Synthesis of new mesogens: Laterally and terminally substituted Schiff base derivatives

To study effect of terminal and lateral substituents, two homologous series of 4(4'-n-alkoxy benzoyloxy) benzylidene 3'' chloro, 4'' fluoro anilines and 4(4'-n-alkoxy benzoyloxy 3 methoxy) benzylidene 3'' chloro, 4-fluoro anilines were prepared by condensing different 4'-n-alkoxy benzoyloxy benzaldehydes and 4(4'-n- alkoxy benzoyloxy 3 methoxy) benzyaldehydes with 3 chloro 4 fluoro aniline. All the synthesized compounds were characterized by elemental analysis and spectroscopic methods. In series 4'-(4-n-alkoxy benzoyloxy) benzylidene 3'' chloro 4 fluoro anilines. First four members are non mesomorphic n-pentyl to n-heptyl derivatives exhibit nematic mesophase and n-octyl to n-hexadecyl derivatives appear with smectic mesophase. In series II 4(4'-n-alkoxy benzoyloxy 3 methoxy) benzylidene 3'' chloro 4'' fluoro anilines lower members n-methyl, n-ethyl, n-propyl and n-hexadecyl derivatives are non mesogenic in nature whereas n-heptyl to n-tetradecyl derivatives exhibit mesophases. The n-nonyl and n-decyl derivatives appear with polymesomorphism. The n-heptyl to n-decyl, derivatives exhibit haematic mesophase and n-nonyl to n-tetradecyl exhibit smectic A phase. The smectic thermal stability of two series are compared with those of other known series.