Two-Dimensional Conjugated Metal-Organic Frameworks for Photochemical Transformations.

Photochemical transformation represents an attractive pathway for the conversion of earth-abundant resources, such as HO, CO, O, and N, into valuable chemicals by utilizing sunlight as an energy source. Recently, two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as the focal points in the field of photo-to-chemical conversion due to their advantages in light harvesting, electrical conductivity, mass transport, tunable electronic and porous structures, as well as abundant active sites. In this review, we highlight various physical and chemical features of 2D c-MOFs that can contribute to enhanced photo-induced exciton generation, charge transport, proton migration and redox catalysis.

Concurrent Ammonia Synthesis and Alcohol Oxidation Boosted by Glutathione-Capped Quantum Dots under Visible Light.

Mother nature accomplishes efficient ammonia synthesis via cascade N oxidation by lightning strikes followed with enzyme-catalyzed nitrogen oxyanion (NO , x = 2,3) reduction. The protein environment of enzymatic centers for NO -to-NH process greatly inspires the design of glutathione-capped (GSH) quantum dots (QDs) for ammonia synthesis under visible light (440 nm) in tandem with plasma-enabled N oxidation. Mechanistic studies reveal that GSH induces positive shift of surface charge to strengthen the interaction between NO and QDs.

Transition-Metal-Free, Site-Selective C-F Arylation of Polyfluoroarenes via Electrophotocatalysis.

Direct C-F arylation is effective and sustainable for synthesis of polyfluorobiaryls with different degrees of fluorination, which are important motifs in medical and material chemistry. However, with no aid of transition metals, the engagement of C-F bond activation has proved difficult. Herein, an unprecedented transition-metal-free strategy is reported for site-selective C-F arylation of polyfluoroarenes with simple (het)arenes.

Photochemistry Journey to Multielectron and Multiproton Chemical Transformation.

The odyssey of photochemistry is accompanied by the journey to manipulate "electrons" and "protons" in time, in space, and in energy. Over the past decades, single-electron (1e) photochemical transformations have brought marvelous achievements. However, as each photon absorption typically generates only one exciton pair, it is exponentially challenging to accomplish multielectron and proton photochemical transformations.

Direct Construction of Isomeric Benzobisoxazole-Vinylene-Linked Covalent Organic Frameworks with Distinct Photocatalytic Properties.

Vinylene/olefin-linked two-dimensional covalent organic frameworks (v-2D-COFs) have emerged as advanced semiconducting materials with excellent in-plane conjugation, high chemical stabilities, and precisely tunable electronic structures. Exploring new linkage chemistry for the reticular construction of v-2D-COFs remains in infancy and challenging. Herein, we present a solid-state benzobisoxazole-mediated aldol polycondensation reaction for the construction of two novel isomeric benzobisoxazole-bridged v-2D-COFs (v-2D-COF-NO1 and v-2D-COF-NO2) with and configurations of benzobisoxazole.

Reductive Carbon-Carbon Coupling on Metal Sites Regulates Photocatalytic CO Reduction in Water Using ZnSe Quantum Dots.

Colloidal quantum dots (QDs) consisting of precious-metal-free elements show attractive potentials towards solar-driven CO reduction. However, the inhibition of hydrogen (H ) production in aqueous solution remains a challenge. Here, we describe the first example of a carbon-carbon (C-C) coupling reaction to block the competing H evolution in photocatalytic CO reduction in water.

Rational Design of Dot-on-Rod Nano-Heterostructure for Photocatalytic CO Reduction: Pivotal Role of Hole Transfer and Utilization.

Inspired by green plants, artificial photosynthesis has become one of the most attractive approaches toward carbon dioxide (CO ) valorization. Semiconductor quantum dots (QDs) or dot-in-rod (DIR) nano-heterostructures have gained substantial research interest in multielectron photoredox reactions. However, fast electron-hole recombination or sluggish hole transfer and utilization remains unsatisfactory for their potential applications.

Mechanistic Insights Into Iron(II) Bis(pyridyl)amine-Bipyridine Skeleton for Selective CO Photoreduction.

