Stem-Volmer law

The fluorescence quantum yield T was defined in Eq. (3.10), where R(t) is exactly the same quantity as N(t) here. Being proportional to the Laplace transformation of the latter, the quantum yield of fluorescence obeys the truly linear Stem-Volmer law ... 

Since As is not a total concentration of electron acceptors c but a neutral fraction of them, the relationship between As and c [4] I A ], as well as the T) 1 (c) dependence, are complex and non-linear at large 7o- In this sense the original Stem-Volmer law breaks down with an increase in light intensity as well as with a decrease in the total quencher concentration c. In both cases one has to find first the As(c) dependence before using it in Eqs. (3.511). As follows from Eq. (3.509b) and the conservation law for acceptors (Nj c 4V), this dependence is given by the following relationship ... 

The insertion of the As(c) dependence into Eq. (3.521) breaks the linearity of the Stem-Volmer law [200]. The resulting curves r 1 (c) are shown in Figure 3.64, taking into account the field dependence of the Stern-Volmer... 

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... 

The relative fluorescence quantum yield defined in Eq. (3.8) is the ratio of the stationary singlet excitation concentration in the presence of quenchers to the same concentration in their absence. By substituting into this definition N from Eq. (3.654a), we confirm that the fluorescence quantum yield obeys the Stem-Volmer law (3.363) with the same constant as in Eq. (3.364), but with the contact [Pg.339]

Stem-Volmer constant responsible for the nonlinearity of the Stem-Volmer law predicted by DET and UT [see Eqs. (3.30)-(3.33) and Fig. 3.61]. All these drawbacks arise because of the limited validity of IET, which is merely the lowest-order approximation with respect to particle concentration c. 

Making a Laplace transformation of Eqs. (3.665) and using (0) inEq. (3.128), one can easily confirm the Stem-Volmer law (3.30), but with the corrected constant ... 

This is the conventional Stem-Volmer law but with the constant defined as follows ... 

However, IET does not describe well the static and long-time asymptote of diffusional quenching that are not of binary origin. These shortages are partially removed by MET. It retains all the advantages of IET but extends the time limits of the theory as in Eq. (3.683) and provides the first nonlinear concentration corrections to the Stem-Volmer law (Section XII). 

Quenching occurs if species are present tiiat can reduce the observed fluorescence by forming complexes with either the groimd state or the excited state of the fluorescent molecule. It cm be described bv the Stem-Volmer Law... 

The Stem-Volmer equations discussed so far apply to solutions of the luminophore and the quencher, where both species are homogeneously distributed and Fick diffusion laws in a 3-D space apply. Nevertheless, this is a quite unusual situation in fluorescent dye-based chemical sensors where a number of factors provoke strong departure from the linearity given by equation 2. A detailed discussion of such situations is beyond the scope of this chapter however, the optosensor researcher must take into account the following effects (where applicable) ... 

The spectra observed with four concentrations of pyrene are shown in Figures 18 and 19. The spectra of normal fluorescence are similar to those previously reported by Forster and Kasper. The relative intensity of the dimer band increases as the concentration of pyrene increases and the simultaneous reduction in fluorescence efficiency, n, of the monomer follows the Stem-Volmer quenching law with a mean quenching constant of 2.0 X 10s liter mole-1 (Table VII). 

Stark-Einstein law, 4 Stem-Volmer plot, 34 slilbene, absorption spectrum, 1 3 cis-trans isomerization, 42 cvclization, 97 excited state energies, 17 styrenes, addition reactions, 58... 

The plot of FJF against [Q does not follow the linear law and shows downward curvature toward the X-axis (Fig. 2a). Such behavior of the Stern-Volmer plot is the feature of two fluorophore populations, one of which is not accessible to a quencher [6]. In such case, the modified Stem-Volmer equation should be used ... 

In this case, Einstein explicitly distinguished primary and secMidaiy photochemical processes [39], a point that was obvious for him but unfortunately not for many chemistry practitioners. This point was even more clearly stated by Stem and Volmer, who evidenced that the Einstein law could not be applied to the chemical products without consideration of the overall process. In fact, a satisfactory rationalization was offered on this basis for some reactions, e.g., assuming that the cleavage... 

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