Sachin Kumar Singh

Perturbation Theroy for Nematic Liquid Crystals of Axially Symmetric Molecules: Properties of a Trial System

Abstract A statistical mechanical perturbation theory for the equilibrium properties of nematic liquid crystals is presented in which the reference potential function is non-spherical and consists of the short-range rapidly varying repulsive part of the pair potential. Calculations are made for a trial system in which molecules are assumed to interact via a pair potential which has repulsive part represented by a repulsion between hard spherocylinders and an attractive part which is function of only r 12 and Ω12 (r 12 is the center of mass distance and Ω12 the relative orientation between the two molecules), and represent approximately the interaction arising from dispersion interaction between two asymmetric molecules. Assuming that the pair correlation function g(r l2, Ω12) for a fluid of hard spherocylinders scales as g[r 12/D(Ω12] where D(Ω12) is angle-dependent range parameter the properties of the reference system and the first order perturbation term are evaluated. The agreement found between the c...

Synthesis, characterisation, mesomorphic investigation and temperature-dependent Raman study of a novel calamitic liquid crystal: methyl 4-(4′-n-alkoxybenzylideneamino)benzoate

A new series of Schiff base calamitic liquid crystal; methyl 4-(4′-n-alkoxybenzylideneamino)benzoate (MABAB), H2n+1C n OC6H4C(H)=NC6H4COOCH3 (n = 6, 8, 10, 12, 14, 16) has been synthesised and characterised by elemental analyses, Fourier transform infrared spectroscopy (FT-IR), 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy. The mesomorphic properties of these compounds were studied by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All members of the series exhibit enantiotropic smectic A (SmA) mesophase. Temperature-dependent micro-Raman study of one of the members, MABAB-10 has been employed to identify phase transitions and the molecular rearrangement therein. Analysis of Raman marker bands; C–H in-plane bending, C–C stretching of phenyl rings and –C(H)=N– linking group of core confirms the transitions clearly as observed through DSC and POM. An in situ Raman measurement of C–H in-plane bending mode has also been performed to visualise the molecular changes more clearly. The Raman study gives an evidence of induced co-planarity of rings at Cr→SmA phase transition. The density functional theoretical (DFT) optimisation of monomer, dimer and rotational conformer of MABAB-10 also support the induced co-planarity at Cr→SmA phase transition.

Synthesis, characterisation and mesomorphic properties of ester containing aroylhydrazones and their nickel(II) complexes

A new series of mesogenic aroylhydrazone-based ligands, N-[4-(4′-alkoxy)benzoyloxybenzylidene]-N′-[4″-alkoxybenzoyl]hydrazine with either the same or different peripheral alkyl chains, and nickel(II) complexes of some of them have been synthesised. They were characterised by elemental analyses, Fourier transform infrared, proton and carbon nuclear magnetic resonance and ultraviolet-visible spectroscopy. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry and polarising optical microscopy. All the aroylhydrazones, except those with no lateral chains on either end of the molecule and where m = n = 14, 16, exhibit a monotropic or enantiotropic smectic C mesophase, which are almost insensitive to the peripheral alkoxy chain length. The square planar nickel(II) complexes of the ligands show only an isotropic phase at higher temperature (>175°C) and no mesogenic nature is observed. Density functional theory calculations have been performed using the GAUSSIAN-03 program at the Becke, three-parameter, Lee–Yang–Parr level to obtain the stable electronic structure of the ligand.

Liquid Crystalline Properties of 3-[4-(4′-Alkoxybenzoyloxybenzylidene) amino]-1,2,4-triazines: Synthesis and Characterization

A new series of 3-[4-(4′-alkoxybenzoyloxybenzylidene)amino]-1,2,4-triazines, C3H2N3N˭CHC6H4OCOC6H4OCmH2m + 1 where m = 6, 7, 8, 9, 10, 11, 12, 14, and 16 have been synthesized. These compounds have been characterized by elemental analyses, FT-IR, UV-visible, 1H, and 13C NMR spectroscopy. Mesomorphic properties of these compounds were studied by differential scanning calorimetry and polarizing microscopy. The mesomorphic nature of these compounds is dependent on the alkoxy chain length. The compounds (m = 6, 7) do not exhibit mesomorphism while the compounds (m = 8, 9, 11, 12, 14) show a monotropic nematic mesophase in cooling cycle. The 3-[4-(4′-decyloxybenzoyloxybenzylidene)amino]-1,2,4-triazine displays an enantiotropic nematic mesophase and the hexadecyloxy compound exhibits the smectic A mesophase.

Microwave-assisted synthesis and mesomorphic investigations of p-substituted aroylhydrazones and their nickel(II) and copper(II) complexes

The present study is focused on the development of green microwave process for the synthesis of mesogenic substituted aroylhydrazones and their nickel(II) and copper(II) complexes. The compounds have been synthesised by microwave-assisted as well as thermal methods for comparison purpose. The compounds were structurally characterised by using suitable spectroscopic techniques. The mesomorphic properties were studied by differential scanning calorimetric analysis and polarising optical microscopy. The stable molecular structures of the mesogenic methylidenehydrazinato-nickel(II) complex have been obtained by density functional theoretical method to understand the structural origin responsible for the mesomorphic property.

