Browsing by Author "Maeta, Nobuyuki"

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Liquid crystalline non-linear S-shaped oligomers consisting of azobenzene and biphenylene units: synthesis, characterisation and influence of central spacer
(2017-01-01)
Osman, Faridah
;
Yeap, Guan-Yeow
;
Maeta, Nobuyuki
;
Ito, Masato M.
;
Lin, Chien-Min
A series of non-linear S-shaped liquid crystal oligomers wherein the molecule consists of biphenylene moiety as a central core unit and two symmetrical side arms azobenzene moieties joined to catechol as a linkage group have been successfully synthesised and characterised. The members in this series possess different inner spacer with carbon number n ranging from 4 to 9 while the outer spacer length located in azobenzene moieties are remains unaltered. The members with even parity exhibit monotropic phase, whereas homologues with odd parity display enantiotropic phase. The appearance of nematic, smectic A and smectic B phases was validated with texture observation under polarised light and X-ray diffraction (XRD). The XRD study on the S-shaped oligomer indicates that the arrangement of smectic phase exists as an intercalated structure. The S-shaped oligomer shows photoisomerisation properties in solution whereby the trans to cis isomerisation for this molecule is accomplished 1140 s, whereas reverse process under thermal back reaction occurred in 4620 min. [GRAPHICS] .
Phase transitional behaviour of S-shaped oligomers incorporating biphenylene and cholesterol entities
(2017-01-01)
Osman, Faridah
;
Yeap, Guan-Yeow
;
Maeta, Nobuyuki
;
Ito, Masato M.
;
Lin, Chien-Ming
A new series of symmetrical S-shaped oligomers 4,4'-bis[(5-cholesteryloxycarbonylpentyl alkoxy)hexyloxy]biphenyl consisting of outer spacers -(COCH2)(n)- as well as an inner spacer -(CH2)(6)- has been synthesised. Their liquid crystalline properties and phase transition temperatures with associated enthalpy changes are recorded. The outer spacers are varied from n=5-8 to 10 and 11. The compounds with even spacer exhibit enantiotropic phase and oligomers with odd parity display monotropic phase. The oligomers with odd membered n=5, 7 and 11 exhibit N* and SmC* phases upon cooling. Whilst upon heating, the homologues with even-numbered member n=6 and 10 show N* phase and upon cooling, both compounds exhibit N* and SmC* phases. However, oligomer with outer spacer n=8 displays enantiotropic N* and SmC* phases. The temperature range of N* phase for even and odd membered decreased as the outer spacers are increased. The odd-even effect has been found in the I-N* transition temperatures where the odd-parity oligomers exhibit lower values when compared to compounds of an even-parity series. The X-ray diffraction measurements reveal the appearance of SmC* phase that can be associated with the monolayer ordering of these oligomers.
Synthesis and liquid crystalline studies of disc-shaped molecule on azo-bridged benzothiazole-phenyl ethers
(2016-11)
Yeap, Guan-Yeow
;
Rahim, Mursyida Abdul
;
Lin, Chien-Min
;
Lin, Hong-Cheu
;
Maeta, Nobuyuki
A new series of triphenylene core attached by six peripheral arms containing benzothiazole-azo with terminal ethoxy unit have successfully been synthesized and their liquid crystalline properties were characterized. The members in this series differ by the length of the methylene unit of-(CH2)(n)-, where n, varied following ascending order from 5 to 10. The molecular structure was characterized by elemental (C, H and N) analysis and spectroscopic methods including Fourier Transform Infrared (FT-IR) and Proton Nuclear Magnetic Resonance (H-1 NMR). The texture and the phase transition temperatures were investigated by using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The disc-shape molecule with shorter spacer (n = 5) showed monotropic nematic phase. The higher homologues with n = 8-10 exhibited enantiotropic nematic phase and monotropic smectic C phase. The XRD diffraction studies further confirm the presence of smectic C without any discotic columnar phase. (C) 2016 Published by Elsevier B.V.
Unveiling the influence of inner spacer length of the non-linear S-shaped chiral oligomers on liquid crystalline phase
(2017-06-01)
Yeap, Guan-Yeow
;
Osman, Faridah
;
Maeta, Nobuyuki
;
Ito, Masato M.
;
Lin, Chien-Min
A series of S-shaped liquid crystal oligomers consisting of biphenylene, catechol and cholesterol moieties have been synthesized and characterized. The members in this series differ by the length of inner spacers -(CH2)(n)-where n are varied from 4 to 9 whereas the outer spacer of undecanoate chain is remained intact. The texture and phase transition temperatures with associated enthalpy changes are recorded. Increase in the number of carbon atom at the inner spacer affects the stability of liquid crystalline phase. The homologues with shorter inner spacers n = 4 and 5 exhibit monotropic N* whilst the analogue with medium spacer n = 6 exhibits monotropic N* and SmC* phase. However, the oligomers with longer spacers n = 7, 8 and 9 exhibit enantiotropic N* and SmC* phase. The I -N* transition temperatures were found to depend on the parity of the inner spacers. An Xray diffraction study reveals that the S-shaped oligomers exist as a monolayer chiral smectic C phase. (C) 2017 Elsevier B.V. All rights reserved.