Triplet-Triplet Energy Transfer: A Simple Strategy for an Efficient Visible Light-Induced Photoclick Reaction

Photoclick reactions combine the advantages offered by light-driven processes and classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photo-crosslinking, and protein labeling. Despite these advances, the dependency of most of the photoclick reactions on UV light poses a severe obstacle for their general implementation, as this light can be absorbed by other molecules in the system resulting in their degradation or unwanted reactivity. However, the development of a simple and efficient system to achieve bathochromically shifted photoclick transformations remains challenging. Here, we introduce triplet-triplet energy transfer as a fast and selective way to enable visible light-induced photoclick reactions. Specifically, we show that 9,10-phenanthrenequinones (PQs) can efficiently react with electron-rich alkenes (ERAs) in the presence of a catalytic amount (as little as 5 mol %) of photosensitizers. The photocycloaddition reaction can be achieved under green (530 nm) or orange (590 nm) light irradiation, representing a bathochromic shift of over 100 nm as compared to the classical PQ-ERAs system. Furthermore, by combining appropriate reactants, we establish an orthogonal, blue and green light-induced photoclick reaction system in which the product distribution can be precisely controlled by the choice of the color of light.

Robust Miniemulsion PhotoATRP Driven by Red and Near-Infrared Light

Photoinduced polymerization techniques have gathered significant attention due to their mild conditions, spatiotemporal control, and simple setup. In addition to homogeneous media, efforts have been made to implement photopolymerization in emulsions as a practical and greener process. However, previous photoinduced reversible deactivation radical polymerization (RDRP) in heterogeneous media has relied on short-wavelength lights, which have limited penetration depth, resulting in slow polymerization and relatively poor control. In this study, we demonstrate the first example of a highly efficient photoinduced miniemulsion ATRP in the open air driven by red or near-infrared (NIR) light. This was facilitated by the utilization of a water-soluble photocatalyst, methylene blue (MB+). Irradiation by red/NIR light allowed for efficient excitation of MB+ and subsequent photoreduction of the ATRP deactivator in the presence of water-soluble electron donors to initiate and mediate the polymerization process. The NIR light-driven miniemulsion photoATRP provided a successful synthesis of polymers with low dispersity (1.09 ≤ Đ ≤ 1.29) and quantitative conversion within an hour. This study further explored the impact of light penetration on polymerization kinetics in reactors of varying sizes and a large-scale reaction (250 mL), highlighting the advantages of longer-wavelength light, particularly NIR light, for large-scale polymerization in dispersed media owing to its superior penetration. This work opens new avenues for robust emulsion photopolymerization techniques, offering a greener and more practical approach with improved control and efficiency.

Sustainable Synthesis through Catalyst-Free Photoinduced Cascaded Bond Formation

The beginning of photochemical reactions revolutionized synthetic chemistry through sustainable practices. This review explores cutting-edge developments in leveraging light-induced processes for generating cascaded C-C and C-hetero bonds without catalysts. Significantly, catalyst-free photoinduced methodologies have garnered considerable attention, especially in the creation of varied heterocyclic frameworks for drug design and the synthesis of natural products. The article delves into underlying mechanisms, addresses limitations, and evaluates various methodologies, emphasizing the potential of photocatalyst and transition metal-free photochemical reactions to enhance sustainability. Divided into two sections, it covers recent strides in C-C and C-heteroatom and multiple C-heteroatom bond formation reactions.

Atom Transfer Radical Addition Reactions of Quinoxalin-2(1H)-ones with CBr4 and Styrenes Using Mes-Acr-MeClO4 Photocatalyst

The atom transfer radical addition (ATRA) reaction is defined as a method for introducing halogenated compounds into alkenes via a radical mechanism. In this study, we present an ATRA approach for achieving regioselective functionalization of quinoxalin-2(1H)-ones by activating C-Br bonds of CBr4 and subsequent trihaloalkyl-carbofunctionalization of styrenes employing the 9-mesityl-10-methylacridinium perchlorate (Fukuzumi) photocatalyst under 3W blue LED (450-470 nm) irradiation. This three-component radical cascade process demonstrates remarkable efficiency in the synthesis of 1-methyl-3-(3,3,3-tribromo-1-(4-chlorophenyl)propyl)quinoxalin-2(1H)-one derivatives.

