PDI-Functionalized Glass Beads: Efficient, Metal-Free Heterogeneous Photocatalysts Suitable for Flow Photochemistry.

Perylene diimides (PDI) have an extraordinary ability to activate both energy and electron transfer processes upon light excitation; however, their extremely low solubility has hindered their wide use as photocatalysts. Here, we show that the combination of solid-supported PDIs with continuous flow photochemistry offers a promising strategy for process intensification and a scalable platform for heterogeneous photocatalysis. The photocatalyst immobilized onto glass beads is highly efficient, easy to separate, and extremely reusable, with a broad synthetic application range.

Fibrous TiO Alternatives for Semiconductor-Based Catalysts for Photocatalytic Water Remediation Involving Organic Contaminants.

Water decontamination remains a challenge in several developed and developing countries. Affordable and efficient approaches are needed urgently. In this scenario, heterogeneous photocatalysts appear as one of the most promising alternatives.

Photosensitized selective semi-oxidation of tetrahydroisoquinoline: a singlet oxygen path.

Selective semi-oxidation of tetrahydroisoquinoline (THIQ) leads to a valuable dihydroisoquinoline (DHIQ) derivative via singlet oxygen photooxidation process. Typical photosensitisers (i.e.

Nitro to amine reductions using aqueous flow catalysis under ambient conditions.

A catalyst based on Pd on glass wool (Pd@GW) shows exceptional performance and durability for the reduction of nitrobenzene to aniline at room temperature and ambient pressure in aqueous solutions. The reaction is performed in a flow system and completed with 100% conversion under a variety of flow rates, 2 to 100 mLmin (normal laboratory fast flow conditions). Sodium borohydride or dihydrogen perform well as reducing agents.

Solar Driven Photocatalytic Activity of Porphyrin Sensitized TiO: Experimental and Computational Studies.

The absence of a secure long-term sustainable energy supply is recognized as a major worldwide technological challenge. The generation of H through photocatalysis is an environmentally friendly alternative that can help solve the energy problem. Thus, the development of semiconductor materials that can absorb solar light is an attractive approach.

Heterogeneous photocatalysis of azides: extending nitrene photochemistry to longer wavelengths.

The photodecomposition of azides to generate nitrenes usually requires wavelengths in the <300 nm region. In this study, we show that this reaction can be readily performed in the UVA region (368 nm) when catalyzed by Pd-decorated TiO2. In aqueous medium the reaction leads to amines, with water acting as the H source; however, in non-protic and non-nucleophilic media, such as acetonitrile, nitrenes recombine to yield azo compounds, while azirine-mediated trapping occurs in the presence of nucleophiles.

Photochemical benzylic radical arylation promoted by supported Pd nanostructures.

We report a novel way to promote photochemical benzylic radical arylations using Pd nanostructures. Traditional benzylic radical reaction pathways are challenged by the presence of metal centres that provoke unprecedented regioselectivity towards more synthetically relevant C(sp3)-C(sp2) couplings. This new C-H activation pathway is rationalised by means of a pseudo-persistent radical effect facilitated by metal centres.

Photochemical Dehalogenation of Aryl Halides: Importance of Halogen Bonding.

Upon UVA irradiation, aryl halides can undergo dehalogenation in the presence of bases and methanol as a hydrogen donor. This catalyst-free photochemical dehalogenation is furnished through a facile radical chain reaction under mild conditions. The chain reaction follows UVA irradiation of the reaction mixture in a transition-metal-free environment.

Perylene-Grafted Silicas: Mechanistic Study and Applications in Heterogeneous Photoredox Catalysis.

A mechanistic study is herein presented for the use of heterogeneous photocatalysts based on perylene moieties. First, the successful immobilization of perylene diimides (PDI) on silica matrices is demonstrated, including their full characterization by means of electronic microscopy, surface area measurements, powder XRD, thermogravimetric analysis, and FTIR, Si and C solid-state NMR, fluorescence, and diffuse reflectance spectroscopies. Then, the photoredox activity of the material was tested by using two model reactions, alkene oxidation and 4-nitrobenzylbromide reduction, and mechanistic studies were performed.

Spectroscopic and Time-Dependent DFT Study of the Photophysical Properties of Substituted 1,4-Distyrylbenzenes.

In this contribution, we examine the photophysical properties of 15 totally 1,4-distyrylbenzene derivatives (DSBs) functionalized with different electron-donating (ED) and electron-withdrawing (EW) groups by experimental and computational methodologies. We use UV-vis and fluorescence spectroscopies to determine the experimental optical properties such as the maximum absorption (λ) and emission (λ) wavelengths, the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps (Δ), the molar extinction coefficients (ε), the fluorescence quantum yields (Φ), and the fluorescence lifetimes (τ). We also calculate the experimental spontaneous emission decay rate () and correlate all of these magnitudes to the corresponding calculated properties, maximum absorption (λ) and emission (λ) wavelengths, vertical transition energies (Δ), oscillator strength (), and spontaneous emission decay rate (), obtained by the time-dependent density functional theory method.

Highly Electrophilic Titania Hole as a Versatile and Efficient Photochemical Free Radical Source.

Photogenerated holes in nanometric semiconductors, such as TiO, constitute remarkable powerful electrophilic centers, capable of capturing an electron from numerous donors such as ethers, or nonactivated substrates like toluene or acetonitrile, and constitute an exceptionally clean and efficient source of free radicals. In contrast with typical free radical precursors, semiconductors generate single radicals (rather than pairs), where the precursors can be readily removed by filtration or centrifugation after use, thus making it a convenient tool in organic chemistry. The process can be described as an example of dystonic proton coupled electron transfer.

