Studies on the Molecular Arrangement in Liquid Crystals by Polarization of Fluorescence
Molecular arrangements in liquid crystals have been studied by the method of fluorescence polarization. Fluorescence molecules with a highly optical anisotropy, dispersed homogeneously in a liquid crystalline material are used as a probe to detect the molecular alignment in the liquid crystal« The angular distribution of the polarized components of the fluorescence gives useful information on the extent as well as the types of molecular orientation. Examples of the application of this method are given for the determination of the molecular arrangement in liquid crystals at the phase transitions from the isotropic liquid state through mesomorphic state to the crystalline state. The results obtained for the nematic state of para-n-octyloxybenzoic acid suggest that the molecules can be regarded as adopting almost perfect parallel alignment over regions much larger than the molecular dimensions. The observed angular distribution patterns of the polarized components of fluorescence can be well explained by assuming a molecular arrangement of uniaxial prolate ellipsoid for the nematic state. Discussion is briefly given to the angular distribution patterns for the smectic and crystalline states.
KeywordsLiquid Crystal Angular Distribution Molecular Orientation Fluorescent Molecule Electric Vector
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