Raman Spectroscopic Study of Liquid Crystalline N-[4-(4-n-Alkoxybenzoyloxy)-2-Hydroxybenzylidene]-Chloroanilines

Abstract

N-[4-(4-n-Alkoxybenzoyloxy)-2-hydroxy-benzylidene]-chloroanilines[nAHmC(n; n=1-8, m; m=2: ortho, m=3: meta, m=4: para)] were synthesized. They exhibited a nematic phase. In addition, 8AH4C exhibited the smectic C and A phases. The temperature dependence of their Raman spectra has been observed in the spectral range of 20–1800 cm⁻¹. In a group of nAHmC, the Raman band at about 980 cm⁻¹ decreased in intensity and wavenumber through the solid-liquid crystal phase transition. In the other group, the corresponding band increased through the phase transition. The bands have been assigned to the CH out-of-plane vibration(980 cm⁻¹) of the benzene ring. Such a behavior can be explained by the molecular conformations with different twist angles of the aniline ring to the salicylaldimino part of the molecule in conjunction with information gained in the photochromic studies of N-2-hydroxy-benzylidenanilines. The temperature dependence of the 1190 cm⁻¹ band ascribed to the ring-N bond stretching vibration gave support to the result of the CH deformation vibration.

Key Words:

• nematic
• smectic A
• salicylidene aniline derivative
• chloroanilines
• Raman spectroscopy
• molecular conformation