Browsing by Author "Ito, Masato M."

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Liquid crystal dimers containing Cholesteryl and Triazole-containing mesogenic units
(1970-01-01)
Al-shargabi, Arwa
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Yeap, Guan-Yeow
;
Mahmood, Wan Ahmad Kamil
;
Han, Chun-Chieh
;
Lin, Hong-Cheu
New liquid crystals categorised as cholesteryl dimers have been successfully synthesised through the reaction between cholesteryl 4-(prop-2-ynyloxy)benzoate moieties with n-azido(cholesteryloxy-carbonyl)alkane. All the dimers display enantiotropic mesophases. Whilst the odd-numbered dimers exhibit chiral nematic (N*), twisted grain boundary (TGB) and chiral smectic C (SmC*) phases, the even-numbered members from the same series show chiral smectic A and C. A detailed inspection on mesophase reveals that the chiral centres and the bent conformation of the odd-numbered members are essential for the induction of TGB phase. However, upon decreasing the temperature, the ratio of the transition temperatures (TSmC*-SmA*/TSmA*-I) is found to be 0.95, which indicate the second order transition according to the McMillan's molecular theory. In addition, the X-ray diffraction study supports the presence of the smectic A phase on the even members rather than the N* by the appearance of the Bragg diffraction peaks at 190 degrees C. A comparison study with the other analogues in which the cholesterol entity is substituted by azobenzene or biphenyl tails has been carried out to assess the relationship between the molecular structure and mesomorphic behaviour. [GRAPHICS] .
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
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Yeap, Guan-Yeow
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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] .
Mesogenic Schiff Base with Bromo End Group: Synthesis and Thermotropic Properties
(2012-08-01)
Ha, Sie-Tiong
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Lee, Teck-Leong
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Lin, Hong-Cheu
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Ito, Masato M.
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Abe, Kazuma
A new homologous series of Schiff base esters comprising a terminal bromo substituent was studied. The bromo substituent contributes to the molecular polarizability, thus, affecting intermolecular interactions, hence, resulting in smectic polymorphism. The mesomorphic properties were studied using differential scanning calorimeter and polarizing optical microscope attached to a Linkam hotstage. Whilst the lower members, n-ethanoyloxy and n-butanoyloxy derivatives were non-mesogens, n-hexanoyloxy member exhibited monotropic (less stable) smectic A and smectic B phases. Further lengthening of the alkanoyloxy chain from C8 to C12 (medium members), led to formation of enantiotropic (more stable) smectic A and smectic B mesophases based on the observation of both phases during heating and cooling cycles. The high members of the series, C14, C16 and C18 exhibited enantiotropic smectic A phase and monotropic smectic B phase. The homologous members were compared with structurally related series to establish their chemical structure-mesomorphic behaviour relationships.
Mesomorphic behavior of new benzothiazole liquid crystals having Schiff base linker and terminal methyl group
(2012-07-01)
Ha, Sie Tiong
;
Foo, Kok Leei
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Lin, Hong Cheu
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Ito, Masato M.
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Abe, Kazuma
"A homologous series of heterocycles, 6-methyl-2-(4-alkoxybenzylidenamino)benzothiazoles, were synthesized and characterized using FT-IR, H-1 and C-13 NMR and mass spectrometric analysis. Enantiotropic nematic phase was observed for shorter members. Smectic A phase only emerged from octyloxy derivative onwards. The terminal methyl group at the benzothiazole fragment and the Schiff base linkage influenced the mesomorphic behavior of the present series. (C) 2012 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved."
Non-conventional three-armed star-shaped mesogens based on 1,3,5-trisubstituted benzene with azobenzene moieties at the periphery: synthesis, and mesomorphic behaviour
(2014-07-03)
Ooi, Yew-Hong
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Yeap, Guan-Yeow
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Han, Chun-Chieh
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Lin, Hong-Cheu
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Shinomiya, Teruo
A series of new symmetrical trimeric star-shaped mesogens in which the molecular architecture composed of three 4-[(4-substituted-phenyl)diazenyl]phenoxy-6-bromohexane connected as the pheripheral units to 1,3,5-positions of the benzene core group have been synthesised and fully characterised by physical measurements and spectroscopic techniques (carbon, hydrogen and nitrogen microanalysis, Fourier transform-infrared spectroscopy and nuclear magnetic resonance: CHN, FT-IR and NMR). At one end of the para-position of the azobenzene fragment consists of different terminal substituents X=F, Cl, Br, I, C2H5 and OC2H5. The thermal behaviour and mesomorphic properties of the star-shaped compounds were investigated by means of differential scanning calorimetry, polarizing optical microscopy (POM) and X-ray diffraction analyses. Moreover, the liquid-crystalline properties of all the intermediates 4-[(4-substituted-phenyl)diazenyl]phenoxy-6-bromohexane were also evaluated. Whilst all the star-shaped compounds exhibit nematic and smectic A phases, the mesogens with chloro- and bromo-terminal substituents were found to show soft crystalline phase. The smectic phase and the possible molecular arrangement of the star-shaped molecule within the anisotropic region were further substantiated by the XRD. In addition to a low-angle sharp peak (reflecting the layered structure), a diffuse wide-angle peak indicating the liquid-like order within the smectic layer was recorded. A comparative study between the properties of the present azo mesogens and the earlier reported star-shaped mesogens from Schiff bases is also discussed.