Nature-Inspired Photocatalytic Azo Bond Cleavage with Red Light

The emerging field of photoredox catalysis in mammalian cells enables spatiotemporal regulation of a wealth of biological processes. However, the selective cleavage of stable covalent bonds driven by low-energy visible light remains a great challenge. Herein, we report that red light excitation of a commercially available dye, abbreviated NMB+, leads to catalytic cleavage of stable azo bonds in both aqueous solutions and hypoxic cells and hence a means to photodeliver drugs or functional molecules. Detailed mechanistic studies reveal that azo bond cleavage is triggered by a previously unknown consecutive two-photon process. The first photon generates a triplet excited state, 3NMB+*, that is reductively quenched by an electron donor to generate a protonated NMBH•+. The NMBH•+ undergoes a disproportionation reaction that yields the initial NMB+ and two-electron-reduced NMBH (i.e., leuco-NMB, abbreviated as LNMB). Interestingly, LNMB forms a charge transfer complex with all four azo substrates that possess an intense absorption band in the red region. A second red photon induces electron transfer from LNMB to the azo substrate, resulting in azo bond cleavage. The charge transfer complex mediated two-photon catalytic mechanism reported herein is reminiscent of the flavin-dependent natural photoenzyme that catalyzes bond cleavage reactions with high-energy photons. The red-light-driven photocatalytic strategy offers a new approach to bioorthogonal azo bond cleavage for photodelivery of drugs or functional molecules.

Isotherms, kinetics and thermodynamic mechanism of methylene blue dye adsorption on synthesized activated carbon

The treatment of methylene blue (MB) dye wastewater through the adsorption process has been a subject of extensive research. However, a comprehensive understanding of the thermodynamic aspects of dye solution adsorption is lacking. Previous studies have primarily focused on enhancing the adsorption capacity of methylene blue dye. This study aimed to develop an environmentally friendly and cost-effective method for treating methylene blue dye wastewater and to gain insights into the thermodynamics and kinetics of the adsorption process for optimization. An adsorbent with selective methylene blue dye adsorption capabilities was synthesized using rice straw as the precursor. Experimental studies were conducted to investigate the adsorption isotherms and models under various process conditions, aiming to bridge gaps in previous research and enhance the understanding of adsorption mechanisms. Several adsorption isotherm models, including Langmuir, Temkin, Freundlich, and Langmuir-Freundlich, were applied to theoretically describe the adsorption mechanism. Equilibrium thermodynamic results demonstrated that the calculated equilibrium adsorption capacity (qe) aligned well with the experimentally obtained data. These findings of the study provide valuable insights into the thermodynamics and kinetics of methylene blue dye adsorption, with potential applications beyond this specific dye type. The utilization of rice straw as an adsorbent material presents a novel and cost-effective approach for MB dye removal from wastewater.

Synthesis and characterization of titanium dioxide nanoparticles from Bacillus subtilis MTCC 8322 and its application for the removal of methylene blue and orange G dyes under UV light and visible light

