Search

The textbook explanation that P680 pigments are the red limit to drive oxygenic photosynthesis must be reconsidered by the recent discovery that chlorophyll f (Chlf)‐containing Photosystem II (PSII) absorbing at 727 nm can drive water oxidation. Two different families of unsymmetrically substituted Zn phthalocyanines (Pc) absorbing in the 700–800 nm spectral window and containing a fused imidazole‐phenyl substituent or a fused imidazole‐hydroxyphenyl group have been synthetized and characterized as a bioinspired model of the Chlf/TyrosineZ/Histidine190 cofactors of PSII. Transient absorption studies in the presence of an electron acceptor and irradiating in the far‐red region evidenced an intramolecular electron transfer process. Visible and FT‐IR signatures indicate the formation of a hydrogen‐bonded phenoxyl radical in ZnPc II‐OH. This study sets the foundation for the utilization of a broader spectral window for multi‐electronic catalytic processes with one of the most robust and efficient dyes. [ABSTRACT FROM AUTHOR]

[Cr(ttpy)2]3+ (ttpy = 4′-(4-methylphenyl)-2,2′:6,2′′-terpyridine) exhibits rich electrochemical and photophysical properties. Cyclic voltammetry performed in CH3CN shows in the cathodic part the presence of three one-electron reversible systems at −0.47, −0.85 and −1.35 V vs. Ag/AgNO3 10−2 M. These systems are attributed to the reduction of the terpyridine ligands with a partial delocalization of the charge on the tolyl for the last reduction event. The three different reduced species were generated by exhaustive electrolysis and characterized by EPR and UV-visible spectroscopy; DFT calculations were performed to locate the spin density of the electrons added during the reduction. Visible light irradiation of [Cr(ttpy)2]3+ induces the population of a luminescent metal-centered excited state with a lifetime of 270 ns in deoxygenated CH3CN. This excited state can be quenched by an electron transfer process with triphenylphosphine (PPh3) or triethanolamine (TEOA). Using TEOA as a sacrificial electron donor, the doubly reduced species (i.e.[Cr(ttpy)2] +) can be generated under continuous irradiation. In the presence of [Ru(bpy)3]2+ as an additional photosensitizer, the photoreduction of [Cr(ttpy)2]3+ towards [Cr(ttpy)2]+ is accelerated. The trinuclear [{RuII(bpy)2(bpy-O-tpy)}2CrIII]7+ complex ([Ru2Cr]7+) in which a CrIII-bis-terpyridine centre is covalently linked to two RuII-tris-bipyridine moieties by oxo bridges has been synthesised. Its electrochemical, photophysical and photochemical properties were investigated in deoxygenated CH3CN. Cyclic voltammetry indicates only a poor electronic communication between the different subunits, whereas luminescence experiments show a strong quenching of the RuII* excited state by an intramolecular process. Continuous irradiation of [Ru2Cr]7+ under visible conditions in the presence of TEOA leads to [Ru2Cr]4+ where three electrons are stored on the [Cr(ttpy)] subunit. [ABSTRACT FROM AUTHOR]

We propose in this work a stepwise approach to construct photoelectrodes. This takes advantage of the self-assembly interactions between thiol with a gold surface and terpyridine ligands with first-row transition metals. Here, a [Ru(bpy)3]2+ photosensitive center bearing a free terpyridine group has been used to construct two linear dyads on gold (Au/[ZnII-RuII]4+ and Au/[CoIII-RuII]5+). The stepwise construction was characterized by electrochemistry, quartz crystal microbalance, and atomic force microscopy imaging. The results show that the dyads behave as rigid layers and are inhomogeneously distributed on the surface. The surface coverages are estimated to be in the order of 10-11 mol cm-2. The kinetics of the heterogeneous electron transfer is determined on modified gold ball microelectrodes using Laviron's formula. The oxidation rates of the terminal Ru(II) subunits are estimated to be 700 and 2300 s-1 for Au/[ZnII-RuII]4+ and Au/[CoIII-RuII]5+, respectively. In the latter case, the rate is limited by the kinetics of electron transfer between an intermediate Co(II) center and the gold surface. For Au/[ZnII-RuII]4+, the Zn-bis-terpyridine center is not involved in the electron-transfer process and the oxidation of the Ru(II) subunit occurs through a superexchange process. In the presence of a tertiary amine in solution, the electrodes at a bias of 0.12 V behave as photoanodes when subjected to visible light irradiation. The magnitude of the photocurrent is around 10 µA cm-2 for Au/[CoIII-RuII]5+ and 5 µA cm-2 for Au/[ZnII-RuII]4+, proving the importance of an electron relay on the photon-to-current conversion. The results suggest an efficient conversion for Au/[CoIII-RuII]5+, since each bound dyad, once excited, injects an electron around 10 times per second. [ABSTRACT FROM AUTHOR]

Abstract: [Rh2(Esp)2] (Esp=α,α,α′,α′‐tetramethyl‐1,3‐benzenedipropionate) is a well‐established catalyst for intra‐ and intermolecular C(sp)3−H bond amination. We have prepared and isolated complex I, [Rh2(Esp)2(NHTces)2]2−, where the catalyst bears sulfonamidate ligands (−NHTces=−NHSO3CH2CCl3) as nitrogen sources in the coordination sphere of the rhodium centre. The possibility for light activation instead of chemical activation of the [Rh2(Esp)2] catalyst and complex I is demonstrated using [Ru(bpy)3]2+ as the photosensitizer. The oxidation of the two dinuclear Rh complexes occurs through two distinct pathways. On one hand, [Rh2(Esp)2] is oxidized in a bimolecular reaction with the RuIII species formed after excitation of the photosensitizer in the presence of an electron acceptor. In contrast, the lower oxidation potential of complex I allows for its oxidation to occur directly from the excited state of the photosensitizer, helped by ion‐pair formation between the negatively charged complex I with [Ru(bpy)3]2+. The charge‐separated state of the oxidized complex I/reduced photosensitizer had a lifetime of 50 μs. [ABSTRACT FROM AUTHOR]

The article discusses the photoelectric conversion at a bipyridine ruthenium chloride-based on metallic triad grafted on a Indium tin oxide (ITO) electrode under the visible light. Topics discussed include interaction between phosphonates with ITO and terpyridine ligands; characterization of all experiments by cyclic voltammetry in acetonitrile and tetrabutylammonium perchlorate; and the redox potential throught out the procedure.

Inside Back Cover: Phthalocyanine as a Bioinspired Model for Chlorophyll f-Containing Photosystem II Drives Photosynthesis into the Far-Red Region (Angew. Bioinspired models, chlorophyll f, far-red region, photosystem II, phthalocyanine Keywords: bioinspired models; chlorophyll f; far-red region; photosystem II; phthalocyanine EN bioinspired models chlorophyll f far-red region photosystem II phthalocyanine 12607 12607 1 05/20/21 20210525 NES 210525 B Chlorophyll b f (Chl I f i )-containing Photosystem II absorbing in the far red has transgressed the red limit of photosynthesis locked by chlorophyll I a i at 680 nm and drives water oxidation at 727 nm. [Extracted from the article]

Keywords: bioinspired models; chlorophyll f; far-red region; photosystem II; phthalocyanine EN bioinspired models chlorophyll f far-red region photosystem II phthalocyanine 12715 12715 1 05/20/21 20210525 NES 210525 B Das Chlorophyll f b (Chl I f i ) enthaltende Photosystem II, das im fernen Rot absorbiert, überwindet das "rote Limit" der Photosynthese, das vom Chlorophyll I a i bei 680 nm festgelegt ist, und vermittelt die Wasseroxidation bei 727 nm. Innenrücktitelbild: Phthalocyanine as a Bioinspired Model for Chlorophyll f-Containing Photosystem II Drives Photosynthesis into the Far-Red Region (Angew. Bioinspired models, chlorophyll f, far-red region, photosystem II, phthalocyanine. [Extracted from the article]

A [Ru(bpy)3](2+)-like complex (L1) bearing two free terpyridine groups at the 5 and 5' positions of the same bipyridine, linked by the rigid and linear 2,5-dimethyl phenylene bridges has been synthesized to open access to two classes of linear molecular wires with photosensitive properties: a bimetallic coordination polymer and an inorganic triad. In this Research Article, we report on the synthesis and characterization of the resulting [{Ru(II_)Fe(II)}n](4n+) alternated bimetallic polymer and the [Co(III_)Ru(II_)Fe(II)](7+) triad based on the building block L1. The [{Ru(II_)Fe(II)}n](4n+) polymer is fully characterized in solution. Cyclic voltammetry and emission lifetime measurements show that the bridging ligand allows interaction between the metal centers in the excited state despite the lack of interactions in the ground state. Under visible irradiation, the polymer can be fully oxidized in the presence of a sacrificial electron acceptor in solution. Thin robust films of the polymer are easily obtained on ITO by a simple electrochemical procedure based on an electroreduction adsorption process. The ITO/[{Ru(II_)Fe(II)}n](4n+)-modified electrode behaves as a photocathode under irradiation in the presence of ArN2(+). The magnitude of the photocurrent is dependent on the film thickness, probably limited by the diffusion of charge in thicker film. On the other hand L1 is also used to construct a well-ordered triad in association with Co(III) and Fe(II) metallic centers as electron acceptor and donor, respectively. The metallic triad is anchored on ITO or on a SiO2 wafer, starting from a terpyridine phosphonate modified surface. AFM images prove the presence of the triad in a linear upward orientation. Irradiation of the ITO/[Co(III_)Ru(II_)Fe(II)](7+) modified surface in the presence of triethanolamine in CH3CN induces the generation of an anodic photocurrent of around 30 μA.cm(-2). The photocurrent density generated by the ITO/[Co(III_)Ru(II_)Fe(II)](7+) electrode, appears to be more stable than in the case of ITO/[{Ru(II_)Fe(II)}n](4n+) because of the presence of the anchoring group. Moreover, this photocurrent magnitude represents an enhancement of 30% compared to our previous triad ( Dalton Trans. 2014 , 43 , 12156 - 12159 ), proving the advantage of a linear and rigid spacer for the construction of such molecular assemblies with photoinduced charge transfer abilities.