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High-Redox-Potential Chromophores for Visible-Light-Driven Water Oxidation at Low pH
journal contribution
posted on 2019-12-13, 20:11 authored by Lei Wang, David W. Shaffer, Gerald F. Manbeck, Dmitry E. Polyansky, Javier J. ConcepcionPhotochemical water oxidation at low pH requires chromophores
with
adequate photophysical properties and high redox potentials capable
of oxidizing the catalysts. We report here a series of homoleptic
Ru(II) polypyridyl complexes and their performances in photochemical
water oxidation at pH 1 using persulfate as the sacrificial electron
acceptor. These chromophores incorporate CF3 or PO3H2 groups to increase the RuIII/II standard
potentials to 1.3–1.6 V versus NHE, while their homoleptic
nature retains photophysical properties (absorption spectra, lifetimes,
emission energies, emission quantum yields) comparable to [Ru(bpy)3]2+. With [(bda)Ru(isq)2] as the catalyst,
the chromophores promote visible-light-driven water oxidation with
high activity at low pH. The chromophores with phosphonate groups
as substituents showed higher activity than expected based on driving
force arguments. In addition, kinetic isotope effects as high as ∼3
were measured, suggesting the involvement of concerted proton-coupled
transfer pathways between the catalyst and the chromophores with the
phosphonate group acting as the proton acceptor. These chromophores
therefore carry out the light absorption, charge migration, and proton
transfer roles of P680, Tyr161, and His190 in Photosystem
II on a single molecule and are good candidates for photoelectrochemical
water oxidation at low pH in dye-sensitized photoelectrochemical cells.
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photoelectrochemical water oxidationRuchromophorePO 3 H 2 groupsIIvisible-light-driven water oxidationLow pH Photochemical water oxidationproton-coupled transfer pathwaysphotophysical propertiesVisible-Light-Driven Water OxidationCFcatalystdye-sensitized photoelectrochemical cellsproton transfer rolesNHEIIIemission quantum yields
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