Over the last decade there has been a huge increase in the green synthesis of nanoparticles. Moreover, there is a continuous increase in harnessing the potential of microorganisms for the development of efficient and biocompatible nanoparticles around the globe. In the present research work, investigators have synthesized TiO2 NPs by harnessing the potential of Bacillus subtilis MTCC 8322 (Gram-positive) bacteria. The formation and confirmation of the TiO2 NPs synthesized by bacteria were carried out by using UV-Vis spectroscopy, Fourier transforms infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX/EDS). The size of the synthesized TiO2 NPs was 80-120 nm which was spherical to irregular in shape as revealed by SEM. FTIR showed the characteristic bands of Ti-O in the range of 400-550 cm-1 and 924 cm-1 while the band at 2930 cm-1 confirmed the association of bacterial biomolecules with the synthesized TiO2 NPs. XRD showed two major peaks; 27.5° (rutile phase) and 45.6° (anatase phase) for the synthesized TiO2 NPs. Finally, the potential of the synthesized TiO2 NPs was assessed as an antibacterial agent and photocatalyst. The remediation of Methylene blue (MB) and Orange G (OG) dyes was carried out under UV- light and visible light for a contact time of 150-240 min respectively. The removal efficiency for 100 ppm MB dye was 25.75% and for OG dye was 72.24% under UV light, while in visible light, the maximum removal percentage for MB and OG dye was 98.85% and 80.43% respectively at 90 min. Moreover, a kinetic study and adsorption isotherm study were carried out for the removal of both dyes, where the pseudo-first-order for MB dye is 263.269 and 475554.176 mg/g for OG dye. The pseudo-second-order kinetics for MB and OG dye were 188.679 and 1666.667 mg/g respectively. In addition to this, the antibacterial activity of TiO2 NPs was assessed against Bacillus subtilis MTCC 8322 (Gram-positive) and Escherichia coli MTCC 8933 (Gram-negative) where the maximum zone of inhibition in Bacillus subtilis MTCC 8322 was about 12 mm, and for E. coli 16 mm.

Facile access to benzofuran derivatives through radical reactions with heteroatom-centered super-electron-donors

The development of suitable electron donors is critical to single-electron-transfer (SET) processes. The use of heteroatom-centered anions as super-electron-donors (SEDs) for direct SET reactions has rarely been studied. Here we show that heteroatom anions can be applied as SEDs to initiate radical reactions for facile synthesis of 3-substituted benzofurans. Phosphines, thiols and anilines bearing different substitution patterns work well in this inter-molecular radical coupling reaction and the 3-functionalized benzofuran products bearing heteroatomic functionalities are given in moderate to excellent yields. The reaction mechanism is elucidated via control experiments and computational methods. The afforded products show promising applications in both organic synthesis and pesticide development.

Red-Light-Driven Atom Transfer Radical Polymerization for High-Throughput Polymer Synthesis in Open Air

Photoinduced reversible-deactivation radical polymerization (photo-RDRP) techniques offer exceptional control over polymerization, providing access to well-defined polymers and hybrid materials with complex architectures. However, most photo-RDRP methods rely on UV/visible light or photoredox catalysts (PCs), which require complex multistep synthesis. Herein, we present the first example of fully oxygen-tolerant red/NIR-light-mediated photoinduced atom transfer radical polymerization (photo-ATRP) in a high-throughput manner under biologically relevant conditions. The method uses commercially available methylene blue (MB+) as the PC and [X-CuII/TPMA]+ (TPMA = tris(2-pyridylmethyl)amine) complex as the deactivator. The mechanistic study revealed that MB+ undergoes a reductive quenching cycle in the presence of the TPMA ligand used in excess. The formed semireduced MB (MB•) sustains polymerization by regenerating the [CuI/TPMA]+ activator and together with [X-CuII/TPMA]+ provides control over the polymerization. This dual catalytic system exhibited excellent oxygen tolerance, enabling polymerizations with high monomer conversions (>90%) in less than 60 min at low volumes (50-250 μL) and high-throughput synthesis of a library of well-defined polymers and DNA-polymer bioconjugates with narrow molecular weight distributions (Đ < 1.30) in an open-air 96-well plate. In addition, the broad absorption spectrum of MB+ allowed ATRP to be triggered under UV to NIR irradiation (395-730 nm). This opens avenues for the integration of orthogonal photoinduced reactions. Finally, the MB+/Cu catalysis showed good biocompatibility during polymerization in the presence of cells, which expands the potential applications of this method.

Phenothiazine-Based Cu(II)-Selective Fluorescent Sensor: GHK-Cu Sensing Applications

Sensing important metals in different environments is an important area and involves the development of a wide variety of metal-sensing materials. The employment of fluorescent sensors in metal sensing has been one of the most widely applied methodologies, and the identification of selective metal sensors is important. We herein report a phenothiazine-based Cu(II) fluorescent sensor that is highly selective to Cu(II) ions compared with other transition metal salts. The Lewis acidity of the Cu(II) salt certainly was found to be a factor for obtaining an enhanced sensing response in MeOH as the solvent, while a ratio of 1:1 was calculated to be the most optimum for getting the desired response.

