Fluorescence quenching Stem-Volmer equation

In order to clear up the mechanism of inactivation of excited states, we examined the processes of quenching of fluorescence and phosphorescence in PCSs by the additives of the donor and acceptor type253,2S5,2S6 Within the concentration range of 1 x 1CT4 — 1 x 10"3 mol/1, a linear relationship between the efficiency of fluorescence quenching [(/0//) — 1] and the quencher concentration was found. For the determination of quenching constants, the Stem-Volmer equation was used, viz. 

Fluorescence quenching may be dynamic, if the photochemical process is the result of a collision between the photoexcited indicator dye and the quencher species, or static, when the luminophore and the quencher are preassociated before photoexcitation of the former20. It may be easily demonstrated that dynamic quenching in isotropic 3-D medium obeys the so-called Stem-Volmer equation (2)21 ... 

In another approach, a fluorescent conjugated polymer was used as the material for the preparation of a chemosensor to detect 2,4,6-trinitrotoluene (TNT) and its related nitroaromatic compounds. To this end, microparticles, made of three-dimensionally cross-linked poly(l,4-phenylene vinylene) (PPV) via emulsion polymerization, were synthesized [61]. This material was chosen due to its high fluorescence intensity and sensitivity to changes in its microenvironment. The chemosensor was exposed to vapour containing different amounts of TNT and quenching of the polymer luminescence at 560 nm was observed after excitation at 430 nm. The dependence of the fluorescence signal in response to the analyte was described by a modified Stem-Volmer equation that assumes the existence of two different cavity types. The authors proposed the modified Stem-Volmer equation as follows ... 

Careful examination reveals that the modified Stem-Volmer equation is mathematically identical to the original nonlinear model developed by Ryan and Weber (22). Fluorescence quenching curves for Cu -FA and application of the modified Stem-Volmer data treatment to the experimental information are shown in figure 2. Since the nonlinear data treatment and the modified Stem-Volmer equations are algebraically identical, their ability to fit experimental data and provide meaningful parameters is the same. 

The Combined Stern-Volmer and Perrin Model A model has been proposed by Morishima et al. [97] which takes account of Manning s theory [98] of polyelectrolytes and introduces a modification into the Stem-Volmer equation to describe sphere-of-action (Perrin) quenching this has been termed combined Stern-Volmer and Perrin Analysis and has been adopted [95,96] in an effort to describe quenching of fluorescence from labeled PMAA by T1+ ions, for example. 

The Stem-Volmer equation was used to quantify the differences in quenching efficiency for various analytes in solution phase studies [46]. In this equation, is the initial fluorescence intensity without analyte, / is the fluorescence intensity with added analyte of concentration [A], and Ksw is the Stem-Volmer constant. 

The accessibility of quenchers to probes in supramolecular structures can be inferred from bimolecular quenching rate constants. The necessary assumptions have been discussed in Section II.B. Quenching can be studied by the decrease of the fluorescence intensity with the addition of a quencher and the data are treated by employing the Stem-Volmer equation ... 

One common approach to fluorescence sensing is to rely on fluorophores which are collisionally quenched by the analyte. There are many known collisional quenchers (andytes) which alter the fluorescence intensity and decay time. These include O2 (27-31), chloride (32-33), chlorinated hydrocarbons (34), iodide (35), bromate (36), xenon (37), acrylamide (38), succinimide (39), sulfur dioxide (40), and halothane (41), to name a few. The quenching process obeys the Stem-Volmer equation ... 

Once again melittin illustrates the effect of protein structure on the fluorescence emission. Acrylamide quenching data for melittin monomer and tetramer are shown in Fig. 8. Stem-Volmer plots are often used to present quenching data. The Stem-Volmer equation is... 

Equation 12.21 is known as the Stem-Volmer equation. Plotting the ratio of lifetimes (ts/t ), or the ratio of fluorescence quantum yields (O /O s), or the ratio of fluorescence intensities (If// ) versus [Q] should yield a straight line with slope fcqTg. If Ts is known, then fcq can be determined. Figure 12.17 shows a Stern-Volmer plot for the quenching of 1,4-dimethoxybenzene fluorescence by allyl chloride in acetonitrile solution. The slope is 4.43 and the lifetime of 1,4-dimethoxybenzene in the absence of quencher is 2.23 ns. Thus, the rate constant for quenching of 1,4-dimethoxybenzene singlets with allyl chloride is 2 X 10 M s . ... 

