Stem-Volmer relation

To study the dynamic quenching in steady state approach, the Stem-Volmer relations are commonly used ... 

When a system contains a fluorophore in different environments (e.g. a fluo-rophore embedded in microheterogeneous materials such as sol-gel matrices, polymers, etc.) or more than one fluorophore (e.g. different tryptophanyl residues of a protein), the preceding relations must be modified. If dynamic quenching is predominant, the Stem-Volmer relation should be rewritten as... 

Electronically excited ionic states, for which the transitions to the ground state are allowed, normally have very short radiative lifetimes, typically on the order of 10 nsec to 1 jLisec, Yet even these states are quite efficiently collisionally deactivated, particularly on interaction with the corresponding parent gases. Several such systems have been studied in detail, and the Stem-Volmer relation has been employed to determine rate coefficients for collisional deactivation.233-239 Some of these reactions and the pertinent kinetic data are displayed in the reactions that follow. 

The atomic fluorescence may be observed under either steady-state or time-dependent conditions. Under steady-state conditions the decrease of fluorescence intensity I is observed when the quenching gas is admixed, and from (II.2a, b) the well-known Stem-Volmer relation is obtained... 

In the dynamic quenching mechanism (Scheme 23A), the Stem-Volmer relation is represented by Eq. (19), where t and To mean the lifetime in the presence and the absence of quencher, respectively, and [Co111] represents the concentration of the cobalt(III) complex. 

Equation 3.38 General Stem Volmer relation for a single step reaction... 

Decisive evidence on whether static quenching is appreciable in a particular system can come from fluorescence lifetime measurements. If the mechanism represented by Equation (6.24) is correct, fluorescence emission occurs only from free A molecules, so the lifetime is unaffected by static quenching and is given by Equation (6.16) above, which may be written in the form of a lifetime Stem-Volmer relation (i.e., to/t[q] = 1 -f- fesroiQ]). A plot of to/t[q] against quencher concentration [Q] will be linear (despite the non-linearity of the corresponding plot of /o//[Q]) with unit intercept and slope whence the value of... 

When the relation between then nonradiative decay processes and the concentration or value of the parameter of interest k A[Parameter]) is not linear (e.g., Eqs. (9.13 and 9.14), the intensity ratio of Eq. (9.31) introduces the well-observed problem of curvature in the Stem-Volmer plot (see Fig. 9.3). 

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

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 ... 

This is the well known Stem-Volmer relationship which relates the number of photons absorbed per unit volume per second (/,) to the number emitted per unit volume per second (/f). The quantity 7f//a is the emission efficiency and is often given the symbol Q. 

In the above sections, nothing was said about the type of reaction between M and Q. This is because the Stem-Volmer equation is model independent, as explained above and also because eqs. (20)-(22) are for a diffusion-controlled reaction. Some information can be obtained regarding an electron transfer from various quenchers of similar chemical structures towards M. In this case, one may derive a relationship between ksv (as obtained from eq. (17)) and the ionization potential of these inhibitors. This is the Rehm-Weller equation, which is schematically depicted in fig. 4. In this plot, the plateau value corresponds to fcdin. For a general overview of problems related to electron transfers, see Pouliquen and Wintgens (1988) (in French). 

From Eqs. (3.178) and (3.179) it is inferred that the Stem-Volmer constants for the reversible and effective irreversible reactions are related to each other as follows ... 

If the energy acceptors are in great excess (c Jf), then the condition (3.556) is not too rigid the interval of relatively weak fields where Bs c is rather wide. Within this interval the conventional Stem-Volmer law is valid and its constant is given by Eq. (3.555). This statement relates to the three upper curves shown in Figure 3.68, which are almost linear in c. However, at a much higher density of fluorophores the inequality (3.556) is inverted at small c and the concentration dependence of the quantum yield becomes curvilinear similar... 

Figure 3.85. The Stem—Volmer constant of reversible energy quenching at zB = oo, A -/ . related to its irreversible analog K as a function of backward energy transfer rate constant kb related to the forward one, ka. The thick line is an IET result, while the thin lines are obtained with MET at different concentrations of A 4na3NA/3 = 0.05,0.15,0.3 (from bottom to top). The remaining parameters are 47ia3Afi/3 = 0.15, = 2t(/, and kD

Upon ultraviolet irradiation in solution, N,N -nonamethylene-blsdlmethylmaleimide polymerizes into high molecular weight macromolecules with cyclobutane rings in the main chain. The reaction could be sensitized by acetophenone and was quenched by oxygen, ferrocene, and 3,3,4,4-tetramethyl-l,2-diazetine-l,2-dioxide. Stem-Volmer plots were linear for all chromophore concentrations and were dependent on the chromophore concentration. Linear quenching relations can be obtained in the following cases (Scheme IV). 

Intensity changes in the natural fluorescence of fulvic acid (FA) caused by the binding of metal ions have been well documented. Various quantitative models have been developed relating the measured fluorescence signal to the amount of metal ion bound to fulvic acid. Stem-Volmer, linear, and nonlinear models developed for 1 1 binding between metal ions and fulvic acid ligand sites have been used to calculate concentrations of FA binding sites (CJ, and conditional stability constants (K). However, the ability of these models to describe metal complexation by the polydispersed fulvic acid system is somewhat limited. 

After determining the simplified equation 9, Ventry (23) postulates that Ires Iq where d is related to the residual and initial fluorescence intensity. Manipulation of mass balance and stepwise formation constant relationships, and application of a similar derivation procedure used in the nonlinear model, yields equation 10. Equation 10, like the nonlinear model equation, relates observed changes in FA fluorescence intensity I, to total metal, with a conditional stability constant (for the metal ion and FA) and the degree of complexation of the FA. The modified Stem-Volmer equation is ... 

The Stem Volmer Equation 3.36 can be used for any photophysical or photochemical single-step process x. Moreover, because quantum yields, x ) / xq, is equal to that of the lifetimes of the reactive excited state or intermediate in the absence and presence of quencher (Equation 3.38). This relation provides a stringent test for the assignment of an intermediate x that is observed by time-resolved methods [fluorescence lifetime measurement (Section 3.5) or kinetic flash photolysis (Section 3.7.1)]. Assignment of on observed intermediate to the one that... 

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