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Joonseok Koh – One of the best experts on this subject based on the ideXlab platform.

  • Synthesis and properties of some novel pyrAzolone-based heterocyclic Azo disperse dyes containing a fluorosulfonyl Group
    Dyes and Pigments, 2012
    Co-Authors: Ajay Singh, Ran Choi, Byunghun Choi, Joonseok Koh

    Abstract:

    A series of heteroarylAzo disperse dyes derived from pyrAzolones and fluorosulfonyl anilines were synthesized, and their thermal and spectral properties were investigated with respect to the effect of substituents on absorption spectra, halochromism, and solvatochromism. HeteroarylAzo disperse dyes, which contain a nitro Group instead of a fluorosulfonyl Group para to the Azo Group in the diAzo component, were also synthesized for comparative purpose. The fluorosulfonylarylAzopyrAzolone dyes had absorption maxima at shorter wavelength and showed lower extinction coefficients than the nitroarylAzopyrAzolone dyes. The synthesized dyes also exhibited positive halochromism and solvatochromism, so the absorption bands of the dyes moved toward longer wavelengths as the acidity or polarity of the solvent increased. 4-Fluorosulfonyl-substituted dyes generally showed lower thermal stability than their 4-nitro-substituted analogs, because the lower electron-withdrawing power in the diAzo components tended to decrease the polarizability and dipole interactions. © 2012 Elsevier Ltd. All rights reserved.

  • Alkali-clearable disperse dyeing of poly(ethyleneterephthalate) with Azohydroxypyridone dyes containing a fluorosulfonyl Group
    Dyes and Pigments, 2006
    Co-Authors: Joonseok Koh

    Abstract:

    Dyeing properties of a series of alkali-clearable Azohydroxypyridone disperse dyes containing a fluorosulfonyl Group on poly(ethyleneterephthalate) have been investigated. The dyes showed reasonably good build-up properties and had a yellow shade on PET. The dyes exhibited excellent fastness properties on PET fabric, irrespective of the clearing method. Specially, the Azohydroxypyridone dyes containing a nitro Group in place of the fluorosulfonyl Group in the para position to Azo Group were synthesised in order to compare their dyeing and fastness properties on poly(ethyleneterephthalate) with those of fluorosulfonyl-substituted analogues. ?? 2005 Elsevier Ltd. All rights reserved.

Byunghun Choi – One of the best experts on this subject based on the ideXlab platform.

  • synthesis and properties of some novel pyrAzolone based heterocyclic Azo disperse dyes containing a fluorosulfonyl Group
    Dyes and Pigments, 2012
    Co-Authors: Ajay Vikram Singh, Ran Choi, Byunghun Choi

    Abstract:

    A series of heteroarylAzo disperse dyes derived from pyrAzolones and fluorosulfonyl anilines were synthesized, and their thermal and spectral properties were investigated with respect to the effect of substituents on absorption spectra, halochromism, and solvatochromism. HeteroarylAzo disperse dyes, which contain a nitro Group instead of a fluorosulfonyl Group para to the Azo Group in the diAzo component, were also synthesized for comparative purpose. The fluorosulfonylarylAzopyrAzolone dyes had absorption maxima at shorter wavelength and showed lower extinction coefficients than the nitroarylAzopyrAzolone dyes. The synthesized dyes also exhibited positive halochromism and solvatochromism, so the absorption bands of the dyes moved toward longer wavelengths as the acidity or polarity of the solvent increased. 4-Fluorosulfonyl-substituted dyes generally showed lower thermal stability than their 4-nitro-substituted analogs, because the lower electron-withdrawing power in the diAzo components tended to decrease the polarizability and dipole interactions.

