Solubility of thioindigo dopants in a smectic liquid crystal host evaluated by 2H NMR spectroscopy |
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Authors: | Kenneth E Maly Gang Wu Robert P Lemieux |
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Institution: | Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6 |
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Abstract: | The solubility of two partially deuterated thioindigo dopants in a smectic liquid crystal host was evaluated by variable temperature 2H NMR spectroscopy and polarized microscopy. 2H NMR spectra showed that the dopant (±)-6,6'-bis(2-octyloxy)-5,5-dinitrothioindigo-d 6 forms a homogeneous solution with the smectic phases of the liquid crystal host (±)-4-(4-methylhexyloxy)phenyl 4-decyloxybenzoate (PhB) up to its saturation point of 3 mol %. These results are consistent with polarized microscopy observations of the dopant crystallizing out of solution upon reaching a concentration of 3 mol %. On the other hand, 2H NMR spectra of (±)-5,5'-dichloro-6,6'-bis(2-octyloxy)thioindigo-d 6 dissolved in PhB showed evidence of a partitioning of the solution between smectic and isotropic microdomains, which increases with increasing dopant concentration—from 1.2 to 9.1 mol %. To a large extent, this smectic/isotropic microphase separation could not be detected by polarized microscopy. These results suggest that 2H NMR spectroscopy can provide a more accurate determination of the occurrence and extent of microphase separation in doped liquid crystal samples. |
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