Details

Autor(en) / Beteiligte

• von Berlepsch, Hans
• Kirstein, Stefan
• Böttcher, Christoph

Titel

Supramolecular Structure of J-Aggregates of a Sulfonate Substituted Amphiphilic Carbocyanine Dye in Solution:  Methanol-Induced Ribbon-to-Tubule Transformation

Ist Teil von

• The journal of physical chemistry. B, 2004-12, Vol.108 (48), p.18725-18733

Ort / Verlag

American Chemical Society

Erscheinungsjahr

2004

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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‘-dioctylbenzimidacarbocyanine (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 ∼3.5%, the absorption spectrum shows a 2-fold split J-band (type II spectrum) characteristic for tubular structures. Above ∼3.5%, 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.