Browsing by Author "Ooi, Yew-Hong"

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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
;
Yeap, Guan-Yeow
;
Han, Chun-Chieh
;
Lin, Hong-Cheu
;
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.
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
;
Yeap, Guan-Yeow
;
Han, Chun-Chieh
;
Lin, Hong-Cheu
;
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.