Importance of Selective Quenching of the Triplet Excited State of Thermally Activated Delayed Fluorescence (TADF) Photosensitizers in Redox-Photosensitized Reactions: Case Studies on Photocatalytic CO Reduction.

Redox photosensitizers exhibiting thermally activated delayed fluorescence (TADF) are widely used in the various research fields. We investigated the roles of the singlet and triplet excited states of such molecules in photocatalytic CO reduction. Two TADF compounds ( and ) were used in combination with a manganese(I) complex as a catalyst and 1,3-dimethyl-2-phenyl-2,3-dihydro-1-benzo[]imidazole (BIH) and triethanolamine (TEOA) as sacrificial electron donors.

The main factor that determines the formation-efficiencies of photochemically derived one-electron-reduced species.

While the quantum yields of photosensitiser-derived one-electron-reduced species (OERSs) significantly impact the overall efficiencies of various redox-photosensitised photocatalytic reactions, the primary factors that influence them remain unclear. In this study, we systematically compared the photochemical formation quantum yields for OERSs associated with Ru(ii) and Os(ii) tris-diimine, , -[Re(diimine)(CO)(PR)], and cyclometalated Ir(iii) complexes in the presence of the same 1,3-dimethyl-2-phenyl-2,3-dihydro-1-benzo[]imidazole (BIH) reductant. The reduction potentials of the excited metal complexes, the heavy-atom effects of the central metal ions, and the oxidation potentials and charges of their OERSs were examined, which reveals that the driving force for photoinduced electron-transfer is the most important factor that determines the quantum yields associated with photochemical OERS formation.

Development of a Highly Durable Photocatalytic CO Reduction Using a Mn-Complex Catalyst: Application of Selective Photosplitting of a Mn(0)-Mn(0) Bond.

-[Mn(diimine)(CO)(L)] has attracted significant attention as a catalyst for the photocatalytic reduction of CO. However, in such photocatalytic systems, the photoexcitation of Mn complexes and reaction intermediates induces their decomposition, which lowers the durability of these systems. In this study, we clarified the primary process whereby the Mn complex catalyst decomposes during the photocatalytic reaction.

Visible-light-responsive hybrid photocatalysts for quantitative conversion of CO to highly concentrated formate solutions.

Photocatalysts can use visible light to convert CO into useful products. However, to date photocatalysts for CO conversion are limited by insufficient long-term stability and low CO conversion rates. Here we report hybrid photocatalysts consisting of conjugated polymers and a ruthenium(ii)-ruthenium(ii) supramolecular photocatalyst which overcome these challenges.

Selective electrochemical CO conversion with a hybrid polyoxometalate.

A multi-component coordination compound, in which ruthenium antenna complexes are connected to a polyoxotungstate core is presented. This hybrid cluster effectively promotes the electrochemical conversion of CO to C1 feedstocks, the selectivity of which can be controlled by the acidity of the media.

A Molecular Z-Scheme Artificial Photosynthetic System Under the Bias-Free Condition for CO Reduction Coupled with Two-electron Water Oxidation: Photocatalytic Production of CO/HCOOH and H O.

Bio-inspired molecular-engineered systems have been extensively investigated for the half-reactions of H O oxidation or CO reduction with sacrificial electron donors/acceptors. However, there has yet to be reported a device for dye-sensitized molecular photoanodes coupled with molecular photocathodes in an aqueous solution without the use of sacrificial reagents. Herein, we will report the integration of Sn - or Al -tetrapyridylporphyrin (SnTPyP or AlTPyP) decorated tin oxide particles (SnTPyP/SnO or AlTPyP/SnO ) photoanode with the dye-sensitized molecular photocathode on nickel oxide particles containing [Ru(diimine) ] as the light-harvesting unit and [Ru(diimine)(CO) Cl ] as the catalyst unit covalently connected and fixed within poly-pyrrole layer (RuCAT-RuC -PolyPyr-PRu/NiO).

