DETERMINATION OF MICROVISCOSITY AND MICROPOLARITY OF LYOMESOPHASES UTILIZING A FLUORESCENT-PROBE

The excimer to monomer emission intensity ratio (E/M) of an intramolecular excimer-forming probe, l,3-bis(l-pyrenyl)propane (DPyP), has been studied in dilute solutions as well as lyomesophases of potassium laurate (KL), sodium decyl sulfate (SDecS), and myristyltrimethylammonium bromide (MTAB). E/Ms in the mesophases are much lower than in dilute solution due to the combined effects of viscosity, orientational order, and specific host-guest interactions. The phase transitions from the disk-like Nl phase to the rod-like Nc phase to the isotropic phase are each accompanied by increases in this ratio. Microviscosities of MTAB, SDecS, and KL are approximately 120, 70, and 60 cP, respectively. The extent of vibrational structure in the monomer emission of DPyP is sensitive to polarity, so DPyP provides a simultaneous measure of both micropolarity and microviscosity. © 1990, American Chemical Society. All rights reserved.