1. Some dye molecules in solution naturally aggregate, and if the aggregates are anisotropic and concentrated, they order into a liquid crystal phase. Isodesmic aggregation is the leading candidate for this process, i.e., the free energy change for a molecule to join an aggregate is independent of aggregate size. Such a process does not possess a critical aggregation temperature. Most systems do not show such a critical temperature (e.g., Bordeaux Dye), but light scattering and magnetic birefringence measurements reveal that such a critical temperature exists in one system (Cromolyn).
Aggregating dyes show a change in the absorption spectrum due to aggregation, but in most cases the peaks overlap to such a great extent that the process cannot be monitored. The infrared absorbing due IR-806 is different, in that the two peaks corresponding to single molecules and aggregates can be resolved. This allows for the aggregation to be followed quantitatively, revealing details not obtainable in other systems.