High-Order Aggregation of Crystal Violet in the Chromonic Lyotropic Mesophases of 7,7′-Disodiumchromoglycate

Abstract

Electronic absorption spectra of Methylene Blue (MB), Crystal Violet (CV), and Ponseau BS (PBS) have been measured in the host of the 7,7′-disodiumchromoglycate (7,7′-DSCG)-water system. In the chromonic mesophases of the 7,7′-DSCG-water system, the metachromasy bands of MB (rod-like cationic guest) is weakened compared with that in water, that of CV (disk-like cationic guest) largely blue-shifted up to 504 nm, and that of PBS (anionic guest) was unchanged. This observation indicates that the association behavior of a guest in these phases depends on the shape and polarity of the guest. The large blue shift observed for CV indicates that the CV molecules are forced to associate in the chromonic lyotropic mesophases of 7,7′-DSCG forming an aggregate with a high aggregation order. A possible mechanism of this high-order aggregation of CV in these mesophases is proposed; a hollow formed by the columns of the stacked 7,7′-DSCG molecules incorporates such a cationic disk-like guest as CV by a cooperative action of the electrostatic force causing a binding of guest molecules to the anionic sites on the surface of the hollow and the dispersion force causing formation of sandwich aggregates of guest molecules.

Key Words:

• aggregation
• crystal violet
• chromonic mesophase
• lyotropic liquid crystal
• disodiumchromoglycate