Ae. Asato et al., The use of prochiral centers for demonstrating asymmetric stacking in aggregates of azulenylazulenium cyanine dyes, ORG LETT, 2(17), 2000, pp. 2559-2562
The diastereotopic methyl signals detected at low temperatures or high conc
entrations of an azulenylazulenium salt containing prochiral centers are co
nsistent only with a model involving monomers in rapid equilibration with d
imers in the staggered ("brickwork") arrangement and not in the "card-stack
ed" arrangement.