogues of methyl viologen, N,N'-bis(carboxyethyl)-4,4'-bipyridyl (CEB), and N,N'-bis(sulfonatopropyl)-4,4'-bipyridyl (SPB) have been studied as electron-transfer quenchers of excited-state photocatalysts. The molecules are formally neutral when oxidized but become negatively charged when reduced. This charge buildup minimizes undesirable back-recombination of the photogenerated redox products. This Coulombic effect is demonstrated both by direct flash photolysis measurements of back-recombination and by catalytic studies of water reduction. Results are compared for the zwitterion quenchers and methyl viologen, reacting with soluble anionic porphyrins and with micelle-associated reactants. For the anionic porphyrin system zinc tetrakis (sulfonatophenyl)porphyrin(4-) the rates of back-recombination are as follows: ZnTSPP/sup 3 -/ + MV/sup +/...-->.. ZnTSPP/sup 4 -/ + MV/sup 2 +/ (k), k = 2 x 10/sup 9/M/sup -1/s/sup -1/; ZnTSPP/sup 3 -/ + CEB/sup -/. ..-->.. ZnTSPP/sup 4 -/ + CEB +- (k), k = 6 x 10/sup 8/ M/sup -1/ s/sup -1/. In a corresponding catalytic system incorporating ZnTPPS as the photoacceptor, CEB or methyl viologen as the quencher, and N-phenylglycine as the electron donor, a >2-fold enhancement of catalysis is observed by replacing MV/sup 2 +/ with CEB. These events can be greatly accentuated by increasing the charge on the components, via micellar localization. Thus, by using an amphiphilic derivative of Ru(bpy)/sub 3//sup 2 +/ as photoactive donor solubilized in anionic micelles and SPB as electron acceptor, one can achieve 200-fold reduction in the rate of the back-reaction.

• OSTI ID: 5678727
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 86:6; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
080106 -- Hydrogen-- Production-- Biosynthesis & Photochemical Processes
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AZINES
BIPYRIDINES
CARBOXYLIC ACIDS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
COMPLEXES
DECOMPOSITION
ELECTRON TRANSFER
ENERGY LEVELS
EXCITED STATES
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
HYDROGEN PRODUCTION
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PORPHYRINS
PYRIDINES
QUENCHING
RECOMBINATION
REDUCTION
RUTHENIUM COMPLEXES
TRANSITION ELEMENT COMPLEXES
WATER
ZINC COMPLEXES