Quenching pyrene fluorescence

The overall oxygen sensitivity exhibited by an optical sensor is basically predefined by the Stern-Volmer constant Ksv. The sensitivity of the final optical oxygen sensor increases with Ksv [65]. Generally, high Ksv values are provided by the Pd- and Pt-porphyrin complexes, by Ru(dpp)3, and by pyrene. Fluorescence quenching by oxygen not only affects the fluorescence intensity of the dye, but also has an influence on its lifetime r (Fig. 6) ... 

Scheme 1. A standard mechanism for pyrene fluorescence quenching by pyrene (P) or A-...

Although dynamic Stern-Volmer plots for pyrene fluorescence quenching by CA, were curved, activation energies could be derived from the limiting slopes which yield k5r (Eqn. 11b). Activation parameters obtained from the Stern-Volmer treatments agree well with those which assume k3+k2 for pyrene in M is the same as in liquid paraffin(33) and which take k3 from the limiting slopes of Fig. 2a. In both, the activation energy for... 

TABLE 2. Activation parameters for pyrene fluorescence quenching hv pyrene In CM ... 

Such a fluorescence dependence upon the concentration of quencher was observed for the pyrene fluorescence quenching by dimethylaniline in SDS micelles [25,26]. Rodgers and Bexendale [27] studied the IRuibpy) ] luminescence quenching by 9-methylanthracene and found that Eq. (24) fitted well in the case of sufficiently fast... 

De Schryver et al. [44] applied this model to analyse the pyrene fluorescence quenching by metal ions in SDS micelles. The situation described by the inequality (40) was observed for nickel, copper and lead ions. The values were determined from the slope of the linear plot of S2/SS vs. [M] [see Eq. (43)]. For europium and chromium ions, both interfacial exchange processes in micelle-micelle and micelle-bulk solution are very slow as compared with pyrene fluorescence decay. Here, the kinetics fits well to Case 2 discussed above. For silver and thallium ions, the rates of the fluorescence... 

The influence of the surfactant concentration upon the quenching process may be caused by the change of the micelles shape, rather than intermicellar exchange of quencher molecules, as it was supposed for pyrene fluorescence quenching by copper ions in SDS micelles [49]. 

Pyrene fluorescence quenching by metal ions in SDS micelles was studied at both constant and pulse illumination by Ziemiecki and Cherry [50, 51]. In order to analyse the kinetic data they applied the same kinetic model as De Schryver et al. The values of kf. obtained at steady-state excitation and at pulse excitation coincide. Thus, the pyrene fluorescence quenching by metal ions in SDS is an example of pure dynamic quenching within the micelles. The data of De Schryver et al. [44] and of Ziemiecki and Cherry [50, 51] are compiled in Table 1. 

Equations (4-5) and (4-7) are alternative expressions for the estimation of the diffusion-limited rate constant, but these equations are not equivalent, because Eq. (4-7) includes the assumption that the Stokes-Einstein equation is applicable. Olea and Thomas" measured the kinetics of quenching of pyrene fluorescence in several solvents and also measured diffusion coefficients. The diffusion coefficients did not vary as t) [as predicted by Eq. (4-6)], but roughly as Tf. Thus Eq. (4-7) is not valid, in this system, whereas Eq. (4-5), used with the experimentally measured diffusion coefficients, gave reasonable agreement with measured rate constants. 

Similar data were reported by Turro et al., [62,63] who synthesized a copolymer of AA with 1.5 mol% of 2-[4-(l-pyrene)butanoyl]aminopropenoic acid, 19 and studied the fluorescence quenching with Tl +, Cu2+, and 1 ions in aqueous solution. 

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. 

Elegant evidence that free electrons can be transferred from an organic donor to a diazonium ion was found by Becker et al. (1975, 1977a see also Becker, 1978). These authors observed that diazonium salts quench the fluorescence of pyrene (and other arenes) at a rate k = 2.5 x 1010 m-1 s-1. The pyrene radical cation and the aryldiazenyl radical would appear to be the likely products of electron transfer. However, pyrene is a weak nucleophile the concentration of its covalent product with the diazonium ion is estimated to lie below 0.019o at equilibrium. If electron transfer were to proceed via this proposed intermediate present in such a low concentration, then the measured rate constant could not be so large. Nevertheless, dynamic fluorescence quenching in the excited state of the electron donor-acceptor complex preferred at equilibrium would fit the facts. Evidence supporting a diffusion-controlled electron transfer (k = 1.8 x 1010 to 2.5 X 1010 s-1) was provided by pulse radiolysis. 

Figure 5.16. Plot of data for the external heavy-atom quenching of pyrene fluorescence in benzene at 20°C. Polaro-graphic half-wave reduction potentials Ein are used as a measure of the electron affinity of the quencher containing chlorine (O), bromine ( ), or iodine (3). From Thomaz and Stevens<148) with permission of W. A. Benjamin, New York.

Bodenant B, Fages F, Delville MH (1998) Metal-induced self-assembly of a pyrene-tethered hydroxamate ligand for the generation of multichromophoric supramolecular systems. The pyrene excimer as switch for iron(III)-driven intramolecular fluorescence quenching. J Am Chem Soc 120 7511-7519... 

Fluorescent cellulose triacetate membranes were prepared by incorporation of pyrene-butyric acid (219), and were applied to in situ detection of ground water contamination by explosives, based on fluorescence quenching by the nitro groups LOD 2 mg/L of DNT (220) and TNT (221) and 10 mg/L for RDX (276) the response follows the Stern-Volmer law for DNT and TNT442. 

Figure 6. Fluorescence quenching of pyrene by MV2+ in water, a) 1, b) 2. Monomer emission ( ), excimer emission ( ).

Table II. Quenching of Pyrene Fluorescence by MV and Quantum Yield of MV Formation...

Fluorescence quenching in micelles. Consider an aqueous solution with a high concentration of micelles (Box 26-1) and relatively low concentrations of the fluorescent molecule pyrene and a quencher (cetylpyridinium chloride, designated Q), both of which dissolve in the micelles. 

The probe molecule pyrene (-10"6 M) was used in time-resolved fluorescence quenching experiments using a single photon counting apparatus, cetylpiridinium chloride (CpyC, 10"3 M) being introduced as a quencher of the pyrene fluorescence[ll-13]. All the experiments were performed at 303K. From these fluorescence studies the micelle aggregation number (N) and the pyrene fluorescence lifetime (x) were obtained [14]. 

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