Quenching reaction bimolecular

The attachment of pyrene or another fluorescent marker to a phospholipid or its addition to an insoluble monolayer facilitates their study via fluorescence spectroscopy [163]. Pyrene is often chosen due to its high quantum yield and spectroscopic sensitivity to the polarity of the local environment. In addition, one of several amphiphilic quenching molecules allows measurement of the pyrene lateral diffusion in the mono-layer via the change in the fluorescence decay due to the bimolecular quenching reaction [164,165]. 

The quenching of benzophenone phosphorescence has been used by Mar and Winnik (1981) as a photochemical probe of hydrocarbon chains in solution. The bimolecular reaction for quenching the triplet state of 4-methoxy-carbonylbenzophenone [24] by 1-pentene occurs at rates which are below the diffusion limit by two to three orders of magnitude. Consequently, the intramolecular quenching reactions of to-alkenyl esters of benzophenone-4-carbo-xylic acid [25] occurs under conformational control. In [25] the point of... 

Such bimolecular quenching reactions occur at diffusion controlled rates. A probability P for reaction per encounter may be included. The rate constant terms in (5.61) become... 

Figure 8 Illustration of the flash-quench technique for measuring intramolecular ET rates. Photoexcitation of Ru(II)(bpy)2(imidazole)(amine)2+, Ru(II)(bpy), bound to ferro-cytochrome c, Fe(II)P, produced an 80-ns lived metal-to-ligand charge transfer (MLCT) excited state, Ru(III)(bpy -), which was oxidatively quenched by bimolecular reaction with Ru(NH3) +. The resulting Ru(III)-complex was then reduced by the Fe(II)P through thermal, protein-mediated ET. Finally bimolecular reaction of the Ru(II)/Fe(III)P product with Ru(NH3) + re-formed the starting Ru(II)-protein-Fe(II)P complex.

It is tempting to use static Ru(II) -emission quenching in bimolecular studies involving donors and acceptors intercalated into DNA to learn about the distance dependence of the ET quenching reaction. However, these studies are always open to two interpretations. One interpretation is that the donors and... 

The photochemical reactions " of Cr(III) include both ligand substitutions and isomerization in solution and solids. Intramolecular redox reactions also are noted when charge-transfer bands are excited as well as intermolecular ones in cases where a long-lived state is quenched by bimolecular electron transfer to another species in solution. ... 

Quenching of the ( CT)[Ru(bipy)3] by [Cr(bipy)]3 has been studied. This is via electron transfer to the Cr complex and a rapid back reaction. The ruthenium complex will also quench the 727 nm emission of the metal-centred doublet excited state of the chromium species, by a similar mechanism. Evidently both ligand- and metal-centred excited states can be quenched by bimolecular redox processes. A number of Ru complexes, e.g. [Ru(bipy)3] and [Ru(phen)3] also have their luminescence quenched by electron transfer to Fe or paraquat. Both the initial quenching reactions and back reactions are close to the diffusion-controlled limit. These mechanisms involve initial oxidation of Ru to Ru [equation (1)]. However, the triplet excited state is more active than the ground state towards reductants as well as... 

In fact, quenching effects can be evaluated and linearized through classic Stem-Volmer plots. Rate constants responsible for dechlorination, decay of triplets, and quenching can be estimated according to a proposed mechanism. A Stern-Volmer analysis of photochemical kinetics postulates that a reaction mechanism involves a competition between unimolecular decay of pollutant in the excited state, D, and a bimolecular quenching reaction involving D and the quencher, Q (Turro N.J.. 1978). The kinetics are modeled with the steady-state approximation, where the excited intermediate is assumed to exist at a steady-state concentration ... 

Bimolecular quenching reactions of excited states are typically represented by the pseudo-first-order reaction kinetics, equation 6a. When a distribution of probe environments exists, the difference between the macroscopic fluorescence decay profile observed and microscopic fluores-... 

Bimolecular quenching reactions of excited states are typically represented by the pseudo-first-order reaction kinetics, Equation (30.6a). When a distribution of probe environments exists, the difference between the macroscopic fluorescence decay profile observed and microscopic fluorescence decay rates present must be recognized. The composite distribution of both unimolecular decay rates and the respective bimolecular reaction rates are combined in the distribution of observable decay rates. Hence, the parameters in Equation (30.6a) have to be redefined in the Gaussian distribution terminology to yield Equation (30.6b). 

Table 8 Bimolecular Quenching Rate Constants for the Oxidadve Quenching Reactions of 25b, 30, and 31 with Pyridinium Acceptors...

The quenching reaction can occur by a number of different pathways. Three commonly observed bimolecular quenching pathways are energy transfer, oxidative quenching, and reductive quenching. Energy transfer can occur when the triplet... 

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