Specific interactions between dye cations in premicellar aggregates as revealed by electric dichroism measurements

Abstract

The electronic absorption and electric dichroism spectra are compared between an SDS solution containing one kind of cationic dye ( D + SDS ) and an SDS solution containing two kinds of cationic dyes (D 1 +/D 2 +/SDS). Here D 1 + and D 2 + are chosen from acridine orange cation (AOH +), N-nonylacridine orange cation (AO +(CH 2) 9H) and thionine cation (Th +). At the investigated SDS concentration (≈5 × 10 −5 M), the aggregate of a 1:1 dye-SDS ion pair is formed, which remains stable in a solution for several hours. In any of the three cases studied, the absorbance and dichroism amplitude for D 1 +/D 2 +/SDS are not expressed by the sum of the ones for D 1 + SDS and D 2 + SDS . The results indicate that the coexistence of two kinds of dyes in the same aggregate induces the rearrangement and orientational change of dye-SDS pairs.