Merging hydrogen (H2) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H2 fuel and high-value chemicals can be coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H2 can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H2 production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H2 production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H2 production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.

Cooperative Coupling of Oxidative Organic Synthesis and Hydrogen Production over Semiconductor-Based Photocatalysts.

The development of efficient catalyst for photoredox-catalyzed selective organic synthesis has always been remaining the attractive objective in recent years. Regarding semiconductor-based photocat...

Selective Organic Transformations over Cadmium Sulfide-Based Photocatalysts

Most organic compounds are conventionally synthesized under high temperature and elevated pressure, resulting in significant energy consumption and wastage. Heterogeneous photocatalytic oxidation has the potential to provide a green route for the synthesis of the majority of industrially important chemicals. The major limiting factor affecting the efficiency of photocatalytic organic synthesis is the lack of high selectivity; therefore, substantial effort has been devoted to solving this problem. Responding to this fast-moving progress, this review gives an overview of the fundamental understanding of the reactive oxygen species involved in photocatalytic organic oxidations and furthermore, the general mechanisms of a few crucial oxidation reactions. The focus of this critical review is on the discussion of diverse strategies to improve the selectivity of high value chemicals, including band engineering, metal loading, hybrid materials, and defect engineering, with the primary aim of highlighting the catalyst design protocols based on the reaction mechanism. Finally, the difficulties and challenges of developing highly selective oxidation photocatalysts are comprehensively discussed in order to help direct the focus of future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.202003216

Strategies and Challenges on Selectivity of Photocatalytic Oxidation of Organic Substances

Solar-driven photocatalytic CO2 reduction is regarded as a promising way to simultaneously mitigate the energy crisis and CO2 pollution. However, achieving high efficiency of photocatalytic CO2 reduction, especially without the assistance of sacrifice reagents or extra alkaline additives, remains a critical issue. Herein, a photocatalyst of 3D ordered macroporous N-doped carbon (NC) supported CdS quantum dots (3DOM CdSQD/NC) is successfully fabricated toward photocatalytic CO2 reduction via an in situ transformation strategy. Additionally, an amines oxidation reaction is introduced to replace the H2 O oxidation process to further boost the photocatalytic CO2 reduction efficiency. Impressively, 3DOM CdSQD/NC exhibits superior activity and selectivity in photocatalytic CO2 reduction coupled with amines oxidation, affording a CO production rate as high as 5210 µmol g-1 h-1 in the absence of any sacrificial agents and alkaline additives. Moreover, 3DOM CdSQD/NC achieves an apparent quantum efficiency of 2.9% at 450 nm. Mechanism studies indicate that the 3D ordered macropores in the NC matrix are beneficial to the transfer of photogenerated carriers. Furthermore, the highly dispersed CdS QDs on the NC skeleton are able to significantly promote the adsorption of both CO2 and amine molecules and depress the CO2 activation energy barriers by stabilizing the *COOH intermediate, directly contributing to the high activity.

Ordered Macroporous Carbonous Frameworks Implanted with CdS Quantum Dots for Efficient Photocatalytic CO2 Reduction.

Developing efficient photocatalysts for synchronously producing H2 and high value-added chemicals holds great promise to enhance solar energy conversion. Herein, a facile strategy of simultaneously engineering Pd cocatalyst and oxygen vacancies (VO s) on TiO2 to promote H2 production coupled with selective oxidation of benzylamine is demonstrated. The optimized PdSA+C /TiO2 -VO photocatalyst containing Pd single atoms (SAs), clusters (C), and VO s exhibits much superior performance to those of TiO2 -VO and PdSA /TiO2 -VO counterparts. The production rates of H2 and N-benzylidenebenzylamine over PdSA+C /TiO2 -VO are 52.7 and 1.5 times those over TiO2 -VO , respectively. Both experimental and theoretical studies have elucidated the synergistic effect of Pd SAs, clusters, and VO s on TiO2 in boosting the photocatalytic reaction. The presence of Pd SAs facilitates the generation and stabilization of abundant VO s by the formation of PdOTi3+ atomic interface, while Pd clusters promote the photogenerated charge separation and afford the optimum active sites for H2 evolution. Surface VO s of TiO2 guarantee the efficient adsorption and dissociation/activation of reactant molecules. This study reveals the effect of active-site engineering on the photocatalysis and is expected to shed substantial light on future structure design and modulation of semiconductor photocatalysts.

Synergistic Pd Single Atoms, Clusters, and Oxygen Vacancies on TiO2 for Photocatalytic Hydrogen Evolution Coupled with Selective Organic Oxidation

Imines are important precursors for pharmaceutical, agricultural, and synthetic chemistry. The state-of-art synthesis of imines via condensation of amines with aldehydes or ketones often uses homog...

Photoimmobilized Ni Clusters Boost Photodehydrogenative Coupling of Amines to Imines via Enhanced Hydrogen Evolution Kinetics

Fluorescent molecular rotors play vital roles in understanding the function of cellular viscosity changes and its abnormal fluctuations are closely associated with many diseases. Despite numerous efforts spent, it remains an urgent and important topic to develop improved viscosity probes with near-infrared fluorescence, high sensitivity and low background. In this manuscript, for the first time, we reported two novel monostyryl boron dipyrromethenes (BODIPYs) bearing a rotatable trifluoromethyl group (CF3) at the meso position and a triphenylphosphonium (4) or morpholine (6) substituent, which could successfully serve as highly sensitive and near-infrared-emitting fluorescent probes for imaging cellular viscosity in mitochondria or lysosome. These probes could be prepared through Knoevenagel condensation under mild conditions and showed negligible emissions in the low viscous solvents. However in high viscous glycerol, strong near-infrared fluorescence at 657 nm appeared, ascribed to the substantially restricted rotation of the CF3 group. Their fluorescence intensity (log I) at 657 nm exhibited a good linear relationship with viscosity (log η) in the whole test range of 1–950 cP. Limit of detection for viscosity of mitochondria-targeting probe 4 was relatively lower than that of lysosome-targeting probe 6. These probes both showed no cytotoxicity and good mitochondrial or lysosomal localization. Interestingly, mitochondria-targeting probe 4 exhibited a remarkable intracellular fluorescence enhancement with viscosity increase induced by LPS or nystatin, which was better than lysosome-targeting probe 6. These two novel BODIPY-based fluorescent rotors provide a new strategy for developing near-infrared-emitting and organelle-specific fluorescent probes for cellular viscosity, which might be useful in exploring the functions of viscosity in various diseases. 

Huizhi Li

Papers

Photoimmobilized Ni Clusters Boost Photodehydrogenative Coupling of Amines to Imines via Enhanced Hydrogen Evolution Kinetics

Novel meso-trifluoromethyl BODIPY-based near-infrared-emitting fluorescent probes for organelle-specific imaging of cellular viscosity