Synthesis and mesomorphic investigation of calamitic liquid crystalline system ethyl-[4-(4'-decyloxy)benzoyloxy]-benzoate (4-EDBB): A temperature dependent micro-Raman study and DFT calculations

A new liquid crystalline material containing diester linking group ethyl-[4-(4'-decyloxy)benzoyloxy]-benzoate (4-EDBB) was synthesized. The phase transition temperatures were noted by differential scanning calorimetry (DSC), the texture pattern were observed by polarizing optical microscopy (POM) and temperature dependent Raman study was employed to observe the transitions as well as to understand the molecular rearrangement during phase transition. The transitions were observed with all the three techniques but the Raman signature of crystal -> smectic A transition is many fold and more precise and accurate. The correlation between intermolecular interaction and phase behaviour has been discussed using temperature dependence Raman data of C-H in-plane bending and C=O stretching vibrations. With the help of DFT method the possible dimers of 4-EDBB were optimized and the rotational isomers were also investigated. There exists weak hydrogen bonds at room temperature, which breaks as the temperature is increased causing the C-H in-plane bending to shift lower and C=O stretching vibrations to shift higher. The discussion of the temperature dependent Raman data reveals that at crystal -> smectic A transition as a result of intra-molecular rotation the molecules transform from transto cis- conformer. (C) 2013 Elsevier B.V. All rights reserved.