Photocatalysts For Organic Synthesis Research Articles

The Application of Porous Organic Polymers as Metal Free Photocatalysts in Organic Synthesis.

Concerns about increasing greenhouse gas emissions and their effect on our environment highlight the urgent need for new sustainable technologies. Visible light photocatalysis allows the clean and selective generation of reactive intermediates under mild conditions. The more widespread adoption of the current generation of photocatalysts, particularly those using precious metals, is hampered by drawbacks such as their cost, toxicity, difficult separation, and limited recyclability. This is driving the search for alternatives, such as porous organic polymers (POPs). This new class of materials is made entirely from organic building blocks, can possess high surface area and stability, and has a controllable composition and functionality. This review focuses on the application of POPs as photocatalysts in organic synthesis. For each reaction type, a representative material is discussed, with special attention to the mechanism of the reaction. Additionally, an overview is given, comparing POPs with other classes of photocatalysts, and critical conclusions and future perspectives are provided on this important field.

Nitrogen-doped carbon dots as photocatalysts for organic synthesis: Effect of nitrogen content on catalytic activity

Nitrogen-doped carbon dots as photocatalysts for organic synthesis: Effect of nitrogen content on catalytic activity

Interfacial Br[sbnd]N bond enables charge shuttle in coulomb blockade Cs3Bi2Br9 perovskite nanocrystals via g-C3N4 heterogenization for selective toluene oxidation

Heterojunction catalysts exhibit great potential in photocatalysis owing to their superior charge separation efficiency. However, precise regulation of interfacial electronic structures and their impact on photocatalytic reactions remains challenging. Here, we present an effective strategy involving accurate control of carrier dynamics through the rational design of interfacial covalent bonds. This strategy achieves high selectivity and productivity in toluene photo-oxidation, with a remarkable C6H5-CHO selectivity of 98.1 % and a conversion ratio of 55.2 %. Our findings reveal that the dot-on-plate Cs3Bi2Br9@g-C3N4 heterojunction, featuring an interfacial Br-N covalent bond and an internal electric field, promotes efficient charge transfer. Moreover, utilizing quasi-in situ EPR, in-situ ATR-FTIR spectra, and DFT calculations, we demonstrate that the interfacial Br-N covalent bond efficiently adsorbs/activates molecules, significantly accelerating the overall reaction and enhancing selectivity. This work underscores the importance of electronic structures based on covalent bond-bridged heterojunctions, offering insights for designing high-performance photocatalysts in organic synthesis.

Heterobinuclear Metallocomplexes as Photocatalysts in Organic Synthesis

Photocatalytic processes under visible light have constantly been finding more and more applications in organic synthesis as they allow a wide range of transformations to proceed under mild conditions. The combination of photoredox catalysis with metal complex catalysis gives an opportunity to employ the advantages of these two methodologies. Covalent bonding of photocatalyst and metal complex catalyst using bridging ligands increases the efficiency of the electron and energy transfer between these two parts of the catalyst, leading to more efficient and selective catalytic systems. Up to now, after numerous investigations of the photocatalytic reduction of CO2 and hydrogen generation, such a strategy was firmly established to substantially increase the catalyst’s activity. This review is aimed at the achievements and perspectives in the field of design and application of heterobinuclear metal complexes as photocatalysts in organic synthesis.

Recent Advances in the Use of Covalent Organic Frameworks as Heterogenous Photocatalysts in Organic Synthesis.

Organic photochemistryisintensely developed in the 1980s, in which the nature of excited electronic states and the energy and electron transfer processes arethoroughly studied and finally well-understood. This knowledge from molecular organic photochemistry can be transferred to the design of covalent organic frameworks (COFs) as active visible-light photocatalysts. COFs constitute a new class of crystalline porous materials with substantial application potentials. Featured with outstanding structural tunability, large porosity, high surface area, excellent stability, and unique photoelectronic properties, COFs are studied as potential candidates in various research areas (e.g., photocatalysis). This review aims to provide the state-of-the-art insights into the design of COF photocatalysts (pristine, functionalized, and hybrid COFs) for organic transformations. The catalytic reaction mechanism of COF-based photocatalysts and the influence of dimensionality and crystallinity on heterogenous photocatalysis performance are also discussed, followed by perspectives and prospects on the main challenges and opportunities in future research of COFs and COF-based photocatalysts.

