Photophysics of 3- and 4-phenyl pyridyl ketones in submicellar and micellar solutions of ionic and non-ionic surfactants

Abstract

The photophysics of the 3- and 4-phenyl pyridyl ketones has been studied in submicellar and micellar solutions of sodium dodecyl sulfate (SLS), Triton X-100 (TX-100) and hexadecyltrimethylammonium bromide (CTAB) by stationary techniques and nanosecond laser flash photolysis. In the presence of CTAB, the main effect is that of the counter-ion Br^–, in SLS and TX-100, the photochemical behaviour is dominated by hydrogen abstraction from the surfactants by the triplet ketones. The rate parameters of this interaction were determined by phosphorescence quenching measurements and the ketyl radicals produced were identified by laser flash photolysis at submicellar concentration. The dynamics of the spin-correlated radical pairs formed in micellar solution were studied; transient absorption spectra and lifetime were determined. By using quenchers that are solubilised in the micelle (biphenyl) or in the bulk water (CuCl₂), intra- and extra-micellar processes were characterised.