Rajib Nandi

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.

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.

Low temperature Raman study of a liquid crystalline system 4-Decyloxy benzoic acid (4DBA)

The Raman spectra of a liquid crystalline system, 4-Decyloxy benzoic acid (4DBA) have been recorded at different temperatures within the interval 300-78 K in order to identify the structural changes in crystalline state of a nematogen and to understand the molecular alignment therein. The earlier predicted dimer structure of 4DBA was optimized with DFT method and the theoretical Raman spectra of dimer as well as monomer have been calculated for comparison with the experimental spectra. The mode specific quartic coupling coefficient; A(i,ω) and phonon frequency; ωi have been calculated using temperature dependent anharmonic perturbation theory. The precise band shape analysis of Raman bands at ~807, ~881, ~1255, ~1282, ~1436, ~1576, ~1604, ~2881 and ~3081cm(-1) gives signature of temperature induced slow crystal modification. The structural changes leading to crystal modification have been discussed.

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

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.

Observation of exceptional ‘de Vries-like’ properties in a conventional aroylhydrazone based liquid crystal

Smectic liquid crystals with ‘de Vries-like’ properties are characterized by a maximum layer contraction of ≤1% upon transition from the non-tilted SmA phase to the tilted SmC phase. A straight alkoxy chain-terminated conventional aroylhydrazone based liquid crystal N-(4-(tetradecyloxy)-2-hydroxybenzylidene)-4′((4′′(hexadecyloxy)benzyl)oxy)benzohydrazide (BSac-1416) undergoes the SmA–SmC phase transition with a maximum layer contraction of 0.65%. The merits of the de Vries reduction factor, i.e. R and f values for this mesogen, are comparable to, or even lower than, those reported for established perfluorinated and polysiloxane-terminated bona fide de Vries-like materials.

In vitro concentration dependent detection of creatinine: a surface enhanced Raman scattering and fluorescence study

An attempt has been made to detect the concentration of creatinine in a very dilute aqueous solution in vitro on the basis of the Jaffe reaction, the commonly used reaction for clinical determination of creatinine concentration in blood serum or urine. For this various spectroscopic techniques viz. Raman spectroscopy, surface enhanced Raman scattering, UV-visible and fluorescence spectroscopy have been used. As a result of the Jaffe reaction using aqueous solutions of creatinine at different concentrations and picric acid and NaOH as reagents, a reddish orange colored Jaffe complex is produced. The concentration dependent SERS spectra of the Jaffe complex show gradual decrease in the intensity of ring deformation mode of creatinine on decreasing creatinine concentration. The concentration dependent absorption spectra of the Jaffe complex show changes in intensity in one of the absorption peaks characteristic of creatinine. The concentration dependent fluorescence emission spectra of the Jaffe complex show a blue shift in emission maxima on reducing the concentration of creatinine in the solution. The observed results suggest the possibility to detect the concentration of creatinine in a very dilute solution in vitro by SERS and fluorescence techniques and the application of these techniques in vivo might aid in a more specific and accurate determination of creatinine in serum or urine.