Dynamic quenching mechanism

In order to quantify the transition metal ion concentration, Jones et al. [107] developed a highly sensitive fluorescent chemosensor in the form of dialkoxy-phenyleneethynylene-thiophene copolymers 68/69. The PAEs were functionalized on the thiophene unit with terpyridine (68), and included 2,2 -bipyridine (69) as a Lewis acid receptor. The terpyridine polymers [108] were found to respond quantitatively to transition metal ions at concentrations as low as 4x10 M (NP, Hg, Cr ", and Co " ). The additionally used bpy-PAE demonstrates that variation in the chelation at the receptor site is an important variable in tuning selectivity. The observed dynamic quenching mechanism, combined with the solubility of this material, provides the opportunity to extend these initial investigations to thin solid films for use in real-time monitoring applications. 

Particle surface charge ideally this should be the same as the charge of the target actinide ion, i.e. cationic, so encouraging electron transfer via a dynamic quenching mechanism with its attendant high quantum efficiencies. 

The enantiomer excess depends on the solvent system isopropanol-water < ethanol-water methanol-water. The best values are 42% in 75% ethanol-water at 25°C and 40% in 75% methanol-water. The reaction mechanism was investigated kinetically. In general, photoreaction takes place via either a dynamic quenching mechanism or a static quenching mechanism, as shown in Scheme 23. 

In the dynamic quenching mechanism (Scheme 23A), the Stem-Volmer relation is represented by Eq. (19), where t and To mean the lifetime in the presence and the absence of quencher, respectively, and [Co111] represents the concentration of the cobalt(III) complex. 

Non-exponential phosphorescence decay is frequently observed for various aromatic chromophores molecularly dispersed in polymer matrices. Various possible mechanisms for non-exponential decay are reviewed, and a dynamic quenching mechanism by polymer matrices including the effect of a time-dependent transient term in the rate coefficient is discussed in some detail. The biphotonic triplet-triplet annihilation mechanism is also introduced for the non-exponential decay under high-intensity and/or repeated laser irradiation. 

Another mathematical model based on the relative contributions of static and dynamic quenching mechanisms in heterogeneous systems was derived by Carraway etal [8]. The light intensity in their model is described by a series of Stern-Volmer relationships... 

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