A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single-electron-transfer (SET) processes with organic substrates upon photoexcitation with visible light.

Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) ruthenium(II), or Ru(bpy)32+ (Figure 1). These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long-lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+) that it may engage in bimolecular electron-transfer reactions in competition with deactivation pathways.3 Although these species are poor single-electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single-electron-transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox-active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes.






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Figure 1


Ruthenium polypyridyl complexes: versatile visible light photocatalysts.

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Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis

Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.

Nanoparticles as Recyclable Catalysts: The Frontier between Homogeneous and Heterogeneous Catalysis

An analyte monitor includes a sensor, a sensor control unit, and a display unit. The sensor has, for example, a substrate, a recessed channel formed in the substrate, and conductive material disposed in the recessed channel to form a working electrode. The sensor control unit typically has a housing adapted for placement on skin and is adapted to receive a portion of an electrochemical sensor. The sensor control unit also includes two or more conductive contacts disposed on the housing and configured for coupling to two or more contact pads on the sensor. A transmitter is disposed in the housing and coupled to the plurality of conductive contacts for transmitting data obtained using the sensor. The display unit has a receiver for receiving data transmitted by the transmitter of the sensor control unit and a display coupled to the receiver for displaying an indication of a level of an analyte. The analyte monitor may also be part of a drug delivery system to alter the level of the analyte based on the data obtained using the sensor.

Analyte Monitoring Device And Methods Of Use

The mean size of the gold (Au) core in the synthesis of dodecanethiolate-stabilized Au cluster compounds can be finely adjusted by choice of the Au:dodecanethiolate ratio and the temperature and rate at which the reduction is conducted. The Au clusters have been examined with a large number of independent analytical tools, producing a remarkably consistent picture of these materials. Average cluster and core dimensions, as ascertained by 1H NMR line broadening, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermogravimetric analysis, vary between diameters of 1.5 and 5.2 nm (∼110−4800 Au atoms/core). The electronic properties of the Au core were examined by UV/vis and X-ray photoelectron spectroscopy; the core appears to remain largely metallic in nature even at the smallest core sizes examined. The alkanethiolate monolayer stabilizing the Au core ranges with core size from ∼53 to nearly 520 ligands/core, and was probed by Fourier transform infrared spectroscopy, diff...

/pdf/alkanethiolate-gold-cluster-molecules-with-core-diameters-9nepdtvvpw.pdf

Alkanethiolate Gold Cluster Molecules with Core Diameters from 1.5 to 5.2 nm: Core and Monolayer Properties as a Function of Core Size

The interaction between an electronically excited photocatalyst and an organic molecule can result in the genertion of a diverse array of reactive intermediates that can be manipulated in a variety of ways to result in synthetically useful bond constructions. This Review summarizes dual-catalyst strategies that have been applied to synthetic photochemistry. Mechanistically distinct modes of photocatalysis are discussed, including photoinduced electron transfer, hydrogen atom transfer, and energy transfer. We focus upon the cooperative interactions of photocatalysts with redox mediators, Lewis and Bronsted acids, organocatalysts, enzymes, and transition metal complexes.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.6b00018

Dual Catalysis Strategies in Photochemical Synthesis

Electrical communication between redox centers of glucose oxidase and electrodes via electrostatically and covalently bound redox polymers

Laser flash photolysis and steady-state photolysis studies show that electrostatic interactions have a dramatic influence on the kinetics for charge separation and hydrogen production in aqueous systems (pH 9.8) of 20-nm diameter TiO/sub 2/-modified SiO/sub 2/ colloids in various combinations with an electron relay, a photosensitizer, and a Pt catalyst. Either direct excitation of the semiconductor or the photosensitizer Ru(bpy)/sub 3//sup 2 +/ (bpy = 2,2'-bipyridine), electrostatically adsorbed to the colloid, initiate electron transfer to either the zwitterionic electron relay, N,N'-bis(3-sulfonatopropyl)-4,4'-bipyridinium (PVS/sup 0/), or N,N'-bis(3-sulfonatopropyl)-2,2'-bipyridinium (DQS/sup 0/), or methyl viologen (MV/sup 2 +/). The rates and quantum yields for the formation of the radical PVS/sup -/ anion in both the TiO/sub 2/-SiO/sub 2//PVS/sup 0/ and the TiO/sub 2/-SiO/sub 2//Ru(bpy)/sub 3//sup 2 +//PVS/sup 0/ systems decline with increasing ionic strength. The rate and quantum yields for H/sub 2/ production in both the TiO/sub 2/-SiO/sub 2//DQS/sup 0//Pt and the TiO/sub 2/-SiO/sub 2//Ru(bpy)/sub 3//sup 2 +//DQS/sup 0//Pt systems also show a similar ionic strength dependence.

Improved charge separation and photosensitized hydrogen evolution from water with titanium dioxide particles on colloidal silica carriers

Photosensitized electron-transfer reactions in .beta.-cyclodextrin aqueous media: effects on dissociation of ground-state complexes, charge separation, and hydrogen evolution

Photosensitized hydrogen evolution from a basic aqueous silicon dioxide (SiO/sub 2/) colloid (pH 9 to 10) is accomplished with N,N'-bis-(3-sulfonatopropyl)-2,2'-bipyridinium (DQS/sup 0/) and colloidal platinum as mediating catalysts. In this system Ru(bpy)/sub 3//sup 2 +/ (ruthenium (bipyridium)/sub 3//sup 2 +/) acts as a photosensitizer and triethanolamine (TEOA) as ultimate electron donor. No hydrogen formation is observed in a homogeneous aqueous solution under similar conditions. The SiO/sub 2/ colloid affects the formation and stabilization of the intermediate photoproducts, Ru(bpy)/sub 3//sup 3 +/ and DQS/sup -/., by means of electrostatic interactions. The electric potential of the particles assists the separation of the products from the initial encounter cage complex and results in the repulsion of the reduced product, DQS/sup -/., from the colloidal interface. Consequently, the recombination rate of DQS/sup -/. with the oxidized product Ru(bpy)/sub 3//sup 3 +/ is retarded. The electrostatic functions of the colloid are confirmed by alteration of the ionic strength and pH of the colloid solution. The structure of DQS/sup 0/ was determined by X-ray crystallography. The compound crystallizes in space group P2/sub 1//n with unit cell dimensions of a = 10.392 (1) A, b = 22.390 (3) A, c = 8.235 (1) A, ..beta.. = 95.07 more » (2)/sup 0/, V = 1909 (1) A/sup 3/, and Z = 4. 4 figures, 4 tables. « less

Photoinduced hydrogen evolution by a zwitterionic diquat electron acceptor. The functions of silicon dioxide colloid in controlling the electron-transfer process

Yinon Degani

Papers

Electrical communication between redox centers of glucose oxidase and electrodes via electrostatically and covalently bound redox polymers

Improved charge separation and photosensitized hydrogen evolution from water with titanium dioxide particles on colloidal silica carriers

Photosensitized electron-transfer reactions in .beta.-cyclodextrin aqueous media: effects on dissociation of ground-state complexes, charge separation, and hydrogen evolution

Photoinduced hydrogen evolution by a zwitterionic diquat electron acceptor. The functions of silicon dioxide colloid in controlling the electron-transfer process

Lasing of rhodamine B in aqueous solutions containing β-cyclodextrin