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Photoinduced Intramolecular Electron Transfer in Ruthenium and Osmium Polyads: Insights from Theory
journal contribution
posted on 2004-09-01, 00:00 authored by Ilaria Ciofini, Philippe P. Lainé, Fethi Bedioui, Carlo AdamoRu(II) and Os(II) complexes (P) of [4‘-(p-phenyl)]terpyridyl ligand (ptpy) derivatized with an electron
acceptor (A) of the triphenylpyridinium (H3TP+) type have been recently proposed as functional models for
electron-transfer (ET) processes in the context of artificial photosynthesis. These inorganic dyads, P−A,
are expected to undergo intramolecular photoinduced ET to form a charge separated (CS) state of pivotal
interest. To draw a complete picture of possible ET processes, the ground- and excited-state properties of
these complexes, both in their native and monoreduced forms, have been studied by the means of density
functional theory (DFT). A time-dependent-DFT approach (TDDFT) was used to interpret the electronic
spectra, while additional spectroscopic measurements have been carried out in order to complete the
available experimental information and to further confirm the theoretical issues. Besides the noticeable
quantitative agreement between computed and experimental absorption spectra, our results allow us to
clarify, by first principles, the actual nature and interplay of the electronic and geometrical coupling between
the acceptor moiety and the photosensitizer. The possibility of a direct (optical) ET from the ground state
to the targeted *[P+−A-] CS state is theoretically postulated and found to be consistent with available
photophysical data (transient absorption spectroscopy). Concerning backward ET (from the CS state), the
occurrence of a quinoidal-like electronic redistribution inherent to the photoreduced acceptor-ligand is
proposed to favor efficient charge recombination.