Quencher

An alternative approach envisages the stimulating idea to produce an all-carbon fullerene polymer in which adjacent fullerenes are linked by covalent bonds and align in well characterized one-, two- and tliree-dimensional arrays. Polymerization of [60]fullerene, with the selective fonnation of covalent bonds, occurs upon treatment under pressure and relatively high temperatures, or upon photopolymerization in the absence of a triplet quencher,... 

Nonradiative reiaxation and quenching processes wiii aiso affect the quantum yieid of fluorescence, ( )p = /cj /(/cj + Rsiative measurements of fluorescence quantum yieid at different quencher concentrations are easiiy made in steady state measurements absoiute measurements (to detemrine /cpjj ) are most easiiy obtained by comparisons of steady state fluorescence intensity with a fluorescence standard. The usefuiness of this situation for transient studies... 

Chou J Z and Fiynn G W 1990 Energy dependence of the reiaxation of highiy excited NO2 donors under singie coiiision conditions vibrationai and rotationai state dependence and transiationai recoii of CO2 quencher moiecuies J. Chem. Rhys. 93 6099-101... 

Uv methods Uv-quenchers Uv radiation uv Radiation Uv Radiation Uv stability Uv stabilizers... 

The carbon black (soot) produced in the partial combustion and electrical discharge processes is of rather small particle si2e and contains substantial amounts of higher (mostly aromatic) hydrocarbons which may render it hydrophobic, sticky, and difficult to remove by filtration. Electrostatic units, combined with water scmbbers, moving coke beds, and bag filters, are used for the removal of soot. The recovery is illustrated by the BASF separation and purification system (23). The bulk of the carbon in the reactor effluent is removed by a water scmbber (quencher). Residual carbon clean-up is by electrostatic filtering in the case of methane feedstock, and by coke particles if the feed is naphtha. Carbon in the quench water is concentrated by flotation, then burned. 

Meta.1 Complexes. The importance of Ni complexes is based on their effectiveness as quenchers for singlet oxygen. Of disadvantage is their low colorfastness and their lower ir-reflectance compared to cyanine dyes (qv) therefore they are used in combination with suitable dyes. Numerous complexes are described in the Hterature, primarily tetrathiolate complexes of Pt or Ni, eg, dithiolatonickel complexes (3). Well known is the practical use of a combination of ben2othia2ole dyes with nickel thiol complexes in WORM disks (Ricoh, TDK) (17). 

Plastics Additives. Many claims have been made for the use of nickel chemicals as additives to various resin systems. By far the most important appHcation is as uv-quenchers in polyolefins (173,174). Among the useful nickel complexes in these systems are dibutyldithiocarbamate nickel [13927-77-0], nickel thiobisphenolates, and nickel amide complexes of bisphenol sulfides (175). The nickel complex of... 

Health and Safety. FEMA has examined cinnamaldehyde and estabhshed its GRAS status (No. 2286). The material has been used in some fragrance compositions, but RJEM (34) has noted its potential for sensiti2ation and limited the use in perfumes for skin contact at 1% in the formula. Eugenol and limonene have been used in conjunction with cinnamaldehyde as quenchers to neutrali2e the irritation reaction that some individuals have toward this aldehyde. 

The quencher arm shoiild be anchored to prevent pipe whip. It should also extend to the length (for horizontal vessels) or the height (for vertical vessels) of the vessel to evenly distribute the vapors in the pool. 

Perform chemical reactivity testing, including the analytical verification of reactants, catalyst, quenchers, initiators, and inhibitors. More details are provided in Appendix 2A of this chapter. 

Excited states can also be quenched. Quenching is the same physical process as sensitization, but the word quenched is used when a photoexcited state of the reactant is deactivated by transferring its energy to another molecule in solution. This substance is called a quencher. 

Another useful technique for measuring the rates of certain reactions involves measuring the quantum yield as a function of quencher concentration. A plot of the inverse of the quantum yield versus quencher concentration is then made Stern-Volmer plot). Because the quantum yield indicates the fraction of excited molecules that go on to product, it is a function of the rates of the processes that result in other fates for the excited molecule. These processes are described by the rate constants (quenching) and k (other nonproductive decay to ground state). 

A plot of 1 versus quencher concentrations, [Q], then gives a line with the slope k /k. It is usually possible to assume that quenching is diffusion-controlled, permitting assignment of a value to k. The rate of photoreaction, k, for the excited intermediate can then be calculated. 

TTie photoreduction can be quenched by known triplet quenchers. The effecti e quenchers are those which have T] states less than 69kcal/moI above S,. Quenchers with higher triplet energies are ineffective because the benzophenone n-n triplet is then not sufficiently energetic to effect energy transfer. 

The bicyclic product is formed by coupling of the two radical sites, while the alkene results from an intramolecular hydrogen-atom transfer. These reactions can be sensitized by aromatic ketones and quenched by typical triplet quenchers and are therefore believed to proceed via triplet excited states. 

For absorption applications, precoolers (e.g., spray chambers, quenchers) may be needed to saturate the gas stream or to reduce the inlet air temperature to acceptable levels to avoid solvent evaporation or reduced absorption rates. 

Emetine andcephaeline, the two major alkaloids of ipecacuanha, begin to fluoresce after treatment with iodine vapor [254], The molecular iodine, which acts as a quencher, must be removed by heating in the drying cupboard or on a hotplate... 

It is possible that Q is an excited state of Q if so, we will assume that its emission spectrum does not contribute to the fluorescence intensity at Vcnr Q is called a quencher, because in its presence the fluorescence intensity of solute A is reduced. 

The quantum yield [Pg.181]

Loscher, m, extinguisher quencher slaker blotter unloader. 

The energy transfer may result in a reactive or nonreac-tive quencher molecule ... 

Thus, chelates are able to dissipate the radiation harmlessly as infrared radiations or heat through resonating structures. Carlsson and Wiles [22] have confirmed in their studies that the quencher slowly migrate through the solid polymer destroying the hydroperoxide group. 

Factors such as dissociation, association, or solvation, which result in deviation from the Beer-Lambert law, can be expected to have a similar effect in fluorescence. Any material that causes the intensity of fluorescence to be less than the expected value given by equation (2) is known as a quencher, and the effect is termed quenching it is normally caused by the presence of foreign ions or molecules. Fluorescence is affected by the pH of the solution, by the nature of the solvent, the concentration of the reagent which is added in the determination of inorganic ions, and, in some cases, by temperature. The time taken to reach the maximum intensity of fluorescence varies considerably with the reaction. 

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