FTIR Investigation of Two Alkyl-p-Terphenyl-4,4″-Dicarboxylates in Their Crystalline, Smectic and Isotropic Phases

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Abstract
Fourier transform infrared spectroscopy is used for studying the conformational changes occurring in the crystalline (K), smectic (S) and isotropic (I) phases of diethyl p-terphenyl-4,4″-dicarboxylate (DETC) and di-n-propyl p-terphenyl-4,4″-dicarboxylate (DPTC). Additional bands observed at the solid-smectic phase transition are interpreted in terms of symmetry and conformational changes both in the aliphatic part and the rigid core. Spectroscopic evidence for modifications of the latter is also observed at the crystal, -crystal2 phase transition in DETC. Wavenumber shifts as well as changes in band intensity and halfwidth are analysed in terms of variations of intra-and inter-molecular interactions.