Stern-Volmer behavior

The non-Stern-Volmer behavior at the higher pressure of benzaldehyde seen in figure IX-L-5 points to benzene and carbon monoxide formation from another excited state that is quenched less effectively. The quantum yields of benzene and CO formed in process (I) following absorption within the n tt region (328, 365 nm) were... 

Significant curvature may be observed in the case of lifetime- (and intensity-) based sensors, mainly when the relation knri [Parameter]) is not linear. Figure 9.4 shows this type of nonlinear behavior for a fiberoptic oxygen sensor. The figure shows Stern-Volmer-type plots (r l versus [02]) at four different temperatures. The curvature is caused by the inability of the carrier to transport oxygen proportionally to the equilibrium partial pressure of oxygen. 

Now we have to specify the Stern-Volmer constant behavior between these two limits, in the interval Ko < k(c) < ko. 

More complex chemical species have been determined using different cappings on the QDs surfaces. Shi et al. have recently demonstrated that QDs coated with oleic acid were efficiently quenched by a diversity of nitroaromatic explosives, such as 2,4,6-trinitrotoluene (TNT) or nitrobenzene.49 Different quenching behaviors were observed for the different molecules. Nevertheless, modified Stern-Volmer equations could be used, in most cases, to provide linear calibration curves. Time domain measurements showed that static quenching was the dominant process as no change in luminescence lifetime was observed in the presence of the analyte. 

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 ... 

Examination of the quenching constants listed in Table 2.3 clearly reveals that, irrespective of the label adopted, or the pH investigated, when nitromethane is used as a quencher, the resultant kq value lies between 4 and 5 x 109 mol 1 dm3 s. This is similar to that for a diffusion-controlled process and is consistent with PAA adopting an expanded state under these conditions the quencher is unhindered by the water-swollen polymer coil as it diffuses toward the excited state. The fact that the kq value observed is constant with pH implies that either PAA is unresponsive to pH in terms of its conformational behavior or the Stern-Volmer experiment is insensitive to any change in conformation that may occur. Further consideration of the data listed in Table 2.3 demonstrates that the kq values at low pH are 10 times greater than that of PMAA using similar labels and solution conditions (see Table 2.2). This provides... 

Further, a similarity was observed between these data plotted using the modified Stern-Volmer equation and the Lineweaver-Burk plot derived from the substrate activity curve for an allosteric enzyme (12). Therefore, by the analogy of curve behavior and related equations, we... 

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