Photo Fenton RAFT Polymerization of (Meth)Acrylates in DMSO Sensitized by Methylene Blue

A novel open-to-air photo RAFT polymerization of a series of acrylate and methacrylate monomers mediated by matching chain transfer agent irradiated by far-red light in DMSO is reported. Hydroxyl radical (•OH) generated from methylene blue (MB) sensitized decomposition of H2 O2 via photo-Fenton like-reaction is used for polymerization initiation. The "living/control" characteristic is evidenced by kinetic study, in which a pseudo first order curve and linearly increases of molecular weight with the increase of monomer conversion are observed. The living end-group fidelity is characterized by MALDI-TOF-MS and 1 H NMR results, and confirmed by successful chain extension. The temporary controllability is proved by light on/off switch experiment.

Visible-light-induced cascade reaction: a sustainable approach towards molecular complexity

Photoredox catalysis has demonstrated rapid evolution in the field of synthetic organic chemistry. On the other hand, the splendour of cascade reactions in providing complex molecular architectures renders them a cutting-edge research area. Therefore, the merging of photocatalysis with cascade synthesis brings out a synthetic paradigm with immense potential. The development of photocascade catalysis for a target molecule with a particular molecular skeleton and stereochemical framework presents certain challenges but provides a robust and environmentally benign synthetic alternative. This comprehensive review assembles all the accomplishments and highlights of visible-light-induced cascade reactions with literature coverage up to October 2022.

Silyl Tether-Assisted Photooxygenation of Electron-Deficient Enaminoesters: Direct Access to Oxamate Formation

Photooxygenation reactions of electron-deficient enaminoesters bearing an oxophilic silyl tether at the α-position of the nitrogen atom using methylene blue (MB) were explored to develop a mild and efficient photochemical strategy for oxidative C-C double bond cleavage reactions via singlet oxygen (¹O₂). Photochemically generated ¹O₂, through energy transfer from the triplet excited state of MB (³MB*) to molecular oxygen (³O₂), was added across a C-C double bond moiety of enaminoesters to form perepoxides, which rearranged to form dioxetane intermediates. The cycloreversion of the formed dioxetane via both C-C and O-O bond cleavage processes led to the formation of oxamates. Importantly, contrary to alkyl group tether-substituted electron-deficient enaminoesters that typically disfavor photooxygenation, the silyl tether-substituted analogues undergo this photochemical transformation efficiently with the assistance of a silyl tether, which facilitates formation of the perepoxide. The observations in this study provide useful information about photosensitized oxygenation reactions of unsaturated C-C bonds, and, moreover, this photochemical strategy can be utilized as a mild and feasible method for the preparation of diversely functionalized carbonyl compounds including oxamates.

Redox-active molecules as organocatalysts for selective oxidative transformations - an unperceived organocatalysis field

Organocatalysis is widely recognized as a key synthetic methodology in organic chemistry. It allows chemists to avoid the use of precious and (or) toxic metals by taking advantage of the catalytic activity of small and synthetically available molecules. Today, the term organocatalysis is mainly associated with redox-neutral asymmetric catalysis of C-C bond-forming processes, such as aldol reactions, Michael reactions, cycloaddition reactions, etc. Organophotoredox catalysis has emerged recently as another important catalysis type which has gained much attention and has been quite well-reviewed. At the same time, there are a significant number of other processes, especially oxidative, catalyzed by redox-active organic molecules in the ground state (without light excitation). Unfortunately, many of such processes are not associated in the literature with the organocatalysis field and thus many achievements are not fully consolidated and systematized. The present article is aimed at overviewing the current state-of-art and perspectives of oxidative organocatalysis by redox-active molecules with the emphasis on challenging chemo-, regio- and stereoselective CH-functionalization processes. The catalytic systems based on N-oxyl radicals, amines, thiols, oxaziridines, ketone/peroxide, quinones, and iodine(I/III) compounds are the most developed catalyst types which are covered here.