A bis(pyridyl)amine-bipyridine-iron(II) framework (Fe(BPAbipy)) of complexes 1-3 is reported to shed light on the multistep nature of CO reduction. Herein, photocatalytic conversion of CO to CO even at low CO concentration (1 %), together with detailed mechanistic study and DFT calculations, reveal that 1 first undergoes two sequential one-electron transfer affording an intermediate with electron density on both Fe and ligand for CO binding over proton. The following 2 H -assisted Fe-CO formation is rate-determining for selective CO -to-CO reduction.

Site-selective DO-mediated deuteration of diaryl alcohols via quantum dots photocatalysis.

Owing to the high synthetic value of deuteration in the pharmaceutical industry, we describe herein the conversion of a range of aromatic ketones to deuterium-labeled products in good to excellent yields. Efficient and site-selective deuteration of benzyl alcohols by DO with visible light irradiation of quantum dots (QDs), together with gram-scale synthesis and photocatalyst recycling experiments indicated the potential of the developed method in practical organic synthesis.

Rational design of isostructural 2D porphyrin-based covalent organic frameworks for tunable photocatalytic hydrogen evolution.

Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. However, their structure-property-activity relationship, which should be beneficial for the structural design, is still far-away explored. Herein, we report the designed synthesis of four isostructural porphyrinic two-dimensional covalent organic frameworks (MPor-DETH-COF, M = H, Co, Ni, Zn) and their photocatalytic activity in hydrogen generation.

Bioinspired metal complexes for energy-related photocatalytic small molecule transformation.

Bioinspired transformation of small-molecules to energy-related feedstocks is an attractive research area to overcome both the environmental issues and the depletion of fossil fuels. The highly effective metalloenzymes in nature provide blueprints for the utilization of bioinspired metal complexes for artificial photosynthesis. Through simpler structural and functional mimics, the representative herein is the pivotal development of several critical small molecule conversions catalyzed by metal complexes, e.

Semiconductor nanocrystals for small molecule activation via artificial photosynthesis.

Facile activation and conversion of small molecules (e.g., HO, CO, N, CH, and CH) into solar fuels or value-added chemicals under mild conditions is an attractive pathway in dealing with the worldwide appeal of energy consumption and the growing demand of industrial feedstocks.

Identifying a Real Catalyst of [NiFe]-Hydrogenase Mimic for Exceptional H Photogeneration.

Inspired by the natural [NiFe]-H ase, we designed mimic 1, (dppe)Ni(μ-pdt)(μ-Cl)Ru(CO) Cl to realize effective H evolution under photocatalytic conditions. However, a new species 2 was captured in the course of photo-, electro-, and chemo- one-electron reduction. Experimental studies of in situ IR spectroscopy, EPR, NMR, X-ray absorption spectroscopy, and DFT calculations corroborated a dimeric structure of 2 as a closed-shell, symmetric structure with a Ru center.

Thiol Activation toward Selective Thiolation of Aromatic C-H Bond.

Direct C-S bond coupling is an attractive way to construct aryl sulfur ether, a building block for a variety of biological active molecules. Herein, we disclose an effective model for regioselective thiolation of the aromatic C-H bond by thiol activation instead of arene activation. Strikingly, this method has been applied into anisole derivatives that are not available in the arene activation approach to forge a single thioether isomer with high reactivity.

Flower-like cobalt carbide for efficient carbon dioxide conversion.

Catalytic conversion of carbon dioxide (CO) to value-added chemicals under mild conditions is highly desired, albeit with significant challenges. Here, in terms of exposure of abundant active sites and excellent photo-to-thermal conversion properties, flower-like CoC has been firstly used for effectively catalysing the cycloaddition of CO with epoxides to produce cyclic carbonates with yields of up to 95% under solar light. Density functional theory (DFT) calculations reveal that Lewis acid sites of the surface Co atoms can activate both CO and epoxide, thus opening up the possibility of a CO-epoxide cycloaddition reaction.

Unveiling Catalytic Sites in a Typical Hydrogen Photogeneration System Consisting of Semiconductor Quantum Dots and 3d-Metal Ions.

Semiconductor quantum dots (QDs) in conjunction with non-noble 3d-metal ions (e.g., Fe, Co, and Ni) have emerged as an extremely efficient, facile, and cost-effective means of solar-driven hydrogen (H) evolution.

