Effects of lateral substituents on mesomorphic behavior. IV. Phenyl 4-(4-alkoxybenzylideneamino)-benzoates

Phenyl 4-(4-alkoxybenzylideneamino)benzoates exhibit both a nematic phase a nd a smectic A phase when the alkyl chain is propyl to decyl. While the 2-X substitution tends to eliminate the smectic phase, the 3-X substitution te nds to eliminate the nematic phase. A smectic A phase is generated by the m ethoxy to decyloxy members of the 3-Me, 3-F and 3-Cl derivatives, by the et hoxy and higher members of the 3-Br derivative and by the butoxy and higher members of the 2-F derivative. The smectic thermal stability can be enhanc ed or depressed by the 3-X substitution depending on the kind of halogen an d the alkyl chain length; for example, 29 degrees C for X=F, 3 degrees C fo r Cl and -11 degrees C forBr in the case of the propoxy member and 5 degree s C for X=F, -15 degrees C for Cl and -24 degrees C for Br in the case of t he decyloxy member.