Fluorescence quenching liquid paraffin

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... 

Supporting evidence for the resonance mechanism comes from experiments in which the solvent has been varied. The predicted proportionality of the rate constant to the overlap Integral J has been directly shown in a study of a donor-acceptor pair (both steroids) in a series of solvents in which J varied 40-fold (Figure 6.19) [40]. The effect of solvent viscosity has also been studied. Since energy transfer by the resonance mechanism does not require collision, the rate would be expected to be independent of solvent viscosity. This has been verified for the quenching by perylene of fluorescence emission from excited 1-chloroanthracene [41] where the rate constant, which is about 2 x lO" M s (about ten times kp) in benzene, is no lower in liquid paraffin whose viscosity is around 100 times larger, nor even in a glass at 90 K. 

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