- Synthesis and mesomorphic properties of novel Schiff base liquid crystalline EDOT derivatives
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Herein, we reported novel banana liquid crystals derived from ethylenedioxythiophene (EDOT) central unit encompass with Schiff base. Structural charecterization of these compounds was carried out from their spectral and elemental analysis. Physical properties of all the newly synthesized compounds were investigated by polarising optical microscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and Raman spectroscopy. EDOT bearing three-ring Schiff base bent-core compounds are non-mesomorphic but all the Schiff bases containing five-rings exhibit enantiotropic mesophase behaviour. The higher homologues show long range nematic phase along with a smectic C phase at lower temperature. While the lower homologues exhibit only N phase. The bent-angle in these compounds is in between of calamitic LCs and banana LCs; therefore, the molecules escape from the polar order packing observed in typical bent core LCs. Detailed XRD investigation endorses the presence of the N phase in lower homologues and Sm C phase in higher homologues.
- Gowda, Ashwathanarayana,Roy, Arun,Kumar, Sandeep
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p. 840 - 847
(2016/12/30)
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- Monolayer to Interdigitated Partial Bilayer Smectic C Transition in Thiophene-Based Spacer Mesogens: X-ray Diffraction and 13C Nuclear Magnetic Resonance Studies
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Mesophase organization of molecules built with thiophene at the center and linked via flexible spacers to rigid side arm core units and terminal alkoxy chains has been investigated. Thirty homologues realized by varying the span of the spacers as well as the length of the terminal chains have been studied. In addition to the enantiotropic nematic phase observed for all the mesogens, the increase of the spacer as well as the terminal chain lengths resulted in the smectic C phase. The molecular organization in the smectic phase as investigated by temperature dependent X-ray diffraction measurements revealed an interesting behavior that depended on the length of the spacer vis-a-vis the length of the terminal chain. Thus, a tilted interdigitated partial bilayer organization was observed for molecules with a shorter spacer length, while a tilted monolayer arrangement was observed for those with a longer spacer length. High-resolution solid state 13C NMR studies carried out for representative mesogens indicated a U-shape for all the molecules, indicating that intermolecular interactions and molecular dynamics rather than molecular shape are responsible for the observed behavior. Models for the mesophase organization have been considered and the results understood in terms of segregation of incompatible parts of the mesogens combined with steric frustration leading to the observed lamellar order.
- Kesava Reddy,Varathan,Lobo, Nitin P.,Roy, Arun,Narasimhaswamy,Ramanathan
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p. 10831 - 10842
(2015/10/12)
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- Phase characterization and study of molecular order of a three-ring mesogen by 13C NMR in smectic C and nematic phases
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Molecules exhibiting a thermotropic liquid-crystalline property have acquired significant importance due to their sensitivity to external stimuli such as temperature, mechanical forces, and electric and magnetic fields. As a result, several novel mesogens have been synthesized by the introduction of various functional groups in the vicinity of the aromatic core as well as in the side chains and their properties have been studied. In the present study, we report three-ring mesogens with hydroxyl groups at one terminal. These mesogens were synthesized by a multistep route, and structural characterization was accomplished by spectral techniques. The mesophase properties were studied by hot-stage optical polarizing microscopy, differential scanning calorimetry, and small-angle X-ray scattering. An enantiotropic nematic phase was noticed for lower homologues, while an additional smectic C phase was found for higher homologues. Solid-state high-resolution natural abundance 13C NMR studies of a typical mesogen in the solid phase and in the mesophases have been carried out. The 13C NMR spectrum of the mesogen in the smectic C and nematic phases indicated spontaneous alignment of the molecule in the magnetic field. By utilizing the two-dimensional separated local field (SLF) NMR experiment known as SAMPI4, 13C-1H dipolar couplings have been obtained, which were utilized to determine the orientational order parameters of the mesogen. ? 2011 American Chemical Society.
- Kalaivani,Narasimhaswamy,Das, Bibhuti B.,Lobo, Nitin P.,Ramanathan
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scheme or table
p. 11554 - 11565
(2011/12/15)
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