Photovoltaic Materials as Heterogeneous Photocatalysts: A Golden Opportunity for Sustainable Organic Syntheses

Heterogeneous Photocatalysts The research in the field of photovoltaic materials applied to the conversion of solar light into electrical energy has boomed in the past years as reviewed by Stefano Protti, Davide Ravelli, and co-workers in article number 2201008. Intriguingly, these derivatives can be exploited as recyclable heterogeneous photocatalysts in organic synthesis as well, enabling the preparation of high added value compounds under sustainable conditions.

Surface Density of Cobalt Single Atoms Manipulating Hydroxyl Radical Generation Via Dual Pathways: Electrons Supply and Active sites

AbstractPhotocatalytic generation of •OH from O3 is an intriguing avenue for aqueous organics degradation due to the high utilization of photogenerated electrons, but ambiguous information about charge transfer and surface‐active sites hinders the optimization of photocatalysts. In this work, a series of cobalt single‐atom catalysts (SACs) anchored on graphitic carbon nitride to improve •OH generation from O3 via electron reduction and catalytic activation dual pathway is synthesized. Various characterization and density functional theory calculations reveal that cobalt single atoms can introduce trap states for holes, which improve the light‐harvesting ability and accelerate the transfer of electrons and holes. Meanwhile, Co single atoms can also act as active sites to accelerate ozone decomposition and produce •OH directly. Particularly, the influence of different surface densities of Co single atoms on photogenerated electron supply and surface reaction is disclosed. A higher density of Co provided more active sites for O3 catalytic activation, but the narrowed distance between oxidation and reduction centers reduces the supply of available electrons by worsening the charge recombination. This work offers an atomic‐level correlation of the isolated metal density and photocatalytic properties, and can scientifically guide the design of high‐performance photocatalysts for organic synthesis and water purification.

Synthesis, properties and catalysis of quantum dots in C–C and C-heteroatom bond formations

Abstract Luminescent quantum dots (QDs) represent a new form of carbon nanomaterials which have gained widespread attention in recent years, especially in the area of chemical sensing, bioimaging, nanomedicine, solar cells, light-emitting diode (LED), and electrocatalysis. Their extremely small size renders some unusual properties such as quantum confinement effects, good surface binding properties, high surface‐to‐volume ratios, broad and intense absorption spectra in the visible region, optical and electronic properties different from those of bulk materials. Apart from, during the past few years, QDs offer new and versatile ways to serve as photocatalysts in organic synthesis. Quantum dots (QD) have band gaps that could be nicely controlled by a number of factors in a complicated way, mentioned in the article. Processing, structure, properties and applications are also reviewed for semiconducting quantum dots. Overall, this review aims to summarize the recent innovative applications of QD or its modified nanohybrid as efficient, robust, photoassisted redox catalysts in C–C and C-heteroatom bond forming reactions. The recent structural modifications of QD or its core structure in the development of new synthetic methodologies are also highlighted. Following a primer on the structure, properties, and bio-functionalization of QDs, herein selected examples of QD as a recoverable sustainable nanocatalyst in various green media are embodied for future reference.

State of the Art of Bodipy‐Based Photocatalysts in Organic Synthesis

AbstractPhotochemistry is a tremendous research field offering many synthetic possibilities to chemists. Breakthroughs in this area have been notably driven by the implementation of new classes of photocatalysts. Within this context, Bodipy (Boron‐dipyrromethene) dyes possess attractive chemical and physical features such as their modularity, strong absorption under visible light irradiation, good thermal and photochemical stabilities, and high fluorescence quantum yields. As such, this class of compounds has found widespread applications in functionalized materials, biology, medicine, or organic chemistry. From an organic‐synthetic point of view, excited states of Bodipy dyes have been harnessed in electron and energy transfer reactions. This minireview collates the relevant literature on the applications of these catalysts in synthetic photochemistry and provides some perspectives of this research area.

Porphyrin-based metal- and covalent-organic frameworks as heterogeneous nanosized photocatalysts in organic synthesis

The porphyrin-containing metal- and covalent-organic frameworks, respectively MOFs and COFs, are quite versatile porous nanomaterials for hetero-photocatalysis.

