Photoreactivity of Surfactant Ketones as a Probe of the Microenvironment of Organized Media

Article abstract of DOI:10.1021/ja00350a035

The Norrish type II photoprocess of surfactant keto acids has been used to examine the relative environment of the ketons in certain organized media.Values for φ of 0.81 in SDS micelles and 0.72 in CTAC micelles were obtained for 1, which are intermediate between the value of 0.29 in benzene and 1.0 in tert-butyl alcohol.The ketone thus experiences a fairly hydrophilic environment in micelles.Addition of heptanol to SDS micelles containing 2 causes a decrease in φ_II values, suggesting that a more hydrophobic region is seen by the ketone, possibly owing to water expulsion from the micelle.Incorporation of 1 into dioctadecylmethylammonium chloride (DODAC) vesicles on irradiation gives values similar to those of a benzene-like medium below the phase-transition temperature, and the φ_II values slowly increase as the temperature increases.Multilayer assemblies of 1 exhibit very little type II reactivity when irradiated, having values φ < 0.01.The close packing of the molecules which prevents the proper six-membered transition-state geometry to be reached can explain the very low φ_II.