Aggregation numbers of aqueous sodium dodecyl sulfate (SDS) in the presence of added salt were estimated using the time-resolved fluorescence quenching method. Tris (2,2′-bipyridyl)ruthenium(II) and 1-ethylpyrene were used as probes and 9-methylanthracene, 3,4-dimethylbenzophenone, and 1-dodecylpyridinium chloride were used as quenchers. It was found that aqueous SDS micelles are monodisperse even in the presence of high salt concentrations contrary to what has been reported. Similar studies were carried out using the nonionic surfactant hexaethylene glycol mono-n-dodecyl ether (HEGDE) in water. Aqueous 33.1% (w/w) HEGDE solutions were found to be polydisperse.

The photophysics and photochemistry of R-terthiophene (RT) in one nonionic, three cationic, and one anionic micellar systems have been investigated. If the micelles are large enough, RT follows a Poissonian distribution among the micelles. The extinction coefficients and the fluorescence quantum yields are independent of the surfactant forming the host micelle. The survival probability of the RT triplet is dependent on the number of RT's per micelle; the lower this number is, the longer the triplet survives. The triplet decays multiexponentially at times close to the excitation event but monoexponentially at longer times. The triplet remains in its host micelle due to a substantially slower intermicellar migration as compared to that of the RT radical cation. Delayed fluorescence emission, due to triplet-triplet annihilation, was detected in all systems. The rate constant of the delayed fluorescence could be correlated to the micellar volume of the ionic surfactants. For the nonionic surfactant, it was assumed that the RT molecule can penetrate the hydrophilic shell between the hydrophobic core of the micelle and the aqueous bulk. The yield of formation of the RT radical cation is the highest in the anionic system and the lowest in the neutral one. For the cationic surfactant micelles, the yield is intermediary and approximately equal. The formation of the radical is found to be biphotonic. The formation of the radical coupling product R-hexathiophene occurred in all micellar systems, proving that the radical can leave its host micelle and migrate via the bulk. The R-hexathiophene yield was highest in the anionic micellar system.

The effects of micellization on the rate constants and Gibbs energy of electron transfer (ΔG et) are studied by time-resolved luminescence quenching of tris(2,2‘-bipyridyl)ruthenium(II) (RUBIPY) and pyrene (PY) by electron acceptors and donors in sodium dodecylsulfate (SDS) micelles. For RUBIPY, which is bound to the SDS micelles and accessible to water, ΔG et is considerably smaller than what is found in organic solutions, though the spectral properties of RUBIPY and the value of diffusion-controlled quenching rate constant are typical for the micellar interior. For this system, dissolution in micelles enables a change of the local reactant concentration and mobility, retaining their higher reactivity in aqueous solution. In contrast, for PY, which is known to be localized in the palisade layer of an SDS micelle, the quenching rate constants coincide well with those found in acetonitrile.

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