Visible-Light Promoted Regioselective Oxygenation of Quinoxalin-2(1H)-ones Using O2 as an Oxidant

A visible-light-mediated sustainable approach for metal-free oxygenation of quinoxalin-2(1H)-one by employing Mes-Acr-MeClO₄ as a photocatalyst without using any additive or cocatalyst is reported here. O₂ served as the eco-friendly and green oxidant source for this conversion. In addition, the protocol exhibited high regioselectivity and tolerance toward a broad spectrum of functional groups to furnish quinoxaline-2,3-diones in good to excellent yields.

Acridine yellow G (AYG) as a photo-induced electron transfer (PET) photocatalyst employed for the radical Michael–Mannich cyclocondensation of imines

A four-component domino Michael–Mannich cyclocondensation of amines, dialkyl acetylenedicarboxylaes, and formaldehyde was utilized to develop a green technique for sans metal combination of polyfunctionalized dihydro-2-oxypyrroles. It involves visible light as an environmentally friendly power source and acridine yellow G (AYG) as a photo-induced electron transfer (PET) photocatalyst. The motivation behind this examination was to expand the utilization of a non-metal dye that is both reasonable and broadly accessible. Photochemically catalyzed AYG flaunts exceptional returns, energy effectiveness, and natural agreeableness, as well as extraordinary iota economy, efficient highlights, and comfort of purpose. Key abilities consist of an easy experimental setup, big substrate tolerance, finance-friendly, clean painting-up strategies within the absence of tedious separation techniques, and minimized the quantity of waste for each organic transformation. The type of yields is pretty uniform (85–97%, average 92.09%), and the shape of reaction times might be very speedy (15–30 min, average 21.59 min), and the factor stated inside the dialogue is that the method tolerates quite a number electron-donating and electron-withdrawing functional groups, while, however, giving extremely good yields. The response within the reason is insensitive to the person of the substituents. Subsequently, many compounds and natural factors can be followed over the course of time. Shockingly, gram-scale cyclization is conceivable, proposing that the strategy could be utilized in industry.

Explorative Sonophotocatalytic Study of C-H Arylation Reaction of Pyrazoles Utilizing a Novel Sonophotoreactor for Green and Sustainable Organic Synthesis

The development of a mild, general, and green method for the C-H arylation of pyrazoles with relatively unreactive aryl halides is an ongoing challenge in organic synthesis. We describe herein a novel sonophotoreactor based on an ultrasonic cleaning bath and blue LED light (visible light) that induce copper-catalyzed monoarylation for pharmacologically relevant pyrazoles. The hybrid effect of ultrasonic irradiation and blue LED is discussed to interpret the observed synergistic action. A broad array of pyrazoles coupled with iodobenzene avoids expensive palladium metal or salts, and certain designed substrates were attained. Only comparatively inexpensive copper(I)iodide and 1,10-phenanthroline were used all together as the catalyst. The presented technique is a greener way to create C-H arylation of pyrazoles. It significantly reduces the amount of energy needed.

Methylene Blue as a Photo-Redox Catalyst: The Development Synthesis of Tetrahydrobenzo[b]pyran Scaffolds via a Single-Electron Transfer/Energy Transfer

In a green tandem reaction using aldehyde derivatives, malononitrile, and dimedone, a radical tandem Knoevenagel–Michael cyclocondensation reaction of tetrahydrobenzo[b]pyran scaffolds was developed. Using visible light as a sustainable energy source, methylene blue (MB⁺)-derived photo-excited state functions were employed in an aqueous solution as single-electron transfer (SET) and energy transfer catalysts. The range of yields is quite uniform (81–98%, average 92.18%), and the range of reaction time is very fast (2–7 min, average 3.7 min), and the point mentioned in the discussion is that the procedure tolerates a range of donating and withdrawing groups, while still giving very excellent yields. The reaction is fairly insensitive to the nature of the substituents. Research conducted in this project aims to develop a non-metallic cationic dye that is both inexpensive and widely available for more widespread use. In addition to energy efficiency and environmental friendliness, methylene blue also offers an excellent atom economy, time-saving features, and ease of use. As a result, a wide range of long-term chemical and environmental properties can be obtained. The turnover number and turnover frequency of tetrahydrobenzo[b]pyran scaffolds have been computed. Surprisingly, gram-scale cyclization is a possibility, implying that the technology may be applied in industries.