Still another example is an initiating system composed of 7-diethylamino-3 -(2 -N-methyl-benzimidazolyl)-coumarin and diphenyliodonium hexafluorophosphate. This composition initiates the polymerization of methyl methacrylate in visible light. After the dye absorbs flic light energy, quick electron transfer takes place from the dye to the iodonium salt to produce free radicals. " The light induced reaction is claimed to occur mainly through the excited singlet state of the coumarin and results in low sensitive to O2. The fluorescence of the coumarin compound was reported to be quenched efficiently by the iodonium salt. " The reaction was observed to be in accord with the Stem-Volmer equation. The influence of the concentration of coumarin on the polymerization rate of methyl methacrylate led to the conclusion that the free radicals from coumarin act mainly as chain terminators. ... 

Fluorescence quenching is due to non-radiative loss of energy from the excited state as a consequence of either collision with a quencher ion (or molecule) in solution or by formation of a non-fluorescent or poorly fluorescent fluorophore-quencher complex. In both cases the quenching process follows the Stem-Volmer equation ... 

Quenching, by any of the mechanisms outlined above, will also compete with the various intramolecular photophysical relaxation routes that deactivate the excited-state. The presence of quenching, therefore, will lead to a reduction in the luminescence intensity (fluorescence or phosphorescence), which is related to the quencher concentration [Q] by the Stem-Volmer equation [67] ... 

The relation (6.19) between fluorescence intensity and quencher concentration is known as the Stem-Volmer equation [4]. It will be expected to apply when the system consists of one fluorophore and one quencher, which do not form a complex in the ground state, and only when quenching is an irreversible process. For such systems, it leads us to expect that 1//[qj will be related linearly to [Q]. If this is observed, the constant k in Equation (6.21) (often called the Stern-Volmer constant ) can be interpreted (in terms of Equation (6.22)) as ksro, and yields the value of k if the lifetime to of the fluorophore in the same solvent in the absence of quenchers has once been independently determined. Absolute values of the intensity are not required, so an ordinary fluorimeter suffices. (Until fluorescence — lifetime apparatus became available in the 1960 s, this was the common method of determining rate constants from fluorescence measurements.)... 

In other words, the Stem-Volmer equation holds also for the I(JI ratio which can be easily obtained from steady-state fluorescence measurements. However, the acquisition of IJI instead of xj-t does not allow for distinguishing dynamic quenching occurring in the excited state of the fluorophore from the so-called static quenching. The latter mechanism consists in the formation of a nonfluorescent complex of the quencher Q with the fluorophore F in the ground state ... 

As an introduction to any experiment which involves the quantitative use of a quenching phenomenon, data for a Stern-Volmer plot should be obtained. These involve the measurements of fluorescence over a range of quencher concentration (cq) and plotting FtJF against Cq. The Stem-Volmer equation is... 

DOM fluorescence quenching is traditionally observed using a Stem-Volmer plot, in which the fractional change in loss of fluorescence (ratio of initial fluorescence, Fq to fluorescence after addition of the quencher, F) is plotted against the concentration of the quencher, Q (Figure 7.1). The slope of the line describing the linear fit is the quenching constant (A"sv) from the Stem-Volmer equation ... 

The Stem-Volmer(52) equation relates fluorescence intensity and the quenching rate constant, kq ... 

In this equation, F0 and F are the fluorescence intensities in the absence and presence of the quencher, t0 and x are the lifetimes of the fluorophore in the absence and presence of the quencher, kq is the biomolecular quenching constant, and [Q] is the concentration of the quencher (in this case, molecular oxygen). The Stem-Volmer quenching constant is Kn, and is calculated as the product of kq and r0. The Smoluchowski equation describes the biomolecular quenching constant, kq, and is given by... 

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