Surfactant-Induced Separation of Stacked J-Aggregates. Cryo-Transmission Electron Microscopy Studies Reveal Bilayer Ribbons

The effect of the ionic surfactants sodium dodecyl sulfate (SDS) and trimethyltetradecylammonium bromide (TTAB) on the morphology of the J -aggregate of the 5,5‘,6,6‘-tetrachloro-1,1‘-dioctyl-3,3‘-bis(4-carboxybutyl)benzimidacarbocyanine dye (C 8 O 4 ) was investigated by absorption spectroscopy, electron microscopy of vitrified samples (cryo-TEM), scanning force microscopy, and optical microscopy. The spectral changes upon adding the surfactants were small, whereas marked morphological changes of the recently characterized J -aggregates (von Berlepsch et al. J. Phys. Chem . B 2000, 104, 5255) occurred. In aqueous sodium hydroxide solution, the dye molecules form stacks of bilayer ribbons, which completely separate into single bilayer ribbons upon addition of surfactants. The solutions of dispersed single ribbons, of about 200 nm width in the case of SDS/C 8 O 4 mixtures, remain stable for weeks. For TTAB/C 8 O 4 mixtures, aggregation leads to precipitation and eventually to the formation of needlelike microcrystals.