Protolytic photodissociation and proton-induced quenching of 1-naphthol and 2-octadecyl-1-naphthol in micelles

Kinetics of excited-state proton-transfer reactions and proton-induced fluorescence quenching of 1-naphthol (IN) and 2-octadecyl-1-naphthol (201N) in micellar solutions of cetyltrimethylammonium bromide (CTAB), polyoxyethylene(23) lauryl ether (Brij 35), and sodium dodecyl sulfate (SDS) was studied by using stationary and time-resolved fluorescence techniques. The ground-state acidity constant of 20 IN in cationic micelles of CTAB was found to be significantly smaller than that of the parent compound (DeltapK = 0.5). However, similar rate and equilibrium constants of the protolytic dissociation were obtained for 1N and 201N in the singlet excited state. Effects of nonionic micelles of Brij 35 closely resemble those of CTAB. In anionic micelles of SDS, the protolytic photodissociation was much slower for 201N than for IN. The protonation rate for the excited anions in micellar solutions increases by approximately 2 orders of magnitude in the series CTAB, Brij 35, SDS. Excited-state kinetics was rationalized within the framework of a pseudophase model, which included micellar effects on the proton-transfer equilibrium and interfacial diffusion of hydronium ions. The electrostatic surface potential of charged micelles was estimated from the acidity constants of naphthols.