AGGREGATION OF PERYLENE DYES IN LIPID VESICLES - THE EFFECT OF OPTICALLY-ACTIVE SUBSTITUENTS

Different optically active and inactive derivatives of the perylene dy e, perylene-3,4:9,10-tetracarboxylic bisimide, solubilized in unilamel lar lipid vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) have been studied by means of polarized light spectroscopic methods. A bsorption and fluorescence spectra become distorted at molar ratios gr eater than one dye molecule per 1000 molecules of DOPC. These observat ions are compatible with the formation of ground-state aggregates. Cir cular dichroism (CD) was not detectable for any perylene dye dissolved in liquid solutions, or diluted in lipid vesicles. However, dyes with optically active substituents reveal CD spectra at dye:lipid ratios o f greater than 1:1000. For dyes with R and S enantiomers, CD spectra a re mirror images, while no CD of racemic mixtures, or optically inacti ve perylene dyes could be detected. The observed absorption and CD spe ctra are qualitatively explained by exciton coupling within dimers and their molecular symmetry.