On ion-pair photoseparation and recombination in micellar aggregates

Perylene (Pe) and tetramethylbenzidine (TMB) have been photoionized under continuous or laser pulse excitation in cationic (Mi⁺), neutral (Mi⁰) or anionic micelles (Mi^-). In the latter case, Mi^- composed of sodium dodecyl sulfate (SDS) surfactant molecules have been swollen upon the addition of various hydrocarbons and the interfacial electric potential ΔΨ modified by electrolyte addition.From previous and present data, the following conclusions can be drawn:

• •(a) Intramicellar ultrafast geminate recombinations are promoted by increasing the micellar volume but counteracted when high electron mobility values characterize the swelling agent;
• •(b) Recombinations involving the hydrated electron ρ^-_aq appear to be suppressed in negatively as well as in positively charged Mi and to occur in Mi⁰ to an extent depending upon the chromophore cation;
• •(c) The overall photoionization yield ø_ion of Pe or TMB is found to increase linearly as ΔΨ becomes more negative; such ΔΨ variation is shown to affect ø_ion through the primary electron ejection stage though the ionization threshold energy does not seem to be appreciably modified;
• •(d) For Mi^- aggregates, the photoionization efficiency curves ø_ion=f(λ) show a linear dependence on the photon excess energy in the threshold region; within such an energy range, the ø_ion(λ) curves would thus approximate the variation with λ of a primary ionization yield of the solute;
• •(e) As a corollary, it may be suggested that the shape of the ø_ion(λ) curves relative to homogeneous liquid solutions would be essentially governed by solute cation-ρ^-_solv recombination reactions.