Orientational Order and Linear Dichroism of a Water Soluble Porphine in a Lyotropic Nematic Liquid Crystal

Aqueous lyotropic nematic liquid crystals can be homogeneously oriented by magnetic fields and are therefore well suited to be used as anisotropic solvents for optical polarization studies of water soluble dye molecules. The potassium laurate (KL)/KCl/H₂O nematic phase, composed of rod-like or cylindrical micelles, was used as a matrix for the study of orientational order and linear dichroism of a substituted free-base porphine (TPPS₄). The results indicate that a significant portion of porphine molecules are incorporated into the micelles with their planes on the average perpendicular to the optic axis of the lyotropic rods. The order parameter of TPPS₄ is much higher in this system than in other nematic lyophases such as KL/decanol/H₂O in which preferential hydrogen bonding occurs between TPPS₄ molecules and the hydroxyl groups of decanol molecules which presumably occupy the surface of the cylindrical micelles. All observed electronic transitions in the 350-700 nm range are found to be polarized in the plane of the porphine ring.