Aggregation Behavior and Chromonic Liquid Crystal Phase of a Dye Derived from Naphthalenecarboxylic Acid

摘要

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 k_BT,a larger value than that found in the one other system where it has been estimated.