  • Synthesis and properties of some novel pyrAzolone-based heterocyclic Azo disperse dyes containing a fluorosulfonyl Group
    Dyes and Pigments, 2012
    Co-Authors: Ajay Singh, Ran Choi, Byunghun Choi, Joonseok Koh

    Abstract:

    A series of heteroarylAzo disperse dyes derived from pyrAzolones and fluorosulfonyl anilines were synthesized, and their thermal and spectral properties were investigated with respect to the effect of substituents on absorption spectra, halochromism, and solvatochromism. HeteroarylAzo disperse dyes, which contain a nitro Group instead of a fluorosulfonyl Group para to the Azo Group in the diAzo component, were also synthesized for comparative purpose. The fluorosulfonylarylAzopyrAzolone dyes had absorption maxima at shorter wavelength and showed lower extinction coefficients than the nitroarylAzopyrAzolone dyes. The synthesized dyes also exhibited positive halochromism and solvatochromism, so the absorption bands of the dyes moved toward longer wavelengths as the acidity or polarity of the solvent increased. 4-Fluorosulfonyl-substituted dyes generally showed lower thermal stability than their 4-nitro-substituted analogs, because the lower electron-withdrawing power in the diAzo components tended to decrease the polarizability and dipole interactions. © 2012 Elsevier Ltd. All rights reserved.

Milada Glogarova – One of the best experts on this subject based on the ideXlab platform.

  • the effect of lactate unit number in compounds with Azo Group in the molecular core
    Liquid Crystals, 2011
    Co-Authors: Vladimira Novotna, Miroslav Kaspar, Milada Glogarova, Alexej Bubnov, Vera Hamplova, Natalia Podoliak, Dorothee Nonnenmacher, Frank Giesselmann

    Abstract:

    A liquid crystalline compound with the Azo Group in the molecular core and three lactic acid units in the chiral chain (n = 3) was synthesised and its mesomorphic properties established. Spontaneous polarisation and tilt angle were determined in the ferroelectric and antiferroelectric smectic C phases. Dielectric spectroscopy in the frequency range of 1 Hz–10 MHz was performed within the temperature range of smectic phases showing the characteristic modes in each phase. Small-angle X-ray diffraction was performed and temperature dependences of layer spacing value calculated. Comparison with previously studied compounds with one (n = 1) and two lactate units (n = 2) is presented to establish the effect of lactate unit number on the liquid crystalline properties.

  • antiferroelectric phase in liquid crystalline compounds containing an Azo Group in their molecular core
    Liquid Crystals, 2011
    Co-Authors: Miroslav Kaspar, Vera Hamplova, Vladimira Novotna, Natalia Podoliak, Dorothee Nonnenmacher, Frank Giesselmann, Milada Glogarova

    Abstract:

    Novel lactic acid derivatives containing an Azo Group in their molecular core have been synthesised and their mesomorphic properties established. Compounds with a short aliphatic non-chiral chain exhibited the SmA* phase and ferroelectric (FE) SmC* phase. The monotropic antiferroelectric (AF) phase was found in the homologues with a longer terminal chain. Spontaneous polarisation and tilt angle were measured for the FE and AF phases. Dielectric spectroscopy in the frequency range 1 Hz–10 MHz was carried out and dielectric properties established within the temperature range of the smectic phases. Two high frequency modes were detected in the AF phase. Small-angle X-ray measurements were conducted, and the temperature dependence of layer spacing values is established and discussed.

  • new ferroelectric liquid crystalline materials with an Azo Group in the molecular core
    Liquid Crystals, 2004
    Co-Authors: Miroslav Kaspar, Alexej Bubnov, Vera Hamplova, Slavomir Pirkl, Milada Glogarova

    Abstract:

    Six series of new liquid crystalline materials with an Azo Group (N=N) located in different parts of the mesogenic core of the molecule have been synthesized and their physical properties studied. The chiral segments of these materials are based on alkoxypropionate or alkyllactate units. It has been found that lateral methyl substitution on a phenyl ring in the molecular core disturbs the packing of the molecules. As a result smectic phases disappear and the phase transition temperatures decrease. In addition, shifting the N=N Group closer to the chiral centre of the molecule leads to the disappearance of the ferroelectric SmC* phase. For the compounds which show the ferroelectric SmC* phase, the temperature dependence of the spontaneous polarization, the spontaneous tilt angle, the helix pitch length and the complex permittivity has been studied. The effect of shifting the Azo Group in the molecular core on the physical properties is discussed.