ABSORPTION SPECTRA AND ACID‐BASE DISSOCIATION OF THE 4‐ALKYL DERIVATIVES OF 7‐HYDROXYCOUMARIN IN SELF‐ASSEMBLED SURFACTANT SOLUTION: COMMENTS ON THEIR USE AS ELECTROSTATIC SURFACE POTENTIAL PROBES

Abstract

Abstract— The absorption spectra of the un‐ionized and ionized forms of 4‐heptadecyl‐7‐hydroxycoumarin (HHC) in aqueous self‐assembled surfactant solution have been investigated. From a comparison with the absorption spectra of 7‐hydroxycoumarin, 7‐hydroxy‐4‐methylcoumarin (MHC) and HHC in neat organic solvents and organic solvent/water mixtures it is shown that the 7‐hydroxycoumarin chromophore of HHC in self‐assembled surfactant solution resides, on average, in an interfacial microenvironment which has a lower effective dielectric constant than that of the bulk aqueous solution. The absorption spectrum of the ionized form of HHC in aggregates of self‐assembled surfactant molecules with cat..