Applications of Sensitized Semiconductors as Heterogeneous Visible-Light Photocatalysts in Organic Synthesis

The industrial transition to more-sustainable chemical manufacturing requires the development of a variety of high-performance heterogeneous catalysts. Recently, new classes of heterogeneous and recyclable catalysts that exploit visible-light activation have emerged in the field of organic synthesis. Among these systems, sensitized semiconductors occupy a strategic place as they are able to initiate single electron transfer processes under heterogeneous conditions and using medium-to-low energy light activation. This technology can promote a range of synthetically useful reactions, such as oxidations, reductions, or additions, including C–C bond formation, under very mild conditions and with high selectivity. Sensitized semiconductors have been known for decades in solar cell technologies (the so-called “Dye-Sensitized Solar Cells”) but applications in organic synthesis are only very recent. This Review provides a comprehensive overview of the mechanisms, reactivity, and scope of this technology, with a focus on their new and promising synthetic applications.

Visible light driven perovskite-based photocatalysts: A new candidate for green organic synthesis by photochemical protocol

Photoredox catalysis, which can legitimately change visible-light (solar energy) into chemical energy, is a swiftly rising and promising approach to instigate chemical reactions because solar energy is clean, inexpensive, boundless and simply available energy resource. For many important organic transformations, photocatalytic alternates such as transition-metal-based photocatalysts, organic dyes and many nanoparticles have been reported to catalyze photocatalytic organic reactions through electron–hole transfer process. Recently, immense efforts and encouraging achievements are accomplished in the area of semiconductor perovskite-type catalytic materials as a photocatalysts in organic synthesis, owing to their ‘structural adjustability and fascinating convenient physicochemical properties’. Hitherto, unique photo-catalytic properties of several perovskite-type catalytic materials as substitutes of noble metals have been advanced and their functions in photoredox catalysis examined. From the beginning of 2017, the research on photoredox catalysis using perovskite as a photocatalyst has meant one of the innovative pattern in heterogeneous photocatalytic organic reactions and is as yet growing. This review covers brand-new accomplishments in soler-driven chemical reactions, for example, C–H activation, redox reaction, bond forming process, coupling reactions, bond cleavage, dehydrogenation, and ring–opening reactions using perovskite-type catalytic materials as a heterogeneous photocatalysts have been reported during last five years.

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches.

In this review we present relevant and recent applications of porphyrin derivatives as photocatalysts in organic synthesis, involving both single electron transfer (SET) and energy transfer (ET) mechanistic approaches. We demonstrate that these highly conjugated photosensitizers show increasing potential in photocatalysis since they combine both photo- and electrochemical properties which can substitute available metalloorganic photocatalysts. Batch and continuous-flow approaches are presented highlighting the relevance of enabling technologies for the renewal of porphyrin applications in photocatalysis. Finally, the reaction scale in which the methodologies were developed are highlighted since this is an important parameter in the authors’ opinion.

Carbon dots as photocatalysts for organic synthesis: metal-free methylene–oxygen-bond photocleavage

We report for the first time that irradiation of four different citric acid-derived carbon dots (CDs), in the absence of any other redox mediators, promotes an organic reaction.

Emerging applications of porous organic polymers in visible-light photocatalysis

Porous organic polymers are efficient photocatalysts in organic synthesis, hydrogen evolution, CO2 reduction, and degradation of organic pollutants.

Perovskites catalyze aldehyde alkylations

Mention perovskites to C&EN readers, and many of them will think of solar cells—and for good reason: organolead halide compounds with the perovskite crystal structure and ABX3 stoichiometry have been the superstars of low-cost photovoltaics for a few years running. A new study shows the perovskites have other tricks up their sleeves. A team led by San Diego State University chemists Xiaolin Zhu and Yong Yan reports that methylammonium lead tribromide and the cesium analog, two of the most studied solar-cell perovskites, double as highly active photocatalysts for organic synthesis (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.8b08720). The researchers used standard methods to prepare the low-cost nanocrystal catalysts and explored their reactivity under blue-light illumination in tests with 2-bromoacetophenone and octanal. The reactions generated a mixture of products, including the aldehyde α-alkylation product (shown), other C-coupling products, and dehalogenated acetophenone. By tuning reaction conditions,...

