Formation of J-aggregates of cyanine dyes in bilayer lipid vesicles

The absorption behavior of cyanine dyes in lipid vesicles prepared from egg lecithin and synthetic dipalmitoylphosphatidylcholine was studied. The molecules of the cyanine dyes are readily redistributed between the vesicles with the characteristic time of several minutes and form J-aggregates when the average number of monomeric dye molecules exceeds 3.2 per vesicle, far below the most common minimum aggregation number, which is between 20 and 50, for cyanine dyes in J-aggregates. The formation of J-aggregates was followed spectroscopically by the appearance of a narrow red-shifted band.