Replacing the pH-sensitive carboxyl substituents of amphiphilic 5,5',6,6'-tetrachlorobenzimidacarbocyanine dyes by sulfonyl substituents promotes the formation of novel types of J-aggregates in aqueous solution. However, due to the dramatically reduced solubility of the examined 3,3'-bis(2-sulfoethyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimidacarboc yanine (abbreviated as C8S2), aggregation in water can only be triggered by predissolution of the dye in organic solvents (e.g., methanol), the addition of surfactant (SDS), or thermal treatment. Depending on the particular preparation method used, different aggregation behavior was observed by spectroscopic and microscopic studies. Effects of methanol were studied in detail. Below a methanol concentration of similar to3.5%, the absorption spectrum shows a 2-fold split J-band (type 11 spectrum) characteristic for tubular structures. Above similar to3.5%, the spectrum is characterized by a pronounced H-and a related narrow J-band (type I spectrum) as observed for molecular aggregates with two dye molecules per unit cell (Davydov splitting). Cryo-transmission electron microscopy (cryo-TEM) revealed tubules or stacks of bilayered ribbons as the prototypical morphologies at low and high methanol concentration, respectively. By changing the methanol content of the solutions, a transition between either structures could be induced. The extremely slow kinetics allows the observation of hybrid-aggregates combining the different structural motifs within one individual entity.