Stern-Volmer constants fluorescence quenching

Stern-Volmer constant from fluorescence quenching data. 

A plot of the inverse quantum yield for the photocycloaddition of 1-aminoanthraqui-nones (AQ) and (E)-piperylene (Q) was found to be linear and the ratio of the slope, 0.20 dm3 mol and intercept, 1.20, of this plot was equal to the Stern Volmer constant for fluorescence quenching of AQ by Q, Ksv = 0.17 dm3 mol It was concluded that the reaction proceeds from the excited singlet state of AQ via an exciplex intermediate (AQ-Q). Explain. [Ref. 270]... 

T tt tp Ks Ky a p Quantum yield of population of the observed triplet Singlet lifetime Triplet lifetime (from T-T absorption) Phosphorescence lifetime Stern-Volmer constant for fluorescence quenching Stern-Volmer constant for triplet quenching Fraction of twisted triplet decaying to the trans form Fraction of twisted excited singlet decaying to the tram form... 

The drawback of these molecular sensors is their lack of selectivity, as shown by the Stern-Volmer constants (Table 10.4). For instance A-l, 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) is mainly used as a Cl -sensitive fluorescent indicator, but its fluorescence is also quenched by several other anions (I-, Br and SCN-, but not by NO ). 

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... 

Table II. Stern-Volmer Constants for Quenching of SNA and MSNA Fluorescence by MV in 0.028 M SDS at 25°C.

Fast generation of the radical ions can be attributed to electron-transfer reaction from the singlet excited state and slow radical generation to that from triplet excited state. Fluorescence of both 326 and 327 was quenched in the presence of CCI4 according to the Stern-Volmer equation. The Stern-Volmer constants were estimated to be 1.55 and 17.7 M 1 for 326 and 327, respectively, and quenching rate constants were estimated to be 1010 and 2.7 x 1010 M 1 s 1. 

In 1977, Scharf and Mattay [123] found that benzene undergoes ortho as well as meta photocycloaddition with 2,2-dimethyl-1,3-dioxole and, subsequently, Leismann et al. [179,180] reported that they had observed exciplex fluorescence from solutions in acetonitrile of benzene with 2,2-dimethyl-l,3-dioxole, 2-methyl-l,3-dioxole, 1,3-dioxole, 1,4-dioxene, and (Z)-2,2,7,7-tetram-ethyl-3,6-dioxa-2,7-disilaoct-4-ene. The wavelength of maximum emission was around 390 nm. In cyclohexane, no exciplex emission could be detected. No obvious correlation could be found among the ionization potentials of the alkenes, the Stern-Volmer constants of quenching of benzene fluorescence, and the fluorescence emission energies of the exciplexes. Therefore, the observed exciplexes were characterized as weak exciplexes with dipole-dipole rather than charge-transfer stabilization. Such exciplexes have been designated as mixed excimers by Weller [181],... 

Figure 42 Stern-Volmer plots for fluorescence quenching of PBAC by Co(phen)3+ in the presence of 0.008% BAZrP. Using 200 nsec as the singlet lifetime of PBAC, the rate constant for quenching is calculated to be 3 X 1012 M-1sec. This is much too fast for a dynamic process and may involve long-range electron transfer. (From Ref. 17. Copyright 1995 Overseas Publishers Association.)...

The overall oxygen sensitivity exhibited by an optical sensor is basically predefined by the Stern-Volmer constant Ksv. The sensitivity of the final optical oxygen sensor increases with Ksv [65]. Generally, high Ksv values are provided by the Pd- and Pt-porphyrin complexes, by Ru(dpp)3, and by pyrene. Fluorescence quenching by oxygen not only affects the fluorescence intensity of the dye, but also has an influence on its lifetime r (Fig. 6) ... 

When a protein possesses two or several Trp residues, when quenchers such as iodide, cesium, or acrylamide are used, and if all Trp residues are not accessible to the quencher, the Stern-Volmer equation yields a downward curvature. In this case, we have selective quenching (Figure 10.5b). From the linear part of the plot, we can calculate the value of the Stern-Volmer constant corresponding to the interaction between the quencher and accessible Trp residues. Upon complete denaturation and loss of the tertiary structure of a protein, all Trp residues will be accessible to the quencher. In this case, the Stern-Volmer plot will show an upward curvature. In summary, inhibition of the protein fluorescence with two or several Trp residues can yield three different representations for the Stern-Volmer equations, depending on the accessibility of the fluorophore to the quencher. 

Stern-Volmer constants of similar size were found for nitro- and cyanostilbenes using ferrocene as quencher [85,118]. Fluorescence quenching by oxygen in saturated solution (1 bar) is small for fram-stilbene [105]. 

TABLE 13 Stern-Volmer Constant Obtained from Fluorescence Quenching of trans Isomers and Fluorescence Lifetime11... 

TABLE n. Inorganic Anions Absolute Rate Constants for Quenching of 02 (k ) and Acetone Triplet (kg) and Stern-Volmer Constants for Quenching of Fluorescence of Methylene Blue (Kjy-.NB) and Rose Bengal (Ksv RB)... 

Aromatic nitriles are strong oxidants in their excited states (see Table I). Since they fluoresce strongly, the involvement of the singlet states can be easily proved by application of fluorescence quenching techniques. In all of the tested cases, it has been found that the Stern Volmer constant obtained from fluorescence analysis and that obtained from the double reciprocal plots of reaction quantum yield vs. quencher concentration are nearly equal, thus proving that the singlet stale is actually involved In the photochemical reaction. Actually it has been observed that a AG < 0 and polar solvents are necessary (although not sufficient, see Section 3) conditions for the photochemical proc-... 

This equation is traditionally used to quantify fluorescence quenching efficiency by additives at low concentrations that bind or otherwise interact with the fluorescent species, where the Stern-Volmer constant ( sv) is conventionally taken as a measure of the quenching efficiency, y, times the diffiision-lirmtod bimolecular rate for the dynamic quenching process. 

A plot of 1/< versus (0) should be a straight line with a slope of and an intercept of l4>t The Stern-Volmer constant can be obtained from the ratio of the intercept and the slope. Dynamic quenching reduces both the fluorescence quantum yield and the fluorescence lifetime. 

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 these reactions, kinetic evidence for the involvement of the amine is shown by the relationship 0 a[amine]. In cases where the halide has detectable fluorescence, the amine may quench fluorescence according to Stern-Volmer kinetics, and emission from the singlet exciplex is frequently observable in nonpolar solvents. For a predominantly singlet state reaction, concordance is seen between (the Stern-Volmer constant for quenching fluorescence) and (the parameter intercept/slope fi"om the plot... 

Stern-Volmer constant for ZnTPP fluorescence quenching by PMPS. "Second-order equivalent rate constant for ZnTPP triplet quenching by PMPS. No CT interaction. 

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