The Use of Prochiral Centers for Demonstrating Asymmetric Stacking in Aggregates of Azulenylazulenium Cyanine Dyes

[structure: see text]The diastereotopic methyl signals detected at low temperatures or high concentrations of an azulenylazulenium salt containing prochiral centers are consistent only with a model involving monomers in rapid equilibration with dimers in the staggered ("brickwork") arrangement and not in the "card-stacked" arrangement.