Stem Volmer relationship

The importance of comparing time-dependent and steady-state fluorescence measurements is well illustrated by the difficulty of resolving purely static from purely dynamic quenching. In either case, the basic relationship between the steady-state fluorescence intensity and quencher concentration is the same. The Stem-Volmer relationship for static quenching due to formation of an intermolecular complex is i... 

The interaction of an extrinsic membrane protein with a lipid bilayer can also be investigated by energy transfer. The interaction of cytochrome c has attracted much attention, and in an early study by Shaklai et al.(()5> the number of binding sites per red cell was determined. It was shown that an equation analogous to the Stem-Volmer relationship could be derived ... 

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. 

Since iodide is known to act in phospholipid vesicles as a collisional quencher for AF probes [6,9] by a diffusive process, fluorescence quenching was described by the Stem-Volmer relationship [6] ... 

The graph below shows the Stem-Volmer plots for quenching of the luminescence of polysilole 1, by TNT in toluene solution. A linear Stem-Volmer relationship is observed for the corresponding polygermole, 2, and the copolymers 3-8, but the Stem-Volmer plot for quenching by picric acid... 

The presence of a freely diffusing quencher, however, underlies the essential difference between energy-transfer studies in the liquid and solid phases, although it is still possible to relate the Stem-Volmer relationship to quenching data in the solid. This has been demonstrated in the quenching of phosphorescence of poly(acenaphthylene) (23), poly(1-vinylnaphthalene) (24) and poly(styrene) (25) by piperylene in glasses at 77°K. 

This is the well known Stem Volmer relationship that relates the fluorescence yield of the sample to the concentration of the added quencher. A plot of or, since 4>p F, F/F versus [Q] should yield a strai t line with an intercept of 1, and the Stem Volmer slope, fCjv = kqTs (Figure 13). 

Fluorescence quenching techniques allow for the quantification of the degree of accessibility of the fluorophore to the quenching agent through the Stem-Volmer relationship ... 

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. 

Dimers (73) and (74) were formed in approximately equal amounts in all cases, although, as in the cases of 2-cyclopentenone and 2-cyclohexenone, the relative amount of (72) (either cis-syn-cis or cis-anti-cis) was found to vary substantially with solvent polarity. As in 2-cyclopentenone, this increase in the rate of head-to-head dimerization was attributed to stabilization of the increase in dipole moment in going to the transition state leading to (72) in polar solvents. It is thought that the solvent effect in this case is not associated with the state of aggregation since a plot of Stem-Volmer plot and complete quenching with 0.2 M piperylene indicate that the reaction proceeds mainly from the triplet manifold. However, the rates of formation of head-to-head and head-to-tail dimers do not show the same relationship when sensitized by benzophenone as in the direct photolysis. This effect, when combined with different intercepts for head-to-head and head-to-tail dimerizations quenched by piperylene in the Stem-Volmer plot, indicates that two distinct excited triplet states are involved with differing efficiencies of population. The nature of these two triplets has not been disclosed. 

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). 

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 ... 

A different explanation was identified in the quenching properties of these heterocycles. Thiophene and mono methyl derivatives are efficient quenchers of triplet benzophenone. The Stem-Volmer plot showed a linear relationship [104, 105]. On the contrary, 2,5-dimethylthiophene (a compound able to give the cycloaddition reaction) is not a good quencher of benzophene [106]. N-Benzoylpyrrole also does not act as a quencher of the triplet benzophenone [106]. On the contrary, pyrrole and selenophene are quenchers of the excited benzophenone [106]. In this case, the Stern-Volmer plot is not linear. This situation is commonly encountered when the quencher employed quenches two excited states. It seems reasonable that pyrrole acts as quencher of both triplet benzophenone and the exciplex between triplet benzophenone and pyrrole [106]. 

Quenching constant See quencher, quenching, Stem-Volmer kinetic relationships. 

Steric requirements, hydrogen and deuterium, 299 Stem-Volmer plot, 181 Stiff differential equations, 109 Stochastic simulation, 109 Stoichiometric coefficients, 11 Stokes-Einstein equation, 135 Stopped flow, 179 Stmetured water, 395 Structure-reactivity relationships, 311 Sublimation energy, 403 Substituent, 313 Substituent constant, 323 alkyl group, 341 electrophilic, 322 Hammett, 316 inductive, 325, 338 normal. 324 polar, 339 primary, 324 resonance, 325... 

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 ... 

In equation 11, v=[ML]/Cl, and all other symbols used are the same as defined previously for nonlinear and modified Stem-Volmer models. Theoretically, a plot of v versus v/[L] should yield a straight line with K as the y intercept and -K as the slope. Algebraic manipulation of Cl and mass balance relationships (equations 4 and 5) and substitution into equation 11, yields equation 12. 

Shetlar has derived non-linear relationships of the Stem-Volmer type suitable for systems in which quenching occurs by more than one mechanism. Rate constants for heavy atom fluorescence quenching of polynuclear aromatic hydrocarbons by 1-iodopropane in benzene have been found to decrease exponentially with the energy difference between the fluorescing state and the nearest lower triplet state (Dreeskamp et al.). Bromocyclopropane has been recommended as a heavy-atom quencher of excited singlet states since it is more photostable than simple alkyl bromides (Flemming, Quina, and Hammond). Laser studies with chlorophyll a have provided evidence for the interesting radiationless intermolecular process Tx + Sx -> T2 + S0 (Menzel). 

Figure 10-15 shows the relationship between the photoexcited triplet lifetime of Cso and oxygen concentration. The triplet lifetimes of Cgo were calculated from the first-order plot. The lifetime decreases with increase in oxygen concentration. Figure 10-16 shows a Stem-Volmer plot of Ceo in a PS film. The Stem-Volmer plot of Ceo exhibits considerable linearity = 0.999) ATsv is estimated to be 0.50% . The limit of oxygen concentration detection was about 0.3%. 

Figure 10-22 shows a Stem-Volmer plot of the relationship between the fluorescence intensities of a PBA film at 474 nm, attributed to PBA excimer emission, and the oxygen concentration. At higher PBA concentrations, the emission of the PBA excimer is sensitized by energy transfer from the PBA monomer. 

At low NP concentrations, fluorescence quenching is dominated by diffusive transport, and a nonequilibrium model for the fluorescence quenching is appropriate. The standard model for this regime is attributed to Stem-Volmer. In particular, the ratio Fq/F at low concentrations is predicted to be linear in concentration of the quenching agent in this theory. Specifically, we then have the relationship... 

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