study of liquid crystalline N -[4-(4- n -alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines

Abstract

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines [nAHmM(n=1-8/10; m=2: ortho, m=3: meta, m=4: para)] were synthesized. They exhibited a nematic phase except for 1AH3M. The temperature dependence of their Raman spectra was observed in the spectral range of 900–1700 cm^-1. In one group of nAHmM compounds, the Raman band at about 1360 cm^-1 abruptly decreased in intensity and wavenumber when the crystalline solid-liquid crystal phase transition was approached. In another group, the corresponding band increased through the phase transition. The bands have been assigned to the coupling mode between the in-plane CCH deformational vibration and the ring-N stretching vibration. Such a behaviour can be explained by the molecular conformation with different twist angles of the aniline ring in relation to the Schiff's base plane of the molecule. Some nAHmMs exhibited photochromism.