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A new hydrogen evolving cobalt catalyst 1 based on a pentapyridine ligand has been synthesized and characterized. Its photocatalytic activity in the presence of a Ru(bpy)3(2+) sensitizer and ascorbic acid as a sacrificial electron donor has been screened in purely buffered aqueous solutions showing TONs and TOFs strongly dependent on both catalyst concentration and pH with the best results obtained at 50 μM 1 and at pH 4 (TON = 187, TOF = 8.1 min(-1)). The photochemical mechanism, as revealed by flash photolysis, involves reaction of the excited sensitizer with ascorbic acid to yield Ru(bpy)3(+) as a primary photo-generated reductant, capable of electron transfer to 1 with a remarkable rate (bimolecular rate constant k = 5.7 (±0.7) × 10(9) M(-1) s(-1)). For hydrogen generation, two one-electron photochemical reduction steps of 1 are needed along with hydride formation and protonation. Under the experimental conditions used, hydrogen evolution is mainly limited by partial decomposition of both the sensitizer and the catalyst. Moreover, accumulation of the oxidation product of the ascorbic acid donor, dehydroascorbic acid, is observed to strongly decrease the hydrogen production yield. As shown by flash photolysis, this species is capable of quenching the reduced ruthenium species (k = 4.4 (±0.5) × 10(7) M(-1) s(-1)) thus competing with electron transfer to the catalyst.

Artificial photosynthesis aims at efficient water splitting into hydrogen and oxygen, by exploiting solar light. As a priority requirement, this process entails the integration of suitable multi-electron catalysts with light absorbing units, where charge separation is generated in order to drive the catalytic routines. The final goal could be the transposition of such an asset into a photoelectrocatalytic cell, where the two half-reactions, proton reduction to hydrogen and water oxidation to oxygen, take place at two appropriately engineered photoelectrodes. We herein report a covalent approach to anchor a Co(II) water oxidation catalyst to a Ru(II) polypyridine photosensitizer unit; photophysical characterisation and the catalytic activity of such a dyad in a light activated cycle are reported, and implications for the development of regenerative systems are discussed.

Efficient photocatalytic hydrogen evolution is obtained from 1 M phosphate buffer at pH 7 in the presence of a Ru(bpy)3(2+) sensitizer, an ascorbic acid sacrificial donor, and a water-soluble Co(II) porphyrin catalyst. Spectroscopic investigation of the system by stationary and time-resolved techniques enables a complete characterization of the photoinduced dynamics.

Photoinduced electron transfer is a topical issue in chemistry. In multicomponent donor-bridge-acceptor systems, electron transfer is usually discussed within the frame of superexchange theory, which takes into account electronic coupling mediated by virtual states involving bridge orbitals. However, the schematization used for superexchange in thermal electron transfer processes is not suitable to immediately understand some intriguing aspects of photoinduced charge separation and recombination processes, which are only uncovered by analyzing the virtual states involved in forward and backward excited-state electron transfer. In particular, for oxidative photoinduced electron transfer, a low-energy virtual state which cannot mediate the forward charge separation can efficiently mediate charge recombination via the hole-transfer superexchange route, whereas for reductive photoinduced electron transfer, a low-energy virtual state which cannot mediate the forward process can efficiently mediate charge recombination via electron-transfer superexchange. As a consequence, to obtain long-lived charge-separated states upon oxidative photoinduced electron transfer in donor-bridge-acceptor systems it is preferable to avoid easy-to-oxidize bridges, whereas easy-to-reduce bridges should better be avoided in reductive photoinduced charge separation. These considerations, exemplified by the analysis of some literature cases, can be useful hints for the design of long-lived charge-separated states.

A salophen cobalt(II) complex enables water oxidation at neutral pH in photoactivated sacrificial cycles under visible light, thus confirming the high appeal of earth abundant single site catalysis for artificial photosynthesis.

Water oxidation catalysts: evolution of [Co(4)(H(2)O)(2)(α-PW(9)O(34))(2)](10-) to catalytically active species is assessed by laser flash photolysis in sacrificial photocatalytic cycles with Ru(bpy)(3)(2+) as a photosensitizer.

According to NMR evidence the metal-mediated sandwich assemblies of porphyrins 2 and 3 undergo in solution a thermally driven motion that resembles that of a stepper: the spontaneous rotational motion of the pyridyl rings is converted into a reciprocating linear motion of the porphyrins.

The tetraruthenium polyoxometalate water oxidation catalyst 1 performs very fast hole scavenging from photogenerated Ru(iii) polypyridine complexes, both in homogeneous solution and at a sensitized nanocrystalline TiO(2) surface.

Three new rod-like dinuclear Ru(ii) polypyridine compounds have been prepared and characterized and their absorption spectra, redox behaviour and photophysical properties have been investigated, by conventional steady-state absorption and luminescence spectroscopic methods and by time-resolved methods operating in the nanosecond and femtosecond time regimes. All the new species contain 1,4-bis(2,2':6',2''-terpyridin-4'-yl)benzene () as bridging ligand and 2,4-bis(2-pyridyl)-6-p-bromophenyl-1,3,5-triazine and/or 4'-(p-bromophenyl)-2,2':6',2''-terpyridine as peripheral ligands. In particular, and are symmetric dyads since the Ru(ii) ions carry identical peripheral ligands (the triazine-based ligands in and the terpyridine-based ligands in the case of ), whereas is a non-symmetric dyad since its two Ru(ii) centers carry two different peripheral ligands (for the structural formulae of the compounds, see ). The absorption spectra and redox behaviour of the new compounds indicate, that each subunit of the dyads maintain its own peculiar properties in the dinuclear system, a requisite confirming the supramolecular nature of the systems. All the species exhibit metal-to-ligand charge-transfer (MLCT) emission, both at room temperature in fluid solution and at 77 K in rigid matrix. Luminescence lifetime and transient absorption spectroscopy reveal that efficient and fast photoinduced energy transfer takes place in the non-symmetric dyad from the subunit containing the terpyridine peripheral ligand to the subunit containing the triazine-based peripheral ligand. However, given the complexity of the transient spectra and the overlapping timescales of the processes of the symmetric and non-symmetric systems, any detailed analysis of the ultrafast results aimed at the identification of specific intercomponent energy transfer steps, and therefore to kinetically characterize the directional energy transfer, appears to be speculative.

A terpyridine-functionalized perylene bisimide chromophore (TPBI) has been used as a building block in the stepwise, layer-by-layer fabrication of self-assembled Fe-TPBI multilayers on gold, with the assembled supramolecular chains oriented approximately perpendicular to the gold surface. Time-resolved spectroscopy measurements seem to indicate that the energy absorbed by the multilayer is promptly dissipated to the gold surface by ultrafast processes.

2.1 nm benzenethiol monolayer protected gold clusters undergo solvent dependant photoinduced deposition with potential applications in the field of nanoparticle film formation.