Quenching rate constants, pyrene

Table 5 Overall Quenching Rate Constants for Pyrene Emission in Sodium Taurocholate (NaTC) obtained in Time-Resolved Experiments... 

Table II. Quenching Rate Constants of Pyrene Fluorescence in Various Systems PA-I8K2...

The bimolecular quenching rate constants, of pyrene fluorescence in various systems are presented in Table II. The values of with the quenchers such as oxygen, nitromethane, and sodium iodide in PA-I8K2 polymer-micellar solutions are much smaller than in water or in homogeneous nonpolar solvents (viz. heptane) and even smaller than in SDS micellar solutions. The data suggest that the penetration of the selected quenchers to the pyrene hosted in the polymer micelle is inhibited by the main chain of the host polymer micelle. This restrictive effect is larger than in simple micellar systems, and it results from the more rigid environment of pyrene in polymer micellar systems. 

Figure 30.11 shows that the observed decay rate constants of both DPA and pyrene vary linearly with surface oxygen concentration when surface oxygen concentration is used as the independent variable. The bimolecular quenching rate constants obtained from the slopes of these plots decrease with a decrease in temperature, as... 

Quenching rate constants from dynamic fluorescence quenching measurements with -tert-butylaniline as quencher and pyrene as fluorescence probe. 

The access of small molecules (eg, and T) to pyrene encapsulated in a host-cavity, without release of the entrapped pyrene, allows quenching-rate constant measurement for singlet-excited-state pyrene inside the capsule (in the previous example, such access occurred via fast opening/closing of capsular complexes). 

A correlation between the rate constants k and free enthalpy change AG of electron transfer was studied by Hashimoto and Thomas [127] for quenching of excited singlet states of both pyrene and N-ethylcarbazol and of the triplet state of N-methylphenothiazine by a number of metal ions and for back electron transfer reactions in micellar sodium taurocholate and sodium dodecylsulfate solutions. Quenching rate constants were determined from Stern-Volmer plots obtained for lifetimes of excited states at high concentration of micelles, where the exponential decay... 

Equations (4-5) and (4-7) are alternative expressions for the estimation of the diffusion-limited rate constant, but these equations are not equivalent, because Eq. (4-7) includes the assumption that the Stokes-Einstein equation is applicable. Olea and Thomas" measured the kinetics of quenching of pyrene fluorescence in several solvents and also measured diffusion coefficients. The diffusion coefficients did not vary as t) [as predicted by Eq. (4-6)], but roughly as Tf. Thus Eq. (4-7) is not valid, in this system, whereas Eq. (4-5), used with the experimentally measured diffusion coefficients, gave reasonable agreement with measured rate constants. 

Elegant evidence that free electrons can be transferred from an organic donor to a diazonium ion was found by Becker et al. (1975, 1977a see also Becker, 1978). These authors observed that diazonium salts quench the fluorescence of pyrene (and other arenes) at a rate k = 2.5 x 1010 m-1 s-1. The pyrene radical cation and the aryldiazenyl radical would appear to be the likely products of electron transfer. However, pyrene is a weak nucleophile the concentration of its covalent product with the diazonium ion is estimated to lie below 0.019o at equilibrium. If electron transfer were to proceed via this proposed intermediate present in such a low concentration, then the measured rate constant could not be so large. Nevertheless, dynamic fluorescence quenching in the excited state of the electron donor-acceptor complex preferred at equilibrium would fit the facts. Evidence supporting a diffusion-controlled electron transfer (k = 1.8 x 1010 to 2.5 X 1010 s-1) was provided by pulse radiolysis. 

Figure 6.10. Rate constants for quenching of sensitizers by cis- and trans-stilbenes (open and filled circles, respectively). Sensitizers are as follows (1) tri-phenylene, (2) thioxanthone, (3) phenanthrene, (4) 2-acetonaphthone, (3) 1-naphthyl phenyl ketone, (6) crysene, (7) fluorenone, (8) 1,2,5,6-dibenzanthracene, (9) benzil, (10) 1,2,3,4-dibenzanthracene, (11) pyrene, (12) 1,2-benzanthracene, (13) benzanthrone, (14) 3-acetyl pyrene, (15) acridine, (16) 9,10-dimethyl-l,2-benzanthracene, (17) anthracene, (18) 3,4-benzpyrene.<57> Reprinted by permission of the American Chemical Society.

The quenching of pyrene monomer emission by 2-bromonaphtha-lene on dry silica gel has also been studied as a function of temperature. Linear Stern-Volmer plots are obtained either with t /t or with tJ/T], and t%/t2 vs tQ] where [Q] Is a surface concentration. Fig. 12 illustrates the f/f0 plot. The rate constants derived from... 

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