Browsing by Author "Lin, Tz-Feng"

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COLL 272-Helical morphologies in the self-assembly of chiral Schiff-based rod-coil amphiphiles
(2007-08-19)
Lin, Tz-Feng
;
Ho, Rong-Ming
;
Sung, Chien-Hung
;
Hsu, Chain-Shu
;
應用化學系
Helical morphologies of thermotropic liquid-crystalline chiral Schiff-based rod-coil amphiphiles
(2006-11-14)
Lin, Tz-Feng
;
Ho, Rong-Ming
;
Sung, Chien-Hung
;
Hsu, Chain-Shu
;
應用化學系
A series of Schiff-based rod-coil molecules possessing thermotropic liquid-crystalline (LC) character have been prepared whereas a sugar-based moiety was introduced to the chain end of the molecules so as to create chiral amphiphiles for self-assembly. The self-assembly of the chiral Schiff-based rod-coil amphiphiles gave rise to a variety of specific LC textures. A banded morphology under polarized light microscopy (PLM) can be observed; the appearance of the banded texture is strongly dependent upon the length of hydrophobic tail that determines the twisting power of self-assembled hierarchical superstructures with helical sense. As a result, the banded spherulites are identified as quaternary helical morphology with a collection of the tertiary chiral structures (i.e., helical twists) so as to give regular extinction in PLM attributed to zero-birefringence effect. Consistent with the observation of helical morphologies, the occurrence of chiral smectic C (SmC*) phase can only be found in samples with enough alkoxyl chain length, suggesting the existence of strong correlation for morphological evolution from molecular level to macroscopic object with the formation of SmC*. A hypothetic model about the bilayer structure within the SmC* structure is thus given to elucidate the morphological evolution. Consequently, the self-assembly of the chiral amphiphiles with thermotropic LC character represents the mechanism for the chirality transfer in different length scales.
Hierarchical Superstructures with Helical Sense in Self-Assembled Achiral Banana-Shaped Liquid Crystalline Molecules
(2008-11-10)
Lin, Shih-Chieh
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Lin, Tz-Feng
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Ho, Rong-Ming
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Chang, Chin-Yen
;
Hsu, Chain-Shu
The self-assembly of 1,3-phenylene bis[4-(4-n-heptyloxybenzoyloxy)-benzoates] (BC7) is studied to examine the formation of helical morphologies from achiral banana-shaped liquid crystal molecules at different self-assembling levels. Various hierarchical superstructures including flat-elongated lamellar crystal, left- and right-handed helical ribbons, and tubular texture are observed while the BC7 molecules self-assemble in THF/H(2)O solution. By contrast, only plate-like morphology is observed in the self-assembly of achiral linear shaped 1,4-phenylene bis[4-(4-n-heptyloxybenzoyloxy)-benzoates] (LC7) molecules, indicating that the chirality of the self-assembled texture is strongly dependent upon the molecular geometry of the achiral molecules. The formation of the helical superstructures, namely hierarchical chirality, is attributed to the conformational chirality from the achiral banana-shaped liquid crystalline molecules, as evidenced by significant optical activity in time-resolved circular dichroism experiments. Selective area electron diffraction is performed to examine the structural packing of the hierarchical superstructures. As observed, the molecular disposition of the lamellar crystal is identical to that of the helical superstructure. Also, the diffraction patterns of the helical superstructures appeared arc-like patterns consisting of a series of reflections, suggesting that the helical morphology resulted from the curving of the lamellar crystals through a twisting and bending mechanism. Consequently, the model of molecular disposition in the self-assembled helical superstructures from the achiral banana-shaped molecules is proposed. The morphological evolution in this study may provide further understanding with respect to the chiral information transfer mechanism from specific molecular geometry to hierarchical chirality in the achiral banana-shaped molecules.
Twist Ferrocene Wires from Self-Assembly of Chiral Rod-Coil Organometallics
(2010)
Lin, Tz-Feng
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Ho, Rong-Ming
;
Sung, Chien-Hung
;
Ho, Ming-Shou
;
Hsu, Chain-Shu
Variation of helical twisting power in self-assembled sugar-appended Schiff base chiral rod-coil amphiphiles
(2008-02-26)
Lin, Tz-Feng
;
Ho, Rong-Ming
;
Sung, Chien-Hung
;
Hsu, Chain-Shu
;
應用化學系
A series of sugar-appended Schiff base chiral rod-coil amphiphiles with various alkoxy chain lengths have been synthesized in order to elucidate the variation of the helical twisting power (HTP), that is, the inverse of the pitch length, of the helical texture in the self-assembly of the amphiphiles. The HTP induced by chiral sugar in the self-assembled helical morphology was dependent upon the alkoxy chain length. Increasing the alkoxy chain length caused the self-assembled morphology to change from platelet-like texture to helical-twist morphology with varying pitch length and then revert to the platelet-like texture. This result demonstrates that the HTP reaches a maximum as the alkoxy chain length changes. The transformation from platelet-like to helical-twist morphology is induced by significant steric hindrance, when the effective size of adjacent alkoxy chains reaches the threshold of helical twisting and bending, resulting in the formation of a chiral smectic C phase. However, as the alkoxy chain length increases further, the disordering of the alkoxy chain conformation in the smectic-like layered structure may give rise to a structural imperfection that reduces the steric-hindrance effect. Eventually, the steric-hindrance effect may reach a compromise with the structural imperfection to produce a platelet-like morphology, leading to the formation of a low-order smectic phase.