Data for the quenching of the fluorescence of two anthracene-derived amphiphilic fluorescence probes (ethyldimethyl-(I) and trimethyl[3-(9-anthracenyl)propyl]a"onium bromide (II)) in aqueous micellar solutions of the quencher detergents N-hexadecylpyridinium chloride (HPCl), bromide (HPBr), and nitrate (HPNO,) are analyzed in terms of a photophysical model which assumes static quenching of the micelle-incorporated probe and dynamic quenching of the residual fluorescence of the unincorporated probe by free detergent monomer and free counterions. This analysis provides values for the ground-state probe incorporation coefficient K, which are compatible with independent estimates based on the quenching of the emission of the micelle-excluded R~(bpy),~+ ion by I under the same conditions. The results of the present study clearly show that K, for incorporation of a charged amphiphilic substrate into the micellar phase of a like-charged detergent is quite sensitive to the concentration of detergent and added salt present. In addition to this general salt dependence, which can be ascribed to the effects of intermicellar ionic strength and intermicellar interactions on the micellar surface potential, the magnitude of K, also exhibits a significant specific salt (counterion) dependence. Consideration of the consequences of selectivity in counterion exchange at the micelle surface on the effective micellar surface potential provides an analytical expression which rationalizes the observed specific counterion effects on K, for this type of substrate. The implications for the quantitative analysis of ground-state reactions and equilibria in ionic micellar solution are pointed out and methods for estimating K, under diverse experimental conditions suggested.
The activation energy for nonradiative decay has been determined to be 5.3 kcal/mol for diphenylbutadiene (DPB) and 4.5 kcal/mol for diphenylhexatriene (DPH). Much lower values were obtained for the corresponding 4,4'-dialkyl-substituted molecules, 4B4A and 4H4A. Evidence for S2 emission and the effect of solvent polarizability on this process have been obtained from fluorescence spectra and lifetimes. The results are discussed in terms of the relationship between the two low-lying excited singlet states and differential solvent and substituent effects on them.
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