Equation Stern-Volmer

Figure5.9 Spectral changes upon addition ofCH3OH to aCH2Cl2 solution of [(8-QNS)2Au(AuPPh3)2]BF4 (7.72 x 10 M) with excitation at 320 nm. Inset Changes in lifetime according to Stern-Volmer equation. Reproduced with permission from [35]. Copyright (2003) American Chemical Society.

This method is applicable when the fluorescence of a ligand is quenched in presence of DNA or RNA and provides base-dependent specificity [135]. In fluorescence quenching experiments the titration data is plotted according to the Stern-Volmer equation ... 

It should be noted that this expression is a general one that can be used for any photochemical reaction that can be quenched. It is commonly called the Stern-Volmer equation. This equation predicts that if the proposed mechanism is correct, the data, when plotted as 4>a0/4>a vs. [Q], should be linear with an intercept equal to unity and a slope equal to kqr. Linear plots were indeed observed out to large d>°/d> values. Assuming a value of 5 x 10 M 1 sec-1 for the quenching rate constant,(7) the data presented in Table 4.1 were obtained. 

If Fq is the yield in the absence of quenchers, F the yield in the presence of quenchers ( concentration Q ), and XQ is the fluorescence lifetime when [Q] = 0, the relative yield as a function of [Q] is given by the Stern-Volmer equation ... 

In dynamic quenching (or diffusional quenching) the quenching species and the potentially fluorescent molecule react during the lifetime of the excited state of the latter. The efficiency of dynamic quenching depends upon the viscosity of the solution, the lifetime of the excited state (x ) of the luminescent species, and the concentration of the quencher [Q], This is summarized in the Stern-Volmer equation ... 

Quencher Q lowers the intensity of phosphorescence. The dependence of the light intensity of phosphorescence /ph on the quencher concentration obeys the Stern-Volmer equation... 

In low viscosity media, the quenching of Phe fluorescence by MEK is dynamic in nature and follows the Stern-Volmer equation (25) ... 

Compare the effectiveness of different quenchers by means of the Stern-Volmer equation. 

In Chapter 6 the Stern-Volmer equation was introduced in relation to fluorescence quenching. The corresponding equation relating to triplet-state quenching is ... 

The Stern-Volmer equation has a linear form and the quantity kQ3x is obtained as the slope of the plot of < >/Q< > against [Q] for different quencher concentrations. 

In contrast to the Stern-Volmer equation (4.10), the ratio Io/I is not linear and shows an upward curvature at high quencher concentrations. At low concentrations, exp(VqNa[Q]) 1 + VqNa[Q], so that the concentration dependence is almost linear (as in the case of the Stern-Volmer plot). 

We focus on luminescence quenching based sensors, but many of the principles are generic. Quenching-based oxygen detectors are probably the most mature. In homogeneous media with only a single component exponential decay the intensity and lifetime forms of the Stern-Volmer equations are ... 

An important class of luminescence sensors are those based on the decrease of luminescence intensity and lifetime of the probes as function of analyte concentration. Assume that the probe intensity decays by a single exponential with an unquenched lifetime tq. If quenching occurs only by a dynamic (collisional) mechanism, then the ratio to/t is equal to Fq/F and is described by the classic Stern-Volmer equation... 

By plotting 1/AOD as a function of [Q], the ratio of fcq/ y[Y ] can be derived. This ratio corresoponds to the k x term of the Stern-Volmer equation. Here r is the lifetime of the carbene in the absence of quenchers. 

KINETICS OF COLLISIONAL QUENCHING STERN-VOLMER EQUATION... 

This expression is known as the Stern-Volmer equation and Ksv as Stern-Volmer constant. Ksv is the ratio of bimolecular quenching constant to unimolecular decay constant and has the dimension of litre/mole. It implies a competition between the two decay pathways and has the ch".acter of an equilibrium constant. The Stern-Volmer expression is linear in quencher concentration and Ksv is obtained as the slope of the plot of 4>f°If vs [Q], if the assumed mechanism of quenching is operative. Here, t is the actual lifetime of the fluorescer molecule in absence of bimolecular quenching and is expressed as... 

The final expression is in the form of the Stern-Volmer equation, where tj, is the monomer lifetime in dilute solution and te is assumed to be excimer lifetime in infinitely dilute solution. 

The quenching of fluorescence by added substance Q at concentrated [Q] is expressed by the Stern-Volmer equation,... 

A representative plot is shown in Figure 1.15 this is known as a Stern-Volmer plot, and 0.16) as a Stern-Volmer equation. This method for obtaining reaction rate constants is again a comparative one, since there is competition between the primary reaction step and the quenching process. A value for the quenching rate constant needs to be known, but in many cases this is independent of the substrate and quencher because triplet quenching is controlled by diffusional collision of the two species. So for a particular solvent at a given temperature K, values are available in the literature as an... 

The Stern-Volmer equation says that, if we measure relative emission (0/q) as a function of quencher concentration and plot this quantity versus [Q], we should observe a straight line. The quantity <3>0/Oq in Equation 19-25 is equivalent to /,/Iq, where /0 is the emission intensity in the absence of quencher and Iq is the intensity in the presence of quencher. 

The molecules M and Q can come into contact (within the sphere of action) through their random diffusional motion. The rate constant kD of diffusion controlled encounters is the upper limit for any bimolecular reaction. This must be multiplied by the probability of an encounter leading to reaction (quenching in the present case), and the luminescence quantum yield then follows the Stern-Volmer equation... 

Depending on the number of these cycles the final oxygen concentration is determined by the residual pressure of the pump. Quantitative analysis of traces of oxygen in liquids can be done by the measurements of long-lived luminescence lifetimes (e.g. pyrene fluorescence) and applying the Stern-Volmer equation. 

Plot the resulting fluorescence intensities as a function of concentration of quencher according to the Stern-Volmer equation (see Fig. B3.6.6A) ... 

Thus, the equivalent of the conventional Stern-Volmer equation becomes ... 

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