Phase transitional behaviour of S-shaped oligomers incorporating biphenylene and cholesterol entities
(2017-01-01)
Osman, Faridah
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Yeap, Guan-Yeow
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Maeta, Nobuyuki
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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
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Rahim, Mursyida Abdul
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Lin, Chien-Min
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Lin, Hong-Cheu
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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.
Synthesis and Mesomorphic Properties of 4-(Methylthio)benzylidene-4 '-n-alkanoyloxyanilines
(2011-10-01)
Ha, Sie-Tiong
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Lee, Teck-Leong
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Yeap, Guan-Yeow
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Lin, Hong-Cheu
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Ito, Masato M.
A homologous series of Schiff base esters, 4-(methylthio)benzylidene-4'-n-alkanoyloxyanilines possessing even number of carbon atoms at the alkanoyloxy chain (C(n-1)H(2n-1)COO, n = 2 to 18) was synthesized. The structure of the 4-(methylthio)benzylidene-4'-n-alkanoyloxyanilines was confirmed by elemental analysis and spectroscopic techniques including FT-IR, (1)H and (13)C NMR and EI-MS. Mesomorphic properties were evaluated by differential scanning calorimetry and polarizing optical microscopy techniques. Whilst n-butanoyloxy to n-octanoyloxy derivatives exhibited monotropic nematic phase, n-ethanoyloxy and n-decanoyloxy to n-octadecanoyloxy derivatives were non-mesogenic compounds. The mesomorphic properties of the present series were compared with other structurally related series to establish the chemical structure-mesomorphic property relationship.
Synthesis and smectogenic properties of novel phloroglucinol-based star-shaped liquid crystals containing three peripheral alkyloxylated Schiff base arms
(2013-04-01)
Ooi, Yew-Hong
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Yeap, Guan-Yeow
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Han, Chun-Chieh
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Lin, Hong-Cheu
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Kubo, Kenji
A series of symmetrical trimeric liquid crystalline compounds of which the molecular structure with a central core of 1,3,5-benzene attached by three rod-like mesogenic Schiff base moieties via the propylene spacers and ether linkages has successfully been synthesised and characterised by infra red and nuclear magnetic resonance spectroscopic techniques. All the star-shaped compounds in this series exhibit predominantly SmC phase except the analogue possessing terminal C8H17 group. It is apparent that the members with even parity from C10H21 to C16H33 show enantiotropic SmC phase while the member with longest terminal chain of C18H37 is inclined to monotropic smectogen. The X-ray diffraction measurements reveal that the tilted smectic layer structures of the SmC phase are confirmed to have an obvious sharp peak at small angles of 2 approximate to 1.03 degrees 1.48 degrees with d-spacing values of 4.014.58 nm, which are corresponding to tilt angles of approximate to 48 degrees in the SmC phase.
Synthesis, characterization and molecular organization for induced smectic phase of triazole ring in non- symmetric liquid crystalline dimer
(2015-06-10)
Yeap, Guan-Yeow
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Alshargabi, Arwa
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Mahmood, Wan Ahmad Kamil
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Han, Chun-Chieh
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Lin, Hong-Cheu
New non-symmetric liquid crystal dimers containing cholesterol, triazole and biphenylene segments have been synthesized via click reaction. Increase in the flexible spacers length affects the mesophase formation. The homologues with short and medium alkyl spacer exhibit SmA* and SmC* phases whilst the analogue with the longest spacer favors the formation of enantiotropic SmA and N* phases. The XRD studies reveal the emergence of the SmA* and SmC* phases that can be associated with the monolayer ordering of these dimers. Further investigation through a comparison study shows that the triazole ring affects the mesophase formation wherein apart from the molecular dipole the subtle electrostatic interaction and van der Waal\'s forces enhance the SmC* phase. (C) 2015 Elsevier Ltd. All rights reserved.
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.