Monitoring the temperature-induced phase transition in a calamitic liquid crystal MABAB-12 via temperature-dependent Raman and DFT study

Abstract

The calamitic liquid crystal methyl 4-(4’-12-alkoxybenzylideneamino) benzoate (MABAB-12) containing a Schiff base as linking group has been synthesised. Mesomorphic properties and phase transition temperatures were probed through temperature-dependent Raman spectroscopy and analysed using density functional theory (DFT). Analysis of Raman marker bands of C-H in-plane bending, C=C stretching of phenyl rings and C=N stretching of the linker gives evidence of phase transitions. To understand the molecular changes more clearly, an in situ Raman measurement of C-H in-plane bending has also been performed. The temperature-dependent Raman study of MABAB-12 reveals the intra-molecular rotation-induced coplanarity of phenyl rings during the Cr→SmA transition. As a result of intra-molecular rotation, significant charge transfer from the phenyl rings to the linking group is observed. Rotational conformational analysis of MABAB-12 has also been performed through density functional theory (DFT), which also supports induced coplanarity of phenyl rings at the Cr→SmA transition. The analysis of Raman spectra reveals the melting of the hitherto rigid core. © 2025 Informa UK Limited, trading as Taylor & Francis Group.