Construction of donor-acceptor type conjugated microporous polymers: A fascinating strategy for the development of efficient heterogeneous photocatalysts in organic synthesis

Metal-free, visible-light driven, solid organic photocatalysts provide a more green and environmentally friendly alternative to traditional metal-based photocatalysts. Donor-Acceepor (D-A) dyads possess a feature of easy to adjust the photoelectric properties, and enhance their photocatalytic performances. Here we report a fascinating strategy for screening excellent organic porous photocatalysts through oxidative coupling of single D-A based monomer, which has still an important advantage to ensure uniformity of polymer structure except for the inherent characteristics of D-A polymers. According to this strategy, three D-A typed conjugated microporous polymer (DA-CMP) photocatalysts consisting of alternating electron-rich (carbazole) and electron-deficient (benzene, 4,7-diphenyl-2,1,3-benzothiadiazole or anthraquinone) units have been synthesized, and their porosity and photoelectric properties including adsorption, emission, lifetime, optical bandgaps, energy levels and transient photocurrent response as well as photocatalytic activity, were conveniently tuned by selecting different D-A monomers with tunable electron-deficient moiety. These DA-CMPs were exploited as metal-free photocatalysts in the oxidative C-H functionalization reactions in the presence of visible-light and molecular oxygen. They showed excellent photocatalytic activity, extensive substrate adaptability and outstanding reusability, due to combining some key features like permanent porosity, outstanding stability and optoelectronic properties. In addition, the reaction mechanism for DA-CMP photocatalyzed C-H functionalization reactions under visible-light irradiation was investigated in detail. Moreover, to prove in depth the benefits of the heterogeneous photocatalysis, a continuous flow procedure has been conducted with an excellent yield.

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. Herein, we highlight the recent advances of QDs used for smart and clean organic transformations.

Influence of the halide and exposed facets on the visible-light photoactivity of bismuth oxyhalides for selective aerobic oxidation of primary amines

Bismuth oxyhalides BiOX (X=Cl, Br, I) are seldom applied as photocatalysts in organic synthesis. Herein, we investigated their potential for the aerobic oxidative coupling of benzylamine to N-benzylidenebenzylamine, as imines are important synthetic intermediates of pharmaceuticals and biologically active nitrogen-containing organic compounds. The influence of the halide and the exposed crystal facets on the photoactivity was investigated. BiOBr showed excellent photoactivity, surpassing BiOCl and BiOI, which have poor light absorption and oxidation ability, respectively. Three differently facetted BiOBr photocatalysts were synthesized. The {001}-facetted BiOBr exhibited higher intrinsic activity than the {010}- or {110}-samples due to efficient charge separation. However, surface area plays an important role as reactions usually occur at the catalyst surface. Because of their much larger surface area, the solvothermally-synthesized BiOBr microspheres with {110}-dominant exposed facet showed the highest photooxidative activity, with 100% conversion and 100% selectivity to N-benzylidenebenzylamine after 14h visible light irradiation at room temperature using oxygen from atmospheric air. This work provides an economical, feasible, sustainable and green process for the synthesis of imines and illustrates the great potential of bismuth oxyhalides as photocatalysts for organic synthesis.

Au–Cu–Ag Nanorods Synthesized by Seed‐Mediated Coreduction and Their Optical Properties

Development of trimetallic nanoparticles can potentially broaden the optical window for plasmonic applications, but can also offer new photocatalysts for organic synthesis. The optical and catalytic properties can be tuned by the ratio between different components and how they are distributed in the nanoparticles, in addition to their size and shape. This work reports a seed‐mediated coreduction method for the fabrication of Au‐Cu‐Ag nanorods in oil phase. The composition and morphology of trimetallic Au‐Cu‐Ag nanostructures can be controlled by adjusting the injection temperature and the concentration of silver precursor. An additional peak (around 395 nm) is observed in extinction spectrum of trimetallic Au‐Cu‐Ag nanorods compared to that of bimetallic Au‐Cu nanorods, caused by the segregated silver composition in the trimetallic nanorods. The reported synthesis can be used to develop a wide range of trimetallic nanostructures with tunable optical properties and functionality.