Zwitterion mediator/quenchers. Coulombic minimization of the back-reaction in photocatalysis
- 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), Vol. 86:6
- Country of Publication:
- United States
- Language:
- English
Similar Records
Photoreduction of methyl viologen mediated by tris(bipyridyl)ruthenium(II) in inert colloidal suspensions
Photoinduced redox reactions in aqueous micelles. Quenching, back-reaction, and competing processes for tetraanionic porphyrins with alkylviologens
Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
08 HYDROGEN
BIPYRIDINES
CATALYTIC EFFECTS
CHEMICAL REACTIONS
PORPHYRINS
RUTHENIUM COMPLEXES
ZINC COMPLEXES
ELECTRON TRANSFER
EXCITED STATES
HYDROGEN PRODUCTION
ORGANIC SULFUR COMPOUNDS
PHOTOLYSIS
QUENCHING
RECOMBINATION
REDUCTION
WATER
AZINES
CARBOXYLIC ACIDS
COMPLEXES
DECOMPOSITION
ENERGY LEVELS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PYRIDINES
TRANSITION ELEMENT COMPLEXES
400500* - Photochemistry
080106 - Hydrogen- Production- Biosynthesis & Photochemical Processes