Static or dynamic quenching

A second nonlinear fluorescence quenching data treatment method developed by Ventry and Ryan may also be used to extract conditional stability constants, and ligand concentrations from titrations of FA with Cu (23). The model designed is a modification of the original Stem-Volmer theory defined by equation 7 which accounts for either static or dynamic quenching of fluorescent species. 

In contrast to fluorescence static or dynamic quenching, for which a coupling between electronic orbitals... 

The DPA moiety is less active in forming the CT complex with viologens than the pyrene moiety e.g., for PMAvDPA the KCT values with MV2+ and SPV are 1.3 x 103 M 1 and almost zero, respectively, at pH 8-9 [60, 77], whereas for PMAvPY they are 7.8 xlO4 and 6.3 x 102 M, respectively, at pH 11 [77]. Therefore, the polymer-bound pyrene system undergoes much more static quenching than the polymer-bound DPA system. As will be discussed in Chapter 6, it is very important for charge separation whether the fluorescence quenching is static or dynamic. 

The commercialization of inexpensive robust LED and laser diode sources down to the uv region (370 nm) and cheaper fast electronics has boosted the application of luminescence lifetime-based sensors, using both the pump-and-probe and phase-sensitive techniques. The latter has found wider application in marketed optosensors since cheaper and more simple acquisition and data processing electronics are required due to the limited bandwidth of the sinusoidal tone(s) used for the luminophore excitation. Advantages of luminescence lifetime sensing also include the linearity of the Stem-Volmer plot, regardless the static or dynamic nature of the quenching mechanism (equation 10) ... 

As far as deactivation by T1+ is concerned, a fluorescent label attached to PMAA is considered [95,96] to undergo a mixture of static and dynamic quenching. (Static quenching [1] can be defined as a process that occurs too fast to resolve within the timescale of the experiment. In other words, a ground-state interaction or complex forms between the quencher and the fluorophore before excitation. Such a situation would perhaps be not unexpected when counterions condense in high concentrations to a polyelectrolyte backbone in close proximity to a fluorescent label.)... 

When the quenching is dominated by either a purely static or dynamic pathway, the quenching behavior follows Equation 14.2 and consequently SV plots of I°/Ivs. [Q] are linear. However, in many situations (as shown below) the SV plots are curved upward (i.e., superlinear). Superlinear SV plots can arise from a variety of processes, including mixed static and dynamic quenching, variation in the association constant with quencher concentration, and chromophore (or polymer aggregation). 

By using dynamic mechanical analysis (DMA), tensile, compression, bending and torsion tests can be carried out under static or dynamic conditions. Elastic moduli can also be obtained by DMA. With DMA, measurements of constant stress or constant strain can also be made. Thus thermal expansion coefficients, stress relaxation and creep can be investigated by DMA. Here we only give an example of the measurement of the thermal expansion coefficient. In Figure 4.96, the thermal expansion curves of Fe-Co-Si-B amorphous alloy are plotted. Curves 1 and 2 are the measured results for a relaxed glass and as-quenched glass. 

The low fluorescence in the FQ complex can be derived from non-radiative decay due to the occurrence of either energy or electron transfer. These processes are difficult to demraistrate, and even more difficult to design. Therefore in the recent literature this approach has not been extensively used for the design of enantioselective sensors, though combination of static and dynamic quenching has been documented in some cases. 

The intensity of fluorescence can be decreased (quenched) by several processes, such as collisions (in solution), excimer or exdplex formation, and energy, electron or proton transfer [5]. In the context of polymer blends studies, the process of collisional fluorescence quenching, either static or dynamic (as described by the Stern-Volmer quenching), is not particularly relevant. 

Fluorescence quenching may be dynamic, if the photochemical process is the result of a collision between the photoexcited indicator dye and the quencher species, or static, when the luminophore and the quencher are preassociated before photoexcitation of the former20. It may be easily demonstrated that dynamic quenching in isotropic 3-D medium obeys the so-called Stem-Volmer equation (2)21 ... 

Figure 5.3. Simulated Stern-Volmer plots of the ratio of the initial fluorescence intensity F0 to the intensity Fin the presence of quencher of concentration [Q] showing (a)static quenching, (b) dynamic quenching (linear), and (c) binding and/or inaccessible quenchers.

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