Investigation of liquid crystalline property of a new calamitic liquid crystalline system methyl 4-(4ʹ-(4ʹʹ-(decyloxy)benzyloxy) benzylideneamino)benzoate

ABSTRACT A new polar calamitic liquid crystal, methyl 4-(4ʹ-(4ʺ-(decyloxy)benzyloxy) benzylideneamino)benzoate (M3BA) containing ether and Schiff base groups as linker with terminal polar ester group, has been synthesised and mesomorphic properties are studied by differential scanning calorimetry, polarising optical microscopy, density functional theory, temperature-dependent X-ray diffraction and temperature-dependent micro- Raman study. The smectic A (SmA) mesophase with focal conic texture has been observed with wide mesomorphic range. Layer thickness in SmA phase is greater than the optimised length of the molecule, indicating partially bilayer SmA phase. Analysis of Raman marker bands of C–H in-plane bending of phenyl rings, C=C stretching of rings, C=N stretching and C=O stretching shows structural changes at molecular level at Cr → SmA phase transition and provides proper intermolecular interactions responsible for dimeric unit in partially bilayer SmA phase. Graphical Abstract

Spectroscopic and structural study of the newly synthesized heteroligand complex of copper with creatinine and urea.

Study of copper complex of creatinine and urea is very important in life science and medicine. In this paper, spectroscopic and structural study of a newly synthesized heteroligand complex of copper with creatinine and urea has been discussed. Structural studies have been carried out using DFT calculations and spectroscopic analyses were carried out by FT-IR, Raman, UV-vis absorption and fluorescence techniques. The copper complex of creatinine and the heteroligand complex were found to have much increased water solubility as compared to pure creatinine. The analysis of FT-IR and Raman spectra helps to understand the coordination properties of the two ligands and to determine the probable structure of the heteroligand complex. The LIBS spectra of the heteroligand complex reveal that the complex is free from other metal impurities. UV-visible absorption spectra and the fluorescence emission spectra of the aqueous solution of Cu-Crn-urea heteroligand complex at different solute concentrations have been analyzed and the complex is found to be rigid and stable in its monomeric form at very low concentrations.

Tuning the thermotropic properties of liquid crystalline p-substituted aroylhydrazones

The synthesis and mesomorphic properties of forty substituted aroylhydrazones with peripheral mono-, di- and tri- alkoxy chains derived from a p-amino aroylhydrazone core are described. The compounds with two side chains exhibited a smectic A phase, while the compounds with six soft alkoxy side chains at symmetrical positions formed a rectangular columnar mesophase. The structures of these mesophases were confirmed by differential scanning calorimetry (DSC) analysis, polarized optical microscopy (POM) and powder X-ray diffraction (XRD) studies. Raman studies with the help of density functional theory on some of the mesogenic members have been performed to understand the changes in the intermolecular interactions during phase transitions. A structure–property relationship has been deduced, and mesogenic properties are found to be dependent on the chain length, density and position of the alkoxy chains around the molecular core.

Investigation of coordination properties of isolated adenine to copper metal: a systematic spectroscopic and DFT study.

The coordination properties of copper with adenine have been studied by the analyzing the changes in Fourier Transform Infra-red (FTIR) and Raman spectra of adenine and adenine-copper complex. The geometry of adenine and adenine copper complex were optimized and theoretical Infra-red and Raman spectra of the optimized structures were calculated using Density Functional Theory (DFT). During synthesis of adenine-copper complex specific procedure was adopted to attach the Cu atom with particular N-atom of adenine (N9). The results of Raman and DFT confirmed the attachment. The Raman bands at 625, 330 and 230 cm(-1) of adenine-copper complex contain significant contribution of the vibrational motions of Cu metal coordinated to N9 and Cl atoms. The DFT calculations give additional vibrational modes containing the Cu, N9 and N9* atoms, which are not observed in FTIR and Raman spectra. The Raman, IR and DFT study confirm that Cu metal has good binding affinity to the isolated adenine base.

Perturbation Theory for Nematic Liquid Crystals of Axially Symmetric Molecules: Extension of Calculations to High Pressures

Abstract We have applied a statistical mechanical perturbation theory to study the thermodynamic properties of nematic liquid crystals under pressure. In this theory the reference potential function is nonspherical and consists of the short range rapidly varying repulsive part of the pair potential. We report calculations on the nematic-isotropic (NI) transition properties for a hard spherocylindrical system superposed with an attractive potential, which is a function of only the centre of mass distance and the relative orientation between the two molecules, and subjected to different external pressures. The interaction arising from dispersion interaction between two asymmetric molecules represents the attractive interaction. The influence of pressure on the stability, ordering and thermodynamic functions for the NI transition is analysed. It is found that the theoretical predictions are in accordance with the experimental observations.