Browsing by Author "Han, Chun-Chieh"

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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
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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.
Effects of Liquid Crystal Compositions on Polymer Stabilized Blue Phase Liquid Crystals
(2010)
Wang, Ling-Yung
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Huang, Tai-Hsiang
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Sugiura, Norio
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Liau, Wei-Lung
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Han, Chun-Chieh
The compositions of polymer stabilized blue phase liquid crystals (PS-BPLCs) relating to the thermal properties and electro-optical ones which are important for both display performance and productivity were investigated in this paper. By optimizing quantity of chiral-dopants and new monomers, temperature range of the BPLCs could successfully be enlarged.
Hydrogen-bonded bent-core blue phase liquid crystal complexes containing various molar ratios of proton acceptors and donors
(2016-01-01)
Han, Chun-Chieh
;
Chou, Yu-Chaing
;
Chen, San-Yuan
;
Lin, Hong-Cheu
;
材料科學與工程學系
Various hydrogen-bonded (H-bonded) bent-core liquid crystal complexes consisting of pyridyl and benzoic acid derivatives were synthesized and compared with their covalent analogues in this study. The molar ratios of pyridyl and benzoic acid derivatives could be tuned to form various H-bonded liquid crystal (LC) diads (with 1 : 1 molar ratio of H-acceptors T and H-donors D) and complexes (with different molar ratios of T and D). By insertion of H-bonds into different positions of bent-core supramolecules, the mesophasic properties of H-bonded bent-core LC complexes were optimized, which could facilitate the most suitable LC components and compositions to be utilized in H-bonded blue phase (BP) LC complexes. In BPLC complexes, the molar ratios, alkyl chain lengths, the lateral fluoro-substitution and the chiral center of H-bonded bent-core supramolecules would affect the temperature ranges of BPs. Accordingly, H-bonded bent-core complex P(III)C9/A(II)F* (3/7 mol mol(-1)) displayed the widest BPI range of Delta T-BPI = 12.0 degrees C at the correspondent H-acceptor T = PIIIC9 and H-donor D = A(II)F*. Since the covalent-bonded bent-core mixture only had narrow ranges of BPIII, we could summarize that the introduction of H-bonds into the bent-core center effectively stabilizes the BPs and easier induces the BPI.
Lateral fluoro-substitution and chiral effects on supramolecular liquid crystals containing rod-like and H-bonded bent-core mesogens
(2016-01-01)
Han, Chun-Chieh
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Yang, Li-Han
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Raghunath, Putikam
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Lin, Ming-Chang
;
Kumar, Rohit
The first series of liquid crystalline supramolecular diads C/D containing asymmetric rod-like and H-bonded bent-core mesogens were designed and synthesised, among which supramolecular diad P*(III)/A*(II) with two chiral centers on both the H-acceptor/H-donor and non-lateral fluoride substitution possessed a wide blue phase (BPI) range of 13.7 degrees C. According to the molecular modeling, a large biaxial parameter (>= 3.2) and an appropriate HTP value (4.2-4.8 mu m(-1)) are the most important factors to stabilize the double twisted cylinder structure (i.e., BPI) in supramolecular diads. Moreover, the bent angles, biaxial parameters and dipole moments of supramolecular diads are mainly affected by the locations and numbers of H-bonds and chiral centers. Not only larger bent angles and biaxial parameters but also smaller dipole moments and HTP values were obtained by removing the lateral fluoride substitution on supramolecular diads to achieve the blue phase of P*(III)/A*(II) (without lateral fluoride substitution). Finally, the special optimal 1 : 1 molar ratio of supramolecular diad P*(III)/A*(II) (i.e., H-donor = 50 mol%) with the widest blue phase range is mainly attributed to its rod-like and H-bonded bent-core mesogens, rather than H-donor = 75 mol% in most supramolecular complexes containing linear H-bonded rod-like mesogens.
Liquid crystal dimers containing Cholesteryl and Triazole-containing mesogenic units
(1970-01-01)
Al-shargabi, Arwa
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Yeap, Guan-Yeow
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Mahmood, Wan Ahmad Kamil
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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] .
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
;
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.
Non-symmetrical liquid crystal dimers armed with azobenzene and 1,2,3-triazole-cholesterol
(2015-09-02)
Alshargabi, Arwa
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Yeap, Guan-Yeow
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Mahmood, Wan Ahmad Kamil
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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.
Self-assembled 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine dimer and its hydrogen-bonded complexes
(2013-07-01)
Yeap, Guan-Yeow
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Balamurugan, Subramanian
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Rakesh, Samikannu
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Han, Chun-Chieh
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Lin, Hong-Cheu
We report the synthesis and investigation of a new self-assembled benzoylhydrazine-based compound, namely 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine and their hydrogen-bonded complexes with different carboxylic acid derivatives, of which some exhibit liquid crystalline properties and some are non-mesogens. The conversion of the non-liquid crystalline target compound that is free from carboxylic acid to liquid crystalline complexes containing various carboxylic acids can probably be rationalised through the breaking of intermolecular hydrogen bonding within the supramolecular assembly by carboxylic acid dopants. The enhancement of liquid crystalline properties of benzoylhydrazine compounds with respect to various carboxylic dopants is documented. Other salient features can be exemplified by the formation of discotic columnar phase as shown by the azo-linkage containing 4-(4-(10-decyloxy)phenylazo)benzoic acid-doped complex.
Self-assembled 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine dimer and its hydrogen-bonded complexes
(2013-07-01)
Yeap, Guan-Yeow
;
Balamurugan, Subramanian
;
Rakesh, Samikannu
;
Han, Chun-Chieh
;
Lin, Hong-Cheu
We report the synthesis and investigation of a new self-assembled benzoylhydrazine-based compound, namely 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine and their hydrogen-bonded complexes with different carboxylic acid derivatives, of which some exhibit liquid crystalline properties and some are non-mesogens. The conversion of the non-liquid crystalline target compound that is free from carboxylic acid to liquid crystalline complexes containing various carboxylic acids can probably be rationalised through the breaking of intermolecular hydrogen bonding within the supramolecular assembly by carboxylic acid dopants. The enhancement of liquid crystalline properties of benzoylhydrazine compounds with respect to various carboxylic dopants is documented. Other salient features can be exemplified by the formation of discotic columnar phase as shown by the azo-linkage containing 4-(4-(10-decyloxy)phenylazo)benzoic acid-doped complex.
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
;
Han, Chun-Chieh
;
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.