Solvent-control of photoinduced electron transfer via hydrogen bonding in a molecular triad made of a dinuclear chromophore subunit

Dinuclear Tridentate Ru(II) Complex with Strong Near-Infrared Light-Triggered Anticancer Activity

The design of the dinuclear Ru(II) complex (Ru2) with strong near-infrared (NIR) absorption properties has been reported for efficient anticancer phototherapy. Under 700 nm LED light excitation, Ru2 exhibited remarkable synergistic type I/II photosensitization ability and photocatalytic activity toward intracellular biomolecules. Ru2 showed impressive 700 nm light-triggered anticancer activity under normoxia and hypoxia compared with the clinically used photosensitizer Chlorin e6. The mechanistic studies showed that Ru2 induced intracellular redox imbalance and perturbed the energy metabolism and biosynthesis in A549 cancer cells. Overall, this work provides a new strategy for developing efficient metal-based complexes for anticancer phototherapy under NIR light.

Photo-driven water oxidation performed by supramolecular photocatalysts made of Ru(II) photosensitizers and catalysts

Two new supramolecular photocatalysts made of covalently linked Ru(II) polypyridine chromophore subunits ([Ru(bpy)3]2+-type species; bpy = 2,2'-bipyridine) and [RuL(pic)2] (L = 2,2'-bipyridine-6,6'-dicarboxylic acid; pic = 4-picoline) water oxidation catalyst subunits have been prepared. The new species, 1 and 2, contain chromophore and catalyst subunits in the molecular ratios 1:1 and 1:2, respectively. The model chromophore species [Ru(bpy)2(L1)]2+ (RuP1; L1=4-[2-(4-pyridyl)-2-hydroxyethyl]-4-methyl-2,2'-bipyridine) and [Ru(bpy)2(L2)]2+ (RuP2; L2 = 4,4'-bis[2-(4-pyridyl)-2-hydroxyethyl]-2,2'-bipyridine) have also been prepared. The absorption spectra, oxidation behavior, and luminescent properties of 1 and 2 have been studied, and the results indicate that each subunit largely maintains its own properties in the supramolecular species. However, the luminescence of the chromophore subunits is significantly quenched in 1 and 2 in comparison with the luminescence of the respective model species. Both 1 and 2 exhibit catalytic water oxidation in the presence of cerium ammonium nitrate, exhibiting an I2M mechanism, with a better efficiency than the known catalyst [RuL(pic)2] under the same experimental conditions. Upon light irradiation, in the presence of persulfate as a sacrificial acceptor agent, 1 and 2 are more efficient photocatalysts than a system made of separated [Ru(bpy)3]2+ and [RuL(pic)2] species, highlighting the advantage of using multicomponent, supramolecular species with respect to isolated species. The O-O bond formation step is I2M, even in the photo-driven process. The photocatalytic process of 2 is more efficient than that of 1, with the turnover frequency reaching a value of 1.2 s-1. A possible reason could be an increased local concentration of catalytic subunits in the needed bimolecular assembly required for the I2M mechanism in 2 with respect to 1, a consequence of the presence of two catalytic subunits in each multicomponent species 2.

Photoinduced Electron Transfer in Organized Assemblies—Case Studies

In this review, photoinduced electron transfer processes in specifically designed assembled architectures have been discussed in the light of recent results reported from our laboratories. A convenient and useful way to study these systems is described to understand the rules that drive a light-induced charge-separated states and its subsequent decay to the ground state, also with the aim of offering a tutorial for young researchers. Assembled systems of covalent or supramolecular nature have been presented, and some functional multicomponent systems for the conversion of light energy into chemical energy have been discussed.

Photoinduced Electron Transfer Coupled to Donor Deprotonation and Acceptor Protonation in a Molecular Triad Mimicking Photosystem II

The first artificial donor-sensitizer-acceptor compound in which photoinduced long-range electron transfer is coupled to donor deprotonation and acceptor protonation is reported. The long-lived photoproduct stores energy in the form of a radical pair state in which the charges of the donor and the acceptor remain unchanged, much in contrast to previously investigated systems that exhibit charge-separated states comprised of electron-hole pairs. This finding is relevant for light-driven accumulation of redox equivalents, because it exemplifies how the buildup of charge can be avoided yet light energy can be stored. Proton-coupled electron transfer (PCET) reactions at a phenol donor and a monoquat acceptor triggered by excitation of a Ru(II) sensitizer enable this form of photochemical energy storage. Our triad emulates photosystem II more closely than previously investigated systems, because tyrosine Z is oxidized and deprotonated, whereas plastoquinone B is reduced and protonated.