Raman spectra of the Schiff 's base liquid crystalline compound 5O5, N-(4- n-pentyloxybenzylidene)-4'-n-pentylaniline, have been recorded as a function of temperature from 22 to 80°C in the 1140-1220 cm-1 and 1550-1640 cm-1 spectral regions. From careful deconvolution of the spectral features using Lorentzian profiles, precise values of peak positions, integrated intensities and linewidths of some selected Raman bands were obtained. The variations of the Raman spectral parameters with temperature are discussed in terms of changes in the molecular alignment and its effect on intra-/inter-molecular interactions at the Cr-G, G-SmF, SmF-SmC and SmA-N phase transitions. From a detailed study, it is inferred that the increased orientational/vibrational freedom of the alkyl chains, as well as the delocalization of the electron clouds, is responsible for the spectral anomalies at the Cr-G transition. Loss of positional ordering and twist around the -C6H4-N= bond takes place at the SmF-SmC transition. In the SmA-N...

Dynamics of phase transitions in a liquid crystal probed by Raman spectroscopy

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 m...

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

The solid to smecticG (SmG) phase transition in a Schiff base liquid crystalline compound, terepthal-bis-heptylaniline (TB7A), is monitored in situ by temperature-dependent Raman microspectroscopy, using the band of a CH in-plane bending mode as a marker. Contrary to the earlier report of a sudden wavenumber shift, the in situ measurement shows very clearly that a new Raman band at ∼1160 cm−1 appears at the Crystal II SmG transition. The dynamics of this phase transition is discussed in terms of a triple well potential below 210 K and a double well potential above 210 K. The phase transition essentially takes place as a result of intra-molecular rotation about the long molecular axis. The optimization energy at various fixed dihedral angles, (CCCN) are calculated using density functional theory (DFT) at the B3LYP/6-31G* level of theory. The relative energy at each dihedral angle is calculated relative to optimization energy obtained without any constraints and plotted as a function of dihedral angle (Φ) between the adjacent phenyl ring planes, which also shows a double well potential at room temperature. Copyright © 2009 John Wiley & Sons, Ltd.

Dynamics and mechanism of the Crystal II → smecticG phase transition in TB7A by a temperature‐dependent micro‐Raman study and DFT calculations

Mesomorphic, micro-Raman and DFT studies of new calamitic liquid crystals; methyl 4-[4-(4-alkoxy benzoyloxy)benzylideneamino]benzoates.

Temperature dependent Raman study of S(B)-->S(C) transition in liquid crystalline compound N-(4-n-pentyloxybenzylidene)-4'-heptylaniline (5O.7).

The precise value of linewidths obtained after correcting for the slitwidth effect for five Raman bands associated with the core of a liquid crystalline compound, terepthal-bis-decyl aniline (TBDA), have been studied in the temperature range of 12-472 K. The variation of the linewidth with temperature confirms two already reported phase transitions at 346 and 427 K. However, the phase transition at 427 K is not purely first order as reported earlier, but of mixed order in nature. From the measured linewidths of the N and CDN modes below room temperature, the estimated activation energy for rotation along the -N bond closely matches with the SI -SC phase transition temperature suggesting that the rotation about the -N bond is closely linked with this transition.

Dynamics of phase transitions in a liquid crystalline compound (TBDA) probed by Raman spectroscopy

The Raman spectra of Terepthalylidene-bis-p-n-declyaniline (TBDA), have been recorded as a function of temperature in the temperature range from 55.0°C (solid) to 199.0°C (isotropic liquid) in the 1100–1200cm−1 and 1520–1650cm−1 regions. The precise values of peak positions, integrated intensities and linewidths of some selected Raman bands have been obtained by deconvoluting the bands. The changes in the molecular alignment and its effect on inter/intra molecular interactions at two particular phase transitions viz., solid-smectic G (K-SG ) and smectic I-Smectic C (SI-Sc ) have been discussed on the basis of variation in the Raman spectral parameters with temperature. From detailed considerations, it is inferred that the increased orientational/vibrational freedom of long alkyl chain on the core is responsible for major spectral changes at the K-SG transition while the changes in the intramolecular interactions of the core part with increased fluidity, is responsible for spectral anomalies at th...

Laser Raman Study of Terepthalylidene-bis-p-n-Decylaniline (TBDA)

A new phase transition in supercooled TBDA probed by low‐temperature Raman study

Pre-resonance Raman spectra of certain liquid crystalline compounds, TB4A, TB7A and TB10A, are reported. The anomaly observed in the pre-resonance Raman spectra in the three compounds was initially explained by the Albrecht-Hutley Model, but its failure leads us to explain the anomalous intensity enhancement mechanism by invoking an interference effect between a weak dipole-forbidden excited state and a nearby strong electronic level via vibrational modes. The presence of a 21Ag dipole-forbidden excited state in TB4A and TB10A is deduced after an elaborate discussion of their centro-symmetric structure. The structural difference of TB7A in comparison with TB4A and TB10A is also discussed by taking their X-ray data into consideration.

Pre-resonance Raman studies of some mesogens-TB4A, TB7A and TB10A

The study investigated the effect of bark powder on circulatory immune complexes and total immunoglobulins level in Kosali breed of cattle environmentally exposed to arsenic contamination through water and fodder. Arsenic concentration was significantly (p<0.05) higher in drinking water, fodder and cattle blood samples collected from the arsenic contaminated area as compared to uncontaminated area (control area). Kosali cattle reared in the arsenic contaminated area showed significantly (p<0.05) elevated circulatory immune complexes with decreased level of plasma total immunoglobulins compared to the control area. bark powder was administered orally @ 40 mg/kg. b. w. daily for 30 days to eight Kosali cattle (treatment group) selected from the arsenic contaminated area. Eight Kosali cattle each from arsenic contaminated and uncontaminated area (without any treatment) served as exposure control and healthy control respectively. Kosali cattle of the treatment group exhibited significant (p<0.05) decrease in the level of circulatory immune complexes; and increase in the total immunoglobulin concentration to the level comparable to that of healthy control.

S. K. Dash

Papers

Dynamics of phase transitions in a liquid crystalline compound (TBDA) probed by Raman spectroscopy

Laser Raman Study of Terepthalylidene-bis-p-n-Decylaniline (TBDA)

A new phase transition in supercooled TBDA probed by low‐temperature Raman study

Pre-resonance Raman studies of some mesogens-TB4A, TB7A and TB10A

Immune complexes in Kosali breed of cattle naturally exposed to arsenic contamination: Attenuation by