Publications by authors named "Simon Cerfontaine"

In natural and artificial photosynthesis, light absorption and catalysis are separate processes linked together by exergonic electron transfer. This leads to free energy losses between the initial excited state, formed after light absorption, and the active catalyst formed after the electron transfer cascade. Additional deleterious processes, such as internal conversion (IC) and vibrational relaxation (VR), also dissipate as much as 20-30% of the absorbed photon energy.

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The ground state and photoinduced mixed valence states (GSMV and PIMV, respectively) of a dinuclear (Dp) ruthenium(II) complex bearing 2,2'-bipyridine ancillary ligands and a 2,2':4',4'':2'',2'''-quaterpyridine (Lp) bridging ligand were investigated using femtosecond and nanosecond transient absorption spectroscopy, electrochemistry and density functional theory. It was shown that the electronic coupling between the transiently light-generated Ru(II) and Ru(III) centers is ∼ 450 cm in the PIMV state, whereas the electrochemically generated GSMV state showed ∼ 0 cm, despite virtually identical Ru-Ru distances. This stemmed from the changes in dihedral angles between the two bpy moieties of Lp, estimated at 30° and 4° for the GSMV and PIMV states, respectively, consistent with a through-bond rather than a through-space mechanism.

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Four trinuclear ruthenium(II) polypyridyl complexes were synthesized, and a detailed investigation of their excited-state properties was performed. The tritopic sexi-pyridine bridging ligands were obtained via or substitution of a central 2,2'-bipyridine fragment. A connection between the 2,2'-bipyridine chelating moieties of the bridging ligand led to a red-shifted MLCT absorption band in the visible part of the spectra, whereas the connection induced a broadening of the LC transitions in the UV region.

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The stereoisomerically pure synthesis of a novel heptanuclear Ru(II)-Os(II) antenna bearing multitopic terpyridine ligands is reported. An unambiguous structural characterization was obtained by H NMR spectroscopy and ion mobility spectrometry (IMS-MS). The heptanuclear complex exhibits large molar absorption coefficients (77900 M cm at 497 nm) and undergoes unitary, downhill, convergent energy transfer from the peripheral Ru(II) subunits to the central Os(II) that displays photoluminescence with a lifetime (τ = 161 ns) competent for diffusional excited-state electron transfer reactivity in solution.

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A detailed photophysical investigation of two dinuclear ruthenium(ii) complexes is reported. The two metallic centers were coordinated to a bis-2,2'-bipyridine bridging ligand, connected either through the para (Lp, Dp) or the meta position (Lm, Dm). The results obtained herein were compared to the prototypical [Ru(bpy)3]2+ parent compound.

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Higher nuclearity photosensitizers produced dehalogenation yields greater than 90% in the reported [Ru(bpy)]-mediated dehalogenation of 4-bromobenzyl-2-chloro-2-phenylacetate to 4-bromobenzyl-2-phenylacetate with orange light in 7 h, whereas after 72 h yields of 49% were obtained with [Ru(bpy)]. Dinuclear (), trinuclear (), and quadrinuclear () ruthenium(II) 2,2'-bipyridine based photosensitizers were synthesized, characterized, and investigated for their photoreactivity. Three main factors were shown to lead to increased yields (i) the red-shifted absorbance of polynuclear photosensitizers, (ii) the more favorable driving force for electron transfer, characterized by more positive (Ru), and (iii) the smaller population of the MC state (<0.

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Ruthenium-based complexes are widely used as photocatalysts, as photosensitizers, or as building blocks for supramolecular assemblies. In the field of solar energy conversion, building light harvesting antenna is of prime interest. Nevertheless, collecting light is mandatory but not sufficient; once collected and transferred, the exciton has to be long-lived enough to be transferred to a catalytic site.

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A one-pot synthesis of substituted multi-2,2':6',2″-terpyridines (multi-tpy) has been achieved using an acetylquaterpyridine precursor with various aryl aldehydes in basic media. This strategy enables ready access to functionalized tri-terpyridines. Utilizing a Suzuki-type cross-coupling, larger structures such as tetra- or even hexa-tpy were obtained from our tri-tpy precursor.

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