Catalytic farming: reaction rotation extends catalyst performance.

The use of heterogeneous catalysis has key advantages compared to its homogeneous counterpart, such as easy catalyst separation and reusability. However, one of the main challenges is to ensure good performance after the first catalytic cycles. Active catalytic species can be inactivated during the catalytic process leading to reduced catalytic efficiency, and with that loss of the advantages of heterogeneous catalysis.

Biocompatibility and photo-induced antibacterial activity of lignin-stabilized noble metal nanoparticles.

One-pot thermal and photochemical syntheses of lignin-doped silver and gold nanoparticles were developed and their antimicrobial properties were studied against and . The nature of the lignin as well as the metal are directly involved in the antimicrobial activity observed in these nanocomposites. Whereas one of the nanocomposites is innocuous under dark conditions and shows photoinduced activity only against , the rest of the lignin-coated silver nanoparticles studied show antimicrobial activity under dark and light conditions for both bacteria strains.

Glass wool: a novel support for heterogeneous catalysis.

Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease of separation and reuse of the catalyst. Here we show that a very inexpensive, manageable and widely available material - glass wool - can act as a catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu, Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical organic reactions including reductive de-halogenation of aryl halides, reduction of nitrobenzene, Csp-Csp couplings, N-C heterocycloadditions (click chemistry) and Csp-Csp couplings (Sonogashira couplings).

How Fast Can Thiols Bind to the Gold Nanoparticle Surface?

Kinetics of gold nanoparticle surface modification with thiols can take more than one hour for completion. 7-mercapto-4-methylcoumarin can be used to follow the process by fluorescence spectroscopy and serves as a convenient molecular probe to determine relative kinetics. SERS studies with aromatic thiols further support the slow surface modification kinetics observed by fluorescence spectroscopy.

Selective Photoinduced Antibacterial Activity of Amoxicillin-Coated Gold Nanoparticles: From One-Step Synthesis to in Vivo Cytocompatibility.

Photoinduced antibacterial gold nanoparticles were developed as an alternative for the treatment of antibiotic-resistant bacteria. Thanks to the amoxicillin coating, they possess high in vivo stability, selectivity for the bacteria wall, a good renal clearance, and are completely nontoxic for eukaryotic cells at the bactericidal concentrations. A simple one-step synthesis of amoxi@AuNP is described at mild temperatures using the antibiotic as both reducing and stabilizing agent.

Thiol-Stabilized Gold Nanoparticles: New Ways To Displace Thiol Layers Using Yttrium or Lanthanide Chlorides.

We use the aurophilic interactions shown by lanthanides to overcome the sulfur-gold interaction. UV-vis and X-ray photoelectron spectroscopy confirm that yttrium or lanthanide chlorides easily displace sulfur ligands from the surface of thiol-stabilized gold nanoparticles.

Visible Light Production of Hydrogen by Ablated Graphene: Water Splitting or Carbon Gasification?

Reduced graphene oxide modified by pulsed laser ablation causes water splitting under visible light illumination (532 nm). When the light source is a pulsed laser, water splitting is accompanied by carbon gasification (CO formation); however, conventional (LED) light sources produce water splitting exclusively.

Photophysics of 7-mercapto-4-methylcoumarin and derivatives: complementary fluorescence behaviour to 7-hydroxycoumarins.

The photophysical behaviour of 7-mercapto-4-methylcoumarin (C-SH) and derivatives has been studied in different solvents. In contrast to 7-hydroxy-4-methylcoumarin, C-SH shows poor emission, but high fluorescence when the thiol is alkylated. The origin and character of the lowest singlet states are discussed, specifically proposing that the thione-like C[double bond, length as m-dash]S resonance form plays a key role in excited state deactivation in C-SH.

Is Single-Molecule Fluorescence Spectroscopy Ready To Join the Organic Chemistry Toolkit? A Test Case Involving Click Chemistry.

Single molecule spectroscopy (SMS) has matured to a point where it can be used as a convenient tool to guide organic synthesis and drug discovery, particularly applicable to catalytic systems where questions related to homogeneous vs heterogeneous pathways are important. SMS can look at intimate mechanistic details that can inspire major improvements of the catalyst performance, its recovery, and reuse. Here, we use the click reaction between alkynes and azides as an example where improvements at the bench have been inspired and validated using single-molecule fluorescence spectroscopy.

From the molecule to the mole: improving heterogeneous copper catalyzed click chemistry using single molecule spectroscopy.

Single molecule spectroscopy (SMS) inspired the optimization of a heterogeneous 'click' catalyst leading to enhanced yields of the Cu-catalyzed reaction of azides with terminal alkynes. Changes in SMS data after optimization confirm the improvements in catalyst performance.

Improving the Sunscreen Properties of TiO through an Understanding of Its Catalytic Properties.

The use of particulate titanium dioxide (TiO) as an active sunscreen ingredient has raised concerns about potential risks from TiO-mediated free radical formation. To date, remediation attempts have concentrated on reducing the yield of free radical generation by TiO upon sunlight exposure. The problem with this approach is that given the band gap in TiO, production of radical and the ensuing reactive oxygen species (ROS) is completely normal.

Heterogeneous Photocatalytic Click Chemistry.

Copper-doped semiconductors are designed to photoassist the alkyne-azide cycloaddition catalysis by Cu(I). Upon irradiation, injection of electrons from the semiconductor into copper oxide nanostructures produces the catalytic Cu(I) species. The new catalysts are air- and moisture-tolerant and can be readily recovered after use and reused several times.