title: Accumulative electron transfer: multiple charge separation in artificial photosynthesis.
abstract: To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru(II)-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme.
authors.affiliation: Department of Photochemistry and Molecular Science, Uppsala University, Box 523, SE-751 20 Uppsala, Sweden.
authors.forename: Susanne
authors.initials: S
authors.lastname: Karlsson
authors.forename: Julien
authors.initials: J
authors.lastname: Boixel
authors.forename: Yann
authors.initials: Y
authors.lastname: Pellegrin
authors.forename: Errol
authors.initials: E
authors.lastname: Blart
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Becker
authors.forename: Fabrice
authors.initials: F
authors.lastname: Odobel
authors.forename: Leif
authors.initials: L
authors.lastname: Hammarström
mesh_terms: D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D056831:Coordination Complexes / Q000737:chemistry / Q000378:metabolism; D004579:Electron Transport; D004583:Electrons; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D010777:Photochemistry; D017785:Photons; D017319:Photosensitizing Agents / Q000737:chemistry; D010788:Photosynthesis; D012428:Ruthenium / Q000737:chemistry* / Q000378:metabolism; D055672:Static Electricity; D014025:Titanium / Q000737:chemistry; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D056831:Coordination Complexes; D017319:Photosensitizing Agents; D014867:Water; D002734:Chlorophyll; C009495:titanium dioxide; D012428:Ruthenium; D014025:Titanium; D010100:Oxygen