Photoelectrochemical cell for P-H/C-H cross-coupling with hydrogen evolution.

Photoelectrochemistry enables the formation of a variety of active intermediates for organic synthesis in an environmentally friendly manner. Herein, a photoelectrochemical cell is fabricated to realize activation of P-H/C-H bonds for cross-coupling hydrogen evolution. As compared with an electrochemical cell, nearly 90% external bias input is saved to drive the C-P bond construction with good to excellent yields.

Regioselective Amination of an Aromatic C-H Bond by Trifluoroacetic Acid via Electrochemistry.

A trifluoroacetic acid-facilitated amination of alkoxyl arene has been established via anodic oxidation in an undivided cell. In the absence of any additional metal or oxidant reagents, a series of aromatic and heteroaromatic amine derivatives have been synthesized in good to excellent yields. Our findings reveal the possibility of achieving complete -selective amination of a simple arene, which emerges as an efficient route for facile and large-scale organic synthesis.

Semiconductor Quantum Dots: An Emerging Candidate for CO Photoreduction.

As one of the most critical approaches to resolve the energy crisis and environmental concerns, carbon dioxide (CO ) photoreduction into value-added chemicals and solar fuels (for example, CO, HCOOH, CH OH, CH ) has attracted more and more attention. In nature, photosynthetic organisms effectively convert CO and H O to carbohydrates and oxygen (O ) using sunlight, which has inspired the development of low-cost, stable, and effective artificial photocatalysts for CO photoreduction. Due to their low cost, facile synthesis, excellent light harvesting, multiple exciton generation, feasible charge-carrier regulation, and abundant surface sites, semiconductor quantum dots (QDs) have recently been identified as one of the most promising materials for establishing highly efficient artificial photosystems.

Quantum Dot Assembly for Light-Driven Multielectron Redox Reactions, such as Hydrogen Evolution and CO Reduction.

Light-driven multielectron redox reactions (e.g., hydrogen (H ) evolution, CO reduction) have recently appeared at the front of solar-to-fuel conversion.

Susceptible Surface Sulfide Regulates Catalytic Activity of CdSe Quantum Dots for Hydrogen Photogeneration.

Semiconducting quantum dots (QDs) have recently triggered a huge interest in constructing efficient hydrogen production systems. It is well established that a large fraction of surface atoms of QDs need ligands to stabilize and avoid them from aggregating. However, the influence of the surface property of QDs on photocatalysis is rather elusive.

Recent Advances in Sensitized Photocathodes: From Molecular Dyes to Semiconducting Quantum Dots.

The increasing demand for sustainable and environmentally benign energy has stimulated intense research to establish highly efficient photo-electrochemical (PEC) cells for direct solar-to-fuel conversion via water splitting. Light absorption, as the initial step of the catalytic process, is regarded as the foundation of establishing highly efficient PEC systems. To make full use of visible light, sensitization on photoelectrodes using either molecular dyes or semiconducting quantum dots provides a promising method.

Self-assembled inorganic clusters of semiconducting quantum dots for effective solar hydrogen evolution.

Owing to promoted electron-hole separation, the catalytic activity of semiconducting quantum dots (QDs) towards solar hydrogen (H2) production has been significantly enhanced by forming self-assembled clusters with ZnSe QDs made ex situ. Taking advantage of the favored interparticle hole transfer to ZnSe QDs, the rate of solar H2 evolution of CdSe QDs can be increased to ∼30 000 μmol h-1 g-1 with ascorbic acid as the sacrificial reagent, ∼150-fold higher than that of bare CdSe QDs clusters under the same conditions.

Photocatalysis with Quantum Dots and Visible Light for Effective Organic Synthesis.

Colloidal semiconductor quantum dots (QDs) have recently attracted widespread interest for diverse applications. Owing to their quantum confinement effects, rich surface binding properties, high surface-to-volume ratios, broad and intense absorption spectra in the visible region, and low cost as well, QDs offer new and versatile ways to serve as photocatalysts for organic synthesis. Most recently, the use of QDs photocatalysts is springing up in organic synthesis.