Water oxidation is a key step common to most artificial photosynthetic reaction schemes.[1] It is a very complex process, involving the 4-electron oxidation of two water molecules, the formation of a new O-O bond, and the release of four protons. As such, it is considered to be the real bottleneck towards artificial photosynthesis.[2] In a standard photocatalytic cycle, a strong oxidant is irreversibly generated by reaction of an excited photosensitizer (P) and a sacrificial electron acceptor (S) that decomposes upon reduction. The photocatalytic mechanism leading to water oxidation is generally assumed to involve four sequential hole transfer steps from the photochemically oxidized sensitizer to the catalyst (C), which then evolves to a series of high valent intermediates. In this communication we present a study addressing the kinetics of hole transfer processes involved in sacrificial systems as described above, where the sensitizer P is Ru(bpy)32+, the sacrificial acceptor S is S2O82-, the decomposition products of S- are SO42- and SO4- and several ruthenium- and cobalt-based tetrametallic molecular clusters are used as the catalyst C. In these type of processes the oxidized sensitizer is irreversibly produced so that, in principle, very fast hole transfer is not a strict requirement. In practice, however, the sensitizers, in their oxidized form, are often unstable under the reaction conditions used and fast hole scavenging is determinant to minimize their decomposition (usually the main limiting factor in terms of turnover performance). On the other hand, fast hole-transfer rates will become absolutely crucial in regenerative systems where the catalyst must be able to scavenge the hole on the photogenerated oxidant in competition with charge recombination.[3] In addition, given the different structural and chemical nature of each catalyst, special attention has been paid to the interactions with the sensitizer in water solution and its photophysical and kinetic consequences.

Tetrametallic Oxygen Evolution Catalysts. Primary Interactions and Photochemical Processes with Ru(bpy)32+ Photosensitizer

NATALI, Mirco;SCANDOLA, Franco
2012

Abstract

Water oxidation is a key step common to most artificial photosynthetic reaction schemes.[1] It is a very complex process, involving the 4-electron oxidation of two water molecules, the formation of a new O-O bond, and the release of four protons. As such, it is considered to be the real bottleneck towards artificial photosynthesis.[2] In a standard photocatalytic cycle, a strong oxidant is irreversibly generated by reaction of an excited photosensitizer (P) and a sacrificial electron acceptor (S) that decomposes upon reduction. The photocatalytic mechanism leading to water oxidation is generally assumed to involve four sequential hole transfer steps from the photochemically oxidized sensitizer to the catalyst (C), which then evolves to a series of high valent intermediates. In this communication we present a study addressing the kinetics of hole transfer processes involved in sacrificial systems as described above, where the sensitizer P is Ru(bpy)32+, the sacrificial acceptor S is S2O82-, the decomposition products of S- are SO42- and SO4- and several ruthenium- and cobalt-based tetrametallic molecular clusters are used as the catalyst C. In these type of processes the oxidized sensitizer is irreversibly produced so that, in principle, very fast hole transfer is not a strict requirement. In practice, however, the sensitizers, in their oxidized form, are often unstable under the reaction conditions used and fast hole scavenging is determinant to minimize their decomposition (usually the main limiting factor in terms of turnover performance). On the other hand, fast hole-transfer rates will become absolutely crucial in regenerative systems where the catalyst must be able to scavenge the hole on the photogenerated oxidant in competition with charge recombination.[3] In addition, given the different structural and chemical nature of each catalyst, special attention has been paid to the interactions with the sensitizer in water solution and its photophysical and kinetic consequences.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2340173
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