Synthesis of New Chiral Dopants Derived from 2-Phenylpropanoic Acid Derivatives for Nematic Liquid Crystals

Bulletin of the Chemical Society of Japan (Impact Factor: 2.22). 01/2001; 74(11):2219-2222. DOI: 10.1246/bcsj.74.2219
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    ABSTRACT: Until recently, it has not been possible to determine, with any real certainty, a complete picture of "chirality" (absolute configuration, optical rotation direction, and helical twisting power) for new chiral compounds without first synthesizing, purifying, characterizing, and testing every new material. Recent advances in computational chemistry now allow the prediction of certain key chiral molecular properties prior to synthesis, which opens the possibility of predetermining the "chiroptical" properties of new liquid crystal dopants and mixtures for advanced optical and photonics applications. A key element to this activity was the development of both the chirality index (G 0) by Osipov et al. , and the scaled chirality index (G 0S ) by Solymosi et al. , that can be used as a "figure of merit" for molecular chirality. Promising correlations between G 0S and both circular dichroism (CD) and the helical twisting power (HTP) of a chiral dopant in a liquid crystal host have been shown by Neal et al. , Osipov, and Kuball. Our work improves the predictive capabilities of G 0S by taking into account the actual mass of each atom in the molecule in the calculations; in previous studies the mass of each atom was assumed to be equal. This "weighted" scaled chirality index (G 0SW ) was calculated and correlated to existing experimental HTP data for each member of a series of existing, well-known chiral compounds. The computed HTP using G 0SW for these model systems correlated to the experimental data with remarkable accuracy. Weighted, scaled chiral indices were also calculated for the first time for a series of novel chiral transition metal dithiolene dyes for near-IR liquid crystal device applications.
    Optics & Photonics 2005; 08/2005
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    ABSTRACT: New chiral derivatives of thiophene fused with menthane, camphor or the 3R-3-methylcyclohexane ring were prepared and studied as chiral dopants in cholesteric liquid crystalline mixtures. The helical twisting power of the most effective compounds of this series, menthothiophenes, was strong enough to obtain selective reflection of visible light at 16 wt% concentration of the dopant in a non-chiral nematic host.
    Liquid Crystals 11/2012; 39(11):1-10. DOI:10.1080/02678292.2012.716459 · 2.35 Impact Factor
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    ABSTRACT: Numerous commercial and military applications exist for guest–host liquid crystal (LC) devices operating in the near- to mid-IR region. Progress in this area has been hindered by the severe lack of near-IR dyes with good solubility in the LC host, low impact on the inherent order of the LC phase, good thermal and chemical stability, and a large absorbance maximum tunable by structural modification over a broad range of the near-IR region. Transition metal complexes based on nickel, palladium, or platinum dithiolene cores show substantial promise in meeting these requirements. These new dye complexes are extraordinarily stable, possess liquid crystalline phases in their own right with the proper terminal functional groups, and can have melting points below room temperature. The latter property is especially significant for producing liquid crystal/dye mixtures with both high dye concentration and good resistance to phase separation. Because transition metal dithiolenes are zerovalent, they can exhibit high solubility in LC hosts (up to 10 wt%). The λmax in these materials can range from 600 to 1500 nm, depending on structure. Depending on their overall molecular geometry and the choice of terminal functional groups, transition metal dithiolenes that show either positive or negative dichroism from the same basic core structure can be readily synthesized. When enantiomerically enriched terminal substituents are employed, nickel dithiolenes can induce a chiral mesophase in a nonchiral nematic host. This finding opens the possibility of generating novel LC mixtures with two degrees of tunability—an electronic absorbance band tunable by synthesis, and a selective reflection band tunable by temperature or applied electric field.
    Molecular Crystals and Liquid Crystals 09/2006; 454(1):47/[449]-79/[481]. DOI:10.1080/15421400600654124 · 0.49 Impact Factor