Photocatalyzed CO reduction to CO by supramolecular photocatalysts made of Ru(II) photosensitizers and Re(I) catalytic subunits containing preformed COTEOA adducts.

Two new supramolecular photocatalysts containing Ru(II) polypyridine units as light-harvesting photosensitizers and Re(I) polypyridine subunits as catalytic centers have been prepared. The new species, RuRe2A and Ru2ReA, contain catalytic Re(I) subunits coordinated by the preformed COTEOA adduct (known to be the effective catalytic subunits; TEOA is triethanolamine) and exhibit quite efficient and selective photoreduction of CO to CO, with outstanding TONs of 2368 and 2695 and a selectivity of 99.9% and 98.

Structural change dynamics of heteroleptic Cu(I) complexes observed by ultrafast emission spectroscopy.

[Cu(I)(dmp)(P)] (dmp = 2,9-dimethyl-1,10-phenanthroline derivatives; P = phosphine ligand) is one of the most promising photosensitizers used in a photo-catalytic system for reducing CO, for which the quantum yield is as high as 57%. In this work, time-resolved emission spectra of Cu(I) complexes in solutions were investigated using femtosecond fluorescence up-conversion and nanosecond time-resolved emission spectroscopic systems. The temporal profiles of emission intensities less than 10 ps in acetonitrile solution were reproduced using a tri-exponential function with three-time constants of 0.

Surface-Specific Modification of Graphitic Carbon Nitride by Plasma for Enhanced Durability and Selectivity of Photocatalytic CO Reduction with a Supramolecular Photocatalyst.

Photocatalytic CO reduction is in high demand for sustainable energy management. Hybrid photocatalysts combining semiconductors with supramolecular photocatalysts represent a powerful strategy for constructing visible-light-driven CO reduction systems with strong oxidation power. Here, we demonstrate the novel effects of plasma surface modification of graphitic carbon nitride (CN), which is an organic semiconductor, to achieve better affinity and electron transfer at the interface of a hybrid photocatalyst consisting of CN and a Ru(II)-Ru(II) binuclear complex ().

Supramolecular multi-electron redox photosensitisers comprising a ring-shaped Re(i) tetranuclear complex and a polyoxometalate.

Redox photosensitisers (PSs) play essential roles in various photocatalytic reactions. Herein, we synthesised new redox PSs of 1 : 1 supramolecules that comprise a ring-shaped Re(i) tetranuclear complex with 4+ charges and a Keggin-type heteropolyoxometalate with 4- charges. These PSs photochemically accumulate multi-electrons in one molecule (three or four electrons) in the presence of an electron donor and can supply electrons with different reduction potentials.

Layered β-ZrNBr Nitro-Halide as Multifunctional Photocatalyst for Water Splitting and CO Reduction.

Developing mixed-anion semiconductors for solar fuel production has inspired extensive interest, but the nitrohalide-based photocatalyst is still in shortage. Here we report a layered nitro-halide β-ZrNBr with a narrow band gap of ca. 2.

Utilization of Low-Concentration CO with Molecular Catalysts Assisted by CO-Capturing Ability of Catalysts, Additives, or Reaction Media.

Increasing concentration of atmospheric CO is a worldwide concern and continues to trigger various environmental problems. Photo- or electrocatalytic CO reduction (CO-Red) using solar energy, i.e.

Photocatalytic Systems for CO Reduction: Metal-Complex Photocatalysts and Their Hybrids with Photofunctional Solid Materials.

ConspectusPhotocatalytic CO reduction is a critical objective in the field of artificial photosynthesis because it can potentially make a total solution for global warming and shortage of energy and carbon resources. We have successfully developed various highly efficient, stable, and selective photocatalytic systems for CO reduction using transition metal complexes as both photosensitizers and catalysts. The molecular architectures for constructing selective and efficient photocatalytic systems for CO reduction are discussed herein.

Development of a panchromatic photosensitizer and its application to photocatalytic CO reduction.