The development of Friedländer heteroannulation through a single electron transfer and energy transfer pathway using methylene blue (MB+)

The radical Friedländer hetero-annulation of 2-aminoaryl ketone and -methylene carbonyl compound was used to develop a green tandem approach for the metal-free synthesis of polysubstitutedquinolines. At room temperature in an ethanol solvent, photo-excited state functions generated from MB+ were used as single-electron transfer (SET) and energy transfer (EnT) catalysts, utilizing visible light as a renewable energy source in the air atmosphere. The purpose of this research is to increase the use of a nonmetal cationic dye that is both inexpensive and widely available. High yields, energy-effectiveness, high atom economy, time-saving features of the reaction, and operational simplicity, and the least amount of a catalyst are the benefits of this study. As a result, a wide range of ecological and long-term chemical properties are obtained. Polysubstitutedquinolines' turnover number (TON) and turnover frequency (TOF) have been calculated. Surprisingly, such cyclization can be accomplished on a gram scale, indicating that the process has industrial potential.

Visible light-induced functionalization of indazole and pyrazole: a recent update

Indazole and pyrazole are renowned as a prodigious class of heterocycles having versatile uses in medicinal as well as industrial chemistry. Considering sustainable approaches, recently, photocatalysis has become an indispensable tool in organic chemistry due to its application for the activation of small molecules and the use of a clean energy source. In this review, we have highlighted the use of metal-based photocatalysts, organic photoredox catalysts, energy transfer photocatalysts and electron-donor-acceptor complexes in the functionalization of indazole and pyrazole. This perspective is arranged based on the types of functionalization reactions on indazole and pyrazole. A detailed discussion regarding the reaction mechanism of each reaction is given to provide a comprehensive guide to the reader. Finally, a summary of existing challenges and the future outlook towards the development of efficient photocatalytic methods for functionalization of these heterocycles is also presented.

The development of imin-based tandem Michael-Mannich cyclocondensation through a single-electron transfer (SET)/energy transfer (EnT) pathway in the use of methylene blue (MB+) as a photo-redox catalyst

A four-component green tandem approach for the metal-free synthesis of polyfunctionalized dihydro-2-oxypyrroles was devised using the Michael–Mannich cyclocondensation of amines, dialkyl acetylenedicarboxylaes, and formaldehyde. Photo-excited state functions generated from methylene blue (MB⁺) were employed as single-electron transfer (SET) and energy transfer (EnT) catalysts at ambient temperature in an ethanol solvent, employing visible light as a renewable energy source in the air atmosphere. This study aims to increase the usage of a non-metal cationic dye that is both inexpensive and widely available. Methylene blue is photochemically produced with the least amount of a catalyst due to its high yields, energy-effectiveness, high atom economy, time-saving features of the reaction, and operational simplicity. As a result, a variety of ecological and long-term chemical features are achieved. Surprisingly, such cyclization can be done on a gram scale, implying that the process has industrial potential.

A four-component green tandem approach for the metal-free synthesis of polyfunctionalized dihydro-2-oxypyrroles was devised using the Michael–Mannich cyclocondensation of amines, dialkyl acetylenedicarboxylaes, and formaldehyde.

Green and Sustainable Visible Light-Mediated Formation of Amide Bonds: An Emerging Niche in Organic Chemistry

Amide bond is one of the most fascinating functional groups in nature due to its stability, conformational diversity, high bond polarity, and abundance in numerous natural products and drug candidates,...

