Crystal structures of mesogenic Schiff base esters

For n-alky1 4-[4'-(4"-n-octyloxybenzoyloxy)benzylidene]aminobenzoates, [chemical formula] all homologues exhibit smectic A and nematic, while smectic C phase also appears for longer members (n≧4). In order to clear relationships between the mesophase behavior and crystal structures, single crystal X-ray analysis has been performed for the ethyl and butyl homologues. Both crystals have smectic-like structures, and each molecule is arranged alternately to cancel dipole moments each other. Furthermore, the core moieties overlap largely in both crystals with the angle of 60° made by nearest neighboring phenyl rings of adjacent molecules. However, in the ethyl crystal, the core moieties are perpendicular to layer plane, while in the butyl crystal, those are tilted (20°) in the layer, corresponding to the adjacent mesophases, S_A (n=2) and S_c (n=4)