Fluorescence quenching complex formation mechanisms

In the next section we show that, in the simplest cases, this scheme accounts for the observed relations between the concentration of the quenching solute and the intensity and lifetime of fluorescence. In subsequent sections we introduce additional processes, such as complex-formation or proton-transfer, in which the product may itself be a fluorophore, so that there are two excited states to be considered. This two-state model covers a variety of fluorescence phenomena. We discuss also the physical mechanisms of the various processes and the ways in which excited molecules lose their excitation energy. 

We have seen earlier that the microemulsion formation is a spontaneous process which is controlled by the nature of amphiphile, oil, and temperature. The mechanical agitation, heating, or even the order of component addition may affect microemulsification. The complex structured fluid may contain various aggregation patterns and morphologies known as microstmctures. Methods like NMR, DLS, dielectric relaxation, SANS, TEM, time-resolved fluorescence quenching (TRFQ), viscosity, ultrasound, conductance, etc. have been used to elucidate the microstructure of microemulsions [25,26]. 

In other words, the Stem-Volmer equation holds also for the I(JI ratio which can be easily obtained from steady-state fluorescence measurements. However, the acquisition of IJI instead of xj-t does not allow for distinguishing dynamic quenching occurring in the excited state of the fluorophore from the so-called static quenching. The latter mechanism consists in the formation of a nonfluorescent complex of the quencher Q with the fluorophore F in the ground state ... 

Mechanisms of fluorescence quenching are usually divided into two groups collisional and complex formation these are also referred to as dynamic and static mechanisms, respectively. The distinction between dynamic and static mechanisms can get blurred, as can the distinction between collision complexes and subsequent more specific interactions (see discussion of diffusion controlled reactions in section 7.4). In addition to these mechanisms there can be internal quenching if the optical density of the solution is high. This last phenomenon, which is the so-called inner filter effect, is only a nuisance and provides no useful information. 

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