Pyrylium salts acting as both energy transfer and electron transfer photocatalysts for E → Z isomerization of activated alkenes and cyclization of cinnamic or biaryl carboxylic acids

Here we report that 2,4,6-triarylpyrylium salts could perform both energy transfer and electron transfer photocatalysis modes for E → Z isomerization of activated alkenes and cyclization of cinnamic or biaryl carboxylic acids.

Performances of Homogeneous and Heterogenized Methylene Blue on Silica Under Red Light in Batch and Continuous Flow Photochemical Reactors

Methylene blue was efficiently immobilized on silica micro- and nanoparticles by electrostatic interactions and the performances of the heterogenized photocatalysts were compared against the homogeneous conditions using the photooxidation of citronellol as a model reaction under red light, in a batch and a continuous flow photochemical reactor. In batch, the heterogeneous photocatalyst outperforms the homogeneous one, presumably due to kinetic and stability effects. The two catalytic systems are also compared in a flow reactor displaying improved mass transfer properties. We demonstrate that this results in a dramatic enhancement in photocatalyst stability, reactivity and productivity. This study highlights the importance of photocatalyst stability under homogeneous versus heterogenized conditions and in batch versus flow photochemistry.

Cellulose citrate: a convenient and reusable bio-adsorbent for effective removal of methylene blue dye from artificially contaminated water

In the present work, we proved the efficacy of cellulose citrate to remove methylene blue (MB) from artificially contaminated water. MB is a widely used dye, but because of its chemical aromatic structure, it is significantly stable with quite slow biodegradation, causing consequent serious health problems for people and significant environmental pollution. Cellulose citrate, the bio-adsorbent proposed and studied by us to remediate water polluted by MB, is produced by a green, cheap and fast procedure that makes use of two abundant natural products, cellulose and citric acid. The average of two citrate groups for each glucose unit of cellulose chains allows this material to have many carboxylic groups available for interaction with the cationic dye. The characterization was carried out through FT-IR, SEM, specific surface area, pore structure parameters and zeta potential. The negative value of the zeta potential at neutral pH is consistent with the affinity of this material for the adsorption of cationic compounds like MB. The activity of the adsorbent at different times, temperatures, pH and concentrations was investigated. The process followed monolayer adsorption typical of the Langmuir model, with a maximum adsorption capacity of 96.2 mg g-1, while for the kinetic studies the process followed a pseudo-second order model. The highest levels of adsorption were reported using solutions of dye with concentrations under 100 mg L-1. The adsorbent can be regenerated several times without a significant loss in the adsorption capacity, and it is not strongly affected by temperature and pH, giving rise to a simple and eco-sustainable procedure for water remediation. Therefore, we conclude that cellulose citrate can be considered as a promising bio-adsorbent for the removal of MB and other cationic pollutants from the environment.

Chlorinative Cyclization of Aryl Alkynoates Using NCS and 9-Mesityl-10-methylacridinium Perchlorate Photocatalyst

In a chlorinative cyclization, Mes-Acr-MeClO₄ acted as a visible-light photocatalyst to obtain 3-chlorocoumarins from aryl alkynoates and N-chlorosuccinimide (NCS). The radical initiated reaction proceeded in a cascading manner via Cl^- addition to alkynoates. Next, 5-exo-trig spirocyclization and subsequent 1,2-ester migration led to the formation of C-C and C-Cl bonds.

The wavelength-regulated stereodivergent synthesis of (Z)- and (E)-1,4-enediones from phosphonium ylides

The wavelength-regulated, photoredox-catalyzed stereodivergent synthesis of (Z)- and (E)-1,4-enediones from phosphonium ylides is reported.

Cyanation: a photochemical approach and applications in organic synthesis

This review summarises the photocatalytic cyanation strategies to construct C(sp²)–CN, C(sp³)–CN and X–CN (X = N, S) bonds.

The dark side of photocatalysis: near-infrared photoredox catalysis for organic synthesis

Near-Infrared photoredox catalysis is now consider as the next evolution of this field.

Visible light mediated functionalization of allenes

This review summarizes the visible light mediated strategies for the functionalization of allenes.