We designed and synthesized a heteroleptic osmium(ii) complex with two different tridentate ligands, . can absorb the full wavelength range of visible light owing to S-T transitions, and this was supported by TD-DFT calculations. Excitation of using visible light of any wavelength generates the same lowest triplet metal-to-ligand charge-transfer excited state, the lifetime of which is relatively long ( = 40 ns).

Supramolecular photocatalysts fixed on the inside of the polypyrrole layer in dye sensitized molecular photocathodes: application to photocatalytic CO reduction coupled with water oxidation.

The development of systems for photocatalytic CO reduction with water as a reductant and solar light as an energy source is one of the most important milestones on the way to artificial photosynthesis. Although such reduction can be performed using dye-sensitized molecular photocathodes comprising metal complexes as redox photosensitizers and catalyst units fixed on a p-type semiconductor electrode, the performance of the corresponding photoelectrochemical cells remains low, , their highest incident photon-to-current conversion efficiency (IPCE) equals 1.2%.

Synthesis and Light-Harvesting Functions of Ring-Shaped Re(I) Trinuclear Complexes Connected with an Emissive Ru(II) Complex.

Ring-shaped Re(I) multinuclear complexes (Re(I) rings) in which Re(I)-diimine-biscarbonyl complexes are connected to each other through bisphosphine bridging ligands exhibit very suitable photophysical and electrochemical properties as redox photosensitizers. We developed two approaches for synthesizing Re(I) rings connected with a Ru(II) complex: cyclization of a linear Re(I) trinuclear complex connected with a Ru(II) complex and Mizoroki-Heck coupling of a ring-shaped Re(I) trinuclear complex and a Ru(II) complex. Photophysical measurements of these heteromultinuclear complexes and comparisons with their model complexes indicated that they exhibit efficient light-harvesting abilities, where energy transfer from the excited ring-shaped Re(I) trinuclear complex unit to the Ru(II) complex unit proceeds efficiently.

Mechanistic study of photocatalytic CO reduction using a Ru(ii)-Re(i) supramolecular photocatalyst.

Supramolecular photocatalysts comprising [Ru(diimine)] photosensitiser and -[Re(diimine)(CO){OC(O)OCHNR}] catalyst units can be used to reduce CO to CO with high selectivity, durability and efficiency. In the presence of triethanolamine, the Re catalyst unit efficiently takes up CO to form a carbonate ester complex, and then direct photocatalytic reduction of a low concentration of CO, , 10% CO, can be achieved using this type of supramolecular photocatalyst. In this work, the mechanism of the photocatalytic reduction of CO was investigated applying such a supramolecular photocatalyst, with a carbonate ester ligand, using time-resolved visible and infrared spectroscopies and electrochemical methods.

Photocatalysis of a Dinuclear Ru(II)-Re(I) Complex for CO Reduction on a Solid Surface.

The development of CO-reduction photocatalysts is one of the main targets in the field of artificial photosynthesis. Recently, numerous hybrid systems in which supramolecular photocatalysts comprised of a photosensitizer and catalytic-metal-complex units are immobilized on inorganic solid materials, such as semiconductors or mesoporous organosilica, have been reported as CO-reduction photocatalysts for various functions, including water oxidation and light harvesting. In the present study, we investigated the photocatalytic properties of supramolecular photocatalysts comprised of a Ru(II)-complex photosensitizer and a Re(I)-complex catalyst fixed on the surface of insulating AlO particles: the distance among the supramolecular photocatalyst molecules should be fixed.

Factors determining formation efficiencies of one-electron-reduced species of redox photosensitizers.

Improvement in the photochemical formation efficiency of one-electron-reduced species (OERS) of a photoredox photosensitizer (a redox catalyst) is directly linked to the improvement in efficiencies of the various photocatalytic reactions themselves. We investigated the primary processes of a photochemical reduction of two series [Ru(diimine)] and [Os(diimine)] as frequently used redox photosensitizers (PS), by 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as a typical reductant in detail using steady-irradiation and time-resolved spectroscopies. The rate constants of all elementary processes of the photochemical reduction of PS by BIH to give the free PS• were obtained or estimated.