Browsing by Author "Takeuchi, Daisuke"

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Alkyl chain self ordering, induction and suppression of mesophase by Cu(II) containing [1,2,3]-triazole-based bidentate salicylaldimine ligands: synthesis, characterisation and X-ray diffraction studies
(2014-12-02)
Heng, Boon-Teck
;
Yeap, Guan-Yeow
;
Mahmood, Wan Ahmad Kamil
;
Han, Chun-Chieh
;
Lin, Hong-Cheu
Some new Cu(II) complexes containing [1,2,3]-triazole-based bidentate salicylaldimine and its analogues with terminal substituent (F, Cl, Br and I) have been synthesieed. All the target complexes and their uncoordinated ligands were elucidated by elemental analysis and spectroscopic techniques (UV-visible, FT-IR, 1D, 2D H-1 and C-13-NMR). The polarising optical microscope and differential scanning calorimetry (DSC) have disclosed all complexes and ligands are mesomorphic except the complex without any terminal substituent. The fluoro-substituted complexes with even parity C14H29 and C16H33 exhibit new enantiotropic nematic phase which was absent in their corresponding ligands, whereas the suppression of SmC phase occurred for all complexes with longer C16H33 and C18H37. X-ray diffraction confirmed the existence of SmA, SmC and N phases for complexes and ligands. The other notable feature is that the self-ordering of terminal alkyl chain occurred in SmA and SmC phases of complexes with even terminal alkyl chain ranging from C14H29 to C18H33. Their corresponding ligands exhibit intercalated structure of SmA and SmC phases. The thermal behaviour studies show that the fluoro-substituted triazole-based complexes possess lowest phase transition temperature and more stable as compared to other substituent which decomposed during the isotropisation.
Influence of terminal substituent on non-linear S-shaped oligomers consisting of azobenzene moieties at the peripheral arm: Synthesis, characterisation and phase transition behaviour
(2017-01-01)
Yeap, Guan-Yeow
;
Osman, Faridah
;
Ito, Keisuke
;
Takeuchi, Daisuke
;
Lin, Chien-Min
A series of symmetrical S-shaped mesogens based on 4,4-bis-(6-bromohexyloxy)biphenyl as a central unit containing two 2-{6-[4-(4-substitutedphenylazo)phenoxy]hexyloxy}phenol as side-chain groups has been successfully synthesised. The terminal substituent was varied from halogen (X=F, Cl, Br and I) to non-halogen (X=C2H5 and OC2H5). The oligomers with C2H5 and OC2H5 substituents exhibit predominantly the monotropic nematic (N) phase. The OC2H5-containing derivatives possess long-range stability of N phase than its C2H5-containing analogue in which it has small range of N phase stability. As for halogen-containing analogues, oligomer with F exhibits monotropic N phase whilst oligomers with Cl and Br exhibit monotropic N and smectic A (SmA) phases. In addition, homologue with Br shows additional phase which is smectic B (SmB) phase upon further cooling. However, the oligomers in which F, Cl and Br were substituted by I exhibits purely monotropic SmA and SmB phases. X-ray diffraction measurements reveal that the smectic phase is inclined to the monolayer structure.
Non-symmetrical liquid crystal dimers armed with azobenzene and 1,2,3-triazole-cholesterol
(2015-09-02)
Alshargabi, Arwa
;
Yeap, Guan-Yeow
;
Mahmood, Wan Ahmad Kamil
;
Han, Chun-Chieh
;
Lin, Hon-Cheu
New non-symmetrical dimers which contain respective side units of azobenzene and 1,2,3-triazole-choloesteral have been synthesised from the reaction between 6-azido-[4-(4-acetylphenylazo)phenoxy]alkane and cholesteryl-4-(prop-2-ynyloxy)benzoate. The results show that the derivatives of 6-bromo[4-(4-acetylphenylazo)phenoxy]alkanes which possess the odd alkyl spacers exhibit dimesomorphism of N and SmA phases whilst the members with even numbers are non-mesogenic. However, the 6-azido-[4-(4-acetylphenylazo)phenoxy]-alkanes show N and SmA phases in a wide temperature range. On heating and cooling the target compounds cholesteryl 4-[(1-(6-(4-(4\'-acetylphenylazo)phenoxy)alkyl)-1H-1,2,3-triazol-4-yl)methoxy]benzoate show chiral nematic (oily streak and fan-shaped texture) and focal conic texture characteristics of smectic A phases with high thermal stability. Present investigation also reveals the effect of the spacer length upon the phase transition temperature. Intercalated arrangement is favoured by the molecules in the smectic phase. The observation is well established by XRD measurement wherein the actual molecular length is smaller than the theoretical value.