Aggregation behavior and chromonic liquid crystal phase of a dye derived from naphthalenecarboxylic acid.
Polarizing microscopy, X-ray scattering, and absorption spectroscopy are used to investigate the aggregation process and chromonic liquid crystal of the anionic compound Bordeaux dye, a product of the sulfonation of the dibenzimidazole derivative of naphthalenetetracarboxylic acid. Polarizing microscopy reveals that the liquid crystal phase forms at room temperature when the concentration is only about 6 wt%, a value lower than what is found in many aggregating systems. The X-ray results indicate that the aggregation is via columns, with a cross-sectional area about 2.5 times larger than the individual molecule. Absorption spectroscopy shows a significant change in the absorption spectrum due to aggregation, which is nicely explained by a simple theory of isodesmic aggregation and excitonic coupling between the molecules in an aggregate. The "stacking free energy change" for a molecule in an aggregate relative to a molecule in solution is estimated to be about 9 kBT, a larger value than that found in the one other system where it has been estimated.
Tomasik
Michelle R
MR
Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA.
Collings
Peter J
PJ
D002264:Carboxylic Acids / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D003460:Crystallization; D012542:Scattering, Radiation; D013057:Spectrum Analysis
D002264:Carboxylic Acids; D004396:Coloring Agents