Design and synthesis of suitable phototriggers for a chiroptical liquid crystal switch
Compounds with potential applications as phototriggers for a chiroptical liquid crystal switch were investigated via several approaches. Chiral exciton coupling theory was first used to design and synthesize a series of axially chiral arylmethylene cyclohexanes in both racemic and optically active forms for use as potential photoresolvable mesogens. It was found that these compounds have two spectrally overlapping chromophores which lead to enhanced circular dichroism. With appropriate substituents, some of them form liquid crystal phases. The photochemical and chiroptical properties of these compounds were studied to assess their suitability as phototriggers. It was found that the Kuhn anisotropy factor (g$\sb\lambda$) of these compound is too small for this application. By incorporating chromophores with electronic forbidden transitions (n$\pi\sp*$) into the design, two chiral bicyclo ketones, 3-phenylmethylenebicyclo (3.2.1) octane-8-one and 8-phenylmenthylenebicyclo (3.2.1) octan-3-one, were synthesized in racemic and optically active forms. Preliminary studies have shown the 8-phenylmethylenebicyclo (3.2.1) octan-3-one is the first photoresolvable bichromophoric molecule with a g$\sb\lambda$ value of 0.051. However, the low solubility of this compound in some nematic liquid crystals make it unsuitable for use as a liquid crystal based phototrigger.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign