摘要
In this study, a series of chiral Schiff-based rod-coil amphiphiles were used for self-assembly to examine the forming mechanisms of helical architectures. The chiral Schiff-based rod-coil amphiphiles exhibited both the lyotropic and thermotropic liquid crystalline behavior. All chiral Schiff-based rod-coil amphiphiles appeared positive Cotton effect, and there is no odd-even effect with respect to the alkyl chain length for the formation of helical microdomain. Interestingly, the helical twisting power (i.e., HTP, the inversed value of pitch length) induced by chiral sugar of the self-assembled helical morphology is dependent upon the alkoxyl chain length. By increasing the alkoxyl chain length, the self-assembled morphologies vary from platelet-like texture to helical twist with different pitch lengths, and finally revert to the platelet-like texture. On the basis of structural characterization and spectroscopic analysis, the transformation from platelet-like morphology to helical twist is induced by significant steric hindrance at which the effective size of adjacent alkoxyl chain reaches the threshold of helical twisting and bending. However, further increasing the alkoxyl chain length, the disordering of the alkoxyl chain conformation in the smectic-like layered structure may give rise to structural imperfection so as to reduce the steric hindrance effect. Eventually, the steric hindrance effect may compromise with the structural imperfection so that a platelet-like morphology was formed. Also, we aim to control the handedness of helical twist from the self-assembly of the chiral rod-coil molecules. Various chiral rod-coil molecules with equal alkoxyl chain length but different chain-end size were designed for the discussion of chain end effect in the self-assembly. The self-assembled helical twists with equivalent helical twisting power but opposite handedness can be obtained from the chiral rod-coil molecules with or without bulky substitution at the alkoxyl chain end. The selection of helicity is resulted to the molecular packing and its Gaussian saddle-like curvature for self-assembly. If the sugar-based chiral rod-coil molecules were modified into acetate-based chiral rod-coil molecules, similar self-assembly results still can be obtained; suggesting that the amphiphilicity of the chiral rod-coil molecules is not critical for the formation of helical twists and its corresponding helicity. Furthermore, we observed a banded morphology in our molecular system under polarized light microscopy (PLM). The appearance of the banded texture is strongly dependent upon the alkoxyl chain length that determines the twisting power of self-assembled hierarchical superstructures with helical sense. The formation of banded spherulites is identified as quaternary helical morphology with a collection of the tertiary chiral superstructures (i.e., helical twists) so as to give regular extinction in PLM attributed to zero-birefringence effect. Consistent to 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 given to elucidate the morphological evolution. Consequently, the self-assembly of the chiral amphiphiles with thermotropic liquid crystalline character represents the mechanism for the chiral information transfer in different length scales. The transfer of chiral information from molecular level to quaternary superstructure can be identified. Finally, an iron-rich spiral superstructures by taking advantage of the self-assembly of chiral Schiff-based rod-coil molecules is proposed for potential optical or mechanical applications. Chiral Schiff-based rod-coil molecules are end-capped with ferrocene moiety as chiral rod-coil organometallics (FC11). We described the self-assembly of FC11 that develops into ferrocene iron-rich spiral superstructure. The fundamentally new self-assembled FC11 spiral superstructure is a fabrication technology which acts as a template for the formation of twist ferrocene wires after pyrolysis treatment. In an attempt to give orientated template, the self-assembly of FC11 is performed under one Tesla external magnetic field due to its intrinsic dielectric constant. Such spiral metallic wires will contribute to the development of microelectronic organic-inorganic functional devices. The well-defined building blocks of ferrocene-based derivatives play an important role in dynamic responsive displays as well as in biological systems which stimulated by external fields.
參考文獻
延伸閱讀
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