Stern Volmer graphs

He and Na atoms [116]. Table 2.2 presents example results of [24, 312] in which the o of a given rovibronic level of NaK and K2 molecules were determined from Stern-Volmer graphs. Such large cross-sections indicate that the partners of collisions interact fairly efficiently at comparatively large distances. 

When [Rh(phi)2(phen)]3+ is titrated into a solution containing [Ru(phen)2(dppz)]2+ and B-form DNA, the photoinduced luminescence of the ruthenium(II) complex is quenched dramatically (53). In these experiments, luminescence is monitored by laser flash as quencher is added. Data are then plotted in Stern-Volmer format, where the ratio of initial intensity/intensity (I0/I) is given as a function of quencher concentration [Q. The degree of lifetime quenching can also be described by plotting the inverse of the lifetime (r0/r) versus [Q. Normally, when chromophore and quencher interact bimolecularly, Stern-Volmer graphs are linear with [Q] and the slope for r0/r is the same as that for I0/I. 

Additional experimental evidence for triplet state involvement is provided by the quenching of both phosphorescence and delayed fluorescence by piperylene, a well known triplet quencher. In fact a study of its quenching effects on the delayed emission demonstrates that at least one of the triplet excitons involved in the fusion process is mobile. This is evident from the phosphoresence quenching curves (Stern-Volmer graphs) of PIVN and 1-ethylnaphthalene illustrated in Fig. 3. 

Fig. 11.11 Upper graph Schematic energy-level diagram showing energy transfer between F3 (left) and the iridium complexes studied by Thompson and coworkers (right). Lower graph Stern-Volmer plot for quenching of the five phosphors by F3. (Legend FP, PPY, B"f PQ, BTP). The table shows the triplet energies of the phosphors and their Stern-Volmer quenching constants [52],...

When a photoexcited molecule undergoes chemical reaction the fluorescence quantum efficiency is reduced, i.e., it is quenched. Fluorescence quenching provides an excellent example of how competition between chemical and physical processes may be used to establish both rate law and mechanism. The reaction of photoexcited acridine (A ) with amines in aqueous solution has been thoroughly studied.Addition of amines reduces the fluorescence efficiency. Data for an analogous system are presented as a Stern-Volmer plot in Fig. 6.6. The relative fluorescence efficiency, (pf c=0)l(pf c), is equal to the ratio of fluorescence intensities without and with quenchers lf c=0)jlf c). If this latter quantity is graphed against amine concentration, c, it appears that... 

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