Synthesis, characterization and texture observations of calamitic liquid crystalline compounds

Analyzing the impact of the size of fluoro and chloro substituents on induced mesomorphism in hydrogen bonded liquid crystals

Synthesis of new supramolecules with specific properties and realistic applications requires a sound knowledge of the structure-property relationships of the synthesized molecules. Non-covalent interaction like hydrogen bonding is conducive in realizing mesomorphism. The induction of the liquid crystalline character is associated with the strength of hydrogen bonds formed between the interacting components, which are affected by the change of polarity and polarizability of both components upon change in their terminal polar substituents. When the polar substituents are similar in their reactivity, how does the size of the polar substituent influence the mesomorphism? New hydrogen bonded liquid crystals are synthesized with fluorine and chlorine as substituents, and the mesomorphic behaviour is studied with the size of the substituent as a critical parameter. The chemical characterization is carried out by FTIR measurements, the phase characterization by polarizing optical microscopy and the thermal characterization by differential scanning calorimetry. The DFT method utilizing wb97x-D theory along with the cc-pVTZ basis set were used for the calculations. The hybrid functional B3LYP-D3 and Gaussian type basis set 6-31G(d,p) were used for studying the orientation of the molecules. It is observed that the ortho substituents reduce the co-planarity, meta substituents lead to the molecular broadening while para substituents exhibited highest mesomorphism by enhancing longitudinal dipole moment. Fluoro substituted compounds are exhibiting higher mesomorphism while the bulky chloro substituents are helping to better stack the molecules possessing longer chain lengths.

Poly(l-Lactide) Liquid Crystals with Tailor-Made Properties Toward a Specific Nematic Mesophase Texture

This paper presents the liquid crystal (LC) properties of poly(l-lactide) (PLLA). Mesophase behavior is investigated using polarized optical microscopy, X-ray diffraction, and differential scanning calorimetry. The performed analyses confirm that pressed PLLA films exhibit the unique capability of self-assembling into a nematic mesophase under the influence of mechanical pressure, temperature, and time. It was originally demonstrated that the chiral nematic mesophase can be obtained by introducing fine powders into the polymer. Based on the research conducted, it was proved that the pressed PLLA films have a chiral nematic mesophase with a nematic-to-isotropic phase transition and a large mesophase stability range overlapping the temperature of the human body, which can persist for years at ambient temperature. The obtained films show tailor-made properties toward a nematic mesophase with a specific texture, including colored planar texture of the chiral nematic mesophase and blue-phase (BP) LC texture. The BP, described for the first time in plain PLLA, occurred over a wider than usual temperature range of stability between isotropic and chiral nematic thermotropic phases (ΔT ≈ 9 °C), which is an advantage of the obtained polymer material, in addition to ease of preparation. This opens up new prospects for advanced photonic green applications.

Probing the Texture of the Calamitic Liquid Crystalline Dimer of 4-(4-Pentenyloxy)benzoic Acid

The liquid crystalline dimer of 4-(4-pentenyloxy)benzoic acid, a member of the n-alkoxybenzoic acid homologous series, was synthesized using potassium carbonate supported on alumina as catalyst. The acid dimer complex exhibited three mesophases; identified as nematic, smectic X1 and smectic X2. Phase transition temperatures and the corresponding enthalpies were recorded using differential scanning calorimetry upon both heating and cooling. The mesophases were identified by detailed texture observations by variable temperature polarized light microscopy. The nematic phase was distinguished by a fluid Schlieren texture and defect points (four and two brushes) while the smectic phases were distinguished by rigid marble and mosaic textures, respectively.