Stern-Volmer kinetics

Integration of this differential equation with the initial condition [M ] = [M ]0 at t = 0 yields  

Time-resolved experiments in the absence and presence of quencher allow us to 

The diffusion coefficient of molecules in most solvents at room temperature is generally of the order of 10 s cm2 s 1. In liquids, ki is about 109-1010 L mol-1 s 1. 

If Rm and Rq are of the same order, the diffusional rate constant is approximately equal to 8RT/3tj. 

Time-resolved experiments in the absence and presence of quencher allow us to check whether the fluorescence decay is in fact a single exponential, and provide directly the value of kq. The fluorescence quantum yield in the presence of quencher is 

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Persistent microheterogeneity exists when the luminescence and quenching decay are fast compared to conformational-environmental rearrangement. Excited molecules can then emit and be quenched in distinctly different chemical environments. Decays can then be nonexponential, multiple emissions may be present, and simple Stern-Volmer kinetics can break down. 

The presence of inorganic particles in the sensitive layer complicates the quenching processes of luminescence-based sensors and provokes departure from the simple Stern-Volmer kinetics observed for homogeneous solutions of a luminophore (Eq. 1) [43] ... 

Stern-volmer kinetic relationships This term apphes broadly to variations of quantum yields of photophysical processes e.g., fluorescence or phosphorescence) or photochemical reaction (usually reaction quantum yield) with the concentration of a given reagent which may be a substrate or a quencher. In the simplest case, a plot of (or /M for emission) vs. concentration of quencher, [Q], is linear, obeying the equation... 

However, Stern Volmer kinetics are obeyed for radiolysis studies of scavenging of toluene fluorescence with benzyl chloride. The electron scavengers CHCl and chlorobenzene reduce the fluorescence yields of arenes in a manner that suggests ... 

Such a concentration dependence would te consistent either with a Foster or Dexter transfer mechanism whose rate is such that Stern-Volmer kinetic behaviour is obeyed or would be consistent with the alternative suggestion of scheme (3) where the excited state naphthalene chromophore experiences intramolecular diffusion controlled self quenching. 

As long as r > 3R0, the fluorescence decay is close to exponential, the lifetime of the donor fluorescence decreases linearly with increasing concentration of A and fluorescence quenching obeys Stern Volmer kinetics (Section 3.9.8, Equation 3.36). However, the bimolecular rate constants ket of energy transfer derived from the observed quenching of donor fluorescence often exceed the rate constants of diffusion kd calculated by Equation 2.26, because resonance energy transfer does not require close contact between D and A. Finally, when r < 3R0, at high concentrations and low solvent viscosity, the kinetics of donor fluorescence become complicated, but an analysis is possible,109,110 if required. 

Incorporation of a I -cyanoethyl group occurs when indoles are irradiated with UV light in the presence of acrylonitrile [13b, 57,58]. With indole, the major product formed is 3-(r-cyanoethyl)indole [13b]. In the case of 3-methylindole, where the 3-position is blocked, the products formed in methanol are shown in Scheme 25 only the 5- and 7-positions of the indole ring are unreactive. The reaction is not quenched by piperylene [13b], while quenching of the indole fluorescence by acrylonitrile follows Stern-Volmer kinetics and yields a rate constant for quenching that is close to the rate... 

In which D is the relative molecular diffusion coefficient of the donor and acceptor, A is the donor excitation energy migration coefficient, and Tq Is the donor luminescence decay time. If r R°, the molecules remain stationary during transfer, and Forster kinetics will be appropriate. When r >> R°, Stern-Volmer kinetics apply. For intermediate cases two theories, due to Voltz et al. (33) and Yokota and Tanlmoto (34), have been developed. 

Model (II) The rate of quencher formation is proportional to the luminance and the quenching follows Stern-Volmer kinetics. The resultant differential equation can be solved to yield this simple equation describing the kinetics of luminance loss ... 

Model (IV) The rate of quencher formation is constant and the quenching follows Stern-Volmer kinetics ... 

Bimolecular Decay of Excited States Stern-Volmer Kinetics... 

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... 

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