Comparative Raman study of two laterally fluorinated LC compounds having different terminal chains

ABSTRACT

In this article, we present the Raman study of two laterally fluorinated liquid crystal compounds, namely, C3PP(23F)P-NCS and C3PP(23F)PC3. The two compounds have different terminal groups, one with NCS which is more polar than the other which has an alkyl group. The Raman bands were deconvoluted with Lorentzian profiles to get the values of spectral parameters. The main feature of the work is the temperature-dependent behaviour of the spectra profiles of the C–H bending mode, C–F stretching modes and aromatic C–C stretching mode in the vicinity of the phase transitions. The effect on the charge distribution over different bonds of the molecule and the vibrational energy of the bonds due to the presence of the more polar group on the terminal chain is well observed. The contrasting behaviours of the spectral profiles at the Cr–N and N–I transitions were also observed which we have ascribed to some pre-transitional effect associated with the breaking of the orientational order near the N–I transition. Density functional theory using B3LYP exchange correlation with the 6-31G (d,p) basis set was also used to generate a theoretical spectra which were found to be matching with the experimental spectra.

GRAPHICAL ABSTRACT

KEYWORDS:

• Raman study
• laterally fluorinated liquid crystals
• phase transition
• isothiocyanato (NCS) compound

Acknowledgments

The authors are grateful to the Department of Physics, NERIST, Arunachal Pradesh, India, in which the Raman spectroscopy experiment was conducted, and the Department of Chemistry, NIT Meghalaya in which the Gaussian program was performed. One author (AB) acknowledges the funds received from DST-SERB (grant no: EMR/2015/002405).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the SERB-DST [EMR/2015/002405].